Left Atrial Reservoir Strain and Recurrence of Atrial Fibrillation Following De-Novo Pulmonary Vein Isolation　- Results of the ASTRA-AF Pilot Study.

BACKGROUND: Achieving early rhythm control and maintaining sinus rhythm are associated with improved outcomes in patients with atrial fibrillation (AF). Pulmonary vein isolation (PVI) is a validated alternative to medical rhythm control. This study determined associations between left atrial strain reservoir (LASR) and AF recurrence after PVI.Methods and Results: In all, 132 patients (88 with paroxysmal AF [PAF], 44 with persisting AF [PersAF]) who presented in sinus rhythm for de novo PVI of AF between December 2017 and January 2019 were included in the study. All patients underwent preprocedural echocardiography. After 12 months, all patients underwent 24-h Holter electrocardiogram monitoring to screen for AF recurrence. Kaplan-Meier curve analysis revealed an association between decreasing LASRand increased AF recurrence, with a cut-off at 31.4%. In univariable Cox regression analysis, LASRdemonstrated an association with AF recurrence, with hazard ratios (HR) of 0.83 (95% confidence interval [CI] 073-0.93; P=0.001) per 5% increase in univariable models and 0.83 (95% CI 073-0.95; P=0.005) in multivariable analysis. When clinical variables with age, sex and type of AF (PAF/PersAF) were included in the multivariable analysis, LASRremained relevant in a model with age (HR 0.86; 95% CI 073-1.00; P=0.046). CONCLUSIONS: In patients undergoing de novo PVI for AF, LASRcould be of use in risk stratification regarding AF recurrence.

Association of atrial mechanical dispersion with atrial fibrillation recurrence following catheter ablation: results of the ASTRA-AF pilot study.

AIMS: For patients with symptomatic drug-refractory atrial fibrillation (AF), catheter ablation to achieve rhythm control is an important therapeutic option. The atrial mechanical dispersion measured as standard deviation of the time to peak strain (SD-TPS) is associated with the risk of AF recurrence following catheter ablation. METHODS: The study cohort prospectively enrolled n = 132 consecutive patients with paroxysmal (n = 88) or persistent AF (n = 44) presenting for de novo pulmonary vein isolation (PVI) and followed for 1 year. We related left atrial (LA) volume, LA ejection fraction, SD-TPS, and global longitudinal strain of the left ventricle and clinical variables (sex, age, and type of AF) to AF recurrence. RESULTS: Kaplan-Meier curves showed higher AF recurrence rate with an increase of SD-TPS with the calculated cut-off of 38.6 ms. Uni- and multivariable Cox regression analysis could show that SD-TPS had the highest relevance regarding AF recurrence with a HR of 1.05 (95% CI, 1.01; 1.09, p = 0.01) and HR of 1.05 (95% CI, 1.01; 1.09, p = 0.02) per 10 ms increase. In the additional analyses for the model including the clinical variables age, sex, and type of AF with paroxysmal or persisting AF, SD-TPS did only show a trend and after adjusting for covariates, SD-TPS showed a HR of 1.04 (95% CI, 0.99; 1.09, p = 0.09) per 10 ms increase. CONCLUSION: Atrial mechanical dispersion was associated with recurrent AF.

Repeat pulmonary vein isolation and anterior line ablation using a novel point-by-point pulsed-field ablation system.

BACKGROUND: Pulsed-field ablation (PFA) is a nonthermal energy source for ablation of cardiac arrhythmias. This study investigated the prospective outcomes of a novel PFA generator in conjunction with a commercially available, contact force-sensing, focal ablation catheter. OBJECTIVE: The purpose of this study was to assess the feasibility, safety, and lesion characteristics of point-by-point PFA in consecutive patients undergoing repeat ablation of atrial fibrillation (AF). METHODS: The study involved reisolation of pulmonary veins (PVs) with electrical reconnection and the creation of an anterior line (AL) in patients with anterior substrate or durable pulmonary vein isolation (PVI). RESULTS: In 24 patients (46% female; mean age 67 ± 10 years; 67% persistent AF), successful reisolation of 27 of 27 reconnected PVs (100%) was performed. In 19 patients, AL ablation was performed, with bidirectional block in 16 (84%), median ablation time 26 [21, 33] minutes, and first-pass bidirectional block in 13 patients (68%). Acute AL reconduction occurred in 8 of 19 patients (42%). Among these 8 patients, a subsequent sustained block of the AL was achieved in 5 (63%). Ultra-high-density electroanatomic mapping revealed homogeneous but relatively large low-voltage areas in the ablated regions. Median procedural, left atrial dwell, and fluoroscopy times were 100 [90, 109] minutes, 83 [75, 98] minutes, and 10 [8, 13] minutes, respectively. No major or minor complications occurred. CONCLUSION: This study demonstrated feasibility, acute efficacy, and safety of point-by-point PFA for repeat PVI and AL ablation. Further studies are warranted to assess the long-term durability and comparison with established ablation methods.

Human induced pluripotent stem cell-derived cardiomyocytes as an electrophysiological model: Opportunities and challenges-The Hamburg perspective.

Models based on human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are proposed in almost any field of physiology and pharmacology. The development of human induced pluripotent stem cell-derived cardiomyocytes is expected to become a step forward to increase the translational power of cardiovascular research. Importantly they should allow to study genetic effects on an electrophysiological background close to the human situation. However, biological and methodological issues revealed when human induced pluripotent stem cell-derived cardiomyocytes were used in experimental electrophysiology. We will discuss some of the challenges that should be considered when human induced pluripotent stem cell-derived cardiomyocytes will be used as a physiological model.

Resting membrane potential is less negative in trabeculae from right atrial appendages of women, but action potential duration does not shorten with age.

AIMS: The incidence of atrial fibrillation (AF) increases with age. Women have a lower risk. Little is known on the impact of age, sex and clinical variables on action potentials (AP) recorded in right atrial tissue obtained during open heart surgery from patients in sinus rhythm (SR) and in longstanding AF. We here investigated whether age or sex have an impact on the shape of AP recorded in vitro from right atrial tissue. METHODS: We performed multivariable analysis of individual AP data from trabeculae obtained during heart surgery of patients in SR (n = 320) or in longstanding AF (n = 201). AP were recorded by sharp microelectrodes at 37 °C at 1 Hz. Impact of clinical variables were modeled using a multivariable mixed model regression. RESULTS: In SR, AP duration at 90% repolarization (APD90) increased with age. Lower ejection fraction and higher body mass index were associated with smaller action potential amplitude (APA) and maximum upstroke velocity (Vmax). The use of beta-blockers was associated with larger APD90. In tissues from women, resting membrane potential was less negative and APA as well as Vmax were smaller. Besides shorter APD20 in elderly patients, effects of age and sex on atrial AP were lost in AF. CONCLUSION: The higher probability to develop AF at advanced age cannot be explained by a shortening in APD90. Less negative RMP and lower upstroke velocity might contribute to lower incidence of AF in women, which may be of clinical relevance.

Regulation of APD and Force by the Na+/Ca2+ Exchanger in Human-Induced Pluripotent Stem Cell-Derived Engineered Heart Tissue.

The physiological importance of NCX in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is not well characterized but may depend on the relative strength of the current, compared to adult cardiomyocytes, and on the exact spatial arrangement of proteins involved in Ca2+ extrusion. Here, we determined NCX currents and its contribution to action potential and force in hiPSC-CMs cultured in engineered heart tissue (EHT). The results were compared with data from rat and human left ventricular tissue. The NCX currents in hiPSC-CMs were larger than in ventricular cardiomyocytes isolated from human left ventricles (1.3 ± 0.2 pA/pF and 3.2 ± 0.2 pA/pF for human ventricle and EHT, respectively, p < 0.05). SEA0400 (10 µM) markedly shortened the APD90 in EHT (by 26.6 ± 5%, p < 0.05) and, to a lesser extent, in rat ventricular tissue (by 10.7 ± 1.6%, p < 0.05). Shortening in human left ventricular preparations was small and not different from time-matched controls (TMCs; p > 0.05). Force was increased by the NCX block in rat ventricle (by 31 ± 5.4%, p < 0.05) and EHT (by 20.8 ± 3.9%, p < 0.05), but not in human left ventricular preparations. In conclusion, hiPSC-CMs possess NCX currents not smaller than human left ventricular tissue. Robust NCX block-induced APD shortening and inotropy makes EHT an attractive pharmacological model.

Muscarinic Receptor Activation Reduces Force and Arrhythmias in Human Atria Independent of IK,ACh.

ABSTRACT: In human hearts, muscarinic receptors (M-R) are expressed in ventricular and atrial tissue, but the acetylcholine-activated potassium current (IK,ACh) is expressed mainly in the atrium. M-R activation decreases force and increases electrical stability in human atrium, but the impact of IK,ACh to both effects remains unclear. We used a new selective blocker of IK,ACh to elaborate the contribution of IK,ACh to M-R activation-mediated effects in human atrium. Force and action potentials were measured in rat atria and in human right atrial trabeculae. Cumulative concentration-effect curves for norepinephrine-induced force and arrhythmias were measured in the presence of carbachol (CCh; 1 µM) or CCh together with the IK,ACh -blocker XAF-1407 (1 µM) or in time-matched controls. To investigate the vulnerability to arrhythmias, we performed some experiments also in the presence of cilostamide (0.3 µM) and rolipram (1 µM), inhibiting PDE3 and PDE4. In rat atria and human right atrial trabeculae, CCh shortened the action potential duration persistently. However, the direct negative inotropy of CCh was only transient in human, but stable in rat atria. In rat and human atria, the negative inotropic effect was insensitive to blockage of IK,ACh by XAF-1407. In the presence of cilostamide and rolipram about 40% of trabeculae developed arrhythmias when exposed to norepinephrine. CCh prevented these concentration-dependent norepinephrine-induced arrhythmias, again insensitive to XAF-1407. Maximum catecholamine-induced force was not depressed by CCh. In human atrium, the direct and the indirect negative inotropic effect of CCh are independent of IK,ACh. The same applies to the CCh-mediated suppression of norepinephrine/PDE-inhibition-induced arrhythmias.

Regulation of basal and norepinephrine-induced cAMP and ICa in hiPSC-cardiomyocytes: Effects of culture conditions and comparison to adult human atrial cardiomyocytes.

BACKGROUND: There is ongoing interest in generating cardiomyocytes derived from human induced pluripotent stem cells (hiPSC) to study human cardiac physiology and pathophysiology. Recently we found that norepinephrine-stimulated calcium currents (ICa) in hiPSC-cardiomyocytes were smaller in conventional monolayers (ML) than in engineered heart tissue (EHT). In order to elucidate culture specific regulation of ß1-adrenoceptor (ß1-AR) responses we investigated whether action of phosphodiesterases (PDEs) may limit norepinephrine effects on ICa and on cytosolic cAMP in hiPSC-cardiomyocytes. Results were compared to adult human atrial cardiomyocytes. METHODS: Adult human atrial cardiomyocytes were isolated from tissue samples obtained during open heart surgery. All patients were in sinus rhythm. HiPSC-cardiomyocytes were dissociated from ML and EHT. Förster-resonance energy transfer (FRET) was used to monitor cytosolic cAMP (Epac1-camps sensor, transfected by adenovirus). ICa was recorded by whole-cell patch clamp technique. Cilostamide (300 nM) and rolipram (10 µM) were used to inhibit PDE3 and PDE4, respectively. ß1-AR were stimulated with the physiological agonist norepinephrine (100 µM). RESULTS: In adult human atrial cardiomyocytes, norepinephrine increased cytosolic cAMP FRET ratio by +13.7 ± 1.5% (n = 10/9, mean ± SEM, number of cells/number patients) and ICa by +10.4 ± 1.5 pA/pF (n = 15/10). This effect was not further increased in the concomitant presence of rolipram, cilostamide and norepinephrine, indicating saturation by norepinephrine alone. In ML hiPSC-cardiomyocytes, norepinephrine exerted smaller increases in cytosolic cAMP and ICa (FRET +9.6 ± 0.5% n = 52/21, number of cells/number of ML or EHT, and ICa + 1.4 ± 0.2 pA/pF n = 34/7, p < 0.05 each) and both were augmented in the presence of the PDE4 inhibitor rolipram (FRET +16.7 ± 0.8% n = 94/26 and ICa + 5.6 ± 1.4 pA/pF n = 11/5, p < 0.05 each). Cilostamide increased the response to norepinephrine on FRET (+12.7 ± 0.5% n = 91/19, p < 0.05), but not on ICa. In EHT hiPSC-cardiomyocytes, norepinephrine responses on both, FRET and ICa, were larger than in ML (FRET +12.1 ± 0.3% n = 87/32 and ICa + 3.3 ± 0.2 pA/pF n = 13/5, p < 0.05 each). Rolipram augmented the norepinephrine effect on ICa (+6.2 ± 1.6 pA/pF; p < 0.05 vs. norepinephrine alone, n = 10/4), but not on FRET. CONCLUSION: Our results show culture-dependent differences in hiPSC-cardiomyocytes. In conventional ML but not in EHT, maximum norepinephrine effects on cytosolic cAMP depend on PDE3 and PDE4, suggesting immaturity when compared to the situation in adult human atrial cardiomyocytes. The smaller ICa responses to norepinephrine in ML and EHT vs. adult human atrial cardiomyocytes depend at least partially on a non-physiological large impact of PDE4 in hiPSC-cardiomyocytes.

Ca2+ currents in cardiomyocytes: How to improve interpretation of patch clamp data?

OBJECTIVES: Variability of ion currents is major issue when used for significance testing. One of the simplest approach to reduce variability is normalization to cell membrane size. However, efficacy of Ca2+ currents (ICa) normalization is unknown. Beside absolute variability, the type of distribution since non-Gaussian distribution makes application of nonparametric test necessary. METHODS: We retrospectively analyzed individual ICa amplitudes measured in ventricular cardiomyocytes from mice, rats and humans and in atrial cardiomyocytes from humans in sinus rhythm and in atrial fibrillation. ICa was normalized to cell membrane size, estimated from capacitance transients. In addition, data were Log transformed to reach Gaussian distribution. Normalized and transformed data were analyzed for variability and applicability of parametric vs. nonparametric tests. RESULTS: There was strong correlation between ICa and cell membrane size. However, correlation coefficient was rather low. Normalizing ICa had an inconsistent effect on variability. Variability of ICa in cells from the same patient/animal was not different cardiomyocytes from humans, rat and mice. Calculation of mean values based on mean values of cells from individuals (patients or animals) vs. mean values calculated for all cells drastically reduces statistical power to detect differences between the groups. Log transformation of ICa allowed application of much higher sensitive parametric testing, compensating loss of power. CONCLUSION: Impact of cell membrane size to ICa is low and may limit efficacy of normalization of ICa to reduce variability. In contrast, Log transformation of ICa data reduces variability and can increase statistical power to detect difference between ICa datasets.

Regulation of ICa,L and force by PDEs in human-induced pluripotent stem cell-derived cardiomyocytes.

BACKGROUND AND PURPOSE: Phosphodiesterases (PDEs) are important regulators of ß-adrenoceptor signalling in the heart. While PDE4 is the most important isoform that regulates ICa,L and force in rodent cardiomyocytes, the dominant isoform in adult human cardiomyocytes is PDE3. EXPERIMENTAL APPROACH: Given the potential of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for biomedical research, this study characterized the contribution of PDE3 and PDE4 isoforms to the regulation of ICa,L and force in hiPSC-CMs in an engineered heart tissue (EHT) model. KEY RESULTS: There was a lower abundance of mRNA for PDE3A and 4A in hiPSC-CM EHT than in non-failing human heart samples. Selective inhibition of PDE3 and 4 with cilostamide and rolipram, respectively, showed that, in hiPSC-CM, PDE4 was the predominant isoform for the regulation of ICa,L (cilostamide: +1.44-fold; rolipram: +1.77-fold). Furthermore, in contrast to cilostamide, rolipram decreased the EC50 of isoprenaline about 15-fold. CONCLUSION AND IMPLICATIONS: The predominance of PDE4 over PDE3 is a peculiarity of hiPSC-CMs and is probably an indicator of immaturity. This finding has implications for the use of hiPSC-CM as pharmacological models to investigate and assess the effects of PDE inhibitors.

Chronic intermittent tachypacing by an optogenetic approach induces arrhythmia vulnerability in human engineered heart tissue.

AIMS: Chronic tachypacing is commonly used in animals to induce cardiac dysfunction and to study mechanisms of heart failure and arrhythmogenesis. Human induced pluripotent stem cells (hiPSC) may replace animal models to overcome species differences and ethical problems. Here, 3D engineered heart tissue (EHT) was used to investigate the effect of chronic tachypacing on hiPSC-cardiomyocytes (hiPSC-CMs). METHODS AND RESULTS: To avoid cell toxicity by electrical pacing, we developed an optogenetic approach. EHTs were transduced with lentivirus expressing channelrhodopsin-2 (H134R) and stimulated by 15 s bursts of blue light pulses (0.3 mW/mm2, 30 ms, 3 Hz) separated by 15 s without pacing for 3 weeks. Chronic optical tachypacing did not affect contractile peak force, but induced faster contraction kinetics, shorter action potentials, and shorter effective refractory periods. This electrical remodelling increased vulnerability to tachycardia episodes upon electrical burst pacing. Lower calsequestrin 2 protein levels, faster diastolic depolarization (DD) and efficacy of JTV-519 (46% at 1 µmol/L) to terminate tachycardia indicate alterations of Ca2+ handling being part of the underlying mechanism. However, other antiarrhythmic compounds like flecainide (69% at 1 µmol/L) and E-4031 (100% at 1 µmol/L) were also effective, but not ivabradine (1 µmol/L) or SEA0400 (10 µmol/L). CONCLUSION: We demonstrated a high vulnerability to tachycardia of optically tachypaced hiPSC-CMs in EHT and the effective termination by ryanodine receptor stabilization, sodium or hERG potassium channel inhibition. This new model might serve as a preclinical tool to test antiarrhythmic drugs increasing the insight in treating ventricular tachycardia.