1236
Full protection from drug-induced torsade de pointes-like arrhythmias by an allosteric Ikr-modulatory mechanism in rat ventricular monolayers
Abstract
Purpose: A significant number of high-potential drugs has been withdrawn from the market because of drug-induced arrhythmia, and thus potential lethality, via unintended blockade of IKr (Kv11.1; hERG). This study investigated whether and how an allosteric modulator of Kv11.1 prevents such pro-arrhythmia also known as Torsade de Pointes.
Methods: Three compounds (VU0405601, ML-T531 and LUF7244) were studied for their allosteric modulatory effects by [3H]dofetilide binding and displacement assays with cell membranes of Kv11.1-transfected HEK293 cells. Dofetilide, astemizole and sertindole were used as typical Kv11.1 blockers. Next, the anti-arrhythmic potential of the most potent modulator was studied by optical voltage mapping in a novel in vitro model of Kv11.1-blockade-induced arrhythmias using neonatal rat ventricular cardiomyocyte (nrvCMC) monolayers at 9 days after culture initiation.
Results: Of the three compounds tested, LUF7244 (10 μM) most strongly reduced the affinity of the Kv11.1 blockers. Treatment of nrvCMC monolayers with unintended Kv11.1 blockers (100 nM astemizole or 1 μM sertindole) caused: 1) prolongation of action potential duration (APD), 2) an increase in APD40 dispersion, 3) followed by early afterdepolarizations (EADs) upon 1-Hz electrical point stimulation, finally resulting in: 4) formation of unstable, self-terminating spiral wave tachyarrhythmias, resembling ‘torsade de pointes’. Importantly, pretreatment of the nrvCMCs with LUF7244 effectively prevented these proarrhythmic effects, resulting in normal electrical activation of the cell monolayers. Control cultures treated with LUF7244 alone displayed the same electrophysiological properties as untreated nrvCMC cultures. Moreover, prolonged exposure of the nrvCMCs to Kv11.1 blocker plus allosteric modulator did not have noticeable effects on their viability, excitability and contractility as assessed by molecular, immunological and electrophysiological assays.
Conclusions: This is the first study to proof that allosteric modulation of IKr could protect against drug-induced arrhythmias in vitro by preventing critical changes in APD properties associated with the initiation of drifting, self-terminating spiral waves, like in ‘torsade de pointes’ arrhythmias. This study could therefore provide a rationale to counteract drug-induced ventricular arrhythmias by pharmacological combination therapy relying on allosteric modulation of Kv11.1 channel activity.
1237
Is left atrial fibrosis quantified using late Ggadoadolinium enhancement magnetic resonance imaging a specific attribute of atrial fibrillation?
Abstract
Study Background: left atrial (LA) fibrosis quantified using LGE MRI is proposed as possible new predictor for atrial fibrillation (AF) ablation efficacy. LA fibrosis (LAf) regions are also proposed as additional ablation targets. However, LAf manifestation under other cardiovascular disease (CVD) and in healthy subjects remains still unclear.
The main goal of this study was assessment of LAf degree and localization in patients with and without AF and heathy volunteers in order to determine LAf quantification diagnostic value in AF.
Materials and Methods: 53 conservatively treated patients with AF (AFp) (mean age 56, 28 with lone AF, with AF and hypertension) during sinus rhythm, 25 patients with hypertension (Hyp) (mean age 50) without history of arrhythmia and 23 healthy volunteers (HV) (mean age 50) underwent standard clinical examination. Then all of them underwent cardiac magnetic resonance imaging including high resolution LGE MRI. From LGE images LA walls were segmented semiautomatically. LAf quantification was performed using algorithm based on estimation LA wall enhancement ratio and comparison with threshold value obtained from HV data calculated by the original software. Fibrosis volume percent in LA myocardium represented its extent.
Results: LAf was registered in 86% of AFp, 74% of Hyp and 43% of HV. AFp had significantly higher level of fibrosis than HV (9 [1,7;19]% vs. 0,8% [0,05;3,5]%, p<0,05). 25% of AFp had 20-70% of LAf. Hyp demonstrated intermediate extent of LAf (3,8 [0,6; 9]%). Predominant LAf localization in study groups was different: AFp in pulmonary vein region, Hyp - diffuse distribution, HV - close to mitral annulus. Multivariate analysis revealed that AF and hypertension were major LAf contributors (OR 5 (95% CI 1,8-13,5)and OR 4.2 (95% CI 1,5-11,7)). In heathy volunteers LAf correlated with age (r=0,65, p<0,001). ROC-analysis demonstrated that LAf 20% grade had 93 % sensitivity and 81 % specificity for AF.
Conclusions: LA fibrosis is not a specific attribute in AF. Hypertension and aging without cardiovascular disease may cause LA fibrosis development. Predominant LA fibrosis localization was different in persons with and without AF. Thus, only high level of fibrosis and its localization in pulmonary vein region compose a specific atrial structural remodeling characteristic for AF.
1238
Creating new trans-species types of myocytes by forced fusion between cardiomyocytes and fibroblasts to counteract arrhythmias: breaking boundaries with muscular mixtures
Abstract
Purpose: The technology-driven, rapid lifestyle changes over the past century exceed the evolutionary and biological adaptability of the human heart, which renders it susceptible to degenerative diseases. Loss of ventricular cardiomyocytes (CMCs) is inadequately compensated by electromechanically incompetent fibroblasts. This maladaptive and pro-arrhythmic cellular response raised our interest in creating a new, cardiomyocyte-like cell type by forced fusion between fibroblasts and surrounding fibroblasts. We hypothesized such forced heterocellular fusion (FHF) transfers desirable electromechanical properties to fibroblasts and thereby ameliorates fibrosis-associated pro-arrhythmic effects on cardiac tissue.
Methods: Human ventricular scar cells (hVSCs) were isolated from myocardial scars of heart failure patients and co-cultured (1:4) with neonatal rat CMCs (nrCMCs) into confluent monolayers. Prior to co-culture, hVSCs were transduced with lentiviral vectors encoding the enhanced green fluorescent protein (eGFP, control cultures) or eGFP and the fusogenic vesicular stomatitis virus G protein (fused cultures). The structural and functional effects of FHF were investigated by (human-specific) immunocytological staining, patch-clamp and optical mapping.
Results: hVSC-nrCMC heterokaryons were only observed in fused (VSV-G expressing) cultures. Such heterokaryons contained 6±3 nuclei (46±18% of human origin). These new, excitable and contractile cells expressed α-actinin and Cx43. Nuclear expression of NKX2.5 was absent in control hVSCs, while hVSC nuclei in heterokaryons stained positive. Expression levels of Cav1.2 and Cx43 did not relate to the percentage of human nuclei (R2=0.05), suggesting phenotypical dominance of CMCs. Additionally, FHF strongly reduced action potential duration (APD80, 313.1±6.3ms vs. 510.7±11.8ms, p<0.05 and dispersion of repolarization (75.1±4.3ms vs. 125.9±9.4ms, p<0.05). Importantly, early afterdepolarizations (EADs) rarely occurred in fused cultures (4.6% [n=65] vs. 43.4% [n=60], p<0.0001). Mechanistically, this enhanced repolarization force was due to an increased outward Kv current, as partial inhibition by tetraethylammonium chloride (TEA) reverted the anti-arrhythmic effects of fusion towards control values (7.9% to 34.2% EADs (p<0.001). Conclusions: FHF between nrCMCs and hVSCs represents a novel approach to counteract pro-arrhythmogeneity of hVSCs by forcing a CMC-like phenotype that increases repolarization reserve. These results provide proof-of-concept for a previously unexplored therapeutic potential of heterocellular fusion.
1239
Conduction disorders in orthotopic heart transplantation: risk factors and clinical relevance
Abstract
Orthotopic heart transplantation (OHT) leads to changes in electrophysiological properties. Atrio-ventricular (AV) and intraventricular (IV) conduction disorders (CD) are reported, but causes and pattern of development are unknown.
Aim: Analyze incidence and development of AV and IV CD, associated risk factors and outcomes
Materials and Methods: We examined the data of 240 consecutive patients which underwent orthotopic heart transplatation with bicaval anastomosis in our center, between January, 1995 and February, 2003, in a retrospective study. We collected clinical and instrumental data of both donors and recipients and followed their evolution in time. We analyzed the presence of AV and IV CD and pacemaker (PM) implantation in three time periods: in the immediate after surgery, after 1 year, and after 3 years till the last follow up. We recorded the presence of acute graft rejection (graded according to the ISHTL histological grading, 1990) and the presence and severity of cardiac allograft vasculopathy (CAV).
Results: Of the 240 heart recipients studied, 89% presented, in the first ECG post surgery, sinus tachycardia with a mean heart rate of 113.9±19.0 bpm, 9.58% presented accelerated junctional rhythm with a mean heart rate of 98.3±24.4 bpm, and 3 (1.25%) patients were stimulated by temporary PM. Six of the patients with sinus rhythm (2.5%) had first degree AV block. In the follow up the total number of patients who needed a definitive PM was 15. Four of them (26.6%) died within the first year and one (6.67%) died within 5 years after surgery. The only IV CD observed was right bundle branch block (RBBB), which was present in 23.8% of patients after surgery, and went up to 33.9% after 3 years. We didn't find any correlation with age, gender and BMI of both donors and recipients, and with gender or blood group mismatch. We found a correlation between the rejection score in the first month and the presence of RBBB in the first year (p=0.036) and between the rejection score in the first month and the development of RBBB in the first months after transplantation (p=0.012). No correlation was found with one-month, one-year and 5-years mortality and with CAV. The incidence of post-surgery RBBB appeared significantly lower than in a control population treated with biatrial anastomosis (40.7% vs 23.75%, p<0.001).
Conclusions: The presence of CD in OHT is largely related to intraoperative factors and to the surgical technique. The acute graft rejection plays a role in the development of RBBB in the first months after transplantation. The presence of CD doesn't affect prognosis.
1240
Value of the frontal QRS-T angle for diagnosis and prognosis in patients with symptoms suggestive of acute myocardial infarction
Abstract
Introduction: Cardiac ischemia results in changes of ventricular repolarization. The angle between the vectors of the QRS complex and the T wave in the 12-lead ECG can be used as a measure for an abnormal depolarization-repolarization relationship. It's value for diagnosis and prognosis in patients with symptoms suggestive of acute myocardial infarction (AMI) are unknown.
Methods: We prospectively enrolled 1711 consecutive patients with symptoms suggestive of AMI. The QRS-T angle was automatically calculated from a digital 12-lead ECG's recorded at presentation to the ED. Patients were followed up for all-cause mortality for 3 years.
Results: AMI was the final diagnosis in 19% of patients, with 3% having STEMI and 16% NSTEMI. Median QRS-T angle was significantly greater in patients with AMI compared to those without (55° (IQR 23-106) vs. 24° (IQR 11-46), p<0.001). The area under the ROC curve for the diagnosis of AMI was 0.68. Overall, 3-year survival rate was 91%. A greater QRS-T angle was significantly associated with a worse prognosis after 3 years (Survival rates 95%, 88%, 76% for patients with a QRS-T angle <50°, 50-100° and >100°, p<0.001). In multivariable analysis, the prognostic value of the QRS-T angle was independent of other important predictors such as age, troponin levels or the QRS-duration.
Conclusion: In patients with symptoms suggestive of AMI, the QRS-T angle automatically derived from the 12-lead ECG was elevated in patients with AMI. It significantly predicted all-cause mortality during 3 years of follow-up independently of age and troponin levels and therefore has the potential to improve risk stratification in these patients.
1241
Positive chronotropic action of liraglutide on isolated rabbit hearts is not mediated by the beta-adrenergic pathway
Abstract
Purpose: Liraglutide (LG), a Glucagon-Like Peptide-1 analog used in treatments of type-2 diabetes, promotes a mild elevation of heart rate (HR) in clinical studies and animal experiments. Mechanisms that mediate this chronotropism are not known. We assessed the chronotropic effects of LG in β-blocked or If-blocked isolated rabbit hearts.
Methods: Langendorff-perfused rabbit hearts were given bolus infusions containing LG (6mg) before and after the addition of the β-adrenergic receptor blocker Propranolol (Prp, 0.5mg) or the If current blocker Ivabradine (Ivb, 1.5mg) into the 1-L perfusion solution. The β-agonist Isoproterenol (Iso, 2μg) was also used to ascertain the adequacy of β-blockade. Cardiac electrical activities were continuously recorded from epicardial surface electrodes for subsequent analysis.
Results: Eleven hearts were analyzed. Mean baseline HR was 185 ± 14 bpm. Two minutes after LG infusion, HR rose by 9.1%. With Prp added to the perfusion (n=6), HR gradually declined in 30 min to a new baseline of 172 ± 9 bpm. A second dose of LG similarly raised HR (7.4%) despite the presence of Prp, which abrogated the HR elevation induced by Iso (Panel A). In similar experiments, LG failed to raise HR in the presence of Ivb (n=5) (Panel B).
Conclusion: Liraglutide elevates heart rate despite β-blockade, suggesting that the mechanism is unlikely to be based on sympathetic stimulation of the heart. On the contrary, the lack of positive chronotropism in the presence of Ivabradine indicates that the chronotropic actions of LG may be mediated via mechanisms that utilize the If current.
Effects on HR of LG and Prp and Ivb
