Search

Background End-stage heart failure is a major risk of mortality. The conductive super-aligned carbon nanotubes sheets (SA-CNTs) has been applied to restore the structure and function of injured myocardium through tissue engineering, and developed as efficient cardiac pacing electrodes. However, the interfacial interaction between SA-CNTs and the surface cells is unclear, and it remains challenge to restore the diminished contraction for a seriously damaged heart. Results A concept of a multifunctional power assist system (MPS) capable of multipoint pacing and contraction assisting is proposed. This device is designed to work with the host heart and does not contact blood, thus avoiding long-term anticoagulation required in current therapies. Pacing electrode constructed by SA-­CNTs promotes the epithelial-mesenchymal transition and directs the migration of pro-regenerative epicardial cells. Meanwhile, the power assist unit reveals an excellent frequency response to alternating voltage, with natural heart mimicked systolic/diastolic amplitudes. Moreover, this system exhibits an excellent pacing when attached to the surface of a rabbit heart, and presents nice biocompatibility in both in vitro and in vivo evaluation. Conclusions This MPS provides a promising non-blood contact strategy to restore in situ the normal blood-pumping function of a failed heart.

Ranolazine (RAN) has previously been shown to lower the onset of cholinergic atrial fibrillation in intact animals; however, its efficacy in the setting of atrial tachycardia (AT) is unknown. The purpose of this study was to investigate the effects of RAN alone or in combination with amiodarone (AMIO) on rapid pacing-evoked right AT in rabbit hearts. Right atrial monophasic action potentials (MAPs) were recorded in 11 anesthetized rabbits, using combination MAP pacing catheters. Vulnerability to AT was tested by employing consecutive trains of rapid burst pacing prior to and after 2.4 mg/kg of RAN alone delivered intravenously and then in combination with 3 mg/kg of AMIO as a 15-minute infusion. Primary endpoints were postdrug AT reproducibility as well as cycle length (CL) and tachycardia duration. MAP duration at 75% repolarization and the effective refractory period (ERP) were assessed during programmed pacing to calculate the atrial postrepolarization refractoriness (aPRR = ERP – MAPD75%). AT was elicited in eight out of 11 rabbits; only these animals were included for further investigation. RAN did not abolish the inducibility of AT in any experiment; however, it prolonged its CL (baseline vs. RAN: 120 ± 16 ms vs. 138 ± 18 ms; p = 0.053). Supplemental AMIO further increased the AT CL (baseline vs. RAN + AMIO: 120 ± 16 ms vs. 152 ± 23 ms; p = 0.006), without affecting arrhythmia reinducibility. Slowing of the tachycardia after RAN or RAN + AMIO was associated with spontaneous termination of the arrhythmia. RAN prolonged the aPRR significantly, while AMIO in addition to RAN potentiated this effect. Neither RAN alone nor its combination with AMIO abolished the elicitation of AT in this model. However, both agents synergistically prolonged the aPRR, resulting in the slowing of AT and promoting spontaneous termination of the arrhythmia.

Background Endurance physical training plays a protective role in against ventricular fibrillation (VF), but the exact underlying mechanisms are not completely understood. It is well-known that modifications in myocardial ventricular properties such as refractoriness, conduction velocity and wavelength are key in the initiation and maintenance of VF; furthermore, vagus nerve stimulation has prophylactic effects on malignant arrhythmias and VF. On the other hand, parasympathetic nervous system activity is increased in trained individuals, which in turn affects different ventricular electrophysiological properties. We hypothesized that physical training increases conduction velocity and wavelength, and that these changes are mediated by myocardial cholinergic neurons. Methods To test this hypothesis, ten rabbits were submitted to a six-week endurance training protocol and twenty controls were not trained (divided in control group, n=10 and sham group n=10). After training, rabbits were euthanized and their hearts excised, isolated and perfused in a Langendorff system. A pacing electrode and a plaque with 240 recoding electrodes acquiring at 1 KHz were positioned on the left ventricle (LV). Extraestimulus test using four different pacing cycle lengths (90% basal cycle length, 250, 200 and 150 ms) was performed before and after atropine (1μM, control and trained groups) or vehicle (tyrode, sham group) infusion. We studied 1) LV effective refractory period (ERP), 2) LV functional refractory period (FRP), 3) LV conduction velocity (CV), and 4) LV wavelength, determined as LV FRP x CV. Factorial ANOVA (mixed model) was used for statistical analysis (p Results Before parasympathetic blockade, LV FRP increased in trained animals (Figure, B) whereas no difference was found in LV CV between trained and control animals at any pacing cycle length (Figure, A). In consequence, LV wavelength increased in trained animals (Figure, C). There were no changes in LV ERP, FRP, CV and wavelength when comparisons were made within groups before and after atropine infusion. In sham animals, vehicle infusion or time-course of the experiment did not modify LV FRP, ERP, CV and wavelength. Conclusion Physical training increases LV wavelength, which can be one electrophysiological mechanism by which endurance training could protect against VF. Since modifications of ventricular refractoriness and wavelength do not seem dependent of intrinsic parasympathetic nervous system activity, other intrinsic mechanisms could be implied and warrant further research. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Instituto de Salud Carlos III, Generalitat Valenciana

Objective. Dibornol-HES, a water-soluble drug based on the derivative of 2,6-diisobornyl-4-methylphenol Dibornol conjugated with hydroxyethyl starch, can reduce the occurrence and severity of arrhythmias by preventive intravenous administration, but it is unknown whether the drug could reduce the myocardial arrhythmogenicity once ischemia has developed at the developed ischemia.Materials and methods. In the model of acute ischemia / reperfusion of the rabbit heart, the effect of Dibornol-HEC (80 mg/kg body weight of the animal) on the electrophysiological indices characterizing myocardial arrhythmogenicity (global and border dispersion of repolarization) was studied during the restoration of blood flow. In the model of acute ischemia / reperfusion with 64 unipolar epicardial leads, the activation-recovery intervals were measured and global and border dispersion of repolarization in the native rabbits (control group, n = 9) and in the rabbits treated by Dibornol-HES (on the 25th minute of occlusion, the experimental group, n = 6).Results. The introduction of Dibornol-HES did not lead to a change in the electrocardiographic parameters of rabbits. By the 30th minute of the coronary occlusion on the ECG in the animals of the control and the experimental groups, the intervals RR, QT, QTc were shortened (p < 0.05). In the animals of both groups by the 30th minute of coronary occlusion, the global dispersion of repolarization increased (p < 0.05), the boundary dispersion of repolarization also increased (p < 0.05), due to the decrease in the duration of the activation-recovery intervals in the ischemic zone (p < 0.05). During the 30-minute reperfusion the magnitude of the global dispersion of repolarization did not change in animals of the both groups, and the magnitude of the border dispersion of repolarization in the control rabbits decreased (p < 0.05), while in the rabbits treated by Dibornol-HES the border dispersion of repolarization did not changed.Conclusion. In rabbits of the experimental group, the values of the global and border dispersions of repolarization did not differ from those of the animals in the control group. Therefore, the administration to Dibornol-HES just prior to reperfusion does not lead to the decrease in the dispersion of repolarization increased as a result of acute ischemic myocardial damage.

Background: NS5806 activates the transient outward potassium current I to, and has been claimed to reproduce Brugada Syndrome (BrS) in ventricular wedge preparations. I to modulates excitation-contraction coupling, which is critical in alternans dynamics. We explored NS5806-arrhythmogenic effects in the intact whole heart and its impact on alternans. Methods: Langendorff-perfused rabbit hearts (n = 20) underwent optical AP and Ca mapping during pacing at decremental cycle lengths (CL). Spontaneous arrhythmias and pacing-induced alternans was characterized at baseline (BL), after perfusing with NS5806, before and after adding verapamil (VP), and SEA0400 (SEA, n = 5 each), to modulate Ca-current and Na-Ca exchange, the main AP-Ca coupling mechanisms. Results: NS5806 induced BrS-like ECG features in 6 out of 20 hearts. NS5806 prolonged steady-state (3 Hz) action potential duration (APD) by 16.8%, Ca decay constant by 34%, and decreased conduction velocity (CV) by 52.6%. After NS5806 infusion, spontaneous ventricular ectopy (VE) and AP/Ca alternans occurred. Pacing-induced alternans during NS5806 infusion occurred at longer CL and were AP/Ca discordant from its onset. Spatially discordant alternans after NS5806 infusion had non-propagation-driven nodal line distribution. No spontaneous phase-2 reentry occurred. Under NS5806 + VP, alternans became AP/Ca concordant and only induced in two out of five; NS5806 + SEA did not affect alternans but suppressed spontaneous ectopy. Conclusions: NS5806 disrupts AP-Ca coupling and leads to Ca-driven, AP/Ca-discordant alternans and VE. Despite BrS-like ECG features, no spontaneous sustained arrhythmias or phase-2 reentry occurred. NS5806 does not fully reproduce BrS in the intact rabbit heart.

… Histamine can stimulate the heart by directly interacting with cardiac histaminereceptors. In the present study we have investigated the H2 receptor activity in isolated rabbitheart. Cimetidine, a specific H2 receptor antagonist was used. The isolated heart was mountedin langendroff apparatus. The heart was perfused at a constant pressure with oxygenatedRinger‘s Locke solution. H2 receptor antagonist produces negative inotropic effect in thepresence of histamine. This indicates that H2 receptors are present in rabbit heart, and plays arole in mediation of positive inotropic effect produced through CAMP by histamine.

The distribution of intramyocardially injected rabbit MSCs, labeled with the near-infrared dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindotricarbo-cyanine-iodide (DiR) using hybrid Fluorescence Molecular Tomography-X-ray Computed Tomography (FMT-XCT) and Multispectral Optoacoustic Tomography (MSOT) imaging technologies, was investigated. Viability and induction of apoptosis of DiR labeled MSCs were assessed by XTT- and Caspase-3/-7-testing in vitro. 2×106, 2×105 and 2×104 MSCs labeled with 5 and 10μg DiR/ml were injected into fresh frozen rabbit hearts. FMT-XCT, MSOT and fluorescence cryosection imaging were performed. Concentrations up to 10μg DiR/ml did not cause apoptosis in vitro (p>0.05). FMT and MSOT imaging of labeled MSCs led to a strong signal. The imaging modalities highlighted a difference in cell distribution and concentration correlated to the number of injected cells. Ex-vivo cryosectioning confirmed the molecular fluorescence signal. FMT and MSOT are sensitive imaging techniques offering high-anatomic resolution in terms of detection and distribution of intramyocardially injected stem cells in a rabbit model.

Diagnosis of heart disease and its treatment are based largely on our understanding of the electrophysiology of adult myocardium. However, the marked difference in the electrical action potential (AP)between neonatal and adult cardiac myocytes suggests a different set of molecular bases in neonatal myocytes, and therefore different treatment for new-borns. In this study we present a new mathematical model of sinoatrial node (SAN) cells of the neonatal rabbit, by modifying densities or kinetics of I Na , I CaL , I f , I Kr , I Ks, and I NaCa in the adult rabbit SAN cell models developed by Zhang et al., based on available experimental data obtained from new-born rabbit SAN cells. The new model reproduced APs similar to experimental recordings from neonatal myocytes, with a faster pacemaking rate. Using the new model, we investigated how age-related changes in ionic currents modulate pacemaking AP morphology, demonstrating the model as a useful tool for testing the effects of drugs on neonatal SAN cells to obtain a better quantitative understanding of differences between neonatal and adult physiology.

Mitochondrial membrane potential (ΔΨm) depolarization has been implicated in the loss of excitability (asystole) during global ischemia, which is relevant for the success of defibrillation and resuscitation after cardiac arrest. However, the relationship between ΔΨm depolarization and asystole during no-flow ischemia remains unknown. We applied spatial Fourier analysis to confocally recorded fluorescence emitted by ΔΨm-sensitive dye tetramethylrhodamine methyl ester. The time of ischemic ΔΨm depolarization ( tmito_depol) was defined as the time of 50% decrease in the magnitude of spectral peaks reflecting ΔΨm. The time of asystole ( tasys) was determined as the time when spontaneous and induced ventricular activity ceased to exist. Interventions included tachypacing (150 ms), myosin II ATPase inhibitor blebbistatin (heart immobilizer), and the combination of blebbistatin and the inhibitor of glycolysis iodoacetate. In the absence of blebbistatin, confocal images were obtained during brief perfusion with hyperkalemic solution and after the contraction failed between 7 and 15 min of ischemia. In control, tmito_depol and tasys were 24.4 ± 6.0 and 26.0 ± 5.0 min, respectively. Tachypacing did not significantly affect either parameter. Blebbistatin dramatically delayed tmito_depol and tasys (51.4 ± 8.6 and 45.7 ± 5.3 min, respectively; both P < 0.0001 vs. control). Iodoacetate combined with blebbistatin accelerated both events ( tmito_depol, 12.7 ± 1.8 min; and tasys, 6.5 ± 1.1 min; both P < 0.03 vs. control). In all groups pooled together, tasys was strongly correlated with tmito_depol ( R2 = 0.845; P < 0.0001). These data may indicate a causal relationship between ΔΨm depolarization and asystole or a similar dependence of the two events on energy depletion during ischemia. Our results urge caution against the use of blebbistatin in studies addressing pathophysiology of myocardial ischemia.

Background. Myocardial ischaemia occurs due to inadequate supply of oxygen to fulfill the myocardial tissue oxygen demand. This leads to angina pectoris or referred pain, whichhappens because of the inability of the brain to distinguish the visceral afferent inputs from the somatic afferent inputs since they run along a common pathway via the dorsal root ganglia. Aims. This study aims to distinguish specific areas of the rabbit heart that are projected to specific dorsal root ganglia, which then associates to its specific dermatomes. Methods. A double-retrograde neurotracing method was used, with True Blue and Nuclear Yellow as the neurotracers. Rabbits were divided into 3 groups, which the first and second groups were ligated at the left anterior descending artery and at the left circumflex artery, respectively.The third group acted as the control group, without ligation.True blue was injected at ischaemic sites following ligation. Nuclear yellowwas injected at the skin, dermatomes T1-T4. Dorsal root ganglia levels T1-T4 were then examined for both neurotracers at 3 days post injection. Results. There is significant association between the site of ligation to the projection of the neurotracers at specific dorsal root ganglia (p

[EN] Panoramic optical mapping is the primary method for imaging electrophysiological activity from the entire outer surface of Langendorff-perfused hearts. To date, it is the only method of simultaneously measuring multiple key electrophysiological parameters, such as transmembrane voltage and intracellular free calcium, at high spatial and temporal resolution. Despite the impact it has already had on the fields of cardiac arrhythmias and whole-heart computational modeling, present-day system designs precludes its adoption by the broader cardiovascular research community because of their high costs. Taking advantage of recent technological advances, we developed and validated low-cost optical mapping systems for panoramic imaging using Langendorff-perfused pig hearts, a clinically-relevant model in basic research and bioengineering. By significantly lowering financial thresholds, this powerful cardiac electrophysiology imaging modality may gain wider use in research and, even, teaching laboratories, which we substantiated using the lower-cost Langendorff-perfused rabbit heart model., The CNIC is supported by the Ministry of Economy, Industry and Competitiveness (MINECO) and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (MINECO award SEV-2015-0505). This work was also partially supported by the following sources: Spanish Society of Cardiology (D.F.R.); Jesus Serra Foundation (D.F.R.); Carlos III Health Institute/European Regional Development Fund (ERDF) Grants: CB16/11/00458 (D.F.R., J.G.Q.), FIS PI12/00993 (C.J.C., J.M.), FIS PI15/00748 (C.J.C., J.M.) and FIS PI15/01408 (F.J.C); Generalitat Valenciana Grants GV/2015/019 (C.J.C.) and PROMETEO/2014/037 (C.J.C., F.J.C., J.M.). We thank Daniel Garcia-Leon for his assistance during the Langendorff-perfused heart experiments

Background: Decaying stem juice ofMusa acuminata ◊ balbisianais commonly used by local communities and traditional herbalist in Central Uganda in the management of cardiovascular conditions like hypertension. Aims: The study investigated the ionotropic and chronotropic effect of fresh and decaying stem juice ofMusa acuminata ◊ balbisianaon the isolated perfused rabbit heart. Materials andMethods :Methods. Study Design: An experimental study.

Alternans of action potential duration (APD) and intracellular calcium ([Ca2+]i) transients in the whole heart are thought to be markers of increased propensity to ventricular fibrillation during ischemia-reperfusion injuries. During ischemia, ATP production is affected and the mitochondria become uncoupled, which may affect alternans formation in the heart. The aim of our study was to investigate the role of mitochondria on the formation of APD and [Ca2+]i alternans in the isolated rabbit heart. We performed dual voltage and [Ca2+]i optical mapping of isolated rabbit hearts under control conditions, global no-flow ischemia ( n = 6), and after treatment with 50 nM of the mitochondrial uncoupler FCCP ( n = 6). We investigated the formation of alternans of APD, [Ca2+]i amplitude (CaA), and [Ca2+]i duration (CaD) under different rates of pacing. We found that treatment with FCCP leads to the early occurrence of APD, CaD, and CaA alternans; an increase of intraventricular APD but not CaD heterogeneity; and significant reduction in conduction velocity compared with that of control. Furthermore, we demonstrated that FCCP and global ischemia have similar effects on the prolongation of [Ca2+]i transients, whereas ischemia induces a significantly larger reduction of APD compared with that in FCCP treatment. In conclusion, our results demonstrate that uncoupling of mitochondria leads to an earlier occurrence of alternans in the heart. Thus, in conditions of mitochondrial stress, as seen during myocardial ischemia, uncoupled mitochondria may be responsible for the formation of both APD and [Ca2+]i alternans in the heart, which in turn creates a substrate for ventricular arrhythmias.

BackgroundIsoprenaline (ISO) acts through β-adrenergic receptors to increase the intracellular Ca2+, which has effects on action potential duration (APD) restitution and arrhythmogenesis. Thus, we investigated the effect of chronic stimulation with isoprenaline on APD restitution and ventricular tachyarrhythmias (VA) in the rabbit heart.Methods and resultsRabbits were randomly selected to receive an injection of isoprenaline (ISO group) or an equal volume of 0.9% saline (CTL group). The S1–S2 protocol (n=15) and S1 dynamic pacing (n=15) were performed to construct APD restitution and to induce APD alternans or arrhythmia in 10 sites of Langendorff-perfused hearts. Compared with the same sites in the control group, long-term ISO administration (7 days) shortened the APD90 and the effective refractory period (ERP), and greatly increased the spatial dispersion of APD and ERP (p

Supplemental Digital Content is available in the text., Background— External chest impacts (commotio cordis) can cause mechanically induced premature ventricular excitation (PVEM) and, rarely, ventricular fibrillation (VF). Because block of stretch-sensitive ATP-inactivated potassium channels curtailed VF occurrence in a porcine model of commotio cordis, VF has been suggested to arise from abnormal repolarization caused by stretch activation of potassium channels. Alternatively, VF could result from abnormal excitation by PVEM, overlapping with normal repolarization-related electric heterogeneity. Here, we investigate mechanisms and determinants of PVEM induction and its potential role in commotio cordis–induced VF. Methods and Results— Subcontusional mechanical stimuli were applied to isolated rabbit hearts during optical voltage mapping, combined with pharmacological block of ATP-inactivated potassium or stretch-activated cation-nonselective channels. We demonstrate that local mechanical stimulation reliably triggers PVEM at the contact site, with inducibility predicted by local tissue indentation. PVEM induction is diminished by pharmacological block of stretch-activated cation-nonselective channels. In hearts where electrocardiogram T waves involve a well-defined repolarization edge traversing the epicardium, PVEM can reliably provoke VF if, and only if, the mechanical stimulation site overlaps the repolarization wave edge. In contrast, application of short-lived intraventricular pressure surges neither triggers PVEM nor changes repolarization. ATP-inactivated potassium channel block has no effect on PVEM inducibility per se, but shifts it to later time points by delaying repolarization and prolonging refractoriness. Conclusions— Local mechanical tissue deformation determines PVEM induction via stretch-activation of cation-nonselective channels, with VF induction requiring PVEM overlap with the trailing edge of a normal repolarization wave. This defines a narrow, subject-specific vulnerable window for commotio cordis–induced VF that exists both in time and in space.

AIMS: Cardiac histo-anatomical organization is a major determinant of function. Changes in tissue structure are a relevant factor in normal and disease development, and form targets of therapeutic interventions. The purpose of this study was to test tools aimed to allow quantitative assessment of cell-type distribution from large histology and magnetic resonance imaging- (MRI) based datasets. METHODS AND RESULTS: Rabbit heart fixation during cardioplegic arrest and MRI were followed by serial sectioning of the whole heart and light-microscopic imaging of trichrome-stained tissue. Segmentation techniques developed specifically for this project were applied to segment myocardial tissue in the MRI and histology datasets. In addition, histology slices were segmented into myocytes, connective tissue, and undefined. A bounding surface, containing the whole heart, was established for both MRI and histology. Volumes contained in the bounding surface (called 'anatomical volume'), as well as that identified as containing any of the above tissue categories (called 'morphological volume'), were calculated. The anatomical volume was 7.8 cm(3) in MRI, and this reduced to 4.9 cm(3) after histological processing, representing an 'anatomical' shrinkage by 37.2%. The morphological volume decreased by 48% between MRI and histology, highlighting the presence of additional tissue-level shrinkage (e.g. an increase in interstitial cleft space). The ratio of pixels classified as containing myocytes to pixels identified as non-myocytes was roughly 6:1 (61.6 vs. 9.8%; the remaining fraction of 28.6% was 'undefined'). CONCLUSION: Qualitative and quantitative differentiation between myocytes and connective tissue, using state-of-the-art high-resolution serial histology techniques, allows identification of cell-type distribution in whole-heart datasets. Comparison with MRI illustrates a pronounced reduction in anatomical and morphological volumes during histology processing.

The non-invasive technique of optical mapping by using voltage-sensitive fluorescent dyes (VSFD), especially near-infrared (NIR) dyes. enables precise evaluation of electrical excitation propagation in the myocardium. However, in spite of considerable advantages when comparing with other clinical methods, OM is limited due to complicated data interpretation, fluorescent dye toxicity, and phototoxic effect, therefore, OM is used only in experimental studies. In this study we investigated the toxicity and phototoxicity of the novel NIR VSFD di 4 ANBDQBS, and their influence on the optical action potential (OAP) upstroke. The OAP upstroke provides information about electrical exitation propagation in cardiac tissue. The experiments were performed using the isolated cardiac cells of the rabbit heart, the right ventricle wall of the guinea pig heart, and the Langerdorf-perfused rabbit heart model. The results revealed that concentrations of 10–50 µM of di-4-ANBDQBS dye did not cause toxicity effects, and only 100 μM was determined as a toxic threshold which causes cardiac cell death. Also, we did not observe the phototoxic effect of the investigated dye in preparations of guinea pig ventricles. Registered temporary AP changes were just surface temperature variation that was caused by the light source. These temporary changes were not related with the phototoxic effect of the dye. Obtained transmural recordings of electrical APs via multiple cell layers in various depths of the LV wall enabled the calculation of averaged transmural-AP (TAP) and depth weighted DWTAP, which allowed evaluation of the OAP upstroke. The direction of excitation wave was simulated by artificial pacing from various cardiac surfaces. Simultaneous registration of OAP (by using di 4 ANBDQBS) and DWTAP (with microelectrodes) enabled to split the OAP upstroke into two components: the depth-weighted and the lateral-scattering, which corresponds to the components of the propagating electrical wave that are transmural (from endocardium to epicardium) and parallel to the epicardium. In this study the obtained data may have great value in evaluation of electrical signal formation and the formation of excitation in the heart under normal and pathological conditions.

Calcium/calmodulin-dependent protein kinase II (CaMKII) regulates the principle ion channels mediating cardiac excitability and conduction, but how this regulation translates to the normal and ischemic heart remains unknown. Diverging results on CaMKII regulation of Na+ channels further prevent predicting how CaMKII activity regulates excitability and conduction in the intact heart. To address this deficiency, we tested the effects of the CaMKII blocker KN93 (1 and 2.75 μM) and its inactive analog KN92 (2.75 μM) on conduction and excitability in the left (LV) and right (RV) ventricles of rabbit hearts during normal perfusion and global ischemia. We used optical mapping to determine local conduction delays and the optical action potential (OAP) upstroke velocity (d V/d tmax). At baseline, local conduction delays were similar between RV and LV, whereas the OAP d V/d tmax was lower in RV than in LV. At 2.75 μM, KN93 heterogeneously slowed conduction and reduced d V/d tmax, with the largest effect in the RV outflow tract (RVOT). This effect was further exacerbated by ischemia, leading to recurrent conduction block in the RVOT and early ventricular fibrillation (at 6.7 ± 0.9 vs. 18.2 ± 0.8 min of ischemia in control, P < 0.0001). Neither KN92 nor 1 μM KN93 depressed OAP d V/d tmax or conduction. Rabbit cardiomyocytes isolated from RVOT exhibited a significantly lower d V/d tmax than those isolated from the LV. KN93 (2.75 μM) significantly reduced d V/d tmax in cells from both locations. This led to frequency-dependent intermittent activation failure occurring predominantly in RVOT cells. Thus CaMKII blockade exacerbates intrinsically lower excitability in the RVOT, which is proarrhythmic during ischemia. NEW & NOTEWORTHY We show that calcium/calmodulin-dependent protein kinase II (CaMKII) blockade exacerbates intrinsically lower excitability in the right ventricular outflow tract, which causes highly nonuniform chamber-specific slowing of conduction and facilitates ventricular fibrillation during ischemia. Constitutive CaMKII activity is necessary for uniform and safe ventricular conduction, and CaMKII block is potentially proarrhythmic.

In the past decade, there has been an increased interest in characterizing cardiac tissue mechanics utilizing newly developed ultrasound-based elastography techniques. These methods excite the tissue mechanically and track the response. Two frequently used methods, acoustic radiation force impulse (ARFI) and shear-wave elasticity imaging (SWEI), have been considered qualitative and quantitative techniques providing relative and absolute measures of tissue stiffness, respectively. Depending on imaging conditions, it is desirable to identify indices of cardiac function that could be measured by ARFI and SWEI and to characterize the relationship between the measures. In this study, we have compared two indices (i.e., relaxation time constant used for diastolic dysfunction assessment and systolic/diastolic stiffness ratio) measured nearly simultaneously by M-mode ARFI and SWEI techniques. We additionally correlated ARFI-measured inverse displacements with SWEI-measured values of the shear modulus of stiffness. For the eight animals studied, the average relaxation time constant ( $\tau$ ) measured by ARFI and SWEI were ( ${69}{\pm }{18}\ \text{ms},\ \textit{R}^{{2}}={0.96}$ ) and ( ${65}{\pm }{19}\ \text{ms},\ \textit{R}^{{2}}={0.99}$ ), respectively ( $\text{ARFI}\hbox{-}\text{SWEI}\ \text{inter-rater agreement} = {0.90}$ ). Average systolic/diastolic stiffness ratios for ARFI and SWEI measurements were ${6.01}{\pm }{1.37}$ and ${7.12}{\pm }{3.24}$ , respectively ( $\text{agreement} = {0.70}$ ). Shear modulus of stiffness (SWEI) was linearly related to inverse displacement values (ARFI) with a 95% CI for the slope of 0.010–0.011 $({1}/\upmu\text{m})/(\text{kPa})$ ( $\textit{R}^{{2}}={0.73}$ ). In conclusion, the relaxation time constant and the systolic/diastolic stiffness ratio were calculated with good agreement between the ARFI- and SWEI-derived measurements. ARFI relative and SWEI absolute stiffness measurements were linearly related with varying slopes based on imaging conditions and subject tissue properties.

Cardiac studies on the uptake, storage and intramyocardial transfer of blood-borne substances require detailed information on the geometric ultrastructural dimensions of myocardial compartments and parts thereof, and the membranes separating these compartments. Such a specific ultrastructural set of data of the heart is yet lacking. In the present study, we quantitatively assessed these dimensions in glutaraldehyde-perfusion fixed rabbit hearts by means of histological and tailored mathematical techniques. We showed the true ellipsoid nature of the myocardial capillary cross section and estimated the mean capillary diameter dcap. After correction for the ellipsoid shape, dcap was found to be 5.21±1.41 μm. Effective widths of the endothelial cell and the pericapillary interstitium (is1), dimensions of importance in diffusion, amounted to 187±7 and 160±10 nm, respectively. The fractional volume of the large vessels (arteries and veins larger than 10 µm), capillaries, endothelium, is1, cardiomyocytes, non-pericapillary interstitium is2, t-tubular compartment and interstitial cells amounted on average to 5.92%, 9.36%, 1.83%, 1.94%, 73.07%, 5.97%, 0.95% and 0.96%, respectively, of total myocardial volume, defined as the cardiac tissue volume, the large blood vessels included. Normalized to total myocardial volume, the surface area of the luminal and abluminal endothelial membranes and of the cardiomyocyte membrane opposing the endothelial cells amounted to 75.2±5.5x103, 82.2±6.0x103 and 89.1±6.5x103 m2/m3, respectively. The present study provides quantitative information about ultrastructural dimensions of the adult rabbit heart, among others, of importance for studies on cardiac uptake, and intramyocardial transfer and storage of blood-supplied substances.

Cardiac electrophysiological heterogeneity related to the washout of acetylcholine (ACh) remains incompletely characterized. The aim of this study was to examine whether positive cardiac inotropic action is associated with electrophysiological heterogeneity between the atrium and the ventricle after ACh perfusion and washout. Epicardial monophasic action potentials (MAPs) from the right ventricle and right atrium, as well as cardiac contractility, were recorded from isolated Langendorff-perfused rabbit hearts using MAP electrodes and a force transducer. The results indicated that rebound positive inotropic actions were induced by ACh washout with adrenaline preconditioning. This effect was accompanied by an increase in MAP amplitude (MAPA) in the right ventricle but not the right atrium. These findings indicate that cholinergic muscarinic stimulation may lead to positive cardiac inotropic action followed by changes in regional electrophysiological heterogeneity between the atrial and ventricular myocardium. Therefore, we hypothesize that electrophysiological heterogeneity is an underlying cause of arrhythmogenesis as well as hemodynamic disturbance elicited by sudden termination of vagus stimulation.

AIMS: Left atrial (LA) stretch-associated electrophysiological changes in patients with mitral stenosis (MS) predispose to atrial fibrillation. We hypothesized that the normalization of the pressure gradient by percutaneous transvenous mitral balloon valvotomy (PTMV) affects LA but not right atrial (RA) conduction, depending on the site of stimulation. Because direction-dependent (asymmetric) changes of conduction may contribute to arrhythmogenesis, we assessed conduction symmetry in MS patients and tested whether it is restored by PTMV. METHODS AND RESULTS: In nine patients with MS, atrial effective refractory period and local activation times (ATs) were determined during stimulation before and after PTMV, with up to four decapolar catheters (LA and RA). Eight patients with ventricular pre-excitation served as controls. ATs at basic cycle length were similar before and after PTMV. With stimulation from either atrium, they were about 45 ms in the ipsilateral atrium and about 115 ms in the contralateral atrium. With premature stimulation, ATs increased dramatically. The shortest ATs were found in the RA with RA stimulation (78 +/- 9 and 80 +/- 6 ns, before and after PTMV). PTMV caused a shortening in LA-ATs (following LA stimulation) from 118 +/- 14 to 82 +/- 5 ms (before and after; P

BACKGROUND The effects of dyssynchrony on global left ventricular (LV) mechanics have been well documented; however, its impact on LV energetics has received less attention. OBJECTIVE To assess the effects of LV contraction dyssynchrony on global LV mechano-energetic function in a pacing-induced acute model of dyssynchrony. METHODS Using blood-perfused isolated rabbit heart preparations (n = 11), LV pressure, coronary flow, and arteriovenous oxygen content difference were recorded for isovolumic contractions under right atrial (RA) pacing (control) and simultaneous RA and right ventricular outflow tract (RVOT) pacing (dyssynchrony). LV mechanical function was quantified by the end-systolic pressure-volume relationship (ESPVR). Myocardial oxygen consumption-pressure-volume area (MVO(2)-PVA) relationship quantified LV energetic function. Internal PVA for MVO(2 RVOT) was calculated based on the MVO(2)-PVA relationship for RA pacing. Thus, lost PVA (internal PVA-PVA(RVOT)) represents the mechanical energy not observable at the global level. RESULTS Compared to RA pacing, RVOT pacing depressed LV mechanics as indicated by a rightward shift of ESPVR (i.e., increase in V(d) from 0.58 +/- 0.10 to 0.67 +/- 0.10 mL, P < 0.05). Despite depressed mechanics, RVOT pacing was associated with greater MVO(2) such that the MVO(2)-PVA relationship intercept was markedly increased from 0.025 +/- 0.003 to 0.029 +/- 0.003 mL*O(2)/beat/100gLV (P < 0.05). Excess MVO(2) (i.e., MVO(2 RVOT)- MVO(2 RA)) significantly correlated with lost PVA (R(2)= 0.54, P < 0.001). CONCLUSION A potential mechanism explaining the observed increase in MVO(2) with dyssynchrony may be that the measured PVA at the global level underestimates the internal PVA at the cellular level, which is likely to be the true determinant of MVO(2).

This study examined the significance of ECG-derived indexes in quantifying ventricular repolarization dispersion (VRD) given its value as a risk marker for severe myocardial arrhythmia. Multilead ECG recordings from an isolated rabbit heart model, including control and globally increased VRD (IVRD) beats, were studied. The IVRD was induced by supplying d-Sotalol (DS) or premature ventricular stimulation (PVS). ECG indexes came from (a) the absolute ECG summation signal, from which we obtained the amplitude and area of the T-wave, and the T-wave width ( T W ), which we consider as IVRD indexes, and (b) the Singular Value Decomposition (SVD) of the ECG, from which the θ PT (angle between the first SVD principal axis and the repolarization axis), T-wave residuum ( T WR ), T-wave morphology dispersion ( T MD ), unnormalized T MD ( UT MD ), and θ RT (the angle between the depolarization and the repolarization vectors) were estimated as IVRD indexes. Results were compared with the classical QT-based VRD indexes ( σ QT e , standard deviation of QT end). The main results are T W : 78.0 ± 10.3 vs. 133.6 ± 29.6 ms, for control vs. IVRD generated using DS, p 0.005 and 95.2 ± 7.9 vs. 118.5 ± 15.7 ms when PVS was used, p 0.007 ; σ QT e : gives 6.5 ± 1.4 vs. 11.6 ± 1.9 ms, for DS p 0.007 and 7.6 ± 2.2 vs. 13.0 ± 3.4 ms for PVS, p 0.007 ; respectively. θ PT : 35 ± 51 ° vs. 117 ± 49 ° , p 0.009 in DS. We concluded that globally induced IVRD is well reflected by the T W parameter, being the most sensitive of the studied ones. The IVRD can also be quantified by using the θ PT index.

The mechanisms underlying ventricular fibrillation (VF) are not well understood. The electrical activity on the heart surface during VF has been recorded extensively in the experimental setting and in some cases clinically; however, correspondingtransmuralactivation patterns are prohibitively difficult to measure. In this paper, we use a high-resolution biventricular heart model to study three-dimensional electrical activity during fibrillation, focusing on the driving sources of VF: “filaments,” the organising centres of unstable reentrant scroll waves. We show, for the first time, specific 3D filamentdynamicsduring simulated VF in a whole heart geometry that includes fine-scale anatomical structures. Our results suggest that transmural activity is much more complex than what would be expected from surface observations alone. We present examples of complex intramural activity, including filament breakup and reattachment, anchoring to the thin right ventricular apex; rapid transitions among various filament shapes; and filament lengths much greater than wall thickness. We also present evidence for anatomy playing a major role in VF development and coronary vessels and trabeculae influencing filament dynamics. Overall, our results indicate that intramural activity during simulated VF is extraordinarily complex and suggest that further investigation of 3D filaments is necessary to fully comprehend recorded surface patterns.

Optical signal is the image created from the propagating electrical signal. Due to optical features (absorption, scattering, etc.) of the heart tissue the coincidence between optical and electrical action potentials (APs) is moderate. Having electrical action potentials recorded transmurally, we aimed to evaluate contribution of the electrical and the optical features on OAP upstroke formation using blue-green and near-infrared (NIR) lights. Here we introduce a new approach in analysis of the electrical activity from the optical mapping (OM) studies by recording transmural-APs with glass-microelectrodes and comparing them with the OAP, obtained using blue-green (di-4-ANEPPS) and NIR (di-4-ANBDQBS) dyes in Langendorff-perfused rabbit heart under atrial/endo-/epicardial pacing. We used averaged upstroke of transmural-APs for isolation of electrical and optical (of dye/tissue) impacts influencing formation of OAP upstroke shape, and this had helped to split the OAP upstroke into components (depth-weighted and lateral-scattering). These components separately reflect the transmural and the parallel to the epicardium electrical propagating wave. In addition, to calculate depth-weighted component, we used the probing-depth constant for fluorescence measurement that was detected directly during the OM experiment, but not from separate measurements of the excitation and the emission light penetration. The detected probing-depth constant (k) for the NIR dye was ∼2 mm, while that magnitude was about twice smaller for the blue-green dye. The results of the study open a new opportunity for the future investigations of the electrical impulse propagation in the heart.This research was funded by the European Social Fund under the Global Grant measure.

Objective: Glucocorticoids have been used in the treatment of a number of diseases due to their widely therapeutic effects. But they have serious side effects. Although glucocorticoid therapy is an effective measure to prevent and treat many diseases in patients, it can cause adverse effects on the cardiovascular system secondary to oxidative stress. It has been suggested that melatonin is a potent antioxidant and that melatonin supplements may protect against such age-related diseases as atherosclerosis, cancer, and Alzheimer disease. In this study, we investigated whether such effects of a single high dose steroid has adverse consequences for the oxidant-antioxidant system of rabbit heart tissue and whether melatonin treatment is protective in the rabbit. For this purpose we measurument some biochemical parameters in the rabbit heart tissue.Methods: Level of malondialdehyde (MDA, a lipid peroxidation product), protein carbonyl (PC, a protein oxidation product) and nitric oxide (NO) were measured from heart tissue samples of all rabbits included in the study. Also antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase activities were measured from heart tissues. In the study, 20 rabbits were used. The rabbits were separated into three groups. Group I: Control group, group II: Methylprednisolone group, group III: Methylprednisolone plus melatonin group.Results: The results of the study; PC levels significantly decreased in methylprednisolone plus melatoninin group compared to the control group (p=0.03). PC levels decreased in methlyprednisolone group compared to the control group and higher than methlyprednisolone + melatonin group but these changes aren’t significant statistically. No statistical difference was determined by MDA, NO levels and SOD, GSH-Px, catalase activities of all groups.Conclusion: According to the results of this study we can say that administration of a single high dose methylprednisolone doesn’t increase oxidative stress Also, melatonine is a potent antioxidant agent in the heart tissue.

Introduction and objectives. The analysis of frequency variability during ventricular fibrillation has yielded inconsistent results. We used an experimental model of ventricular fibrillation, with a short timescale, to analyze variations in frequency and their associated spatial distribution. Methods. Epicardial recordings of ventricular fibrillation were made in 10 perfused isolated rabbit heart preparations using a multiple electrode system (i.e., 240 unipolar electrodes). Both spectral and time-frequency analysis were used to derive the dominant frequency in the anterolateral wall of the left ventricle. Results. Linear regression analysis showed that there was a good correlation between the dominant frequency obtained using the two signal analysis methods: frequency (spectral analysis) = 1.01 × frequency (time-frequency analysis) ‐ 0.4 (r=0.9; P

Background— The basis for the unique effectiveness of long-term amiodarone treatment on cardiac arrhythmias is incompletely understood. The present study investigated the pharmacogenomic profile of amiodarone on genes encoding ion-channel subunits. Methods and Results— Adult male mice were treated for 6 weeks with vehicle or oral amiodarone at 30, 90, or 180 mg · kg −1 · d −1 . Plasma and myocardial levels of amiodarone and N -desethylamiodarone increased dose-dependently, reaching therapeutic ranges observed in human. Plasma triiodothyronine levels decreased, whereas reverse triiodothyronine levels increased in amiodarone-treated animals. In ECG recordings, amiodarone dose-dependently prolonged the RR, PR, QRS, and corrected QT intervals. Specific microarrays containing probes for the complete ion-channel repertoire (IonChips) and real-time reverse transcription–polymerase chain reaction experiments demonstrated that amiodarone induced a dose-dependent remodeling in multiple ion-channel subunits. Genes encoding Na + (SCN4A, SCN5A, SCN1B), connexin (GJA1), Ca 2+ (CaCNA1C), and K + channels (KCNA5, KCNB1, KCND2) were downregulated. In patch-clamp experiments, lower expression of K + and Na + channel genes was associated with decreased I to,f , I K,slow , and I Na currents. Inversely, other K + channel α- and β-subunits, such as KCNA4, KCNK1, KCNAB1, and KCNE3, were upregulated. Conclusions— Long-term amiodarone treatment induces a dose-dependent remodeling of ion-channel expression that is correlated with the cardiac electrophysiologic effects of the drug. This profile cannot be attributed solely to the amiodarone-induced cardiac hypothyroidism syndrome. Thus, in addition to the direct effect of the drug on membrane proteins, part of the therapeutic action of long-term amiodarone treatment is likely related to its effect on ion-channel transcripts.

This paper presents the development of a bidomain model of electrical defibrillation and post-shock arrhythmogenesis of the rabbit heart. The model incorporates a realistic representation of cardiac geometry, fiber structure, and membrane ionic processes. Fibrillation is induced in the rabbit heart with burst pacing. Defibrillation shocks of various strengths are delivered to the model in an attempt to terminate the arrhythmia. Two sets of defibrillation simulations are conducted based on the waveform of the defibrillation shock: monophasic and biphasic. The simulations presented here demonstrate the feasibility of modeling realistically the effect of the defibrillation shock on the heart.

Cardiac ischemia causes beat-to-beat fluctuation in action potential duration (APD) alternans, which leads to T wave alternans and arrhythmias. Occurrence of APD alternans that is out of phase at two sites is especially important, but most APD alternans studies have involved rapid pacing of normal myocardium rather than ischemia. To determine the spatial features of APD alternans during ischemia, blood-perfused rabbit hearts were stained with 4-{β-[2(di- n-butylamino)-6-napthyl]vinyl}pyridinium (di-4-ANEPPS) and imaged with a high-resolution camera. Hearts were perfused with oxygenated Tyrode solution at 37°C for staining and then switched to a 50:50% blood/Tyrode mixture. Hearts were paced from the right ventricle at 3/s, and made ischemic by stopping flow for 6 min. Images of 10,000 pixels were obtained at 300 frames/s. Motion artifact was controlled by immobilization and by manual selection of undistorted single-pixel records. Upstroke propagation and conduction isochrones were displayed by computerized image processing. APD alternans was demonstrated in six of seven hearts, and was out of phase in different regions of the image in three hearts. The largest spatial variation in the onset of depolarization to 50% repolarization (APD50) was 155%. This caused beat-to-beat reversal of repolarization. An alternans map could be constructed for well-immobilized portions of the image. There were discrete regions of APD alternans separated by a boundary, as occurs with intracellular Ca2+ concentration alternans. Pixels as close together as 1.1 mm showed an APD alternans that was out of phase. The out-of-phase APD alternans was not due to conduction alternans, as shown by upstroke intervals and conduction isochrones. This contrasts with rapid pacing, where a causal relationship appears to exist. These new observations suggest distinct mechanisms for the genesis of arrhythmias during ischemia.