What causes sudden death in heart failure?

The role of Akt/GSK-3beta signaling in familial hypertrophic cardiomyopathy

Mutations in cardiac troponin T (TnT) are a cause of familial hypertrophic cardiomyopathy (FHC). Transgenic mice expressing a missense mutation (R92Q) or a splice site donor mutation (Trunc) in the cardiac TnT gene have mutation-specific phenotypes but mice of both models have smaller hearts compared to wild type and exhibit hemodynamic dysfunction. Because growth-related signaling pathways in the hearts of mice expressing TnT mutations are not known, we evaluated the impact of increased Akt or glycogen synthase kinase-3beta (GSK-3beta) activity in both mutant TnT mice; molecules that increase heart size via physiologic pathways and block pathologic growth, respectively. Expression of activated Akt dramatically augments heart size in both R92Q and Trunc mice; however, this increase in heart size is not beneficial, since Akt also increases fibrosis in both TnT mutants and causes some pathologic gene expression shifts in the R92Q mice. Activated GSK-3beta results in further decreases in left ventricular size in both R92Q and Trunc hearts, but this decrease is associated with significant mutation-specific phenotypes. Among many pathologic consequences, activating GSK-3beta in R92Q hearts decreases phosphorylation of troponin I and results in early mortality. In contrast, increased GSK-3beta activity in Trunc hearts does not significantly impact cardiac phenotypes. These findings demonstrate that increased Akt and its downstream target, GSK-3beta can impact both cardiac size and phenotype in a mutation-specific manner. Moreover, increased activity of these molecules implicated in beneficial cardiac phenotypes exacerbates the progression of disease in the R92Q TnT mutant.

Mechanisms of recurrent ventricular fibrillation in a rabbit model of pacing-induced heart failure

BACKGROUND

Successful defibrillation may be followed by recurrent spontaneous ventricular fibrillation (VF). The mechanisms of postshock spontaneous VF are unclear.

OBJECTIVE

The purpose of this study was to determine the mechanisms of spontaneous VF after initial successful defibrillation in a rabbit model of heart failure (HF).

METHODS

Simultaneous optical mapping of intracellular calcium (Ca(i)) and membrane potential (Vm) was performed in 12 rabbit hearts with chronic pacing-induced heart failure, in 4 sham-operated hearts, and in 5 normal hearts during fibrillation-defibrillation episodes.

RESULTS

Twenty-eight spontaneous VF episodes were recorded after initial successful defibrillation in 4 failing hearts (SVF group) but not in the remaining 8 failing hearts (no-SVF group) or in the normal or sham-operated hearts. The action potential duration (APD(80)) before pacing-induced VF was 209 +/- 9 ms in the SVF group and 212 +/- 14 ms in the no-SVF group (P = NS). After successful defibrillation, APD(80) shortened to 147 +/- 26 ms in the SVF group and to 176 +/- 14 ms in the no-SVF group (P = .04). However, the duration of Ca(i) after defibrillation was not different between the two groups (246 +/- 21 ms vs 241 +/- 17 ms, P = NS), resulting in elevated Ca(i) during late phase 3 or phase 4 of the action potential. Standard glass microelectrode recording in an additional 5 failing hearts confirmed postshock APD shortening and afterdepolarizations. APD(80) of normal and sham-operated hearts was not shortened after defibrillation.

CONCLUSION

HF promotes acute shortening of APD immediately after termination of VF in failing hearts. Persistent Ca(i) elevation during late phase 3 and phase 4 of the shortened action potential result in afterdepolarizations, triggered activity, and spontaneous VF.

Beta-adrenoceptor stimulation exacerbates detrimental effects of ischemia and reperfusion in isolated guinea pig ventricular myocytes

We investigated whether beta-adrenoceptor stimulation exacerbates detrimental effects of ischemia and reperfusion on electrical and contractile function and on intracellular Ca(2+) homeostasis in isolated guinea pig ventricular myocytes. Myocytes were exposed to 20 min of simulated ischemia (37 degrees C) in the absence or presence of isoproterenol (10 nM, applied prior to and during ischemia) and reperfused with Tyrode's solution for 30 min. Unloaded cell shortening, Ca(2+) transients (fura-2), and cell viability were recorded at 5 min intervals in field-stimulated cells (2 Hz). In experiments using microelectrodes, membrane potentials, contractions, and transmembrane currents also were recorded at 5 min intervals. In the absence of ischemia, 10 nM isoproterenol had little effect on either contractile function or Ca(2+) homeostasis. In contrast, when cells were exposed to ischemia, isoproterenol increased the size of contractions and Ca(2+) transients and augmented the increase in diastolic Ca(2+) concentration during ischemia in field-stimulated myocytes. Exposure to isoproterenol also promoted contractile depression in reperfusion. In voltage clamp experiments, isoproterenol abolished the decrease in the magnitude of L-type Ca(2+) current caused by ischemia. Isoproterenol also increased the incidence of abnormal contractile activity and induced delayed afterdepolarizations and the arrhythmogenic transient inward current in ischemia. Additionally, the decline in cell viability in ischemia and reperfusion was exacerbated by isoproterenol. This study shows that beta-adrenoceptor stimulation strongly potentiates adverse effects of ischemia and reperfusion on electrical and contractile function. These adverse effects of isoproterenol are likely caused by an increase in intracellular Ca(2+) accumulation during ischemia.

Arrhythmia mechanisms in the failing heart

BACKGROUND

Heart failure (HF) claims over 200,000 lives annually in the United States alone. Approximately 50% of these deaths are sudden and unexpected, and presumably the consequence of lethal ventricular tachyarrhythmias. Electrical remodeling that occurs at the cellular and tissue network levels predisposes patients with HF to malignant arrhythmias. Our limited understanding of fundamental arrhythmia mechanisms has hampered the development of effective treatment strategies for these patients.

METHODS AND CONCLUSIONS

In this review, we outline recent advances in our understanding of arrhythmia mechanisms in the failing heart, highlighting various aspects of remodeling of ion channels, calcium handling proteins, and gap junction-related molecules. As will be discussed, these changes promote the prolongation of the action potential, the enhancement of spatio-temporal gradients of repolarization, the formation of calcium-mediated triggers and conduction abnormalities, all of which combine to form an electrophysiological substrate that is ripe for the genesis of lethal arrhythmias and sudden cardiac death.

Tachycardia-induced early afterdepolarizations: insights into potential ionic mechanisms from computer simulations

Although early afterdepolarizations (EADs) are classically thought to occur at slow heart rates, mounting evidence suggests that EADs may also occur at rapid heart rates produced by tachyarrhythmias, due to Ca overload of the sarcoplasmic reticulum (SR) leading to spontaneous SR Ca release. We hypothesized that the mechanism of tachycardia-induced EADs depends on the spatial and temporal morphology of spontaneous SR Ca release, and tested this hypothesis in computer simulations using a ventricular action potential mathematical model. Using two previously suggested spontaneous release morphologies, we found two distinct tachycardia-induced EAD mechanisms: one mechanistically similar to bradycardia-induced EADs, the other to delayed afterdepolarizations (DADs).

Calcitriol ameliorates capillary deficit and fibrosis of the heart in subtotally nephrectomized rats

BACKGROUND

Remodelling of the heart, characterized by hypertrophy, fibrosis and capillary/myocyte mismatch, is observed in patients with chronic renal failure. Low vitamin D levels have been associated with increased cardiovascular risk. In the present experimental study, we studied the effects of non-hypercalcaemic doses of calcitriol on microvascular disease and interstitial fibrosis of the heart.

METHODS

Three-month-old male Sprague-Dawley rats were randomized to subtotal nephrectomy (SNX) or sham operation and received calcitriol (6 ng/kg) or vehicle starting immediately thereafter. Blood pressure was measured by tail pletysmography. Albuminuria was measured by rat-specific ELISA. Capillary length density, volume density of interstitial tissue, immunohistochemistry and western blots (vitamin D receptor, collagen I, III, TGF-beta(1), MAP kinases and nitrotyrosine) were assessed after 12 weeks of treatment.

RESULTS

After SNX blood pressure, albuminuria and heart weight were elevated, capillary length density reduced and interstitial fibrosis increased. Treatment with calcitriol reduced albuminuria and prevented reduction of capillary density and expansion of interstitium without affecting significant blood pressure and heart weight after perfusion fixation. Calcitriol left high VEGF unchanged, but upregulated VEGF receptor 2 (presumably reversing VEGF resistance). Calcitriol reduced expression of profibrotic TGF-beta(1) and the accumulation of collagens I and III.

CONCLUSIONS

Non-hypercalcaemic doses of calcitriol ameliorated, directly or indirectly, cardiac remodelling in sub- totally nephrectomized rats.

Late sodium current is a new therapeutic target to improve contractility and rhythm in failing heart

Most cardiac Na+ channels open transiently within milliseconds upon membrane depolarization and are responsible for the excitation propagation. However, some channels remain active during hundreds of milliseconds, carrying the so-called persistent or late Na+ current (I(NaL)) throughout the action potential plateau. I(NaL) is produced by special gating modes of the cardiac-specific Na+ channel isoform. Experimental data accumulated over the past decade show the emerging importance of this late current component for the function of both normal and especially failing myocardium, where I(NaL) is reportedly increased. Na+ channels represent a multi-protein complex and its activity is determined not only by the pore-forming alpha subunit but also by its auxiliary beta subunits, cytoskeleton, and by Ca2+ signaling and trafficking proteins. Remodeling of this protein complex and intracellular signaling pathways may lead to alterations of I(NaL) in pathological conditions. Increased I(NaL) and the corresponding Na+ influx in failing myocardium contribute to abnormal repolarization and an increased cell Ca2+ load. Interventions designed to correct I(NaL) rescue normal repolarization and improve Ca2+ handling and contractility of the failing cardiomyocytes. New therapeutic strategies to target both arrhythmias and deficient contractility in HF may not be limited to the selective inhibition of I(NaL) but also include multiple indirect, modulatory (e.g. Ca(2+)- or cytoskeleton- dependent) mechanisms of I(NaL) function.

Remodelling of cardiac repolarization: how homeostatic responses can lead to arrhythmogenesis

Cardiac action potentials (APs) are driven by ionic currents flowing through specific channels and exchangers across cardiomyocyte membranes. Once initiated by rapid Na(+) entry during phase 0, the AP time course is determined by the balance between inward depolarizing currents, carried mainly by Na(+) and Ca(2+), and outward repolarizing currents carried mainly by K(+). K(+) currents play a major role in repolarization. The loss of a K(+) current can impair repolarization, but there is a redundancy of K(+) currents so that when one K(+) current is dysfunctional, other K(+) currents increase to compensate, a phenomenon called 'repolarization reserve'. Repolarization reserve protects repolarization under conditions that increase inward current or reduce outward current, threatening the balance that governs AP duration. This protection comes at the expense of reduced repolarization reserve, potentially resulting in unexpectedly large AP prolongation and arrhythmogenesis, when an additional repolarization-suppressing intervention is superimposed. The critical role of appropriate repolarization is such that cardiac rhythm stability can be impaired with either abnormally slow or excessively rapid repolarization. In cardiac disease states such as heart failure and atrial fibrillation (AF), changes in ion channel properties appear as part of an adaptive response to maintain function in the face of disease-related stress on the cardiovascular system. However, if the stress is maintained the adaptive ion channel changes may themselves lead to dysfunction, in particular cardiac arrhythmias. The present article reviews ionic remodelling of cardiac repolarization, and focuses on how potentially adaptive repolarization changes with congestive heart failure and AF can have arrhythmogenic consequences.

Increased QT variability in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

BACKGROUND AND PURPOSE

Although sudden death (SD) accounts for numerous cases of premature mortality in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the risk factors responsible for this dramatic event remain unclear. We sought possible differences in the QT variability index (QTVI) -- a well-known index of temporal dispersion in myocardial repolarization strongly associated with the risk of SD -- between a group of patients with CADASIL and healthy controls.

METHODS

A total of 13 patients with CADASIL and 13 healthy volunteers underwent a 5-min electrocardiogram recording to calculate the QTVI. All the patients also underwent a clinical assessment, including functional status by Rankin score, and a magnetic resonance imaging (MRI) brain scan for quantitative analysis of T2-weighted (T2-W) and T1-weighted (T1-W) lesion volume (LV).

RESULTS

Short-term QT-interval analysis showed significantly higher QTVI (P = 0.029) in patients than in controls. In patients, notwithstanding the limitations of the small sample size, QTVI also well correlated with T1-W LV (r = 0.747, P = 0.003) and T2-W LV (r = 0.731, P = 0.005).

CONCLUSION

Because patients with CADASIL have increased temporal cardiac repolarization variability as assessed by QTVI, this mechanism could underlie these patients' risk of SD. Whether this easily assessed, non-invasive marker could be used to stratify the risk of malignant ventricular arrhythmias in patients with CADASIL and, possibly, to guide their therapeutic management warrants confirmation from larger prospective studies.

Mechanisms underlying rate-dependent remodeling of transient outward potassium current in canine ventricular myocytes

Transient outward K+ current (I to) downregulation following sustained tachycardia in vivo is usually attributed to tachycardiomyopathy. This study assessed potential direct rate regulation of cardiac I(to) and underlying mechanisms. Cultured adult canine left ventricular cardiomyocytes (37 degrees C) were paced continuously at 1 or 3 Hz for 24 hours. I to was recorded with whole-cell patch clamp. The 3-Hz pacing reduced I to by 44% (P<0.01). Kv4.3 mRNA and protein expression were significantly reduced (by approximately 30% and approximately 40%, respectively) in 3-Hz paced cells relative to 1-Hz cells, but KChIP2 expression was unchanged. Prevention of Ca2+ loading with nimodipine or calmodulin inhibition with W-7, A-7, or W-13 eliminated 3-Hz pacing-induced I to downregulation, whereas downregulation was preserved in the presence of valsartan. Inhibition of Ca2+/calmodulin-dependent protein kinase (CaMK)II with KN93, or calcineurin with cyclosporin A, also prevented I to downregulation. CaMKII-mediated phospholamban phosphorylation at threonine 17 was increased in 3-Hz paced cells, compatible with enhanced CaMKII activity, with functional significance suggested by acceleration of the Ca2+i transient decay time constant (Indo 1-acetoxymethyl ester microfluorescence). Total phospholamban expression was unchanged, as was expression of Na+/Ca2+ exchange and sarcoplasmic reticulum Ca2+-ATPase proteins. Nuclear localization of the calcineurin-regulated nuclear factor of activated T cells (NFAT)c3 was increased in 3-Hz paced cells compared to 1-Hz (immunohistochemistry, immunoblot). INCA-6 inhibition of NFAT prevented I to reduction in 3-Hz paced cells. Calcineurin activity increased after 6 hours of 3-Hz pacing. CaMKII inhibition prevented calcineurin activation and NFATc3 nuclear translocation with 3-Hz pacing. We conclude that tachycardia downregulates I to expression, with the Ca2+/calmodulin-dependent CaMKII and calcineurin/NFAT systems playing key Ca2+-sensing and signal-transducing roles in rate-dependent I to control.

Elevated temporal lability of myocardial repolarization after coronary artery bypass grafting

INTRODUCTION

Ventricular arrhythmias are uncommon after coronary artery bypass grafting (CABG), but the incidence and mortality are high in certain subsets of patients during the early recovery after surgery. Elevated temporal lability of myocardial repolarization has been associated with sudden cardiac death. The aim of the current study was to explore temporal variability of myocardial repolarization during both early and longtime follow-up after CABG.

METHODS AND RESULTS

Patients (n = 61) who had undergone CABG and healthy subjects (HS, n = 33) were examined. Electrocardiogram and beat-to-beat blood pressure were recorded at 5 weeks and 5 months after surgery. The QT variability index (QTVI) was calculated as the log ratio between the temporal variabilities of the QT and RR intervals. The QTVI and QT variances were elevated by 40% and 44%, whereas RR variances were reduced by 40% among patients 5 weeks after CABG compared to HS (-0.90 +/- 0.59, 29 +/- 30, and 1223 +/- 1895 ms(2) vs -1.50 +/- 0.29, 15 +/- 16, and 2200 +/- 2877 ms(2) for HS; P < .01 for all). The QTVI and QT variances decreased by 38% and 31% between 5 weeks and 5 months after CABG, whereas the RR variances increased by 51% (P < .01 for all). The QTVI values remained elevated among patients compared to HS at 5 months after CABG (P < .01), whereas QT and RR variances did not differ.

CONCLUSION

Elevated temporal lability of myocardial repolarization prevails particularly during the early recovery phase after CABG and may reflect increased susceptibility to ventricular arrhythmia.

Cardiac sodium channel overlap syndromes: different faces of SCN5A mutations

Cardiac sodium channel dysfunction caused by mutations in the SCN5A gene is associated with a number of relatively uncommon arrhythmia syndromes, including long-QT syndrome type 3 (LQT3), Brugada syndrome, conduction disease, sinus node dysfunction, and atrial standstill, which potentially lead to fatal arrhythmias in relatively young individuals. Although these various arrhythmia syndromes were originally considered separate entities, recent evidence indicates more overlap in clinical presentation and biophysical defects of associated mutant channels than previously appreciated. Various SCN5A mutations are now known to present with mixed phenotypes, a presentation that has become known as "overlap syndrome of cardiac sodium channelopathy." In many cases, multiple biophysical defects of single SCN5A mutations are suspected to underlie the overlapping clinical manifestations. Here, we provide an overview of current knowledge on SCN5A mutations associated with sodium channel overlap syndromes and discuss a possible role for modifiers in determining disease expressivity in the individual patient.

Epac activation, altered calcium homeostasis and ventricular arrhythmogenesis in the murine heart

The recently described exchange protein directly activated by cAMP (Epac) has been implicated in distinct protein kinase A-independent cellular signalling pathways. We investigated the role of Epac activation in adrenergically mediated ventricular arrhythmogenesis. In contrast to observations in control conditions (n = 20), monophasic action potentials recorded in 2 of 10 intrinsically beating and 5 of 20 extrinsically paced Langendorff-perfused wild-type murine hearts perfused with the Epac activator 8-pCPT-2'-O-Me-cAMP (8-CPT, 1 microM) showed spontaneous triggered activity. Three of 20 such extrinsically paced hearts showed spontaneous ventricular tachycardia (VT). Programmed electrical stimulation provoked VT in 10 of 20 similarly treated hearts (P < 0.001; n = 20). However, there were no statistically significant accompanying changes (P > 0.05) in left ventricular epicardial (40.7 +/- 1.2 versus 44.0 +/- 1.7 ms; n = 10) or endocardial action potential durations (APD(90); 51.8 +/- 2.3 versus 51.9 +/- 2.2 ms; n = 10), transmural (DeltaAPD(90)) (11.1 +/- 2.6 versus 7.9 +/- 2.8 ms; n = 10) or apico-basal repolarisation gradients, ventricular effective refractory periods (29.1 +/- 1.7 versus 31.2 +/- 2.4 ms in control and 8-CPT-treated hearts, respectively; n = 10) and APD(90) restitution characteristics. Nevertheless, fluorescence imaging of cytosolic Ca(2+) levels demonstrated abnormal Ca(2+) homeostasis in paced and resting isolated ventricular myocytes. Epac activation using isoproterenol in the presence of H-89 was also arrhythmogenic and similarly altered cellular Ca(2+) homeostasis. Epac-dependent effects were reduced by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibition with 1 microM KN-93. These findings associate VT in an intact cardiac preparation with altered cellular Ca(2+) homeostasis and Epac activation for the first time, in the absence of altered repolarisation gradients previously implicated in reentrant arrhythmias through a mechanism dependent on CaMKII activity.

Molecular basis of funny current (If) in normal and failing human heart

I(f) overexpression has been functionally demonstrated in ventricular myocytes from failing human hearts. Altered expression of I(f)-channels as a consequence of electrophysiological remodeling may represent an arrhythmogenic mechanism in heart failure; however, the molecular basis of I(f) overexpression in human cardiac disease is unknown. HCN1, 2 and 4 subtypes, which encode I(f)-channels, have been identified in the heart. The present study was designed to characterize HCN isoform expression in failing and non-failing hearts. Ventricular and atrial samples were obtained from normal or failing hearts explanted from patients with end-stage ischemic cardiomyopathy. I(f) was recorded in patch-clamped left ventricular myocytes. mRNA and protein expression of HCN subunits were measured in both atria and ventricles of control and diseased hearts. HCN2 and HCN4 were detected in human myocardium. Both mRNA and protein levels of HCN2/4 were significantly augmented in failing ventricles (p<0.01 for mRNA, p<0.05 for protein). These results are consistent with the electrophysiological data showing that, in failing ventricular myocytes, I(f) is of larger amplitude and activates at less negative potential. Changes in mRNA and protein expression of both HCN2/4 isoforms in atrial specimens from patients with heart failure mirrored those observed in ventricles (p<0.001 for mRNA, p<0.05 for protein). No disease-dependent alteration was detected for MiRP1, the putative beta-subunit of the I(f)-channel. In conclusion, HCN4 is the predominant channel subtype in normal human heart, and its expression is further amplified by disease. HCN upregulation likely contributes to increased I(f) and may play a role in ventricular and atrial arrhythmogenesis in heart failure.

Effects of pink grapefruit juice on QT variability in patients with dilated or hypertensive cardiomyopathy and in healthy subjects

Recent evidence shows that pink grapefruit juice, which is a recommended dietary addition that contains high amounts of the antioxidant flavonoid naringenin, prolongs the corrected QT (QT(c)), a noninvasive electrophysiological marker of spatial myocardial repolarization, and does so by inhibiting the rapid component of the delayed rectifier K+ current (I(Kr)). Prompted by the observation that all class III antiarrhythmic drugs inhibit this current, thereby sometimes provoking torsades de pointes, we compared the effects of a liter of freshly squeezed pink grapefruit juice with those of 2 commonly used class III antiarrhythmics amiodarone and sotalol on the major noninvasive markers of temporal variability in myocardial repolarization used to stratify the risk of sudden death from malignant ventricular arrhythmias. In 32 subjects, 10 with postischemic dilated cardiomyopathy, 12 with hypertensive cardiomyopathy, and 10 healthy, we assessed QT(c) and QT variability index (QTVI) after administration of fresh pink grapefruit juice, placebo, amiodarone, or sotalol. After pink grapefruit juice and sotalol, all these indexes increased significantly from values observed after placebo (P<0.05) and from values after amiodarone (P<0.05). Conversely, after amiodarone, QT(c), but not QTVI, increased significantly from values after placebo (P<0.05). Presumably because of its high naringenin glycoside content, pink grapefruit juice prolongs cardiac repolarization and concurrently increases temporal cardiac repolarization dispersion. The potential proarrhythmic actions of pink grapefruit juice might be of concern in patients with major myocardial structural disorders.

Genomics, heart failure and sudden cardiac death

Sudden cardiac death (SCD) is among the most common causes of death in developed countries throughout the world. Despite decreased overall cardiac mortality, SCD rates appear to be increasing in concert with escalating global prevalence of coronary disease and heart failure, the two major conditions predisposing to SCD. This unfavorable trend is a consequence of our inability to identify those who will die suddenly from lethal ventricular arrhythmias and to develop effective therapies for all populations at risk. The known risk factors for SCD lack the predictive power needed to generate preventive strategies for the large number of fatal arrhythmic events that occur among lower-risk subsets of the population. Even among recognized high-risk subsets, prediction of SCD remains challenging. With the exception of the implantable cardioverter defibrillator (ICD) there are few effective strategies for the prevention and treatment of SCD. This article discusses the prospect of genomic science as an approach to the identification of patients at high-risk for SCD. While the final common pathway for SCD is malignant ventricular arrhythmias, there are many potential contributors, pathways, and mechanisms by which common genetic variants (polymorphisms) could affect initiation and propagation of life-threatening cardiac arrhythmias. Recent advances in genomic medicine now provide us with novel approaches to both identify candidate genes/pathways and relatively common polymorphisms which may predispose patients to increased risk for SCD. Improved understanding of the relationship between common polymorphisms and SCD will not only improve risk stratification such that ICDs can be targeted to those patients most likely to benefit from them but also provide new insight into the pathophysiology of SCD.

Modulation of late sodium current by Ca2+, calmodulin, and CaMKII in normal and failing dog cardiomyocytes: similarities and differences

Augmented and slowed late Na(+) current (I(NaL)) is implicated in action potential duration variability, early afterdepolarizations, and abnormal Ca(2+) handling in human and canine failing myocardium. Our objective was to study I(NaL) modulation by cytosolic Ca(2+) concentration ([Ca(2+)](i)) in normal and failing ventricular myocytes. Chronic heart failure was produced in 10 dogs by multiple sequential coronary artery microembolizations; 6 normal dogs served as a control. I(NaL) fine structure was measured by whole cell patch clamp in ventricular myocytes and approximated by a sum of fast and slow exponentials produced by burst and late scattered modes of Na(+) channel gating, respectively. I(NaL) greatly enhanced as [Ca(2+)](i) increased from "Ca(2+) free" to 1 microM: its maximum density increased, decay of both exponentials slowed, and the steady-state inactivation (SSI) curve shifted toward more positive potentials. Testing the inhibition of CaMKII and CaM revealed similarities and differences of I(NaL) modulation in failing vs. normal myocytes. Similarities include the following: 1) CaMKII slows I(NaL) decay and decreases the amplitude of fast exponentials, and 2) Ca(2+) shifts SSI rightward. Differences include the following: 1) slowing of I(NaL) by CaMKII is greater, 2) CaM shifts SSI leftward, and 3) Ca(2+) increases the amplitude of slow exponentials. We conclude that Ca(2+)/CaM/CaMKII signaling increases I(NaL) and Na(+) influx in both normal and failing myocytes by slowing inactivation kinetics and shifting SSI. This Na(+) influx provides a novel Ca(2+) positive feedback mechanism (via Na(+)/Ca(2+) exchanger), enhancing contractions at higher beating rates but worsening cardiomyocyte contractile and electrical performance in conditions of poor Ca(2+) handling in heart failure.

Anti- and pro-arrhythmic effects of cardiac resynchronization therapy: point of view

Cardiac resynchronization therapy (CRT) in patients with heart failure and bundle branch block (BBB) improves regional muscle mechanics and mechanical pump function of the heart. In addition, modulation of wall motion timing and contraction can exert an antiarrhythmic effect, reducing the potential of sudden cardiac death. This effect of CRT could also be attributed to the improvement in excitation-contraction coupling, mechanical synchronization, and improved myocardial perfusion. However, it can be hypothesized that the BBB results in a concealed reentry, in which a delayed depolarization wave re-enters during phase two of the action potential. This concealed phase 2 reentry can lead to early after depolarizations and cardiac arrhythmias. By synchronizing the two ventricles, CRT eliminates the reentry substrate and the resulting arrhythmias. This hypothesis and the potential arrhythmogenic effects of CRT are discussed with regard to ventricular remodeling and mechano-electrical feedback in this setting.

Delivery of nano-objects to functional sub-domains of healthy and failing cardiac myocytes

Cardiovascular disease, including heart failure, is one of the leading causes of mortality in the world. Delivery of nano-objects as carriers for markers, drugs or therapeutic genes to cellular organelles has the potential to sharply increase the efficiency of diagnostic and treatment protocols for heart failure. However, cardiac cells present special problems to the delivery of nano-objects, and the number of papers devoted to this important area is remarkably small. The present review discusses fundamental aspects, problems and perspectives in the delivery of nano-objects to functional sub-domains of failing cardiomyocytes. What size nano-objects can reach cellular sub-domains in failing hearts? What are the mechanisms for their permeation through the sarcolemma? How can we improve the delivery of nano-objects to the sub-domains? Answering these questions is fundamental to identifying cellular targets within the failing heart and the development of nanocarriers for heart-failure therapy at the cellular level.

Sudden cardiac death: prevalence, pathogenesis, and prevention

Sudden cardiac death (SCD), also known as sudden arrest, is a major health problem worldwide. It is usually defined as an unexpected death from a cardiac cause occurring within a short time in a person with or without preexisting heart disease. The pathogenesis of SCD is complex and multifaceted. A dynamic triggering factor usually interacts with an underlying heart disease, either genetically determined or acquired, and the final outcome is the development of lethal tachyarrhythmias or, less frequently, bradycardia. It has increasingly been highlighted that a reliable clinical and diagnostic approach might be effective to unmask the most important genetic and environmental factors, allowing the construction of a rational personalized medicine framework that can be applied in both the preclinical and clinical settings of SCD. The aim of the present article is to provide a concise overview of prevalence, pathogenesis, clinical presentation, and diagnostic approach to this challenging disorder.

Late sodium current in failing heart: friend or foe?

Most cardiac Na+ channels open transiently upon membrane depolarization and then are quickly inactivated. However, some channels remain active, carrying the so-called persistent or late Na+ current (INaL) throughout the action potential (AP) plateau. Experimental data and the results of numerical modeling accumulated over the past decade show the emerging importance of this late current component for the function of both normal and failing myocardium. INaL is produced by special gating modes of the cardiac-specific Na+ channel isoform. Heart failure (HF) slows channel gating and increases INaL, but HF-specific Na+ channel isoform underlying these changes has not been found. Na+ channels represent a multi-protein complex and its activity is determined not only by the pore-forming alpha subunit but also by its auxiliary beta subunits, cytoskeleton, calmodulin, regulatory kinases and phosphatases, and trafficking proteins. Disruption of the integrity of this protein complex may lead to alterations of INaL in pathological conditions. Increased INaL and the corresponding Na+ flux in failing myocardium contribute to abnormal repolarization and an increased cell Ca2+ load. Interventions designed to correct INaL rescue normal repolarization and improve Ca2+ handling and contractility of the failing cardiomyocytes. This review considers (1) quantitative integration of INaL into the established electrophysiological and Ca2+ regulatory mechanisms in normal and failing cardiomyocytes and (2) a new therapeutic strategy utilizing a selective inhibition of INaL to target both arrhythmias and impaired contractility in HF.

Neural remodeling may partly contribute to the abnormality of excitation–contraction coupling in heart failure

Heart failure (HF) is a major and growing public health problem in the world. About 50% of deaths in HF occur suddenly due to malignant arrhythmia. Therefore, exploring the further mechanisms of chronic HF and finding new therapy targets are essential for the progression of HF treatment. Recently, some published papers suggested that myocardial neural remodeling and abnormal excitation-contraction (EC) coupling might partly contribute to the development of HF and sudden cardiac death. Even though a few studies have demonstrated that the sympathetic nerve system (SNS) may have significant impact on the functional states of myocardial EC coupling through the beta-adrenergic signaling pathway, so far, it still remains unknown that whether neural remodeling affects the EC coupling. Studies from Marks' group demonstrated that 70% of cardiac ryanodine receptors (RyR2), which located on the sarcoplasmic reculum (SR) controlling intracellular Ca(2+) release and muscle contraction in the heart, from failing hearts were abnormal and only 15% exhibited the most severe defects. In addition, Litwin et al. observed that temporal and spatial heterogeneities in local Ca(2+) release events in a rabbit model of HF after myocardial infarction. Because some studies have demonstrated that chronic SNS hyperactivity in HF led to protein kinase A (PKA) hyperphosphorylation of RyR2 in the heart, and the myocardial sympathetic nerve distribution become heterogeneous in the setting of HF. Thus, it is reasonable for us to propose the hypothesis that neural remodeling may partly account for the abnormality of EC coupling in HF.

Prognostic value of T-wave alternans in patients with heart failure due to nonischemic cardiomyopathy: results of the ALPHA Study

OBJECTIVES

The aim of this study was to assess the prognostic value of T-wave alternans (TWA) in New York Heart Association (NYHA) functional class II/III patients with nonischemic cardiomyopathy and left ventricular ejection fraction (LVEF) < or =40%.

BACKGROUND

There is a strong need to identify reliable risk stratifiers among heart failure candidates for implantable cardioverter-defibrillator (ICD) prophylaxis. T-wave alternans may identify low-risk subjects among post-myocardial infarction patients with depressed LVEF, but its predictive role in nonischemic cardiomyopathy is unclear.

METHODS

Four hundred forty-six patients were enrolled and followed up for 18 to 24 months. The primary end point was the combination of cardiac death + life-threatening arrhythmias; secondary end points were total mortality and the combination of arrhythmic death + life-threatening arrhythmias.

RESULTS

Patients with abnormal TWA (65%) compared with normal TWA (35%) tests were older (60 +/- 13 years vs. 57 +/- 12 years), were more frequently in NYHA functional class III (22% vs. 19%), and had a modestly lower LVEF (29 +/- 7% vs. 31 +/- 7%). Primary end point rates in patients with abnormal and normal TWA tests were 6.5% (95% confidence interval [CI] 4.5% to 9.4%) and 1.6% (95% CI 0.6% to 4.4%), respectively. Unadjusted and adjusted hazard ratios were 4.0 (95% CI 1.4% to 11.4%; p = 0.002) and 3.2 (95% CI 1.1% to 9.2%; p = 0.013), respectively. Hazard ratios for total mortality and for arrhythmic death + life-threatening arrhythmias were 4.6 (p = 0.002) and 5.5 (p = 0.004), respectively; 18-month negative predictive values for the 3 end points ranged between 97.3% and 98.6%.

CONCLUSIONS

Among NYHA functional class II/III nonischemic cardiomyopathy patients, an abnormal TWA test is associated with a 4-fold higher risk of cardiac death and life-threatening arrhythmias. Patients with normal TWA tests have a very good prognosis and are likely to benefit little from ICD therapy.

Different ventricular remodelling and autonomic modulation after long-term beta-blocker treatment in hypertensive, ischaemic and idiopathic dilated cardiomyopathy

OBJECTIVE

In this retrospective analysis, we investigated the influence of aetiology on autonomic modulation and reverse ventricular remodelling induced by beta-blockade in heart failure.

METHODS

Twenty-three heart failure patients without comorbidities (mean age 61 +/- 4 years, New York Heart Association class 3.1 +/- 0.1, treated with angiotensin-converting enzyme inhibitors and diuretics) were divided into three groups according to aetiology: hypertensive (group 1, n = 7), ischaemic (group 2, n = 6), and idiopathic (group 3, n = 10). Before and after 6 months of carvedilol (53 +/- 10 mg/day), patients underwent cardiopulmonary test, echocardiography and autonomic evaluation with spectral analysis of RR variability (10 min of rest plus 10 min of standing: the low frequency/high frequency ratio between low and high frequency components of each spectrum was the index of sympathovagal balance).

RESULTS

Carvedilol improved New York Heart Association class and exercise performance. In group 1, ejection fraction and left ventricular end-diastolic volume normalised, and interventricular septum thickness increased. No remodelling occurred in group 2. In group 3, interventricular septum thickness was unchanged, ejection fraction and left ventricular end-diastolic volume improved. Also autonomic modulation differed. At baseline, adrenergic activation was observed either at rest or during standing. After carvedilol treatment, group 1 did not show any change in the low frequency/high frequency ratio in both conditions, whereas groups 2 and 3 showed reduced adrenergic activation at rest and normal response to standing.

CONCLUSIONS

Despite favourable ventricular remodelling, the poor autonomic modulation observed with beta-blockade indicates a persistent central adrenergic activation in hypertensive heart failure patients.

Human heart failure is associated with abnormal C-terminal splicing variants in the cardiac sodium channel

Heart failure (HF) is associated with reduced cardiac Na+ channel (SCN5A) current. We hypothesized that abnormal transcriptional regulation of this ion channel during HF could help explain the reduced current. Using human hearts explanted at the transplantation, we have identified 3 human C-terminal SCN5A mRNA splicing variants predicted to result in truncated, nonfunctional channels. As compared with normal hearts, the explanted ventricles showed an upregulation of 2 of the variants and a downregulation of the full-length mRNA transcript such that the E28A transcript represented only 48.5% (P<0.01) of the total SCN5A mRNA. This correlated with a 62.8% (P<0.01) reduction in Na+ channel protein. Lymphoblasts and skeletal muscle expressing SCN5A also showed identical C-terminal splicing variants. Variants showed reduced membrane protein and no functional current. Transfection of truncation variants into a cell line stably transfected with the full-length Na+ channel resulted in dose-dependent reductions in channel mRNA and current. Introduction of a premature truncation in the C-terminal region in a single allele of the mouse SCN5A resulted in embryonic lethality. Embryonic stem cell-derived cardiomyocytes expressing the construct showed reductions in Na+ channel-dependent electrophysiological parameters, suggesting that the presence of truncated Na+ channel mRNA at levels seen in HF is likely to be physiologically significant. In summary, chronic HF was associated with an increase in 2 truncated SCN5A variants and a decrease in the native mRNA. These splice variations may help explain a loss of Na+ channel protein and may contribute to the increased arrhythmic risk in clinical HF.

Imaging cardiac neuronal function and dysfunction

In recent years, the importance of alterations of cardiac autonomic nerve function in the pathophysiology of heart diseases including heart failure, arrhythmia, ische-mic heart disease, and diabetes has been increasingly recognized. Several radiolabeled compounds have been synthesized for noninvasive imaging, including single photon emission CT and positron emission tomography (PET). The catecholamine analogue I-123 metaiodobenzylguanidine (MIBG) is the most commonly used tracer for mapping of myocardial presynaptic sympathetic innervation on a broad clinical basis. In addition, radiolabeled catecholamines and catecholamine analogues are available for PET imaging, which allows absolute quantification and tracer kinetics modeling. Postsynaptic receptor PET imaging added new insights into mechanisms of heart disease. These advanced imaging techniques provide noninvasive, repeatable in vivo information of autonomic nerve function in the human heart and are promising for providing profound insights into molecular pathophysiology, monitoring of treatment, and determination of individual outcome.

Functional sarcoplasmic reticulum for calcium handling of human embryonic stem cell-derived cardiomyocytes: insights for driven maturation

Cardiomyocytes (CMs) are nonregenerative. Self-renewable pluripotent human embryonic stem cells (hESCs) can differentiate into CMs for cell-based therapies. In adult CMs, Ca(2+)-induced Ca(2+) release from the sarcoplasmic reticulum (SR) via the ryanodine receptor (RyR) is key in excitation-contraction coupling. Therefore, proper Ca(2+) handling properties of hESC-derived CMs are required for their successful functional integration with the recipient heart. Here, we performed a comprehensive analysis of CMs differentiated from the H1 (H1-CMs) and HES2 (HES2-CMs) hESC lines and human fetal (F) and adult (A) left ventricular (LV) CMs. Upon electrical stimulation, all of H1-, HES2-, and FLV-CMs generated similar Ca(2+) transients. Caffeine induced Ca(2+) release in 65% of FLV-CMs and approximately 38% of H1- and HES2-CMs. Ryanodine significantly reduced the electrically evoked Ca(2+) transient amplitudes of caffeine-responsive but not -insensitive HES2- and H1-CMs and slowed their upstroke; thapsigargin, which inhibits the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) pump, reduced the amplitude of only caffeine-responsive HES2- and H1-CMs and slowed the decay. SERCA2a expression was highest in ALV-CMs but comparable among H1-, HES2-, and FLV-CMs. The Na(+)-Ca(2+) exchanger was substantially expressed in both HES2- and H1-CMs relative to FLV- and ALV-CMs. RyR was expressed in HES2-, H1-, and FLV-CMs, but the organized pattern for ALV-CMs was not observed. The regulatory proteins junctin, triadin, and calsequestrin were expressed in ALV-CMs but not HES2- and H1-CMs. We conclude that functional SRs are indeed expressed in hESC-CMs, albeit immaturely. Our results may lead to driven maturation of Ca(2+) handling properties of hESC-CMs for enhanced contractile functions. Disclosure of potential conflicts of interest is found at the end of this article.

Giα1-Mediated Cardiac Electrophysiological Remodeling and Arrhythmia in Hypertrophic Cardiomyopathy

BACKGROUND

Cardiac hypertrophy is a major risk factor for arrhythmias and sudden cardiac death. However, the underlying signaling mechanisms involved in the induction of arrhythmia and electrophysiological remodeling in cardiac hypertrophy are unclear.

METHODS AND RESULTS

Using an inducible gene-switch approach, we achieved tissue-specific and temporally regulated induction of a well-established hypertrophic pathway, the Ras-Raf-mitogen-activated protein kinases pathway, in adult mouse heart. On Ras activation, the transgenic animal developed ventricular hypertrophy and arrhythmias. The development of ventricular arrhythmias was temporally correlated with electrophysiological remodeling in isolated ventricular myocytes, including action potential prolongation, increased sodium-calcium exchanger activity, reduced outward potassium currents, sarcoplasmic reticulum Ca2+ defects, and loss of protein kinase A-dependent phospholamban phosphorylation. From genome-wide expression profiling, we discovered a selective induction of G alpha inhibiting subunit 1 (Gi alpha1) expression in the Ras transgenic heart. Treatment of transgenic animals with the Gi/o inhibitor pertussis toxin normalized the phospholamban phosphorylation by protein kinase A, reversed the action potential prolongation, and significantly reduced the frequency of cardiac arrhythmias in Ras transgenic animals.

CONCLUSIONS

These data suggest that selective induction of G alpha inhibiting subunit 1 expression and activity is a novel downstream event in hypertrophic signaling that may be a critical factor leading to cellular electrophysiological remodeling and cardiac arrhythmias in hypertrophic cardiomyopathy.

Prognostic significance of circadian variability of RR and QT intervals and QT dynamicity in patients with chronic heart failure

BACKGROUND

In patients with chronic heart failure (CHF), circadian variability of RR and QT intervals may be altered because of neurohumoral activation and functional and structural remodeling of the heart.

OBJECTIVE

The aim of this study was to evaluate the prognostic significance of circadian variability of the RR and QT intervals and QT dynamicity (QT/RR slope) in CHF patients.

METHODS

We prospectively enrolled 121 patients with stable CHF in sinus rhythm (age 67 +/- 14 years, mean +/- SD; range 34 to 87 years). The RR, QT, and rate-corrected QT (QTc) intervals and the QT/RR slope measured from 24-hour Holter electrocardiogram were fitted by cosine curves.

RESULTS

During the follow-up period of 34 +/- 17 months, 40 (33%) patients died of cardiac causes, 10 of which were sudden. All patients showed significant circadian rhythms in the RR, QT, and QTc intervals and the QT/RR slope by cosine-curve fitting. In addition to the expected higher heart rate, longer QT interval, and steeper QT/RR slope, we found that patient who died of cardiac causes had reduced circadian variability of QT interval (10 +/- 10 ms vs 21 +/- 13 ms) and a later maximum RR interval (4.1 +/- 0.9 AM vs 2.3 +/- 2.1 AM) compared with survivors, among many other statistically significant circadian parameter differences. These 2 parameters were independent predictors of cardiac death in multivariate Cox proportional hazards regression analysis.

CONCLUSION

Circadian variability analyses of Holter-derived RR and QT intervals may provide prognostic information beyond that provided by 24-hour averages of these parameters.

Dynamic changes in conduction velocity and gap junction properties during development of pacing-induced heart failure

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.

Increased QT variability in young asymptomatic patients with beta-thalassemia major

BACKGROUND

Despite recent progress in iron chelation therapy, sudden cardiac death due to malignant ventricular arrhythmias remains a vexing, clinical problem in patients with beta-thalassemia major (TM). In this study we assessed whether the major indices of QT variability, emerging tools for risk stratification of sudden cardiac death, differ in young asymptomatic patients with TM and healthy persons.

METHODS

Thirty patients with TM and 30 healthy control subjects underwent a 5-min electrocardiography recording to calculate the following variables: QT variance (QT(v)), QT(v) normalized for mean QT (QTVN) and QT variability index (QTVI). All subjects also underwent a two-dimensional and Doppler echocardiography study and magnetic resonance imaging (MRI) to determine cardiac and hepatic T2* values.

RESULTS

No differences were observed in clinical and conventional echo-Doppler findings in healthy control subjects and patients with TM whereas QT(v), QTVN and QTVI values were significantly higher in patients than those in controls (QT(v), P < 0.001; QTVN, P < 0.05 and QTVI, P < 0.001) and cardiac T2* and hepatic MRI T2* values were significantly lower in patients with TM (P < 0.001). The indices of temporal QT variability correlated significantly with MRI data.

CONCLUSIONS

Young asymptomatic patients with TM have increased cardiac repolarization variability as assessed by QT variability indices, probably due to cardiac iron deposition. These easily assessed, non-invasive markers could be used to identify increased myocardial repolarization lability early in asymptomatic patients with TM.

Upregulation of KCNE1 induces QT interval prolongation in patients with chronic heart failure

BACKGROUND

Prolongation of the action potential duration (APD) is observed in ventricular myocytes isolated from the failing heart. The rapid component (I(Kr)) and the slow component (I(Ks)) of the delayed-rectifier potassium current (I(K)) are major determinants of the APD, but less information is available on the genomic modulation of I(K) in the remodeled human heart. The aim of the current study was to examine the relationship between I(K) transcripts and QT interval in surface electrocardiogram in patients with chronic heart failure (CHF).

METHODS AND RESULTS

Total RNA was extracted from right ventricle endomyocardial biopsy samples in 21 CHF patients (age: 53+/-4 years, mean +/- SEM). The KCNH2 and KCNQ1 levels did not differ significantly between controls (New York Heart Association (NYHA) I, n=10) and CHF patients (NYHA II or III, n=11), whereas the KCNE1 level was significantly higher in CHF patients than in controls (relative mRNA levels normalized to GAPDH expression: 6.16+/-0.31 vs 7.70+/-0.46, p<0.05). The KCNE1/KCNQ1 ratio was higher in CHF patients than in controls (0.92+/-0.02 vs 1.06+/-0.05, p<0.05) and the KCNE1-KCNQ1 ratio was positively correlated with QT interval (r=0.70, p<0.05). Increasing the KCNE1 concentration caused a shift in activation voltage and slowed the activation kinetics of the KCNE1-KCNQ1 currents expressed in Xenopus oocytes. Prolongation of the APD and decrease in I(Ks) with increasing the amount of KCNE1 concentration were well predicted in a computer simulation.

CONCLUSIONS

In mild-to-moderate CHF patients, the relative abundance of KCNE1 compared to KCNQ1 genes, at least in part, might contribute to the preferential prolongation of QT interval through reducing the net outward current during the plateau of the action potential.

Abrupt changes in FKBP12.6 and SERCA2a expression contribute to sudden occurrence of ventricular fibrillation on reperfusion and are prevented by CPU86017

AIM

The occurrence of ventricular fibrillation (VF) is dependent on the deterioration of channelopathy in the myocardium. It is interesting to investigate molecular changes in relation to abrupt appearance of VF on reperfusion. We aimed to study whether changes in the expression of FKBP12.6 and SERCA2a and the endothelin (ET) system on reperfusion against ischemia were related to the rapid occurrence of VF and whether CPU86017, a class III antiarrhythmic agent which blocks I(Kr), I(Ks), and I(Ca.L), suppressed VF by correcting the molecular changes on reperfusion.

METHODS

Cardiomyopathy (CM) was produced by 0.4 mg/kg sc L-thyroxin for 10 d in rats, and subjected to 10 min coronary artery ligation/reperfusion on d 11. Expressions of the Ca2+ handling and ET system and calcium transients were conducted and CPU86017 was injected (4 mg/kg, sc) on d 6-10.

RESULTS

A high incidence of VF was found on reperfusion of the rat CM hearts, but there was no VF before reperfusion. The elevation of diastolic calcium was significant in the CM myocytes and exhibited abnormality of the Ca2+ handling system. The rapid downregulation of mRNA and the protein expression of FKBP12.6 and SERCA2a were found on reperfusion in association with the upregulation of the expression of the endothelin-converting enzyme (ECE) and protein kinase A (PKA), in contrast, no change in the ryanodine type 2 receptor (RyR2), phospholamban (PLB), endothelin A receptor (ETAR), and iNOS was found. CPU86017 removed these changes and suppressed VF.

CONCLUSION

Abrupt changes in the expression of FKBP12.6, SERCA2a, PKA, and ECE on reperfusion against ischemia, which are responsible for the rapid occurrence of VF, have been observed. These changes are effectively prevented by CPU86017.

Angiotensin II-induced sudden arrhythmic death and electrical remodeling

Rats harboring the human renin and angiotensinogen genes (dTGR) feature angiotensin (ANG) II/hypertension-induced cardiac damage and die suddenly between wk 7 and 8. We observed by electrocardiogram (ECG) telemetry that ventricular tachycardia (VT) is a common terminal event in these animals. Our aim was to investigate electrical remodeling. We used ECG telemetry, noninvasive cardiac magnetic field mapping (CMFM) at wk 5 and 7, and performed in vivo programmed electrical stimulation at wk 7. We also investigated whether or not losartan (Los; 30 mg x kg(-1) x day(-1)) would prevent electrical remodeling. Cardiac hypertrophy and systolic blood pressure progressively increased in dTGR compared with Sprague-Dawley (SD) controls. Already by wk 5, untreated dTGR showed increased perivascular and interstitial fibrosis, connective tissue growth factor expression, and monocyte infiltration compared with SD rats, differences that progressed through time. Left-ventricular mRNA expression of potassium channel subunit Kv4.3 and gap-junction protein connexin 43 were significantly reduced in dTGR compared with Los-treated dTGR and SD. CMFM showed that depolarization and repolarization were prolonged and inhomogeneous. Los ameliorated all disturbances. VT could be induced in 88% of dTGR but only in 33% of Los-treated dTGR and could not be induced in SD. Untreated dTGR show electrical remodeling and probably die from VT. Los treatment reduces myocardial remodeling and predisposition to arrhythmias. ANG II target organ damage induces VT.