Search

Background Pulseless electrical activity (PEA) is a common initial rhythm in cardiac arrest. A substantial number of PEA arrests are caused by coronary ischemia in the setting of acute coronary occlusion, but the underlying mechanism is not well understood. We hypothesized that the initial rhythm in patients with acute coronary occlusion is more likely to be PEA than ventricular fibrillation in those with prearrest severe left ventricular dysfunction. Methods and Results We studied the initial cardiac arrest rhythm induced by acute left anterior descending coronary occlusion in swine without and with preexisting severe left ventricular dysfunction induced by prior infarcts in non–left anterior descending coronary territories. Balloon occlusion resulted in ventricular fibrillation in 18 of 34 naïve animals, occurring 23.5±9.0 minutes following occlusion, and PEA in 1 animal. However, all 18 animals with severe prearrest left ventricular dysfunction (ejection fraction 15±5%) developed PEA 1.7±1.1 minutes after occlusion. Conclusions Acute coronary ischemia in the setting of severe left ventricular dysfunction produces PEA because of acute pump failure, which occurs almost immediately after coronary occlusion. After the onset of coronary ischemia, PEA occurred significantly earlier than ventricular fibrillation (

Background: Phosphodiesterase type-1 (PDE1) hydrolyzes cAMP and cGMP and is constitutively expressed in the heart, although cardiac effects from its acute inhibition in vivo are largely unknown. Existing data are limited to rodents expressing mostly the cGMP-favoring PDE1A isoform. Human heart predominantly expresses PDE1C with balanced selectivity for cAMP and cGMP. Here, we determined the acute effects of PDE1 inhibition in PDE1C-expressing mammals, dogs, and rabbits, in normal and failing hearts, and explored its regulatory pathways. Methods: Conscious dogs chronically instrumented for pressure-volume relations were studied before and after tachypacing-induced heart failure (HF). A selective PDE1 inhibitor (ITI-214) was administered orally or intravenously±dobutamine. Pressure-volume analysis in anesthetized rabbits tested the role of β-adrenergic and adenosine receptor signaling on ITI-214 effects. Sarcomere and calcium dynamics were studied in rabbit left ventricular myocytes. Results: In normal and HF dogs, ITI-214 increased load-independent contractility, improved relaxation, and reduced systemic arterial resistance, raising cardiac output without altering systolic blood pressure. Heart rate increased, but less so in HF dogs. ITI-214 effects were additive to β-adrenergic receptor agonism (dobutamine). Dobutamine but not ITI-214 increased plasma cAMP. ITI-214 induced similar cardiovascular effects in rabbits, whereas mice displayed only mild vasodilation and no contractility effects. In rabbits, β-adrenergic receptor blockade (esmolol) prevented ITI-214–mediated chronotropy, but inotropy and vasodilation remained unchanged. By contrast, adenosine A 2B -receptor blockade (MRS-1754) suppressed ITI-214 cardiovascular effects. Adding fixed-rate atrial pacing did not alter the findings. ITI-214 alone did not affect sarcomere or whole-cell calcium dynamics, whereas β-adrenergic receptor agonism (isoproterenol) or PDE3 inhibition (cilostamide) increased both. Unlike cilostamide, which further enhanced shortening and peak calcium when combined with isoproterenol, ITI-214 had no impact on these responses. Both PDE1 and PDE3 inhibitors increased shortening and accelerated calcium decay when combined with forskolin, yet only cilostamide increased calcium transients. Conclusions: PDE1 inhibition by ITI-214 in vivo confers acute inotropic, lusitropic, and arterial vasodilatory effects in PDE1C-expressing mammals with and without HF. The effects appear related to cAMP signaling that is different from that provided via β-adrenergic receptors or PDE3 modulation. ITI-214, which has completed phase I trials, may provide a novel therapy for HF.

BackgroundPulseless electrical activity (PEA) is a very common rhythm in cardiac arrest and survival is ≈ 5%. Population data suggest coronary ischemia significantly contributes to PEA, but the mechanism is unknown.ObjectivesWe hypothesize ischemic preconditioning (IPC) in the setting of left ventricular (LV) dysfunction can convert ischemia-induced ventricular fibrillation (VF) into ischemia-induced PEA.MethodsUsing percutaneous coronary interventions in anesthetized swine, we studied the effect of IPC prior to ischemia on arrhythmic burden in normal animals and in animals with LV dysfunction. IPC protocol: four cycles of three minutes of coronary occlusion followed by seven minutes of reperfusion. Chronic LV dysfunction protocol: two serial infarcts in two coronary territories, separated by one week of recovery.ResultsIn normal animals, IPC prior to ischemia significantly reduced VF incidence (2/8 IPC vs. 7/8 control). In IPC animals with VF, the time to VF was significantly delayed (37.2 ± 7.3 min vs. 20.7 ± 4.9 min, pConclusionIPC delays/prevents VF. IPC with LV dysfunction prior to ischemia produces prolonged PEA. IPC with LV dysfunction prior to ischemia is likely an important mechanism for human PEA arrest. This is the first animal model of ischemic pulseless electrical activity.

Background— The nitroxyl (HNO) donor, Angeli’s salt, exerts positive inotropic, lusitropic, and vasodilator effects in vivo that are cAMP independent. Its clinical usefulness is limited by chemical instability and cogeneration of nitrite which itself has vascular effects. Here, we report on effects of a novel, stable, pure HNO donor (CXL-1020) in isolated myoctyes and intact hearts in experimental models and in patients with heart failure (HF). Methods and Results— CXL-1020 converts solely to HNO and inactive CXL-1051 with a t 1/2 of 2 minutes. In adult mouse ventricular myocytes, it dose dependently increased sarcomere shortening by 75% to 210% (50–500 μmol/L), with a ≈30% rise in the peak Ca 2+ transient only at higher doses. Neither inhibition of protein kinase A nor soluble guanylate cyclase altered this contractile response. Unlike isoproterenol, CXL-1020 was equally effective in myocytes from normal or failing hearts. In anesthetized dogs with coronary microembolization-induced HF, CXL-1020 reduced left ventricular end-diastolic pressure and myocardial oxygen consumption while increasing ejection fraction from 27% to 40% and maximal ventricular power index by 42% (both P Conclusions— These data show the functional efficacy of a novel pure HNO donor to enhance myocardial function and present first-in-man evidence for its potential usefulness in HF. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifiers: NCT01096043, NCT01092325.

Background— Slowed Na + current ( I Na ) decay and enhanced late I Na ( I Na-L ) prolong the action potential duration (APD) and contribute to early afterdepolarizations. Cardiac resynchronization therapy (CRT) shortens APD compared with dyssynchronous heart failure (DHF); however, the role of altered Na + channel gating in CRT remains unexplored. Methods and Results— Adult dogs underwent left-bundle branch ablation and right atrial pacing (200 beats/min) for 6 weeks (DHF) or 3 weeks followed by 3 weeks of biventricular pacing at the same rate (CRT). I Na and I Na-L were measured in left ventricular myocytes from nonfailing, DHF, and CRT dogs. DHF shifted voltage-dependence of I Na availability by −3 mV compared with nonfailing, enhanced intermediate inactivation, and slowed recovery from inactivation. CRT reversed the DHF-induced voltage shift of availability, partially reversed enhanced intermediate inactivation but did not affect DHF-induced slowed recovery. DHF markedly increased I Na-L compared with nonfailing. CRT dramatically reduced DHF-induced enhanced I Na-L , abbreviated the APD, and suppressed early afterdepolarizations. CRT was associated with a global reduction in phosphorylated Ca 2+ /Calmodulin protein kinase II, which has distinct effects on inactivation of cardiac Na + channels. In a canine AP model, alterations of I Na-L are sufficient to reproduce the effects on APD observed in DHF and CRT myocytes. Conclusions— CRT improves DHF-induced alterations of Na + channel function, especially suppression of I Na-L , thus, abbreviating the APD and reducing the frequency of early afterdepolarizations. Changes in the levels of phosphorylated Ca 2+ /Calmodulin protein kinase II suggest a molecular pathway for regulation of I Na by biventricular pacing of the failing heart.

To establish the relationship between HIV-induced cardiac diastolic dysfunction, immune responses, and virus replication in the heart using the simian immunodeficiency virus (SIV)/macaque model.Cardiac diastolic dysfunction is common in HIV-infected individuals including asymptomatic patients and those treated with combination antiretroviral therapy. SIV-infected macaques develop cardiac dysfunction, serving as a useful model to establish mechanisms underlying HIV-induced cardiac dysfunction. To understand the relationship between functional cardiac impairment, viral replication in the heart, and associated host inflammatory responses, cardiac function was evaluated in SIV-infected macaques and functional decline was correlated with features of the host immune response and the extent of viral replication in both the myocardium and plasma.Cardiac function was evaluated longitudinally in 22 SIV-infected and eight uninfected macaques using mitral inflow and tissue Doppler echocardiography. Myocardial macrophage populations were evaluated by CD68 and CD163 immunostaining. SIV RNA levels in both myocardium and plasma were measured by qRT-PCR.Echocardiographic abnormalities developed in SIV-infected macaques that closely resembled diastolic dysfunction reported in asymptomatic HIV-infected individuals. Although CD68 and CD163 were upregulated in the myocardium of SIV-infected animals, neither macrophage marker correlated with functional decline. SIV-induced diastolic dysfunction was strongly correlated with extent of SIV replication in the myocardium, implicating virus or viral proteins in the initiation and progression of cardiac dysfunction.This study demonstrated a strong correlation between cardiac functional impairment and extent of SIV replication in the myocardium, suggesting that persistent viral replication in myocardial macrophages induces cardiomyocyte damage manifest as diastolic dysfunction.

Background— Cardiac electromechanical dyssynchrony causes regional disparities in workload, oxygen consumption, and myocardial perfusion within the left ventricle. We hypothesized that such dyssynchrony also induces region-specific alterations in the myocardial transcriptome that are corrected by cardiac resynchronization therapy (CRT). Methods and Results— Adult dogs underwent left bundle branch ablation and right atrial pacing at 200 bpm for either 6 weeks (dyssynchronous heart failure, n=12) or 3 weeks, followed by 3 weeks of resynchronization by biventricular pacing at the same pacing rate (CRT, n=10). Control animals without left bundle branch block were not paced (n=13). At 6 weeks, RNA was isolated from the anterior and lateral left ventricular (LV) walls and hybridized onto canine-specific 44K microarrays. Echocardiographically, CRT led to a significant decrease in the dyssynchrony index, while dyssynchronous heart failure and CRT animals had a comparable degree of LV dysfunction. In dyssynchronous heart failure, changes in gene expression were primarily observed in the anterior LV, resulting in increased regional heterogeneity of gene expression within the LV. Dyssynchrony-induced expression changes in 1050 transcripts were reversed by CRT to levels of nonpaced hearts (false discovery rate Conclusions— Our results demonstrate a profound effect of electromechanical dyssynchrony on the regional cardiac transcriptome, causing gene expression changes primarily in the anterior LV wall. CRT corrected the alterations in gene expression in the anterior wall, supporting a global effect of biventricular pacing on the ventricular transcriptome that extends beyond the pacing site in the lateral wall.

Background— Cardiac resynchronization therapy (CRT) is the first clinical heart failure treatment that improves chamber systolic function in both the short-term and long-term yet also reduces mortality. The mechanical impact of CRT is immediate and well documented, yet its long-term influences on myocyte function and adrenergic modulation that may contribute to its sustained benefits are largely unknown. Methods and Results— We used a canine model of dyssynchronous heart failure (DHF; left bundle ablation, atrial tachypacing for 6 weeks) and CRT (DHF for 3 weeks, biventricular tachypacing for subsequent 3 weeks), contrasting both to nonfailing controls. CRT restored contractile synchrony and improved systolic function compared with DHF. Myocyte sarcomere shortening and calcium transients were markedly depressed at rest and after isoproterenol stimulation in DHF (both anterior and lateral walls), and CRT substantially improved both. In addition, β 1 and β 2 stimulation was enhanced, coupled to increased β 1 receptor abundance but no change in binding affinity. CRT also augmented adenylate cyclase activity over DHF. Inhibitory G-protein (Gα i ) suppression of β-adrenergic stimulation was greater in DHF and reversed by CRT. Gα i expression itself was unaltered; however, expression of negative regulators of Gα i signaling (particularly RGS3) rose uniquely with CRT over DHF and controls. CRT blunted elevated myocardial catecholamines in DHF, restoring levels toward control. Conclusions— CRT improves rest and β-adrenergic–stimulated myocyte function and calcium handling, upregulating β 1 receptors and adenylate cyclase activity and suppressing G i -coupled signaling associated with novel RGS upregulation. The result is greater rest and sympathetic reserve despite reduced myocardial neurostimulation as components underlying its net benefit.

Background— Cardiac dyssynchrony in the failing heart worsens global function and efficiency and generates regional loading disparities that may exacerbate stress-response molecular signaling and worsen cell survival. We hypothesized that cardiac resynchronization (CRT) from biventricular stimulation reverses such molecular abnormalities at the regional and global levels. Methods and Results— Adult dogs (n=27) underwent left bundle-branch radiofrequency ablation, prolonging the QRS by 100%. Dogs were first subjected to 3 weeks of atrial tachypacing (200 bpm) to induce dyssynchronous heart failure (DHF) and then randomized to either 3 weeks of additional atrial tachypacing (DHF) or biventricular tachypacing (CRT). At 6 weeks, ejection fraction improved in CRT (2.8±1.8%) compared with DHF (−4.4±2.7; P =0.02 versus CRT) dogs, although both groups remained in failure with similarly elevated diastolic pressures and reduced dP/dtmax. In DHF, mitogen-activated kinase p38 and calcium-calmodulin–dependent kinase were disproportionally expressed/activated (50% to 150%), and tumor necrosis factor-α increased in the late-contracting (higher-stress) lateral versus septal wall. These disparities were absent with CRT. Apoptosis assessed by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling staining, caspase-3 activity, and nuclear poly ADP-ribose polymerase cleavage was less in CRT than DHF hearts and was accompanied by increased Akt phosphorylation/activity. Bcl-2 and BAD protein diminished with DHF but were restored by CRT, accompanied by marked BAD phosphorylation, enhanced BAD–14-3-3 interaction, and reduced phosphatase PP1α, consistent with antiapoptotic effects. Other Akt-coupled modulators of apoptosis (FOXO-3α and GSK3β) were more phosphorylated in DHF than CRT and thus less involved. Conclusions— CRT reverses regional and global molecular remodeling, generating more homogeneous activation of stress kinases and reducing apoptosis. Such changes are important benefits from CRT that likely improve cardiac performance and outcome.

Uncoordinated contraction from electromechanical delay worsens heart failure pathophysiology and prognosis, but restoring coordination with biventricular pacing, known as cardiac resynchronization therapy (CRT), improves both. However, not every patient qualifies for CRT. We show that heart failure with synchronous contraction is improved by inducing dyssynchrony for 6 hours daily by right ventricular pacing using an intracardiac pacing device, in a process we call pacemaker-induced transient asynchrony (PITA). In dogs with heart failure induced by 6 weeks of atrial tachypacing, PITA (starting on week 3) suppressed progressive cardiac dilation as well as chamber and myocyte dysfunction. PITA enhanced β-adrenergic responsiveness in vivo and normalized it in myocytes. Myofilament calcium response declined in dogs with synchronous heart failure, which was accompanied by sarcomere disarray and generation of myofibers with severely reduced function, and these changes were absent in PITA-treated hearts. The benefits of PITA were not replicated when the same number of right ventricular paced beats was randomly distributed throughout the day, indicating that continuity of dyssynchrony exposure is necessary to trigger the beneficial biological response upon resynchronization. These results suggest that PITA could bring the benefits of CRT to the many heart failure patients with synchronous contraction who are not CRT candidates.

Heart failure (HF) with dyssynchrony treated with biventricular pacing (CRT) displays enhanced global and cellular function even compared to always synchronous HF. This suggests while HF is worsened by sustained dyssynchrony, it may paradoxically be improved by brief periods of Pacemaker Induced Transient Asynchrony (PITA). We tested this hypothesis in dogs tachypaced for 6 wks to induce HF. The HF group received atrial pacing and was compared to PITA (atrial pacing during day; right ventricular pacing, producing dyssynchrony, from 0000-0600). PITA blunted dilation (end diastolic and end systolic volumes reduced by 11 and 19%, respectively), reduced end-diastolic pressures from 22 to 13 mmHg, and improved the contractile response to dobutamine by 29%. Myocyte sarcomere shortening and calcium transient amplitude were depressed in HF and little improved by β adrenergic (βA) stimulation. PITA improved baseline function slightly, but virtually restored βA stimulated reserve. Membrane βA receptor density increased with PITA by 36% as well. Another contributor to the change in functional reserve was found in myofilament maximal calcium activated force (Fmax) normalized to cell cross sectional area (CSA). This declined ~40% in HF vs. Control, but was fully restored by PITA. However, as CSA was greater in HF and normalized by PITA, raw Fmax was similar despite hypertrophy in HF, suggesting HF myocytes had dysfunctional myofilaments, which PITA prevented. Electron microscopy confirmed normal myofilament structure in Control and PITA, whereas 40% of HF sarcomeres displayed deteriorated z-disks and loss of normal registration of the thick and thin filaments. In HF, 39% of HF isolated myofibrils produced virtually zero maximal force, whereas Control and PITA fibers functioned normally. Thus, there are two populations of myofibrils within HF hypertrophied cells, with ~40% structurally and functionally disrupted. PITA reverses this to restore force-calcium activation and with improved βA receptor signaling, restores functional reserve, suppressing chronic maladaptive remodeling. This surprising finding indicates PITA can ameliorate HF pathobiology and improve reserve function. Further studies are needed to test if such benefits translate to humans.

Background : Cardiac dyssynchrony due to intraventricular conduction delay produces heterogeneous regional wall stress and worsens arrhythmia susceptibility in failing hearts. We examined whether chronic dyssynchrony per se induces regionally heterogeneous electrophysiological remodeling. Methods and results : Adult dogs ( n =9) underwent left bundle branch radiofrequency ablation (QRS duration increased from 50 ± 7 to 104 ± 7 ms); 6 untreated dogs served as controls. A subset of ablated ( n =3) and control ( n =4) dogs underwent tagged MR imaging to confirm ablation-induced left ventricular (LV) dyssynchrony. Four weeks later, hearts were excised and early (anterior)- and late (lateral)-activated myocardial segments were isolated. Conduction velocity (CV), action potential duration (APD), and refractory period (RP) of paced, arterially perfused myocardial wedges were studied by extracellular and optical mapping, and arrhythmia susceptibility was assessed by programmed stimulation. Regional stress-response kinase, calcium cycling, and gap junction protein expression were assayed by Western blotting, and the subcellular distribution of connexin43 was analyzed by immunofluorescence microscopy. CV, APD, and RP were significantly reduced in the late-activated, lateral wall of dyssynchronous hearts compared to the anterior wall. Normal differences in CV (endocardial>epicardial) were reversed in the dyssynchronous lateral LV. While the total expression of connexin43 was unaltered in dyssynchronous models, its subcellular location was redistributed in late-activated myocardium from intercalated discs to lateral myocyte membranes. Arrhythmias were rare in tissue from normal and dyssynchronous models. Total expression of calcium-cycling proteins (sarcoplasmic reticulum Ca2+-ATPase and phospholamban) and the stress-response kinase phospho-ERK did not vary regionally in either model. Conclusions : Dyssynchrony even in the absence of LV dysfunction induces regionally specific changes in conduction and repolarization. These changes support a novel mechanism linking mechanical dyssynchrony to persistent electrophysiological remodeling and heterogeneity.

Background— Left ventricular (LV) mechanical dyssynchrony induces regional heterogeneity of mechanical load and is an independent predictor of mortality and sudden death in heart failure (HF) patients. We tested whether dyssynchrony also induces localized disparities in the expression of proteins involved with mechanical stress, function, and arrhythmia susceptibility. Methods and Results— Eleven dogs underwent tachycardia-induced HF pacing, either from the right atrium or high right ventricular free wall. Whereas global LV dysfunction was similar between groups, LV contractile coordination assessed by tagged MRI was markedly dyssynchronous with right ventricular pacing but synchronous with right atrial pacing. In dyssynchronous failing hearts, the lateral LV endocardium displayed a 2-fold increase in phosphorylated erk mitogen-activated protein kinase expression (with no change in phospho- p38 or phospho- jnk ), a 30% decline in sarcoplasmic reticulum Ca 2+ -ATPase, an 80% reduction in phospholamban, and a 60% reduction in the gap junction protein connexin43, relative to neighboring myocardial segments. In contrast, hearts from both right atrial–paced HF dogs and an additional 4 noninstrumented control animals showed minimal regional variability in protein expression. Conclusions— LV dyssynchrony in failing hearts generates myocardial protein dysregulation concentrated in the late-activated, high-stress lateral endocardium. Such molecular polarization within the LV creates transmural and transchamber expression gradients of calcium handling and gap junction proteins that may worsen chamber function and arrhythmia susceptibility.

Background Patients with acute myocardial infarction (MI), left bundle branch block (LBBB), and marked left ventricular (LV) decompensation suffer from nearly 50% early mortality. Whether cardiac resynchronization therapy (CRT) improves hemodynamic status in this condition is unknown. We tested CRT in this setting by using a canine model of delayed lateral wall (LW) activation combined with 2 hours of coronary artery occlusion-reperfusion. Objective This study aimed to evaluate the acute hemodynamic effects of CRT during and immediately after MI. Methods Adult dogs (n = 8) underwent open-chest 2-hour mid-left anterior descending artery occlusion followed by 1-hour reperfusion. Four pacing modes were compared: right atrial pacing, pseudo-left bundle block (right ventricular pacing), and CRT with the LV lead positioned at either the LW (LW-CRT) or the peri-infarct zone (peri-infarct zone-CRT). Continuous LV pressure-volume data, regional segment length, and proximal left anterior descending flow rates were recorded. Results At baseline, both right ventricular pacing and peri-infarct zone CRT reduced anterior wall regional work by ~50% (vs right atrial pacing). During coronary occlusion, this territory became dyskinetic, and dyskinesis rose further with both CRT modes as compared to pseudo-LBBB. Global cardiac output, stroke work, and ejection fraction all still improved by 11%–23%. After reperfusion, both CRT modes elevated infarct zone regional work and blood flow by ~10% as compared to pseudo-LBBB, as well as improved global function. Conclusion CRT improves global chamber systolic function in left ventricles with delayed LW activation during and after sustained coronary occlusion. It does so while modestly augmenting infarct zone dyskinesis during occlusion and improving regional function and blood flow after reperfusion. These findings support CRT in the setting of early post-MI dyssynchronous heart failure.

Abstract —Allopurinol, an inhibitor of xanthine oxidase, increases myofilament calcium responsiveness and blunts calcium cycling in isolated cardiac muscle. We sought to extend these observations to conscious dogs with and without pacing-induced heart failure and tested the prediction that allopurinol would have a positive inotropic effect without increasing energy expenditure, thereby increasing mechanical efficiency. In control dogs (n=10), allopurinol (200 mg IV) caused a small positive inotropic effect; (dP/dt) max increased from 3103±162 to 3373±225 mm Hg/s (+8.3±3.2%; P =0.01), but preload-recruitable stroke work and ventricular elastance did not change. In heart failure (n=5), this effect was larger; (dP/dt) max rose from 1602±190 to 1988±251 mm Hg/s (+24.4±8.7%; P =0.03), preload-recruitable stroke work increased from 55.8±9.1 to 84.9±12.2 mm Hg (+28.1±5.3%; P =0.02), and ventricular elastance rose from 6.0±1.6 to 10.5±2.2 mm Hg/mm ( P =0.03). Allopurinol did not affect myocardial lusitropic properties either in control or heart failure dogs. In heart failure dogs, but not controls, allopurinol decreased myocardial oxygen consumption (–49±4.6%; P =0.002) and substantially increased mechanical efficiency (stroke work/myocardial oxygen consumption; +122±42%; P =0.04). Moreover, xanthine oxidase activity was ≈4-fold increased in failing versus control dog hearts (387±125 versus 78±72 pmol/min · mg –1 ; P =0.04) but was not detectable in plasma. These data indicate that allopurinol possesses unique inotropic properties, increasing myocardial contractility while simultaneously reducing cardiac energy requirements. The resultant boost in myocardial contractile efficiency may prove beneficial in the treatment of congestive heart failure.

Cardiac resynchronization therapy (CRT), the application of biventricular stimulation to correct discoordinate contraction, is the only heart failure treatment that enhances acute and chronic systolic function, increases cardiac work, and reduces mortality. Resting myocyte function also increases after CRT despite only modest improvement in calcium transients, suggesting that CRT may enhance myofilament calcium responsiveness. To test this hypothesis, we examined adult dogs subjected to tachypacing-induced heart failure for 6 weeks, concurrent with ventricular dyssynchrony (HFdys) or CRT. Myofilament force-calcium relationships were measured in skinned trabeculae and/or myocytes. Compared with control, maximal calcium-activated force and calcium sensitivity declined globally in HFdys; however, CRT restored both. Phosphatase PP1 induced calcium desensitization in control and CRT-treated cells, while HFdys cells were unaffected, implying that CRT enhances myofilament phosphorylation. Proteomics revealed phosphorylation sites on Z-disk and M-band proteins, which were predicted to be targets of glycogen synthase kinase-3beta (GSK-3beta). We found that GSK-3beta was deactivated in HFdys and reactivated by CRT. Mass spectrometry of myofilament proteins from HFdys animals incubated with GSK-3beta confirmed GSK-3beta-dependent phosphorylation at many of the same sites observed with CRT. GSK-3beta restored calcium sensitivity in HFdys, but did not affect control or CRT cells. These data indicate that CRT improves calcium responsiveness of myofilaments following HFdys through GSK-3beta reactivation, identifying a therapeutic approach to enhancing contractile function.

Selective and specific changes in gene expression characterize the end-stage failing heart. However, the pattern and relation of these changes to evolving systolic and diastolic dysfunction during development of heart failure remains undefined. In the present study, we assessed steady-state levels of mRNAs encoding a group of cardiac proteins during the early development of left ventricular dysfunction in dogs with pacing-induced cardiomyopathy. Corresponding hemodynamic assessments were made in the conscious state in the same animals and at the same time points at baseline, after 1 week of ventricular pacing, and at the onset of clinical heart failure. Systolic dysfunction dominated after 1 week of pacing, whereas diastolic dysfunction was far more pronounced with the onset of heart failure. Atrial natriuretic factor mRNA was undetectable in 7 of 12 hearts at baseline but was expressed in all hearts at 1 week (P < .01 by chi 2 test), and it increased markedly with progression to failure (P = .05). Creatine kinase-B mRNA also rose markedly with heart failure (P < .01). Levels of mRNA encoding beta-myosin heavy chain, mitochondrial creatine kinase, phospholamban, and sarcoplasmic reticulum Ca(2+)-ATPase did not significantly change from baseline, despite development of heart failure. Additional analysis to determine if these mRNA changes were related to the severity of diastolic or systolic dysfunction revealed that phospholamban mRNA decreased in hearts with larger net increases in end-diastolic pressure (+19.2 +/- 1.9 mm Hg) compared with those hearts in which it did not change (+4.0 +/- 4.9, P < .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Dogs are susceptible to different tickborne infections, including members of the Anaplasmataceae (Ehrlichia canis, E. ewingii, E. chaffeensis, Anaplasma phagocytophilum, A. platys), Borrelia burgdorferi, and Rickettsia rickettsii. These diseases can manifest with clinical signs including fever, anorexia, malaise, lameness, rash, and bleeding episodes; however, these signs are nonpathognomonic, and infections can occur in the absence of clinical signs. Hematologic abnormalities can include leukopenia, thrombocytopenia, hyperproteinemia and hypergammaglobulinemia. In biomedical research, diseases such as canine monocytic ehrlichiosis, Lyme disease, and Rocky Mountain spotted fever may cause morbidity among exposed dogs and confound research results. Random-source dogs are susceptible to these diseases because of their increased risk of arthropod exposure. Nonpurpose bred, randomly selected conditioned dogs (n = 21) were examined; blood samples were taken for hematology, biochemistry analysis, tickborne pathogen serology, and PCR. Of these, 2 dogs (10% of the population) presented with illness characterized by fever, malaise, lameness, or hemostatic abnormalities, and 15 (71%) had antibodies to one or more tickborne pathogens. No specific hematologic or biochemical differences were apparent between seronegative dogs and seropositive dogs reactive to all 3 pathogens. E. canis and B. burgdorferi PCR of tissues and blood were negative for all dogs. PCR amplification of several Ehrlichia and Anaplasma genes yielded no positive samples. From this cohort of dogs, serologic and molecular results indicate prior exposure without active infection or clinical disease. Exposure to and potential for infection with these bacteria and other pathogens may contribute to blood and tissue alterations that could confound experiments and lead to misinterpretation of data in canine models.

End-stage heart failure (HF) is characterized by changes in conduction velocity (CV) that predispose to arrhythmias. Here, we investigate the time course of conduction changes with respect to alterations in connexin 43 (Cx43) properties and mechanical function during the development of HF. We perform high-resolution optical mapping in arterially perfused myocardial preparations from dogs subjected to 0, 3, 7, 14, and 21 days of rapid pacing to produce variable degrees of remodeling. CV is compared with an index of mechanical function [left ventricular end-diastolic pressure (LVEDP)] and with dynamic changes in the expression, distribution, and phosphorylation of Cx43. In contrast to repolarization, CV was preserved during early stages of remodeling (3 and 7 days) and significantly reduced at later stages, which were associated with marked increases in LVEDP. Measurements of differentially phosphorylated Cx43 isoforms revealed early, sustained downregulation of pan-Cx43 that preceded changes in CV and LVEDP, a gradual rise in a dephosphorylated Cx43 isoform to over twofold baseline levels in end-stage HF, and a late abrupt increase in pan-Cx43, but not dephosphorylated Cx43, lateralization. These data demonstrate that 1) CV slowing occurs only at advanced stages of remodeling, 2) total reduction of pan-Cx43 is an early event that precedes mechanical dysfunction and CV slowing, 3) changes in Cx43 phosphorylation are more closely associated with the onset of HF, and 4) Cx43 lateralization is a late event that coincides with marked CV reduction. These data reveal a novel paradigm of remodeling based on the timing of conduction abnormalities relative to changes in Cx43 isoforms and mechanical dysfunction.

Background— The efficacy of cardiac resynchronization therapy (CRT) depends on placement of the left ventricular lead within the late-activated territory. The geographic extent and 3-dimensional distribution of left ventricular (LV) locations yielding optimal CRT remain unknown. Methods and Results— Normal or tachypacing-induced failing canine hearts made dyssynchronous by right ventricular free wall pacing or chronic left bundle-branch ablation were acutely instrumented with a nonconstraining epicardial elastic sock containing 128 electrodes interfaced with a computer-controlled stimulation/recording system. Biventricular CRT was performed using a fixed right ventricular site and randomly selected LV sites covering the entire free wall. For each LV site, global cardiac function (conductance catheter) and mechanical synchrony (magnetic resonance imaging tagging) were determined to yield 3-dimensional maps reflecting CRT impact. Optimal CRT was achieved from LV lateral wall sites, slightly more anterior than posterior and more apical than basal. LV sites yielding ≥70% of the maximal dP/dtmax increase covered ≈43% of the LV free wall. This distribution and size were similar in both normal and failing hearts. The region was similar for various systolic and diastolic parameters and correlated with 3-dimensional maps based on mechanical synchrony from magnetic resonance imaging strain analysis. Conclusions— In hearts with delayed lateral contraction, optimized CRT is achieved over a fairly broad area of LV lateral wall in both nonfailing and failing hearts, with modest anterior or posterior deviation still capable of providing effective CRT. Sites selected to achieve the most mechanical synchrony are generally similar to those that most improve global function, confirming a key assumption underlying the use of wall motion analysis to optimize CRT.

Objectives The aim of this work was to test whether acute phosphodiesterase 5 (PDE5) inhibition via sildenafil (SIL) mimics and/or potentiates cardiorenal effects of exogenous natriuretic peptide (NP) infusion. Background Heart failure (HF) is often accompanied by elevated NP secretion yet blunted responsiveness. Such NP resistance may, in part, relate to increased cyclic guanosine monophosphate (cGMP) catabolism by PDE5. Methods Dogs (n = 7) were studied before and after tachypacing-induced HF. Animals received 30-min infusion of B-type natriuretic peptide (BNP) (2 μg/kg bolus, 0.02 μg/kg/min), and on a separate day SIL (1 mg/kg, intravenous), followed by BNP (SIL + BNP). Phosphodiesterase 5 activity was measured in lung, vasculature, and kidney. Results At baseline (non-failing), BNP lowered central venous, pulmonary capillary wedge, diastolic, mean pulmonary artery, and mean arterial pressure. Sildenafil had no effects, and SIL + BNP was similar to BNP alone. In contrast, SIL lowered these pressures similarly to BNP in dogs with HF, and SIL + BNP was additive in further reducing pulmonary pressures over BNP alone. Plasma cGMP/plasma BNP ratio was markedly reduced with HF, indicating NP resistance. Sildenafil plus BNP increased this ratio in HF, but had no effect in non-failing animals. Sildenafil had no independent diuretic/natriuretic effects nor did it enhance BNP effects under baseline or HF conditions. In HF, PDE5 activity was significantly increased in the systemic and pulmonary vasculature and in the kidney. Conclusions The PDE5 activity in systemic and pulmonary vasculature increases in HF rendering hemodynamic responses to PDE5 inhibition identical to those from BNP infusion. Natriuretic peptide desensitization in HF relates, in part, to increased PDE5 activity, supporting a therapeutic role for PDE5 inhibition.

Alterations of cardiac gene expression are central to ventricular dysfunction in human heart failure (HF). The canine tachycardia pacing-induced HF model is known to reproduce the main hemodynamic, echocardiographic and electrophysiological changes observed in human HF. In this study, we use this HF model to compare gene expression profiles in the left and right ventricles (LV, RV) of normal and end-stage failing canine hearts and compare the transcription profiles to those in human and murine models of HF. In end-stage HF, the LV exhibits down regulation of genes involved in energy production, cardiac contraction, and modulation of excitation-contraction coupling as compared with normal LV. The majority of transcriptomic changes between normal and end-stage canine HF were shared by the RV and LV. Genes down regulated only in the LV included those involved in aerobic energy production pathways, regulation of actin filament length, and enzyme-linked receptor protein signaling pathways. In normal canine hearts, genes encoding specific components of the contractile apparatus exhibit LV-RV asymmetric expression patterns; in failing hearts, cardiac fetal transcription factors MEF2 and MITF and the stress-responsive transcription factor ATF4 showed interventricular differences in expression. The comparison among the canine tachypacing, mouse transgenic, and human HF reveals that human disease involves down regulation of genes in a broad range of biological processes while experimentally induced HF is associated with down regulation of energy pathways, and that human ischemic HF and canine HF share a similar over representation of transcriptional pathways in the up regulated genes. This study provides insights into the molecular pathways leading to end-stage tachycardia-induced HF, and into global transcriptomic differences between the animal HF models and human HF.

Heart Failure (HF) is associated with an increased risk of sudden death caused by ventricular tachyarrhythmias. Recent studies have implicated repolarization abnormalities and, in particular, exaggerated heterogeneity of transmural repolarization in the genesis of polymorphic ventricular tachycardia in a canine model of nonischemic dilated cardiomyopathy. The presence and degree to which conduction abnormalities play a role in arrhythmogenesis in this model are uncertain. HF was produced in dogs by rapid RV-pacing for 3 to 4 weeks. High-resolution optical action potentials were recorded from epicardial and endocardial surfaces of arterially perfused canine wedge preparations isolated from LV and RV of normal and failing dogs. Cellular and molecular determinants of conduction were investigated using patch-clamp recordings, Western blot analysis, and immunocytochemistry. HF was associated with marked prolongation (by 33%) of the QRS duration of the volume conducted electrocardiogram and significant (>20%) slowing of epicardial and endocardial conduction velocities (CV) in both LV and RV. Cx43 expression was reduced by >40% in epicardial and endocardial layers of the LV, but was unchanged in the RV of failing hearts. Despite greater epicardial than endocardial Cx43 expression, epicardial CV was consistently slower ( P P P =0.8, not significant), and Masson trichrome staining revealed no significant change in fibrosis content in HF. Nonischemic dilated cardiomyopathy is associated with significant slowing of CV that was not directly related to reduced Cx43 expression. Changes in phosphorylation and localization of Cx43 may contribute to gap-junction dysfunction, CV slowing, and arrhythmias in HF.

Background— Biventricular (BiV) and left ventricular (LV) pacing similarly augment systolic function in left bundle-branch block (LBBB)-failing hearts despite different electrical activation. We tested whether electrical synchrony is required to achieve mechanical synchronization and functional benefit from pacing. Methods and Results— Epicardial mapping, tagged MRI, and hemodynamics were obtained in dogs with LBBB-failing hearts during right atrial, LV, and BiV stimulation. BiV and LV both significantly improved chamber hemodynamics (eg, 25% increase in dP/dt max and aortic pulse pressure) compared with atrial pacing-LBBB, and this improvement correlated with mechanical resynchronization. Electrical dispersion, however, decreased 13% with BiV but increased 23% with LV pacing ( P Conclusion— Improved mechanical synchrony and function do not require electrical synchrony. Mechanical coordination plays the dominant role in global systolic improvement with either pacing approach.

Abstract —Myocardial NO signaling appears elevated in heart failure (HF). Whether this results from increased NO production, induction of the high-output NO synthase (NOS)2 isoform, or changes in NOS regulatory pathways (such as caveolae) remains controversial. We tested the hypothesis that increased abundance of caveolin-3 and/or sarcolemmal caveolae contribute to increased NO signaling in pacing-induced HF. Abundance of caveolin-3 (0.59±0.08 versus 0.29±0.08 arbitrary units, P =0.01) but not caveolin-1 was increased in HF compared with control conditions, assessed by Western blot. Additionally, transmission electron microscopy revealed increased caveolae (2.7±0.4 versus 1.3±0.3 per micrometer myocyte membrane, P l - N G -methylarginine hydrochloride (L-NMMA) on β-adrenergic inotropy was assessed in conscious dogs before and after HF. In control dogs, dobutamine (5 μg · kg −1 · min −1 ) increased +dP/dt by 36±7%, and this was augmented to 66±24% by 20 mg/kg L-NMMA ( P =0.04 versus without L-NMMA, n=8) but not affected by 10 mg/kg L-NMMA (34±10%, P =NS; n=8). In HF, dobutamine +dP/dt response was depressed ( P −1 · min −1 , 48±7%). L-NMMA enhanced +dP/dt responses similarly at 10 mg/kg (61±17%, P =0.02; n=4) and 20 mg/kg (54±7%, P =0.04; n=7). Caveolin-3 abundance positively correlated with L-NMMA augmentation of dobutamine inotropic responses in HF ( r =0.9, P =0.03; n=4). Thus, in canine pacing-induced HF, expression of caveolin-3 and of sarcolemmal caveolae is increased. This increase is associated with augmented agonist-stimulated NO signaling, likely via a compartmentation effect.

Objectives. We sought to determine whether heart failure results in loss of cardiac magnesium sufficient to alter cellular electrophysiology. Background. Free magnesium has numerous intracellular roles affecting metabolism, excitability and RNA synthesis. Total cardiac magnesium content is reduced in heart failure, but it is unclear whether magnesium loss is primary or iatrogenic. Furthermore, it is unknown whether free magnesium levels are affected or whether a change in free magnesium would alter cellular electrophysiology. Methods. Eight mongrel dogs underwent demand ventricular pacing (VVI) at 250 beats/min for 3 weeks to induce heart failure. Sublingual epithelial magnesium was measured before pacing and at death. Left ventricular myocytes were isolated and loaded with Mag-Indo-1 to measure free magnesium ([Mg2+]i); myocytes from eight normal dogs served as controls. To test whether changes in [Mg2+]iin this range could alter cellular repolarization, current-clamped myocytes were dialyzed with 0.5 or 1.0 mmol/liter MgCl2. Results. Mean sublingual epithelial magnesium fell significantly in the paced animals, from 36.9 ± 0.5 to 33.9 ± 0.7 mEq/liter (p < 0.01). Mean cardiac [Mg2+]iwas significantly lower in the dogs with heart failure—0.49 ± 0.06 versus 1.06 ± 0.15 mmol/liter (p < 0.003). Time to 90% repolarization was significantly shorter in cells dialyzed with 1.0 mmol/liter compared with 0.5 mmol/liter MgCl2in myocytes from normal dogs or dogs with heart failure (596 ± 34 vs. 760 ± 58 ms in normal dogs and 586 ± 29 vs. 838 ± 98 ms in dogs with heart failure; p < 0.05 for each). Conclusions. Experimental heart failure results in both tissue and cardiac magnesium loss in the absence of drug therapy. Free cardiac magnesium is significantly reduced, possibly contributing to abnormal repolarization in heart failure.

Objectives. This study sought to determine whether the canine model of tachycardia-induced heart failure (HF) is an effective model for sudden cardiac death (SCD) in HF. Background. Such a well established HF model that also exhibits arrhythmias and SCD, along with repolarization abnormalities that could trigger them, may facilitate the study of SCD in HF, which still eludes effective treatment. Methods. Twenty-five dogs were VVI-paced at 250 beats/min for 3 to 5 weeks. Electrocardiograms were obtained, and left ventricular endocardial monophasic action potentials (MAPs) were recorded at six sites at baseline and after HF. Weekly Holter recordings were made with pacing suspended for 24 h. Results. Six animals (24%) died suddenly, one with Holter-documented polymorphic ventricular tachycardia (VT). Holter recordings revealed an increased incidence of VT as HF progressed. Repolarization was significantly (p < 0.05) prolonged, as indexed by a corrected QT interval (mean [±SD] 311 ± 25 to 338 ± 25 ms) and MAP duration measured at 90% repolarization (MAPD90) (181 ± 19 to 209 ± 28 ms), and spatial MAPD90dispersion rose by 40%. We further tested whether CsCl inhibition of repolarizing K+currents, which are reportedly downregulated in HF, might preferentially prolong the MAPD90in HF. With 1 mEq/kg body weight of CsCl, MAPD90rose by 86 ± 100 ms in dogs with HF versus only 28 ± 16 ms in control animals (p = 0.002). Similar disparities in CsCl sensitivity were observed in myocytes isolated from normal and failing hearts. Conclusions. Tachycardia-induced HF exhibits malignant arrhythmia and SCD, along with prolonged, heterogeneous repolarization and heightened sensitivity to CsCl at chamber and cellular levels. Thus, it appears to be a useful model for studying mechanisms and therapy of SCD in HF.

Background Age is an independent risk factor for increased mortality from ischemic heart disease. Arterial stiffening with widening of the pulse pressure may contribute to this risk by exacerbating cardiac dysfunction after total coronary artery occlusion. Methods and Results To test the above hypothesis, 14 open-chest dogs underwent surgery in which the intrathoracic aorta was bypassed with a stiff plastic tube. Directing ventricular outflow through the bypass widened the arterial pulse pressure from 41 to 115 mm Hg at similar mean pressure and flow. Hearts ejecting into the native aorta (NA) exhibited only modest dysfunction after 2 minutes of mid–left anterior descending coronary artery occlusion. However, the same occlusion applied during ejection into the bypass tube (BT) induced far more severe cardiodepression (ie, systolic pressure fell by −41±10 mm Hg for BT versus −15±3 mm Hg for NA, and end-systolic volume rose by 15±3 versus 6±2 mL), with a threefold greater decline in ejection fraction. This disparity was not due to higher baseline work loads because total pressure-volume area was similar in both cases. Furthermore, marked increases in basal work load and wall stress induced by angiotensin II infusion (in four additional studies) did not reproduce this behavior. Although peak systolic chamber stress was greater with the BT, this did not increase systolic dyskinesis as measured in the central ischemic zone. However, the total mass of myocardium that was rendered severely ischemic (ie, flow reduced by ≥80%) was twice as large with BT ejection, likely expanding the region of dyskinesis. This disparity may relate to altered phasic coronary flow during BT ejection, which displays marked enhancement of systolic flow and renders the heart more vulnerable to diminished mean and systolic perfusion pressures. Conclusions Cardiac ejection into a stiff systemic vasculature augments cardiac dysfunction and ischemia due to coronary occlusion by tightening the link between cardiac systolic performance and myocardial perfusion. This may contribute to the higher mortality risk from ischemic heart disease due to age.

This study tests the hypothesis that arterial vascular stiffening adversely influences in situ left ventricular contractile function and energetic efficiency. Ten reflex-blocked anesthetized dogs underwent a bypass operation in which a Dacron graft was sewn to the ascending aorta and connected to the infrarenal abdominal aorta via a plastic conduit. Flow was directed through either native aorta or plastic conduit by placement of vascular clamps. Arterial properties were measured from aortic pressure-flow data, and ventricular function was assessed by pressure-volume (PV) relations. Coronary sinus blood was drained via an extracorporeal circuit for direct measurement of myocardial O2 consumption (MVO2). Data at multiple steady-state preload volumes were combined to derive chamber function and energetics relations. Energetic efficiency was assessed by the inverse slope of the MVO2-PV area relation. Directing flow through plastic versus native aorta resulted in a 60-80% reduction in compliance but little change in mean resistance. Arterial pulse pressure rose from 34 to 99 mm Hg (p less than 0.001). Contractile function assessed by the end-systolic PV relation, stroke work-end-diastolic volume relation, and dP/dtmax at matched end-diastolic volume did not significantly change. However, MVO2 increased by 32% (p less than 0.01) and was matched by a rise in PV area, such that the MVO2-PV area relation and efficiency was unaltered. The MVO2 required to sustain a given stroke volume, however, increased from 20% to 40%, depending on the baseline level (p less than 0.001). Thus, whereas the contractile function and efficiency of normal hearts are not altered by ejection into a stiff vascular system, the energetic cost to the heart for maintaining adequate flow is increased. This suggests a mechanism whereby human vascular stiffening may yield little functional decrement at rest but limit reserve capacity under conditions of increased demand.

ObjectivesWe sought to test the efficacy of a passive elastic containment device to reverse chronic chamber remodeling and adrenergic down-regulation in the failing heart, yet still maintaining preload reserve.BackgroundProgressive cardiac remodeling due to heart failure is thought to exacerbate underlying myocardial dysfunction. In a pressure–volume analysis, we tested the impact of limiting progressive cardiac dilation by an externally applied passive containment device on both basal and adrenergic-stimulated function in failing canine hearts.MethodsIschemic dilated cardiomyopathy was induced by repeated intracoronary microembolizations in six dogs. The animals were studied before and three to six months after surgical implantation of a thin polyester mesh (cardiac support device [CSD]) that surrounded both cardiac ventricles. Pressure–volume relations were measured by a conductance micromanometer catheter.ResultsLong-term use of the CSD lowered end-diastolic and end-systolic volumes by −19 ± 4% and −22 ± 8%, respectively (both p < 0.0001) and shifted the end-systolic pressure–volume relation to the left (p < 0.01), compatible with reverse remodeling. End-diastolic pressure and chamber diastolic stiffness did not significantly change. The systolic response to dobutamine markedly improved after CSD implantation (55 ± 8% rise in ejection fraction after CSD vs. −10 ± 8% before CSD, p < 0.05), in conjunction with a heightened adenylyl cyclase response to isoproterenol. There was no change in the density or affinity of beta-adrenergic receptors. Diastolic compliance was not adversely affected, and preload-recruitable function was preserved with the CSD, consistent with a lack of constriction.ConclusionsReverse remodeling with reduced systolic wall stress and improved adrenergic signaling can be achieved by passive external support that does not generate diastolic constriction. This approach may prove useful in the treatment of chronic heart failure.