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Background Mortality for infants on the heart transplant wait list remains unacceptably high, and available mechanical circulatory support is suboptimal. Our goal is to demonstrate the feasibility of utilizing genetically engineered pig (GEP) heart as a bridge to allotransplantation by transplantation of a GEP heart in a baboon. Methods Four baboons underwent orthotopic cardiac transplantation from GEP donors. All donor pigs had galactosyl-1,3-galactose knocked out. Two donor pigs had human complement regulatory CD55 transgene and the other 2 had human complement regulatory CD46 and thrombomodulin. Induction immunosuppression included thymoglobulin, and Anti-CD20. Maintenance immunosuppression was Rapamycin, AntiCD-40 and methylprednisolone. One donor heart was preserved with University of Wisconsin (UW) solution and the other three with del Nido solution. Results All baboons weaned from cardiopulmonary bypass. B217 received a donor heart preserved with UW. Ventricular arrhythmias and depressed cardiac function resulted in early death. All recipients of del Nido preserved hearts easily weaned from cardiopulmonary bypass with minimal inotropic support. B15416 and B1917 survived for 90 days and 241 days respectively. Histopathology in B15416 revealed no significant myocardial rejection but cellular infiltrate around Purkinje fibers. Histopathology in B1917 was consistent with severe rejection. B37367 had uneventful transplant but developed significant respiratory distress with a cardiac arrest. Conclusions Survival of B15416 and B1917 demonstrates the feasibility of pursuing additional research to document the ability to bridge an infant to cardiac allotransplant with a GEP heart.

Background Shocks near defibrillation threshold (nDFT) strength commonly extinguish all ventricular fibrillation (VF) wavefronts, but a train of rapid, well-organized postshock activations (PAs) typically appears before sinus rhythm ensues. If one of the PA waves undergoes partial propagation block (wavebreak), reentry may be induced, causing VF to reinitiate and the shock to fail. Objective The purpose of this study was to determine whether wavebreak leading to VF reinititation following nDFT shocks occurs preferentially at the right ventricular insertion (RVI), which previous studies have identified as a key site for wavebreak. Methods We used panoramic optical mapping to image the ventricular epicardium of 6 isolated swine hearts during nDFT defibrillation episodes. After each experiment, the hearts were fixed and their geometry scanned with magnetic resonance imaging (MRI). The MRI and mapping datasets were spatially coregistered. For failed shocks, we identified the site of the first wavebreak of a PA wave during VF reinitiation. Results We recorded 59 nDFT failures. In 31 of these, the first wavebreak event occurred within 1 cm of the RVI centerline, most commonly on the anterior side of the right ventricular insertion (aRVI) (23/31). The aRVI region occupies 16.8% ± 2.5% of the epicardial surface and would be expected to account for only 10 wavebreaks if they were uniformly distributed. By χ2 analysis, aRVI wavebreaks were significantly overrepresented. Conclusion The anterior RVI is a key site in promoting nDFT failure. Targeting this site to prevent wavebreak could convert defibrillation failure to success and improve defibrillation efficacy.

Double-Sequential Defibrillation (DSD) is the near-simultaneous use of two defibrillators to treat refractory VF. We hypothesized that (1) risk of DSD-associated defibrillator damage depends on shock vector and (2) the efficacy of DSD depends on inter-shock time.Part 1: risk of defibrillator damage was assessed in three anaesthetized pigs by applying two sets of defibrillation electrodes in six different configurations (near-orthogonal or near-parallel vectors). Ten 360J shocks were delivered from one set of pads and peak voltage was measured across the second set. Part 2: the dependence of DSD efficacy on inter-shock time was assessed in ten anaesthetized pigs. Electrodes were applied in lateral-lateral (LL) and anterior-posterior positions. Control (LL Stacked Shocks; one vector, two shocks ∼10 s apart) and DSD therapies (Overlapping, 10 ms, 50 ms, 100 ms, 200 ms, 500 ms, 1000 ms apart) were tested in a block randomized design treating electrically-induced VF (n = ∼89 VF episodes/therapy). Shock energies were selected to achieve 25% shock success for a single LL shock.Part 1: peak voltage delivered was 1833 ± 48 V (mean ± 95%CI). Peak voltage exposure was, on average, 10-fold higher for parallel than orthogonal vectors (p 0.0001). Part 2: DSD efficacy compared to Stacked LL shocks was higher for Overlapping, 10 ms, and 100 ms (p 0.05); lower at 50 ms (p 0.05); and not different at 200 ms or longer inter-shock times.Risk of DSD-associated defibrillator damage can be mitigated by using near-orthogonal shock vectors. DSD efficacy is highly dependent on the inter-shock time and can be better, worse, or no different than stacked shocks from a single vector.University of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 06860.

Background: Rodent hearts can regenerate myocardium lost to apical resection or myocardial infarction for up to 7 days after birth, but whether a similar window for myocardial regeneration also exists in large mammals is unknown. Methods: Acute myocardial infarction (AMI) was surgically induced in neonatal pigs on postnatal days 1, 2, 3, 7, and 14 (ie, the P1, P2, P3, P7, and P14 groups, respectively). Cardiac systolic function was evaluated before AMI and at 30 days post-AMI via transthoracic echocardiography. Cardiomyocyte cell cycle activity was assessed via immunostaining for proliferation and mitosis markers, infarct size was evaluated histologically, and telomerase activity was measured by quantitative polymerase chain reaction. Results: Systolic function at day 30 post-AMI was largely restored in P1 animals and partially restored in P2 animals, but significantly impaired when AMI was induced on postnatal day 3 or later. Hearts of P1 animals showed little evidence of scar formation or wall thinning on day 30 after AMI, with increased measures of cell-cycle activity seen 6 days after AMI (ie, postnatal day 7) compared with postnatal day 7 in noninfarcted hearts. Conclusions: The neonatal porcine heart is capable of regeneration after AMI during the first 2 days of life. This phenomenon is associated with induction of cardiomyocyte proliferation and is lost when cardiomyocytes exit the cell cycle shortly after birth.

Background: Human induced pluripotent stem cells with normal (wild-type) or upregulated (overexpressed) levels of CCND2 (cyclin D2) expression were differentiated into cardiomyocytes (CCND2 WT CMs or CCND2 OE CMs, respectively) and injected into infarcted pig hearts. Methods: Acute myocardial infarction was induced by a 60-minute occlusion of the left anterior descending coronary artery. Immediately after reperfusion, CCND2 WT CMs or CCND2 OE CMs (3×10 7 cells each) or an equivalent volume of the delivery vehicle was injected around the infarct border zone area. Results: The number of the engrafted CCND2 OE CMs exceeded that of the engrafted CCND2 WT CMs from 6- to 8-fold, rising from 1 week to 4 weeks after implantation. In contrast to the treatment with the CCND2 WT CMs or the delivery vehicle, the administration of CCND2 OE CM was associated with significantly improved left ventricular function, as revealed by magnetic resonance imaging. This correlated with reduction of infarct size, fibrosis, ventricular hypertrophy, and cardiomyocyte apoptosis, and increase of vascular density and arterial density, as per histologic analysis of the treated hearts. Expression of cell proliferation markers (eg, Ki67, phosphorylated histone 3, and Aurora B kinase) was also significantly upregulated in the recipient cardiomyocytes from the CCND2 OE CM-treated than from the CCND2 WT CM-treated pigs. The cell proliferation rate and the hypoxia tolerance measured in cultured human induced pluripotent stem cell cardiomyocytes were significantly greater after treatment with exosomes isolated from the CCND2 OE CMs (CCND2 OE Exos) than from the CCND2 WT CMs (CCND2 WT Exos). As demonstrated by our study, CCND2 OE Exos can also promote the proliferation activity of postnatal rat and adult mouse cardiomyocytes. A bulk miRNA sequencing analysis of CCND2 OE Exos versus CCND2 WT Exos identified 206 and 91 miRNAs that were significantly upregulated and downregulated, respectively. Gene ontology enrichment analysis identified significant differences in the expression profiles of miRNAs from various functional categories and pathways, including miRNAs implicated in cell-cycle checkpoints (G2/M and G1/S transitions), or the mechanism of cytokinesis. Conclusions: We demonstrated that enhanced potency of CCND2 OE CMs promoted myocyte proliferation in both grafts and recipient tissue in a large mammal acute myocardial infarction model. These results suggest that CCND2 OE CMs transplantation may be a potential therapeutic strategy for the repair of infarcted hearts.

There is a critical shortage of deceased human donor organs for transplantation. The need is perhaps most acute in neonates and infants with life-threatening congenital heart disease, in whom mechanical support devices are largely unsuccessful. If orthotopic (life-supporting) heart transplantation (OHTx) were consistently successful in the genetically engineered pig-to-nonhuman primate (NHP) model, a clinical trial of bridging with a pig heart in such patients might be justified. However, the results of pig OHTx in NHPs have been mixed and largely poor. We hypothesise that a factor is the detrimental effects of the inflammatory response that is known to develop (a) during any surgical procedure that requires cardiopulmonary bypass, and (b) immediately after an NHP recipient is exposed to a pig xenograft. We suggest that the combination of these two inflammatory responses has a direct detrimental effect on pig heart graft function, but also, and possibly of more importance, on recipient baboon pulmonary function, which further impacts survival of the pig heart graft. In addition, the inflammatory response almost certainly adversely impacts the immune response to the graft. If our hypothesis is correct, the potential steps that could be taken to reduce the inflammatory response or its effects (with varying degrees of efficacy) include (a) white blood cell filtration, (b) complement depletion or inactivation, (c) immunosuppressive therapy, (d) high-dose corticosteroid therapy, (e) cytokine/chemokine-targeted therapy, (f) ultrafiltration or CytoSorb hemoperfusion, (g) reduction in the levels of endogenous catecholamines, (h) triiodothyronine therapy and (i) genetic engineering of the organ-source pig. Prevention of the inflammatory response, or attenuation of its effects, by judicious anti-inflammatory therapy may contribute not only to early survival of the recipient of a genetically engineered pig OHTx, but also to improved long-term pig heart graft survival. This would open the possibility of initiating a clinical trial of genetically engineered pig OHTx as a bridge to allotransplantation.

Mechanical chest compression devices allow for variation in chest compression (CCs) characteristics from moment to moment, enabling therapy that is not feasible for manual CCs. Effects of varying compressions over time have not been studied. In a randomized trial in an experimental model of prolonged cardiac arrest, we compared time-varying CPR (TVCPR), alternating between 100 and 200 compressions per minute (cpm) every 6 s, to guidelines CPR (Control).Ventricular fibrillation (VF) was electrically induced in 20 anesthetized pigs (28.4-45.8 kg). Following 10 min of untreated VF, cardiopulmonary resuscitation (CPR) began, randomized to TVCPR or Control. Rate of return of spontaneous circulation (ROSC), 4-h survival, and hemodynamics during the first 5 min of CPR were compared between groups. Moment-to-moment hemodynamic effects of changing the CC rate were analyzed.TVCPR improved the proportion of ROSC over time compared to Control (p 0.05) but ROSC (9/10 vs. 5/10) and 4-h survival (8/10 vs 5/10) did not differ significantly between groups. During CPR, coronary and cerebral perfusion pressures and femoral artery pressure did not differ between groups; however, end-tidal COTime-varying CPR significantly improved indicators of net forward blood flow and proportion of ROSC over time without negatively impacting perfusion pressures. Alternating CC rate alternates between perfusion pressures favoring the brain and those favoring the heart. Time-varying CPR represents a new avenue of research for optimizing CPR.University of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 140406860.

Mammalian cardiomyocytes exit the cell cycle shortly after birth. As a result, an occurrence of coronary occlusion-induced myocardial infarction often results in heart failure, postinfarction LV dilatation, or death, and represents one of the most significant public health morbidities worldwide. Interestingly however, the hearts of neonatal pigs have been shown to regenerate following an acute myocardial infarction (MI) occuring on postnatal day 1 (P1); a recovery period which is accompanied by an increased expression of markers for cell-cycle activity, and suggests that early postnatal myocardial regeneration may be driven in part by the MI-induced proliferation of pre-existing cardiomyocytes. In this study, we identified signaling pathways known to regulate the cell cycle, and determined of these, the pathways persistently upregulated in response to MI injury. We identified five pathways (mitogen associated protein kinase [MAPK], Hippo, cyclic [cAMP], Janus kinase/signal transducers and activators of transcription [JAK-STAT], and Ras) which were comprehensively upregulated in cardiac tissues collected on day 7 (P7) and/or P28 of the P1 injury hearts. Several of the initiating master regulators (e.g., CSF1/CSF1R, TGFB, and NPPA) and terminal effector molecules (e.g., ATF4, FOS, RELA/B, ITGB2, CCND1/2/3, PIM1, RAF1, MTOR, NKF1B) in these pathways were persistently upregulated at day 7 through day 28, suggesting there exists at least some degree of regenerative activity up to 4 weeks following MI at P1. Our observations provide a list of key regulators to be examined in future studies targeting cell-cycle activity as an avenue for myocardial regeneration.

Background: Here, we generated human cardiac muscle patches (hCMPs) of clinically relevant dimensions (4 cm × 2 cm × 1.25 mm) by suspending cardiomyocytes, smooth muscle cells, and endothelial cells that had been differentiated from human induced-pluripotent stem cells in a fibrin scaffold and then culturing the construct on a dynamic (rocking) platform. Methods: In vitro assessments of hCMPs suggest maturation in response to dynamic culture stimulation. In vivo assessments were conducted in a porcine model of myocardial infarction (MI). Animal groups included: MI hearts treated with 2 hCMPs (MI+hCMP, n=13), MI hearts treated with 2 cell-free open fibrin patches (n=14), or MI hearts with neither experimental patch (n=15); a fourth group of animals underwent sham surgery (Sham, n=8). Cardiac function and infarct size were evaluated by MRI, arrhythmia incidence by implanted loop recorders, and the engraftment rate by calculation of quantitative polymerase chain reaction measurements of expression of the human Y chromosome. Additional studies examined the myocardial protein expression profile changes and potential mechanisms of action that related to exosomes from the cell patch. Results: The hCMPs began to beat synchronously within 1 day of fabrication, and after 7 days of dynamic culture stimulation, in vitro assessments indicated the mechanisms related to the improvements in electronic mechanical coupling, calcium-handling, and force generation, suggesting a maturation process during the dynamic culture. The engraftment rate was 10.9±1.8% at 4 weeks after the transplantation. The hCMP transplantation was associated with significant improvements in left ventricular function, infarct size, myocardial wall stress, myocardial hypertrophy, and reduced apoptosis in the periscar boarder zone myocardium. hCMP transplantation also reversed some MI-associated changes in sarcomeric regulatory protein phosphorylation. The exosomes released from the hCMP appeared to have cytoprotective properties that improved cardiomyocyte survival. Conclusions: We have fabricated a clinically relevant size of hCMP with trilineage cardiac cells derived from human induced-pluripotent stem cells. The hCMP matures in vitro during 7 days of dynamic culture. Transplantation of this type of hCMP results in significantly reduced infarct size and improvements in cardiac function that are associated with reduction in left ventricular wall stress. The hCMP treatment is not associated with significant changes in arrhythmogenicity.

The mortality of patients suffering from acute myocardial infarction is linearly related to the infarct size. As regeneration of cardiomyocytes from cardiac progenitor cells is minimal in the mammalian adult heart, we have explored a new therapeutic approach, which leverages the capacity of nanomaterials to release chemicals over time to promote myocardial protection and infarct size reduction. Initial screening identified 2 chemicals, FGF1 and CHIR99021 (a Wnt1 agonist/GSK-3β antagonist), which synergistically enhance cardiomyocyte cell cycle in vitro. Poly-lactic-co-glycolic acid nanoparticles (NPs) formulated with CHIR99021 and FGF1 (CHIR + FGF1-NPs) provided an effective slow-release system for up to 4 weeks. Intramyocardial injection of CHIR + FGF1-NPs enabled myocardial protection via reducing infarct size by 20%-30% in mouse or pig models of postinfarction left ventricular (LV) remodeling. This LV structural improvement was accompanied by preservation of cardiac contractile function. Further investigation revealed that CHIR + FGF1-NPs resulted in a reduction of cardiomyocyte apoptosis and increase of angiogenesis. Thus, using a combination of chemicals and an NP-based prolonged-release system that works synergistically, this study demonstrates a potentially novel therapy for LV infarct size reduction in hearts with acute myocardial infarction.

Cell therapy treatment of myocardial infarction (MI) is mediated, in part, by exosomes secreted from transplanted cells. Thus, we compared the efficacy of treatment with a mixture of cardiomyocytes (CMs; 10 million), endothelial cells (ECs; 5 million), and smooth muscle cells (SMCs; 5 million) derived from human induced pluripotent stem cells (hiPSCs), or with exosomes extracted from the three cell types, in pigs after MI. Female pigs received sham surgery; infarction without treatment (MI group); or infarction and treatment with hiPSC-CMs, hiPSC-ECs, and hiPSC-SMCs (MI + Cell group); with homogenized fragments from the same dose of cells administered to the MI + Cell group (MI + Fra group); or with exosomes (7.5 mg) extracted from a 2:1:1 mixture of hiPSC-CMs:hiPSC-ECs:hiPSC-SMCs (MI + Exo group). Cells and exosomes were injected into the injured myocardium. In vitro, exosomes promoted EC tube formation and microvessel sprouting from mouse aortic rings and protected hiPSC-CMs by reducing apoptosis, maintaining intracellular calcium homeostasis, and increasing adenosine 5'-triphosphate. In vivo, measurements of left ventricular ejection fraction, wall stress, myocardial bioenergetics, cardiac hypertrophy, scar size, cell apoptosis, and angiogenesis in the infarcted region were better in the MI + Cell, MI + Fra, and MI + Exo groups than in the MI group 4 weeks after infarction. The frequencies of arrhythmic events in animals from the MI, MI + Cell, and MI + Exo groups were similar. Thus, exosomes secreted by hiPSC-derived cardiac cells improved myocardial recovery without increasing the frequency of arrhythmogenic complications and may provide an acellular therapeutic option for myocardial injury.

This study tested the hypothesis that a biphasic defibrillation waveform with an ascending first phase (ASC) causes less myocardial damage by pathology and injury current than a standard biphasic truncated exponential (BTE) waveform in a swine model.Although lifesaving, defibrillation shocks have significant iatrogenic effects that reduce their benefit for patient survival.An ASC waveform with an 8-ms linear ramp followed by an additional positive 0.5-ms decaying portion with amplitudes of 20 J (ASC 20J) and 25 J (ASC 25J) was used. The control was a 25-J BTE conventional waveform (BTE 25J) RESULTS: The ASC 20J and ASC 25J shocks were both successful in 6 of 6 pigs, but the BTE 25J was successful in only 6 of 14 pigs (p 0.05). Post-shock ST-segment elevation (injury current) in the right ventricular electrode was significantly greater with BTE 25J than with ASC 20J and ASC 25J. With a blinded pathology reading, hemorrhage, inflammation, thrombi, and necrosis 24 h post-shock were significantly greater with BTE 25J than with ASC 20J and ASC 25J. Troponin levels were also markedly lower at 3, 4, 5, and 6 h post-shock.Defibrillation shocks cause electrophysiological, histological, and biochemical signs of myocardial damage and necrosis. These signs of damage are markedly less for an ASC waveform than for a conventional BTE waveform.

Dysregulation of adrenal glucocorticoid production is increasingly recognized to play a supportive role in the metabolic syndrome although the mechanism is ill defined. The adrenal cytochrome P450 (CYP) enzymes, CYP17 and CYP21, are essential for glucocorticoid synthesis. The omega-3 and omega-6 polyunsaturated fatty acids (PUFA) may ameliorate metabolic syndrome, but it is unknown whether they have direct actions on adrenal CYP steroidogenic enzymes. The aim of this study was to determine whether PUFA modify adrenal glucocorticoid synthesis using isolated porcine microsomes. The enzyme activities of CYP17, CYP21, 11β-hydroxysteroid dehydrogenase type 1, hexose-6-phosphate dehydrogenase (H6PDH), and CYP2E1 were measured in intact microsomes treated with fatty acids of disparate saturated bonds. Cortisol production was measured in a cell-free in vitro model. Microsomal lipid composition after arachidonic acid (AA) exposure was determined by sequential window acquisition of all theoretical spectra-mass spectrometry. Results showed that adrenal microsomal CYP21 activity was decreased by docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), eicosapentaenoic acid, α-linolenic acid, AA, and linoleic acid, and CYP17 activity was inhibited by DPA, DHA, eicosapentaenoic acid, and AA. Inhibition was associated with the number of the PUFA double bonds. Similarly, cortisol production in vitro was decreased by DPA, DHA, and AA. Endoplasmic enzymes with intraluminal activity were unaffected by PUFA. In microsomes exposed to AA, the level of AA or oxidative metabolites of AA in the membrane was not altered. In conclusion, these observations suggest that omega-3 and omega-6 PUFA, especially those with 2 or more double bonds (DPA, DHA, and AA), impede adrenal glucocorticoid production.

Introduction: We aimed at to investigate whether activation of both FGF1 and Wnt1 synergistically enhances angiogenesis and render the cardioprotection in hearts with post infarction LV remodeling. Materials and methods: CHIR99021 (a Wnt1 activator) and FGF1 were encapsulated into poly lactic-co-glycolic acid nanoparticles (CHIR99021/FGF1-NPs). Ischemic heart models were generated in C57BL/6 mice or Yorkshire swine by ligation of the left anterior descending coronary. The mice were randomly divided into 6 groups: Myocardial infarction (MI) Only (n=11), MI with nanoparticles (CHIR99021 or/and FGF1 loaded) injection (n=12, each), MI with non-loaded nanoparticles injection (n=11) and Sham group (n=10). The swine were divided into 3 groups: ischemic reperfusion injury (IRI) (n=4), IRI with CHIR99021/FGF-NPs injection (n=4) and Sham group (n=4). Left ventricle function 4 week after surgery were evaluated by Echocardiography. Cell proliferation was assessed via immunostaining in ischemic hearts and in cultivated human umbilical vein endothelial cells (HUVECs) and Human vascular smooth muscle cells (HVSMCs) using the following markers: Ki67, Brdu, PH3, and Aurora B. Apoptosis was determined with TUNEL staining. Cardiac fibrosis was evaluated via Sirius red and Fast green staining (mice) and magnetic resonance imaging (swine). Results: CHIR99021/FGF1-NPs treatment attenuated fibrosis and preserved heart contractile function in mice and swine models of postinfarction LV remodeling. The proportion of cells that expressed cell cycle markers (Ki67; BrdU; Aurora B and PH3) was significantly greater in CHIR99021+FGF1 treatment group than CHIR99021, FGF1 and PBS treatment group. The proportion of apoptotic cells was significantly smaller in CHIR99021+FGF1 treatment group than in groups of control, VEGF, CHIR99021, or FGF1 treatment alone. Conclusions: CHIR99021 and FGF synergistically activate cell cycle and reduce apoptosis, which accompanied by a significant improvement of cardiac function.

The aim of this study is to develop and evaluate a novel imaging method (SSF, Spatial gradient Sparse in Frequency domain) for the reconstruction of activation sequences of ventricular arrhythmia from noninvasive body surface potential map (BSPM) measurements. We formulated and solved the electrocardiographic inverse problem in the frequency domain, and the activation time was encoded in the phase information of the imaging solution. A cellular automaton heart model was used to generate focal ventricular tachycardia (VT). Different levels of Gaussian white noise were added to simulate noisecontaminated BSPM. The performance of SSF was compared with that of WMN (weighted minimum norm) inverse solution. We also evaluated the method in a swine model with simultaneous intracardiac and body surface recordings. Four reentrant VTs were observed in pigs with myocardial infarction generated by left anterior descending artery occlusion. The imaged activation sequences of reentrant VTs were compared with those obtained from intracardiac unipolar electrograms. In focal VT simulation, SSF increased the correlation coefficient (CC) by 5% and decreased localization errors (LEs) by 2.7 mm on average under different noise levels. In the animal validation with reentrant VT, SSF achieved an average CC of 88% and an average LE of 6.3 mm in localizing the earliest and latest activation site in the reentry circuit. Our promising results suggest SSF provides noninvasive imaging capability of detecting and mapping macroreentrant circuits in 3-dimensional ventricular space. SSF may become a useful imaging tool of identifying and localizing the potential targets for ablation of focal and reentrant ventricular tachycardia.

Background: Acute regional ischemia is a leading cause of death. Ectopic beats may initiate ventricular arrhythmias in the first hour after coronary occlusion; however, the origin of these beats remains poorly understood. Some studies suggest that abnormal mechanical stretch at the ischemic border zone may contribute to the initiation of ectopy. If mechanical stretch plays a major role in triggering ectopic beats, we therefore expect: I , left ventricular working (LVW) hearts will have higher frequency of post-occlusion ectopic activity than non-beating (NB) hearts; II , in LVW hearts, ectopic beats will arise from ventricular sites undergoing mechanical stretch. Methods and Results: Isolated pig hearts were assigned to NB or LVW groups (8 per group) and prepared for Langendorff or LVW perfusion, respectively. Contraction of NB hearts was suppressed with 10 μM blebbistatin. Acute regional ischemia was induced by LAD occlusion. Using a newly developed optical mapping system, electrical activity and mechanical deformation were simultaneously recorded from 0 to 60 minutes after LAD occlusion. Mechanical stretch (positive strain in 2 principal directions) was observed in the ischemic and border zones of LVW but not NB hearts (Figure, Panel A). There was no significant difference in the number of ectopic events in LVW hearts compared to NB hearts (58±35 vs. 32±36, p=0.17). Of the 45 ectopic events that originated from the LV mapping region in LVW hearts, Conclusion: Mechanical stretch does not play a major role in triggering ectopic beats in early acute regional ischemia in this model.

Mechanical stimulation can elicit electrical activation of the heart. This mechanosensitivity can start life-threatening arrhythmias (commotio cordis) or terminate them (precordial thump). Mechanosensitivity may also be involved in arrhythmogenesis in other settings. Stretch-activated ion channels (SACs) are thought to be important in mechanosensitivity and a number of agents that block them have been identified. Such agents could potentially be used as tools in experimental investigation of mechanosensitivity. However, studies using them in intact-heart preparations have yielded inconsistent results. In the present study, we used isolated, perfused hearts from 25–35 kg pigs and a computer-controlled device that repeatably delivered focal mechanical stimuli. The concentration-dependent ability of the SAC blocker gadolinium to suppress mechanical activation was assessed by the success rate of mechanical stimulation and by the delay between successful mechanical stimulation and electrical activation. In six hearts, perfusate was recirculated. In an additional six hearts, perfusate was not recirculated to prevent gadolinium from forming complexes with metabolic waste and possibly precipitating. Gadolinium did not suppress mechanically-induced activation. Although gadolinium has been shown to be an effective SAC blocker in isolated cells, using it to probe the role of mechanical stimulation in whole heart preparations should be done with great caution.

Background Improved understanding of the details of gastric slow wave propagation could potentially inform new diagnosis and treatment options for stomach motility disorders. Optical mapping has been used extensively in cardiac electrophysiology. Although optical mapping has a number of advantages relative to electrical mapping, optical signals are highly sensitive to motion artifact. We recently introduced a novel cardiac optical mapping method that corrects motion artifact and enables optical mapping to be performed in beating hearts. Here, we reengineer the method as an experimental tool to map gastric slow waves. Methods The method was developed and tested in 12 domestic farm pigs. Stomachs were exposed by laparotomy and stained with the voltage-sensitive fluorescence dye di-4-ANEPPS through a catheter placed in the gastroepiploic artery. Fiducial markers for motion tracking were attached to the serosa. The dye was excited by 450 or 505 nm light on alternate frames of an imaging camera running at 300 Hz. Emitted fluorescence was imaged between 607 and 695 nm. The optical slow wave signal was reconstructed using a combination of motion tracking and excitation ratiometry to suppress motion artifact. Optical slow wave signals were compared with simultaneously recorded bipolar electrograms and suction electrode signals, which approximate membrane potential. Key results The morphology of optical slow waves was consistent with previously published microelectrode recordings and simultaneously recorded suction electrode signals. The timing of the optical slow wave signals was consistent with the bipolar electrograms. Conclusions and inferences Optical mapping of slow wave propagation in the stomach is feasible.

Defibrillation is essential for resuscitating patients with ventricular fibrillation (VF), but shocks often fail to defibrillate. We hypothesized that small variations in pad placement affect shock success, and that defibrillation waveform and shock dose could compensate for suboptimal pad placement. In 10 swine experiments, electrode pads were attached at 3 adjacent anterolateral positions, less than 3 centimeters apart. At each position, 24 episodes of VF were induced and shocked, 8 episodes for each of 3 defibrillation therapies. This resulted in 9 tested combinations of pad position and defibrillation therapy, with 80 episodes of VF for each combination. An episode consisted of 15 seconds of untreated VF, followed by a first shock and, if necessary, a repeat shock. Episodes were separated by four minutes of recovery. Both electrode pad position and therapy order were randomized by experiment. Primary outcome was defined as successful VF termination after the first shock; secondary outcome was the cumulative success of the first and second shocks. First shock efficacy varied widely across the 9 tested combinations of pad position and defibrillation therapy, ranging from 11.3% to 86.3%. When grouped by therapy, first shock efficacy varied significantly between the 3 pad positions: 38.3%, 48.3%, 36.7% (p = 0.02, ANOVA), and, when grouped by pad position, it varied significantly between therapies: 15.0%, 32.5%, 75.8% (p < 0.001, ANOVA). Cumulative 2-shock success varied significantly with therapy (p < 0.001, ANOVA) but not with pad position (p = 0.30, ANOVA). The lowest first shock success was at one position in 6 of 10 animals, at another position in 4 of 10 animals, and never at the third position. Small variations in pad placement can significantly affect defibrillation shock efficacy. However, anatomical variation between individuals and the challenging conditions of real-world resuscitations make optimal pad placement impractical. Suboptimal pad placement can be overcome with defibrillation waveform and shock dose.

Objectives The purpose of this study was to assess the feasibility of pulmonary vein (PV) isolation using low-intensity collimated ultrasound. Background Contemporary approaches to PV isolation are limited by the technical complexity of mapping and ablation. We describe a novel approach to left atrial anatomic rendering and PV isolation that aims to overcome some of these limitations by using low-intensity collimated ultrasound (LICU) system, which allows for near real-time geometry creation and automated ablation in a porcine model. Methods Twenty swine were anesthetized, and the LICU ablation catheter was placed in the left atrium via percutaneous transseptal access. Ultrasound M-mode–based anatomies of the inferior PVs were successfully created, and ablation was performed under automatic robotic control along a user-defined lesion path. One animal was excluded because of device failure. Results All target PVs in the 19 remaining animals were isolated acutely, requiring a mean of 1.6 applications. Ten animals were sacrificed acutely, and the remaining 9 survived for 35 ± 11 days. Of these 9, 1 animal was excluded from analysis because the index lasso position could not be reliably recreated. PVs in 5 of 8 animals remained isolated at sacrifice. Of the 77 total histological sections, 62 lesions (80.5%) were noted to be transmural. Lesions were homogeneous and characterized by coagulative necrosis and fibrous tissue. The mean myocardial thickness was 2.66 ± 1.80 mm, and the mean lesion depth was 4.28 ± 1.97 mm. No extra cardiac or collateral lesions were noted. Conclusions This study demonstrates the safety and efficacy of a novel noncontact ultrasound mapping and ablation system to produce continuous transmural lesions that can isolate PVs in a porcine model.

Sudden cardiac arrest (SCA) remains an important public health challenge. Despite a dramatic decrease in the age-adjusted risk of SCA, the cumulative number of fatal SCAs in the United States remains large. Estimates range from 450 000 fatal SCAs per year; a figure in the range of 300 000 to 370 000 per year is likely the best current estimate.1 SCA appears to account for ≈50% of all cardiovascular deaths,2 and it is estimated that 50% of the SCAs are the first clinical expression of previously undiagnosed heart disease.2,3 Most out-of-hospital cardiac arrests (80%) occur in private homes or other living facilities.4 Electric mechanisms associated with SCA are broadly classified into tachyarrhythmic and nontachyarrhythmic categories, the latter including pulseless electric activity (PEA; formerly referred to as electromechanical dissociation), asystole, extreme bradycardia, and other mechanisms often associated with noncardiac factors (Table). The first approaches to the problem of SCA focused on ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). An early impact on the prevention and treatment of VF and VT was realized in patients with acute coronary syndromes >50 years ago,5 followed by the development of strategies for responding to out-of-hospital cardiac arrest, implantable cardioverter-defibrillators, and defibrillation by lay responders. View this table: Table. Tachyarrhythmic and Nontachyarrhythmic Cardiac Arrest Data from the Seattle emergency rescue system6 and elsewhere7–9 have identified progressive reductions in the number of responses to SCA over 2 to 3 decades. This change was due primarily to a reduction in the number of ventricular tachyarrhythmic events identified by emergency medical services responders. In the Seattle data, the incidences of PEA and asystole had not changed over the 3 decades of observation and therefore have emerged as proportionately more frequent mechanisms than VT/VF. Whether this also reflects the …

Aims c-Jun N-terminal kinase (JNK) activation is implicated in cardiovascular diseases and ageing, which are linked to enhanced propensity to atrial fibrillation (AF). However, the contribution of JNK to AF remains unknown. Thus, we assessed the role of JNK in remodelling of gap junction connexin43 (Cx43) and development of AF. Methods and results AF induction, optical mapping, and biochemical assays were performed in young and aged New Zealand white rabbit left atria (LA) and cultured HL-1 atrial cells. In aged rabbit LA, pacing-induced atrial arrhythmias were dramatically increased and conduction velocity (CV) was significantly slower compared with young controls. Aged rabbit LA contained 120% more activated JNK and 54% less Cx43 than young LA. Young rabbits treated with JNK activator anisomycin also exhibited increased pacing-induced atrial arrhythmias and reduced Cx43 (by 34%), similar to that found in aged LA. In HL-1 cell cultures, anisomycin treatment for 16 h led to 42% reduction in Cx43, 24% reduction in CV, and an increased incidence of irregular rapid spontaneous activities. These effects were prevented by a specific JNK inhibitor, SP600125. Moreover, a 63% reduction in Cx43 after anisomycin treatment for 24 h led to further slowed CV (by 41%) along with dramatically increased irregular rapid spontaneous activity and highly discontinuous conduction. These JNK-induced functional abnormalities were completely reversed by overexpressed exogenous wild-type Cx43, but not by inactive Cx43. Conclusion JNK activation contributes to Cx43 reductions that promote development of AF. Modulation of JNK may be a potential novel therapeutic approach to prevent and treat AF.

Background— We tested the hypothesis that the shape of the shock waveform affects not only the defibrillation threshold but also the amount of cardiac damage. Methods and Results— Defibrillation thresholds were determined for 11 waveforms—3 ascending-ramp waveforms, 3 descending-ramp waveforms, 3 rectilinear first-phase biphasic waveforms, a Gurvich waveform, and a truncated exponential biphasic waveform—in 6 pigs with electrodes in the right ventricular apex and superior vena cava. The ascending, descending, and rectilinear waveforms had 4-, 8-, and 16-millisecond first phases and a 3.5-millisecond rectilinear second phase that was half the voltage of the first phase. The exponential biphasic waveform had a 60% first-phase and a 50% second-phase tilt. In a second study, we attempted to defibrillate after 10 seconds of ventricular fibrillation with a single ≈30-J shock (6 pigs successfully defibrillated with 8-millisecond ascending, 8-millisecond rectilinear, and truncated exponential biphasic waveforms). Troponin I blood levels were determined before and 2 to 10 hours after the shock. The lowest-energy defibrillation threshold was for the 8-milliseconds ascending ramp (14.6±7.3 J [mean±SD]), which was significantly less than for the truncated exponential (19.6±6.3 J). Six hours after shock, troponin I was significantly less for the ascending-ramp waveform (0.80±0.54 ng/mL) than for the truncated exponential (1.92±0.47 ng/mL) or the rectilinear waveform (1.17±0.45 ng/mL). Conclusions— The ascending ramp has a significantly lower defibrillation threshold and at ≈30 J causes 58% less troponin I release than the truncated exponential biphasic shock. Therefore, the shock waveform affects both the defibrillation threshold and the amount of cardiac damage.

Aims The first seconds of ventricular fibrillation (VF) are well organized and can consist of just one to two rotating waves (rotors). New rotors are spawned when local propagation block causes wave fragmentation. We hypothesized that this process, which leads to fully developed VF, begins at a consistent anatomic site. Methods and results We initiated VF with a stimulus timed to the local T-wave in 10 isolated pig hearts. Hearts were stained with a voltage-sensitive dye and four video cameras recorded electrical propagation panoramically across the epicardium. In each VF episode, we identified the position of the first wavebreak event that produced new rotor(s) that persisted for at least one cycle. The first such wavebreak occurred along the anterior right ventricular insertion (ARVI) in 26 of 32 VF episodes. In these episodes, wavebreak sites were 6 ± 4 mm from the midline of the ARVI. In the remaining 6 episodes, wavebreak sites were 24 ± 5 mm from the midline on either the LV or RV. During rapid pacing, conduction speed was locally depressed at the ARVI when waves crossed parallel to the midline. Action potential duration (APD) was slightly longer (2.2 ± 2.1 ms) at the ARVI compared with other sites ( P < 0.01). Temporal APD alternans were small and not unique to the break site, suggesting that dynamic APD properties were not the cause of wavebreak. Conclusion The ARVI is the dominant site for wavebreak at the onset of VF in normal myocardium. This may be due to the anatomic complexity of the region.

Since the initial development of the defibrillator, there has been concern that, while delivery of a large electric shock would stop fibrillation, it would also cause damage to the heart. This concern has been raised again with the development of the biphasic defibrillator.To compare defibrillation efficacy, postshock cardiac function, and troponin I levels following 150-J and 360-J shocks.Nineteen swine were anesthetized with isoflurane and instrumented with pressure catheters in the left ventricle, aorta, and right atrium. The animals were fibrillated for 6 minutes, followed by defibrillation with either low-energy (n = 8) or high-energy (n = 11) shocks. After defibrillation, chest compressions were initiated and continued until return of spontaneous circulation (ROSC). Epinephrine, 0.01 mg/kg every 3 minutes, was given for arterial blood pressure50 mmHg. Hemodynamic parameters were recorded for four hours. Transthoracic echocardiography was performed and troponin I levels were measured at baseline and four hours following ventricular fibrillation (VF).Survival rates at four hours were not different between the two groups (low-energy, 5 of 8; high-energy, 7 of 11). Results for arterial blood pressure, positive dP/dt (first derivative of pressure measured over time, a measure of left ventricular contractility), and negative dP/dt at the time of lowest arterial blood pressure (ABP) following ROSC were not different between the two groups (p = not significant [NS]), but were lower than at baseline. All hemodynamic measures returned to baseline by four hours. Ejection fractions, stroke volumes, and cardiac outputs were not different between the two groups at four hours. Troponin I levels at four hours were not different between the two groups (12 +/- 11 ng/mL versus 21 +/- 26 ng/mL, p = NS) but were higher at four hours than at baseline (19 +/- 19 ng/mL versus 0.8 +/- 0.5 ng/mL, p0.05, groups combined).Biphasic 360-J shocks do not cause more cardiac damage than biphasic 150-J shocks in this animal model of prolonged VF and resuscitation.

Pauses during chest compressions are thought to have a detrimental effect on resuscitation outcome. The Guidelines 2005 have recently eliminated the post-defibrillation pause. Previous animal studies have shown that multiple pauses of increasing duration decrease resuscitation success. We investigated the effect of varying the characteristics of a single pause near defibrillation on resuscitation outcome.Part A: 48 swine were anesthetized, fibrillated for 7min and randomized. Chest compressions were initiated for 90s followed by defibrillation and then resumption of chest compressions. Four groups were studied-G2000: 40s pause beginning 20s before, and ending 20s after defibrillation, A1: a 20s pause just before defibrillation, A2: a 20s pause ending 30s prior to defibrillation, and group A3: a 10s pause ending 30s prior to defibrillation. Part B: 12 swine (Group B) were studied with a protocol identical to Part A but with no pause in chest compressions. Primary endpoint was survival to 4h.The survival rate was significantly higher for groups A1, A2, A3, and B (5/12, 7/12, 5/12, and 5/12 survived) than for the G2000 group (0/12, p0.05). Survival did not differ significantly among groups A1, A2, A3, and B.These results suggest that the Guidelines 2005 recommendation to omit the post-shock pulse check and immediately resume chest compressions may be an important resuscitation protocol change. However, these results also suggest that clinical maneuvers further altering a single pre-shock chest compression pause provide no additional benefit.

Background— Although return of spontaneous circulation is frequently achieved during resuscitation for sudden cardiac arrest, systolic blood pressure can then decrease, requiring additional myocardial support. Previous studies have shown that a series of 1-ms electric pulses delivered through the defibrillation patches during ventricular fibrillation can stimulate the autonomic nervous system to increase myocardial function after defibrillation. We hypothesized that a similar series of electric pulses could increase myocardial function and blood pressure during the early postresuscitation period. Methods and Results— Six swine were studied that underwent 6 to 7 minutes of fibrillation. Each animal received 5, 10, 15, or 20 pulse packets consisting of six 10-A, 1-ms pulses every 3 to 4 s in random order whenever systolic blood pressure became Conclusions— Electric stimulation during regular rhythm after prolonged ventricular fibrillation and resuscitation can increase blood pressure and cardiac function to above prestimulation levels.

Summary Purpose Conventional biphasic truncated exponential (BTE) waveforms have been studied extensively but less is known about “chopping modulated” BTE shocks. Previous studies comparing chopped and unchopped waveforms have found conflicting results. This study compared the defibrillation thresholds (DFTs) of a variety of chopped and unchopped BTE waveforms. Methods Six anesthetized pigs were defibrillated after 15 s of electrically induced ventricular fibrillation (VF). Three waveform types were studied: unchopped BTE, “short” duration chopped, and “long” duration chopped waveforms. Each type included waveforms generated with 50, 100, and 200 μF capacitances, giving 9 total waveforms. Shocks were delivered in a standard up-down protocol and the order of the waveforms was randomized. Defibrillation thresholds were calculated using a Bayesian logistic regression model. Results DFTs of the 50, 100, and 200 μF unchopped waveforms were 122 ± 22, 124 ± 22, and 126 ± 22 J. Short chopped DFTs were at least 75 ± 23 J higher than unchopped DFTs. Long chopped DFTs averaged 66 ± 20 J more than short chopped DFTs. There is a 99.5% probability that the best of the chopped waveforms has a higher DFT than the worst of the unchopped waveforms, and a 95% probability that the difference is at least 37 J. DFT differences between capacitor values were less than 7 J for all waveform types. Conclusions When treating swine with short-duration VF, chopped waveforms require more energy to defibrillate than unchopped waveforms. More study is required to assess the performance of chopped waveforms when treating cardiac arrest patients.

During ventricular fibrillation (VF), activation waves are fragmented and the heart cannot contract synchronously. It has been proposed that VF waves emanate from stable sources (“mother rotors”). Previously, we used new optical mapping technology to image VF wavefronts from nearly the entire epicardial surface of six isolated swine hearts. We found that VF was not driven by epicardial rotors, but could not exclude the presence of stable rotors hidden within the ventricular walls. Here, we use graph theoretic analysis to show that, in all 17 VF episodes we analyzed, it was always possible to trace sequences of wavefronts through series of fragmentation and collision events from the beginning to the end of the episode. The set of wavefronts that were so related (the dominant component) consisted of 92%±1% of epicardial wavefronts. Because each such wavefront sequence constitutes a continuous activation front, this finding shows that complete reentrant pathways were always present on the epicardial surface and therefore, that wavefront infusion from nonepicardial sources was not strictly necessary for VF maintenance. These data suggest that VF in this model is not driven by localized sources; thus, new anti-VF treatments designed to target such sources may be less effective than global interventions.

Introduction: Ischemic post-conditioning (IPC) has shown promise in mitigating ischemia-reperfusion injury. Controlled pauses during CPR (CP-CPR) following cardiac arrest (CA) and prolonged downtime may help invoke IPC mechanisms and have been shown to improve neurological outcome in swine. We tested whether CP-CPR would improve return of spontaneous circulation (ROSC) and/or 4-hr survival rates, compared with standard CPR from a mechanical chest compression device (M-CPR), following prolonged downtime in a porcine model of ventricular fibrillation (VF)-induced CA. Methods: Twenty anesthetized and instrumented pigs were block randomized to two protocols. Following 10 min of VF, mechanical CPR was initiated (100 comp/min, 50% duty cycle, 2 inch depth). Over the first 5 minutes of CPR, the M-CPR protocol group received continuous chest compressions, while the CP-CPR protocol included four 20-sec pauses in compressions starting at 40, 100, 160, and 220 sec. All other interventions were the same in the two groups. After 5 minutes, a first shock was delivered during a pause. If the shock failed to convert to a perfusing rhythm for ≥ 30 s with a systolic aortic pressure (sAoP) ≥ 50 mmHg for at least the first three contiguous sAoP values, CPR was continued in 2 min cycles, followed by a shock (if indicated) at the end of each cycle, for up to 10 cycles. As soon as these criteria were met between two CPR cycles, ROSC was documented and a post-resuscitation protocol was initiated. During the post-resuscitation protocol, inotropic agents were provided as needed to maintain sAoP ≥ 50 mmHg. Survival was declared if the sAoP was maintained above threshold for 4 hrs following ROSC. Results: Nineteen animals were successfully instrumented for data gathering (9 CP-CPR, 10 M-CPR). In the CP-CPR and M-CPR groups respectively, 3/9 (33%) vs. 5/10 (50%) achieved ROSC (p = 0.46); when ROSC was achieved, time to ROSC was 7.7±1.2 min vs. 5.8±1.1 min (p = 0.08). All animals that achieved ROSC survived to 4 hours. Conclusions: In a porcine model of CA following prolonged VF, CP-CPR did not improve ROSC or 4-hr survival. The trend towards delayed time to ROSC suggests controlled pauses may impair initial resuscitation, even if they ultimately improve neurological outcome. Further studies are warranted.

During ventricular fibrillation (VF), electrical activation waves are fragmented, and the heart cannot contract in synchrony. It has been proposed that VF waves emanate from stable periodic sources (often called “mother rotors”). The objective of the present study was to determine if stable rotors are consistently present on the epicardial surface of hearts comparable in size to human hearts. Using new optical mapping technology, we imaged VF from nearly the entire ventricular surface of six isolated swine hearts. Using newly developed pattern analysis algorithms, we identified and tracked VF wave fronts and phase singularities (PS; the pivot point of a reentrant wave front). We introduce the notion of a compound rotor in which the rotor's central PS can change and describe an algorithm for automatically identifying such patterns. This prevents rotor lifetimes from being inappropriately abbreviated by wave front fragmentation and collision events near the PS. We found that stable epicardial rotors were not consistently present during VF: only 1 of 17 VF episodes contained a compound rotor that lasted for the entire mapped interval of 4 s. However, shorter-lived rotors were common; 12.2 (SD 3.3) compound rotors with lifetime >200 ms were visible on the epicardium at any given instant. We conclude that epicardial mother rotors do not drive VF in this experimental model; if mother rotors do exist, they are intramural or septal. This paucity of persistent rotors suggests that individual rotors will eventually terminate by themselves and therefore that the continual formation of new rotors is critical for VF maintenance.

Introduction: Patients with bradycardia can have severe tachyarrhythmias but it is unclear whether bradycardia alone can induce arrhythmias or whether an additional substrate is necessary. While several animal models of ventricular tachycardia (VT) exist, no model has been reported to mimic the clinical condition of spontaneous VT and sudden cardiac death (SCD) in the presence of bradycardia and chronic myocardial infarction (MI) in large animals without manipulation of the autonomic nervous system. We tested the hypothesis that MI and bradycardia cause more spontaneous sustained VT than does bradycardia alone. Methods and Results: Sheep (42–56 kg) underwent atrioventricular (AV) node catheter ablation alone (n = 5) or AV node ablation and 150 minutes of angioplasty balloon occlusion of the left anterior descending coronary artery (n = 9). An implantable cardioverter defibrillator delivered rescue shocks and demand pacing at 90 beats per minute for the first week and at 40 beats per minute thereafter. Electrograms were continuously radiotelemetered and recorded for 6 weeks. Acute post-MI VT disappeared by day 4. The sudden bradycardia on day 8 triggered numerous premature ventricular contractions (PVCs) and episodes of sustained VT lasting >30 seconds during the next 5 weeks. There were 43 episodes of sustained VT and no spontaneous ventricular fibrillation (VF) with bradycardia alone. However, in the presence of both MI and bradycardia there were 970 episodes of VT/VF (P < 0.05) and three deaths at days 13, 15, and 34. The average 24-hour count of PVCs was similar at day 7 between the two groups but by days 11 and 40, the PVC counts were 35 times and 4 times greater, respectively, in the presence of bradycardia and chronic MI compared to bradycardia alone. No significant difference in the incidence of PVCs was detected because of large individual variation between the two groups (P = 0.21). A high PVC count did not appear to predict SCD. Conclusion: The combination of MI and bradycardia secondary to AV node ablation in sheep produces a higher incidence of VT than bradycardia alone, suggesting that this preparation can serve as a model for the study of VT and sudden cardiac death.

Objectives The purposes of this study were to examine the first activations following atrial defibrillation shocks to help understand how and where atrial fibrillation (AF) relapsed following failed shocks and to assess the difference in postshock activation between failed and successful shocks. Background While many studies have investigated the mechanism of ventricular defibrillation, much less is known about the mechanisms of AF. Methods Sustained AF was induced electrically after pericardial infusion of methylcholine in 10 sheep. Biphasic subthreshold shocks were delivered to three configurations: right atrium to distal coronary sinus (RA-CS), sequential shocks with RA-CS as the first pathway followed by proximal CS to superior vena cava as the second pathway (Sequential), and right ventricle to superior vena cava plus can (V-triad). In eight sheep, global atrial mapping was performed with 504 electrodes spaced 3 to 4 mm apart. Results Earliest postshock activations mostly arose from the left atrium for V-triad but arose from either atrium for RA-CS and Sequential. Preshock AF cycle lengths were significantly shorter at the earliest activation sites than at seven of eight other sites globally distributed over both atria. In all type B successful episodes in which one or more rapid activations occurred after the shock and in 50 of the 72 failed episodes analyzed, activation fronts spread away from the earliest site in a focal pattern, and discrete nonfragmented activation complexes were present in the first derivatives of the electrograms. In the other 22 failed episodes, earliest activation fronts spread in a nonfocal pattern, and earliest postshock electrogram derivatives were fractionated. To better interpret the activation pattern in the fragmented regions, a 504 electrode plaque with 1.5-mm electrode spacing was placed on the right atrial appendage in two additional sheep. In 11 of 108 failed episodes, earliest postshock activation appeared inside the plaque and spread in a focal pattern with nonfragmented electrogram derivatives in 10 episodes and in a reentrant pattern with fragmented electrogram derivatives in the other. Conclusions (1) The electrode configuration influenced the location of earliest postshock activation. (2) Earliest postshock activation occurred where the preshock AF cycle length was short. (3) Earliest activations following all type B successful and most failed episodes were not fragmented and spread in a focal pattern. (4) The region of earliest postshock activation in the failed episodes without a focal postshock activation pattern exhibited regions of fragmented electrogram derivatives that may represent conduction block and possibly reentry.

The objective of this study was to test the hypothesis that on the epicardium of the in vivo human heart, ventricular fibrillation (VF) consists of chaotic small wavefronts that constantly change paths.Despite the significance of VF to cardiovascular mortality, little is known about the wavefronts that constitute VF in humans.In 9 patients undergoing cardiac surgery, a single VF episode was induced by rapid pacing immediately after institution of cardiopulmonary bypass while recordings were made from 504 electrodes spaced 2 mm apart in a 20 cm(2) plaque held against the anterior left ventricle epicardium. A total of 26 segments of VF, each 2 s long, were analyzed. A computer algorithm identified individual wavefronts and classified them into groups that followed similar activation sequences.The mean activation rate was 5.8 +/- 1.8 (mean +/- SD) cycles/s. The wavefronts during each epoch were grouped into 9.4 +/- 7.1 different activation pathways, and 8.3 +/- 2.3 wavefronts followed each pathway. Individual wavefronts spread to activate an area of 5.1 +/- 3.0 cm(2) in the mapped region. The majority of the wavefronts propagated into the mapped region and/or propagated out of the mapped region into adjacent tissue, suggesting that the wavefronts were larger than 5.1 cm(2). Reentry was identified in only 16 of the 26 (62%) 2-s segments, always completed2 cycles, and lasted for 9.5 +/- 6.6% of these 16 epochs, which is 5.8% of the total duration of all the segments analyzed.VF wavefronts on the human epicardium are usually large, repeatedly follow distinct pathways, and only occasionally reenter. If these results for the left ventricular epicardium are representative of those for the entire ventricular mass, they do not support the hypothesis that human VF consists of small, constantly changing wavefronts, but rather suggest that there is significant organization of human VF.

Background: Determining whether a linear catheter radio frequency (RF) ablation lesion is transmural may be difficult, especially during atrial fibrillation. We hypothesized that changes in pacing thresholds and electrogram amplitude during atrial fibrillation and sinus rhythm could be used to assess whether a radiofrequency ablation resulted in transmural necrosis. Methods: A hexapolar, linear, RF ablation catheter was positioned between the caval veins in the right atrium of seven sheep. Pacing thresholds and electrogram amplitudes during atrial fibrillation and sinus rhythm were measured before and after the application of RF energy. Sites along the linear lesion were assessed histologically. Results: The electrogram amplitude in atrial fibrillation decreased significantly more at transmural sites (unipolar recording: 33 ± 11% transmural vs. 22 ± 13% non-transmural, p ≤ 0.01; bipolar recording: 62 ± 9% transmural vs. 43 ± 15% non-transmural, p ≤ 0.01). The electrogram amplitude in sinus rhythm decreased significantly more at transmural sites (unipolar recording: 49 ± 18% transmural vs. 15 ± 20% non-transmural, p < 0.001; bipolar recording: 63 ± 17% transmural vs. 42 ± 19% non-transmural, p = 0.002). The pacing threshold increased significantly more at sites with transmural necrosis (unipolar: increased by 378 ± 103% transmural vs. 207 ± 93% non-transmural, p < 0.001; bipolar: 370 ± 80% transmural vs. 259 ± 60% non-transmural, p < 0.001). Conclusions: The amplitude of the atrial electrogram from an ablation catheter can be used to discriminate areas with transmural necrosis from those without transmural necrosis during either atrial fibrillation or sinus rhythm. Termination of atrial fibrillation may not be necessary to estimate the histologic characteristics of an ablation lesion.

Before recommendations for using an automatic external defibrillator on pediatric patients can be made, a protocol for the energy of a biphasic waveform energy dosing needs to be determined that will allow ventricular defibrillation of 8 year olds while causing only a minimal amount of cardiac damage to infants. Pediatric- and adult-sized electrode patches were alternately applied to 10 isoflurane-anesthetized piglets weighing 3.8-20.1 kg to approximate the body weights of newborns to children < 8 years old. The defibrillation threshold (DFT) was determined for biphasic truncated exponential waveform shocks. Additional shocks, varying from the DFT to 360 Joules (J), were delivered during sinus rhythm or following 30 s of ventricular fibrillation (VF). The DFT was 2.4+/-0.81 and 2.1+/-0.65 J/kg for pediatric and adult patches, respectively (P = N.S.). The change in left ventricular (LV) dP/dt from baseline as a function of shock strength was significantly different at 1 and 10 s after shocks of increasing energy that were delivered in sinus rhythm, and 1, 10, 20, and 30 s after defibrillation shocks. There was no significant difference in LV dP/dt with increasing shock energy at 60 s with either patch size. The time to return of sinus rhythm, ST-segment deviation, and cardiac output were also not significantly different from baseline 60 s following shocks of up to 360 J delivered during sinus rhythm or VF with either patch. The same amount of energy delivered with a biphasic external defibrillator successfully defibrillated VF whether adult or pediatric patches were used. Cardiac rhythm and hemodynamic variables were unaltered at 60 s after shocks delivered at energies of up to 360 J. These data suggest that there is a substantial safety margin above a DFT strength shock for this biphasic waveform in piglets.

Reduction of Shock Strength with Balanced Sequential Shocks.Introduction: The aim of this study was to determine the atrial defibrillation threshold (ADFT) of a first shock across the standard right atrium (RA) to distal coronary sinus (dCS) configuration followed by a second shock along the atrial septum with a standard sequential waveform (the second shock leading edge equaled the first shock trailing edge) and a balanced sequential waveform (the leading edges of both shocks were equal). Methods and Results: In nine sheep atrial fibrillation was induced with acetyl-β-methylcholine and burst pacing. A catheter was placed with electrodes in the dCS, proximal coronary sinus (pCS), and RA. A J-shaped catheter was positioned with an electrode at Bachmann's bundle (BB) while another catheter was positioned with an electrode in the superior vena cava (SVC). The ADFTs of six single- and dual-pathway configurations were determined with single, standard sequential, or balanced sequential shocks. The ADFT of the RAdCS configuration (0.86 ± 0.27 J, 159 ± 29 V, 2.42 ± 0.36 A) was significantly reduced when followed by an SVCpCS (0.58 ± 0.17 J, 112 ± 20 V, 1.64 ± 0.39 A) or a BBpCS shock (0.64 ± 0.16 J, 119 ± 18 V, 1.81 ± 0.38 A) with standard sequential shocks. With balanced sequential shocks, the peak voltage and current ADFTs were further significantly reduced (85 ± 11 V and 1.24 ± 0.21 A for second shock SVCpCS, and 93 ± 13 V and 1.38 ± 0.27 A for second shock BBpCS). Conclusion: The ADFT of the standard RAdCS shock is significantly reduced when followed by a second shock along the atrial septum delivered between electrodes in the pCS and either SVC or BB and ADFT is further reduced with balanced sequential shocks.

HUANG, J., et al.: Effect of Electrode Location in Great Cardiac Vein on the Ventricular Defibrillation Threshold. This study tested the hypothesis that the DFT could be lowered by delivering a weak auxiliary shock in conjunction with a stronger primary shock with the auxiliary shock electrode near the cardiac region where the primary shock electric field is weakest. This hypothesis was tested by determining the DFTs with the auxiliary shock delivered from different locations within the great cardiac vein (GCV). In 15 dogs, catheters with defibrillation electrodes were placed transvenously in the RV apex, the SVC, and the GCV. An active can electrode and the SVC electrodes were electrically coupled to serve as a return electrode for the RV and GCV electrodes. DFTs were determined for a primary shock through the RV electrode with and without a subsequent auxiliary shock of lower amplitude through the GCV electrode. The leading edge voltage and current at DFT were significantly lowered by addition of the auxiliary shock (17% and 19% decreased, respectively), but energy was not changed. The animals were divided into three groups according to the location of the GCV electrode. The leading edge voltage, current, and total delivered energy at the DFT were significantly lower in animals with the GCV electrode near the apex (22%, 24%, and 13% reduction, respectively) compared with those where the GCV electrode was positioned away from apex (8%, 10% reduction and 18% increase, respectively, P < 0.001). Application of an auxiliary shock to the apical region, near the region where previous studies have indicated that the RV primary shock has its weakest effects, caused the greatest decrease in DFT.

Introduction: We have previously shown that waveforms with an ascending ramp in both phases have a lower internal defibrillation threshold (DFT). The purpose of this study was to test whether waveforms with rectilinear, ascending and descending ramps in the second phase would reduce the DFT compared with a standard exponential biphasic waveform with external defibrillation shocks. Methods: In 6 pigs, DFTs were determined for 10 waveforms: a standard truncated exponential biphasic waveform with 60% tilt (Fig 1, #1) and 9 biphasic waveforms with an 8 ms ascending ramp 1st phase and one of 3 rectilinear, ascending ramp or descending ramp 2nd phases. The 3 rectilinear 2nd phases were: 1 ms, 200% of peak voltage of phase 1 (#2); 2 ms, same voltage as phase (#3); 3 ms, half the voltage of phase 1 (#4). The 3 ascending ramp 2nd phases were: 2 ms, 200% of voltage of phase 1(#5); 3 ms, same voltage as phase 1(#6); 4.5 ms, half the voltage of phase 1(#7). The 3 descending ramp 2nd phases were: 2 ms, 200% of voltage of phase 1(#8); 3 ms, same voltage as phase 1(#9); 4.5 ms, half the voltage of phase 1(#10). Results: Phase 2 ascending ramp (#7) and descending ramp (#8, #9) waveforms had the lowest DFTs, which were significantly smaller than for the truncated exponential waveform. (Fig 1, *indicates p Conclusions: Waveforms with a ramp in phase 2 (#7, #8, #9) have a lower DFT.

Background: Defibrillation is essential in treating cardiac arrest patients with ventricular fibrillation (VF). The success of the shock in terminating VF depends on many previously studied factors, including waveform and energy dose. It has been observed clinically that defibrillation electrode placement varies widely. The goal of this study was to assess the effect of small differences in defibrillation electrode placement on first shock defibrillation success rates in swine. Methods: In 10 anesthetized swine weighing 32.7 ± 2.5 kg (mean ± standard deviation), electrode pads were attached at 3 different symmetric positions: the medial edge of each electrode was placed 3% (2.1 ± 0.1 cm), 7% (4.7 ± 0.1 cm), or 11% (7.5 ± 0.2 cm) around the circumference of the chest from mid-sternum (Fig. 1). Biphasic impedance-compensated shocks were delivered through the pads with a 50-ohm resistor added in series to replicate human impedance. The order of the 3 positions was block randomized for each experiment. At each electrode position, 24 episodes were run: VF was electrically induced and up to 2 shocks were delivered. Primary outcome was defined as successful VF termination after the first shock; secondary outcome was the cumulative success of both the first and second shock. Results: Across all experiments, at the 3%, 7%, and 11% positions, first shock success was 38.3% (92/240), 48.3% (116/240), and 36.7% (88/240) (p = 0.02, Chi-square Test); cumulative 2-shock success was 59.6% (143/240), 63.8% (153/240), and 55.4% (133/240) (p = 0.18), respectively. The lowest first shock success was at the 3% position in 6 of 10 animals, at the 11% position in 4 of 10 animals, and never at the 7% position. Conclusions: Small changes in electrode pad placement can significantly affect defibrillation shock success. Although anatomic differences may prevent the existence of one optimal electrode position, one position may be more effective for VF termination than another in a given patient.