David Benoist

Electrophysiological changes in heart failure and their implications for arrhythmogenesis

Heart failure is the final common pathway of various cardiac pathologies and is associated with sudden cardiac death, mostly caused by ventricular arrhythmias. In this paper we briefly review the electrophysiological remodeling and the alterations in intracellular calcium handling, and the resulting arrhythmogenic mechanisms associated with heart failure. Intercellular uncoupling and fibrosis are identified as a major arrhythmogenic factors. Diet and ventricular wall stretch are discussed as modulating factors. Finally, emphasis is placed on the hitherto poorly studied aspects of right ventricular failure. This article is part of a Special Issue entitled: Heart failure pathogenesis and emerging diagnostic and therapeutic interventions.

Proarrhythmic remodelling of the right ventricle in a porcine model of repaired tetralogy of Fallot

Objective The growing adult population with surgically corrected tetralogy of Fallot (TOF) is at risk of arrhythmias and sudden cardiac death. We sought to investigate the contribution of right ventricular (RV) structural and electrophysiological remodelling to arrhythmia generation in a preclinical animal model of repaired TOF (rTOF). Methods and results Pigs mimicking rTOF underwent cardiac MRI functional characterisation and presented with pulmonary regurgitation, RV hypertrophy, dilatation and dysfunction compared with Sham-operated animals (Sham). Optical mapping of rTOF RV-perfused wedges revealed a significant prolongation of RV activation time with slower conduction velocities and regions of conduction slowing well beyond the surgical scar. A reduced protein expression and lateralisation of Connexin-43 were identified in rTOF RVs. A remodelling of extracellular matrix-related gene expression and an increase in collagen content that correlated with prolonged RV activation time were also found in these animals. RV action potential duration (APD) was prolonged in the epicardial anterior region at early and late repolarisation level, thus contributing to a greater APD heterogeneity and to altered transmural and anteroposterior APD gradients in rTOF RVs. APD remodelling involved changes in Kv4.3 and MiRP1 expression. Spontaneous arrhythmias were more frequent in rTOF wedges and more complex in the anterior than in the posterior RV. Conclusion Significant remodelling of RV conduction and repolarisation properties was found in pigs with rTOF. This remodelling generates a proarrhythmic substrate likely to facilitate re-entries and to contribute to sudden cardiac death in patients with rTOF.

Identification of Region-Specific Myocardial Gene Expression Patterns in a Chronic Swine Model of Repaired Tetralogy of Fallot

Surgical repair of Tetralogy of Fallot (TOF) is highly successful but may be complicated in adulthood by arrhythmias, sudden death, and right ventricular or biventricular dysfunction. To better understand the molecular and cellular mechanisms of these delayed cardiac events, a chronic animal model of postoperative TOF was studied using microarrays to perform cardiac transcriptomic studies. The experimental study included 12 piglets (7 rTOF and 5 controls) that underwent surgery at age 2 months and were further studied after 23 (+/- 1) weeks of postoperative recovery. Two distinct regions (endocardium and epicardium) from both ventricles were analyzed. Expression levels from each localization were compared in order to decipher mechanisms and signaling pathways leading to ventricular dysfunction and arrhythmias in surgically repaired TOF. Several genes were confirmed to participate in ventricular remodeling and cardiac failure and some new candidate genes were described. In particular, these data pointed out FRZB as a heart failure marker. Moreover, calcium handling and contractile function genes (SLN, ACTC1, PLCD4, PLCZ), potential arrhythmia-related genes (MYO5B, KCNA5), and cytoskeleton and cellular organization-related genes (XIRP2, COL8A1, KCNA6) were among the most deregulated genes in rTOF ventricles. To our knowledge, this is the first comprehensive report on global gene expression profiling in the heart of a long-term swine model of repaired TOF.

Magnetic resonance-compatible model of isolated working heart from large animal for multimodal assessment of cardiac function, electrophysiology and metabolism

To provide a model close to the human heart, and to study intrinsic cardiac function at the same time as electromechanical coupling, we developed a magnetic resonance (MR)-compatible setup of isolated working perfused pig hearts. Hearts from pigs (40 kg, n = 20) and sheep (n = 1) were blood perfused ex vivo in the working mode with and without loaded right ventricle (RV), for 80 min. Cardiac function was assessed by measuring left intraventricular pressure and left ventricular (LV) ejection fraction (LVEF), aortic and mitral valve dynamics, and native T1 mapping with MR imaging (1.5 Tesla). Potential myocardial alterations were assessed at the end of ex vivo perfusion from late-Gadolinium enhancement T1 mapping. The ex vivo cardiac function was stable across the 80 min of perfusion. Aortic flow and LV-dP/dtmin were significantly higher (P < 0.05) in hearts perfused with loaded RV, without differences for heart rate, maximal and minimal LV pressure, LV-dP/dtmax, LVEF, and kinetics of aortic and mitral valves. T1 mapping analysis showed a spatially homogeneous distribution over the LV. Simultaneous recording of hemodynamics, LVEF, and local cardiac electrophysiological signals were then successfully performed at baseline and during electrical pacing protocols without inducing alteration of MR images. Finally, (31)P nuclear MR spectroscopy (9.4 T) was also performed in two pig hearts, showing phosphocreatine-to-ATP ratio in accordance with data previously reported in vivo. We demonstrate the feasibility to perfuse isolated pig hearts in the working mode, inside an MR environment, allowing simultaneous assessment of cardiac structure, mechanics, and electrophysiology, illustrating examples of potential applications.

Lipid metabolites and their differential pro-arrhythmic profiles: of importance in the development of a new anti-arrhythmic pharmacology

Arrhythmias have been treated for a long time with drugs that mainly target the ionic pumps and channels. These anti-arrhythmic regimens per se introduce new arrhythmias, which can be detrimental to patients. Advances in development of novel pharmacology without introduction of iatrogenic arrhythmias are thus favorable for an effective treatment of arrhythmias. Electrophysiological stability of the heart has been shown to be closely associated with cardiac metabolism. The present effective anti-arrhythmic drugs such as beta-blockers and amiodarone have profound beneficial effects in regulating myocardial metabolism. Aiming at decreasing production of toxic metabolites or preventing accumulation of arrhythmogenic lipids perhaps is a good strategy to effectively control arrhythmias. Therefore, a better understanding of the pro-arrhythmic profiles of cardiac metabolites helps to explore a new generation of metabolically oriented anti-arrhythmic medications. In this review, we present several lipid metabolites and summarize their arrhythmogenic characteristics.

Microstructural substrate in RVOT for Brugada syndrome

Background Brugada syndrome is linked to ventricular fibrillation (VF), a precursor to sudden cardiac death. This patient population suffers from electrical abnormalities originating from the right ventricular outflow tract (RVOT). The mechanisms underlying such arrhythmic activity remain unclear, but clinical electrophysiological observations have indicated conduction abnormalities in the RVOT. Objective To mimic sub-clinical epicardial microstructural defects in the RVOT to provide a substrate for conduction delay as a possible mechanism of BrS. Methods Dual coronary-perfused left and right ventricular wedge preparations were studied in 20 pigs (35–45xa0kg). Patchy microlesions were created through an array of ablation needles in either the RVOT, right ventricle (RV) or both (DOUBLE ablation) and compared to a control group in the absence of ablation. Paced and arrhythmic activity were assessed by optical mapping of the epicardial surface in the presence and absence of the sodium channel blocker, flecainide. Results At baseline, the action potential duration (APD80) is shorter in the RVOT region compared to the RV free wall (209.8xa0msxa0±xa026.91 vs. 212.6xa0±xa037.19, Pxa0=xa00.026). APD80 of the RVOT is prolonged by ablation (228.1xa0msxa0±xa023.02 for RVOT ablation and 231.2xa0msxa0±xa027.18 for double ablation vs 202.5xa0msxa0±xa045.37 for RV ablation and 209.8xa0msxa0±xa026.91 for control, Pxa0 Conclusion Microstructural defects in the RVOT provides the substrate for sustained ventricular arrhythmias.

0181: Mechanisms of ventricular dysfunction and dyssynchrony in repaired tetralogy of Fallot: an animal study

Background Tetralogy of Fallot (TOF) is associated with increasingly recognized late morbidity due to arrhythmias and right heart failure. Better understanding of the underlying mechanisms of these issues is needed to facilitate new therapeutic approaches. We aim to identify mechanisms generating arrhythmias in a swine model of repaired TOF with progressive right ventricular (RV) dysfunction. Methods Surgery to mimic repaired TOF was done in 24 piglets (using a previously validated model); 24 animals served as control. Two, 4 and 6 months after surgery respectively, animals were sacrified for subsequent analysis. Haemodynamic parameters and ventricular remodeling were analyzed by cardiac magnetic resonance (CMR) and echocardiography before sacrifice. In isolated perfused hearts, electrical activity was measured by optical mapping. Sarcoplasmic reticular calcium handling and proteins involved in calcium management were studied in single myocytes. Results Compared with control animals, a right bundle branch block was present and the action potential (AP) duration was increased in the RV with a mechanical delay observed at 2 and 4 months post-operative in operated groups (p Conclusions Electromechanical and calcium management dysfunctions are progressive in the RV and may partly explain arrhythmias in repaired TOF. These mechanisms are potential therapeutic targets for the correction of arrhythmias in failing right ventricles.

0298 : Action potential shortening in the pig right ventricular outflow tract epicardium

The right ventricular outflow tract (RVOT) has a distinct embryological origin from the rest of the right ventricle (RV) and is a frequent origin for idiopathic and disease-related arrhythmias. We hypothesised that heterogeneous action potential duration (APD) across the right ventricle (RV) may contribute to RVOT arrhythmia generation. Pigs were anesthetized and monophasic action potentials (MAPs) recorded in sinus rhythm from the epicardium of the RV free wall and RVOT. The RV was isolated and perfused via both right and left anterior coronary arteries. The preparation was paced (1-5Hz) and the electrical activity optically mapped (di-4-ANEPPS, 10μM) on both epicardial (EPI) and endocardial (ENDO) surfaces. The expression of potassium channels was assessed by RT-PCR. In vivo, MAP durations measured at 20% and 80% repolarization were both significantly shorter in the RVOT than in the RV free wall EPI (P

0305 : Heterogeneous conduction properties in the pig right ventricle

The right ventricular outflow tract (RVOT) has a distinct embryological origin and is a common anatomical source of arrhythmias in the healthy and diseased myocardium. We hypothesised that specific RVOT activation and conduction properties may underlie the preferential RVOT origin of arrhythmias. Pig right ventricular (RV) wedge preparations were perfused via the left anterior descending and right coronary arteries. Electrical activation and conduction properties were obtained by optical mapping of the epicardial surface (di-4- ANEPPS 10μM) upon electrical stimulation of the preparation. Transmural needles were inserted in the RV free wall and RVOT and unipolar electrograms (EGMs) were recorded. Fiber orientation was obtained by diffusion tensor MRI. Regional mRNA expression was determined by RT-PCR and fibrosis was assessed histologically. Longitudinal and transverse conduction velocities were significantly reduced in RVOT compared to RV free wall (P Conduction is slower in the pig RVOT and is associated with fractionated unipolar electrograms. Conduction slowing was related to (i) reduced connexin and sodium channel expression and (ii) region-specific structural properties which may generate a substrate for RVOT arrhythmias.

0363 : Development of a cell isolation method in large mammals: regional differences in calcium signaling across left atrium from sheep

Atrial fibrillation (AF) is the most common sustained form of arrhythmia in human. Numerous studies have showed that Ca2+ signaling is altered during AF, although it has not been established whether Ca2+ remodeling is homogenous across the different regions of the atria. Given the importance of the pulmonary veins (PV) in the treatment of AF (NEJM, 1998, 339:659-66), we have studied the characteristics of Ca2+ transients in 4 different regions of the left atrium (LA) in an animal model close to human. LA myocytes were obtained by enzymatic dissociation of sheep hearts. Animals were euthanized by injection of pentobarbital and the heart was rapidly excised (guidelines approved by ethical committee). The aorta was cannulated and heart was rinsed with cardioplegic solution. The ventricles and right atrium were removed. LA was cannulated by the circumflex artery and mounted into a Langendorff perfusion system after suture of the leaky atrial branches. LA was perfused with a Ca2+-free solution (~10xa0min), then collagenase and protease solution (0,08mM Ca2+) and recirculated for ~25xa0min. Enzymes were washed out with a 0,2mM Ca2+ solution. LA was separated into 4 regions: Endocardium, Epicardium, roof and PV. Cells were re-suspended into a 1,8mm Ca2+ solution by steps. Ca2+ transients were recorded (Fura-2, field stimulation) using an IonOptix system and cell membrane was stained with di-8 ANNEPS and visualized under confocal microscopy. Ca2+ tolerant myocytes were obtained from the 4 LA regions. Ca2+ amplitude was similar across all regions, however the time to peak and the time to decay showed significant differences: Epicardium vs roof and PV. Confocal microscopy study showed the presence of t-tubules in all regions. Those results suggest regional differences in Ca2+ transient may play a major role in the development of atrial arrhythmia. This study will be completed by the development of a sheep model in persistent AF.