Virginie Dubes

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.

Calcium signalling induced by in vitro exposure to silicium dioxide nanoparticles in rat pulmonary artery smooth muscle cells

The development and use of nanomaterials, especially engineered nanoparticles (NP), is expected to provide many benefits. But at the same time the development of such materials is also feared because of their potential human health risks. Indeed, NP display some characteristics similar to ultrafine environmental particles which are known to exert deleterious cardiovascular effects including pro-hypertensive ones. In this context, the effect of NP on calcium signalling, whose deregulation is often involved in hypertensive diseases, remain poorly described. We thus assessed the effect of SiO2 NP on calcium signalling by fluorescence imaging and on the proliferation response in rat pulmonary artery smooth muscle cells (PASMC). In PASMC, acute exposure to SiO2 NP, from 1 to 500μg/mL, produced an increase of the [Ca2+]i. In addition, when PASMC were exposed to NP at 200μg/mL, a proliferative response was observed. This calcium increase was even greater in PASMC isolated from rats suffering from pulmonary hypertension. The absence of extracellular calcium, addition of diltiazem or nicardipine (L-type voltage-operated calcium channel inhibitors both used at 10μM), and addition of capsazepine or HC067047 (TRPV1 and TRPV4 inhibitors used at 10μM and 5μM, respectively) significantly reduced this response. Moreover, this response was also inhibited by thapsigargin (SERCA inhibitor, 1μM), ryanodine (100μM) and dantrolene (ryanodine receptor antagonists, 10μM) but not by xestospongin C (IP3 receptor antagonist, 10μM). Thus, NP induce an intracellular calcium rise in rat PASMC originating from both extracellular and intracellular calcium sources. This study also provides evidence for the implication of TRPV channels in NP induced calcium rise that may highlight the role of these channels in the deleterious cardiovascular effects of NP.

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.

Unexpected Internalization of a Pulmonary Artery Band in a Porcine Model of Tetralogy of Fallot.

Background: We report our experience of an unexpected complication of internalization of a pulmonary artery (PA) band in the vascular lumen, which occurred in a chronic porcine model of repaired tetralogy of Fallot (TOF). Methods: Twelve piglets were divided into 3 groups: (1) TOF model animals (PA band plus pulmonary valvotomy, n = 4), (2) pulmonary insufficiency (PI) animals (pulmonary valvotomy, n = 4), and (3) control animals (n = 4). A nonabsorbable, coated braided polyester tape was used to perform the main pulmonary artery banding. Echocardiography was performed 4 months postoperatively. After each animal was euthanized, PA histological analysis was performed in animals with band internalization. Results: Significant postsurgical pulmonary regurgitation and right ventricular enlargement were present in the TOF and PI, compared with control animals, whereas no significant pulmonary stenosis was observed in TOF animals when compared with PI group. Postmortem examination of all TOF animals revealed the constricting band to be intact but partially internalized into the PA lumen, allowing blood flow around the stenosis. Histological sections of the banded PA in the area of internalization showed a significant disorganization of the medial layer, with significant scarring and fibrotic reaction surrounding the outside of the band and the presence of inflammatory cells suggesting a significant inflammatory response during band internalization. Conclusions: Band internalization may occur after PA banding using a nonabsorbable, coated braided polyester tape in a chronic porcine model of repaired TOF. This unusual complication was likely due to the type of material used for banding.

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.

January 16th, Friday 20150244: Pro-arrhythmic ventricular remodeling in a porcine model of repaired tetralogy of Fallot

Ventricular arrhythmias are frequent in patients with repaired tetralogy of Fallot but their underlying mechanisms remain unclear. In this study, ventricular electrical and structural remodelling was assessed in an animal model that mimics postoperative tetralogy of Fallot. Piglets underwent a tetralogy of Fallot repair-like surgery (rTOF N=6) or were sham-operated (Sham N=5). Following cardiac function assessment in vivo by MRI 3-4 months after surgery, pigs were euthanized and their hearts rapidly excised. Electrophysiological properties of right (RV) and left ventricles (LV) were obtained by optical mapping. Fibrosis was assessed histologically. RV dysfunction was evident while LV function remained unaltered in rTOF pigs. LV action potential duration (APD) was significantly longer on the epicardium (Sham 280±50ms; rTOF 390±76ms) and endocardium (Sham 301±20ms; rTOF 403±34ms) of rTOF animals (P

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.