Utilizing Human-Induced Pluripotent Stem Cells to Study Cardiac Electroporation Pulsed-Field Ablation.

BACKGROUND: Electroporation is a promising nonthermal ablation method for cardiac arrhythmia treatment. Although initial clinical studies found electroporation pulsed-field ablation (PFA) both safe and efficacious, there are significant knowledge gaps concerning the mechanistic nature and electrophysiological consequences of cardiomyocyte electroporation, contributed by the paucity of suitable human in vitro models. Here, we aimed to establish and characterize a functional in vitro model based on human-induced pluripotent stem cells (hiPSCs)-derived cardiac tissue, and to study the fundamentals of cardiac PFA. METHODS: hiPSC-derived cardiomyocytes were seeded as circular cell sheets and subjected to different PFA protocols. Detailed optical mapping, cellular, and molecular characterizations were performed to study PFA mechanisms and electrophysiological outcomes. RESULTS: PFA generated electrically silenced lesions within the hiPSC-derived cardiac circular cell sheets, resulting in areas of conduction block. Both reversible and irreversible electroporation components were identified. Significant electroporation reversibility was documented within 5 to 15-minutes post-PFA. Irreversibly electroporated regions persisted at 24-hours post-PFA. Per single pulse, high-frequency PFA was less efficacious than standard (monophasic) PFA, whereas increasing pulse-number augmented lesion size and diminished reversible electroporation. PFA augmentation could also be achieved by increasing extracellular Ca2+ levels. Flow-cytometry experiments revealed that regulated cell death played an important role following PFA. Assessing for PFA antiarrhythmic properties, sustainable lines of conduction block could be generated using PFA, which could either terminate or isolate arrhythmic activity in the hiPSC-derived cardiac circular cell sheets. CONCLUSIONS: Cardiac electroporation may be studied using hiPSC-derived cardiac tissue, providing novel insights into PFA temporal and electrophysiological characteristics, facilitating electroporation protocol optimization, screening for potential PFA-sensitizers, and investigating the mechanistic nature of PFA antiarrhythmic properties.

Prevalence of Cardiac Sarcoidosis in Middle-Aged Adults Diagnosed with High-Grade Atrioventricular Block.

INTRODUCTION: Atrioventricular block may be idiopathic or a secondary manifestation of an underlying systemic disease. Cardiac sarcoidosis is a significant underlying cause of high-grade atrioventricular block, posing diagnostic challenges and significant clinical implications. This study aimed to assess the prevalence and clinical characteristics of cardiac sarcoidosis among younger patients presenting with unexplained high-grade atrioventricular block. METHODS: We evaluated patients aged between 18 and 65 years presenting with unexplained high-grade atrioventricular block, who were systematically referred for cardiac magnetic resonance imaging, positron emission tomography-computed tomography, or both, prior to pacemaker implantation. Subjects with suspected cardiac sarcoidosis based on imaging findings were further referred for tissue biopsy. Cardiac sarcoidosis diagnosis was confirmed based on biopsy results. RESULTS: Overall, 30 patients with high-grade atrioventricular block were included in the analysis. The median age was 56.5 years (interquartile range 53-61.75, years). In 37%, cardiac magnetic resonance imaging, positron emission tomography-computed tomography, or both, were suggestive of cardiac sarcoidosis, and in 33% cardiac sarcoidosis was confirmed by tissue biopsy. Compared with idiopathic high-grade atrioventricular block patients, all cardiac sarcoidosis patients were males (100% vs 60%, P = .029), were more likely to present with heart failure symptoms (50% vs 10%, P = .047), had thicker inter-ventricular septum on echocardiography (12.2 ± 2.7 mm vs 9.45 ± 1.6 mm, P = .002), and were more likely to present with right ventricular dysfunction (33% vs 10%, P = .047). CONCLUSIONS: Cardiac sarcoidosis was confirmed in one-third of patients ≤ 65 years, who presented with unexplained high-grade atrioventricular block. Cardiac sarcoidosis should be highly suspected in such patients, particularly in males who present with heart failure symptoms or exhibit thicker inter-ventricular septum and right ventricular dysfunction on echocardiography.

Differential effect of high-frequency electroporation on myocardium vs. non-myocardial tissues.

AIMS: Pulsed-field ablation (PFA) is an emerging non-thermal ablation method based on the biophysical phenomenon of electroporation. Data on PFA cardiac selectivity nature and tissue-specific thresholds are lacking. We aim to compare the in vivo differential effect of high-frequency irreversible electroporation (HF-IRE) protocols on various tissues. METHODS AND RESULTS: Twenty-three Sprague-Dawle rodents were allocated into three different protocols of 300, 600, and 900 V, respectively, while delivering twenty 100 µs bursts of a 150 kHz biphasic square wave to five tissues; cardiac muscle, skeletal muscle, liver, carotid artery and sciatic nerve. Lesions were evaluated quantitatively by histologic analysis and by morphometric evaluation. There were eight, seven and eight animals in the 300, 600, and 900 V protocols, respectively. High-frequency electroporation protocols showed a graded effect on myocardial tissue with larger lesions in the 900 V protocol compared with the other two protocols as demonstrated by width (P = 0.02), length (P = 0.01) and fibrosis ratio (P = 0.001). This effect was not observed for other tissues with attenuated degree of damage. No damage to the carotid artery was observed in all protocols. Partial damage to the sciatic nerve was observed in only two samples (25%) in the 600 V group and in one sample (14.3%) in the 900 V group. CONCLUSION: Electroporation effect is tissue-specific such that myocardium is more prone to electroporation damage compared with neural and vascular tissues. Our results suggest no neural or vascular damage with using a low-amplitude HF-IRE protocol. Further investigation is warranted to better identify other tissue-specific thresholds.

The Association between Marital Status and Outcomes of Patients Hospitalized with Heart Failure.

BACKGROUND: Little is known about the association between marital status and long-term outcomes of patients hospitalized with heart failure (HF). We aimed to examine the association between marital status and early as well as long-term outcomes of patients hospitalized with HF. METHOD: We analyzed data of 4089 patients hospitalized with HF and were enrolled in the multicenter national survey in Israel between March and April 2003 and were followed until December 2014. Patients were classified into married (N = 2462, 60%) and unmarried (N = 1627, 40%). RESULTS: Married patients were more likely to be males, younger, and more likely to have past myocardial infarction and previous revascularization. Also, they tended to have higher rates of diabetes mellitus (DM) and dyslipidemia, as well as smokers. Survival analysis showed that unmarried patients had higher mortality rates at 1 and 10 years (33% vs. 25%, at 1 year, 89% vs. 80% at 10 years, all p < 0.001). Consistently, multivariable analysis showed that unmarried patients had independently 44% and 35% higher risk of mortality at 1- and 10-year follow-up respectively (1-year HR = 1.44; 95%CI 1.14-1.81; p = 0.002, 10-year HR = 1.35; 95%CI 1.19-1.53; p ≤ 0.001). Other consistent predictors of mortality at both 1- and 10-year follow-up include age, renal failure, and advanced HF. CONCLUSIONS: Being unmarried is independently associated with worse short- and long-term outcomes, particularly among women. Thus, attempts to intensify secondary preventive measures should focus mainly on unmarried patients and mainly women.

Characterization of the mechanism by which a nonsense variant in RYR2 leads to disordered calcium handling.

Heterozygous missense variants of the cardiac ryanodine receptor gene (RYR2) cause catecholaminergic polymorphic ventricular tachycardia (CPVT). These missense variants of RYR2 result in a gain of function of the ryanodine receptors, characterized by increased sensitivity to activation by calcium that results in an increased propensity to develop calcium waves and delayed afterdepolarizations. We have recently detected a nonsense variant in RYR2 in a young patient who suffered an unexplained cardiac arrest. To understand the mechanism by which this variant in RYR2, p.(Arg4790Ter), leads to ventricular arrhythmias, human induced pluripotent stem cells (hiPSCs) harboring the novel nonsense variant in RYR2 were generated and differentiated into cardiomyocytes (RYR2-hiPSC-CMs) and molecular and calcium handling properties were studied. RYR2-hiPSC-CMs displayed significant calcium handling abnormalities at baseline and following treatment with isoproterenol. Treatment with carvedilol and nebivolol resulted in a significant reduction in calcium handling abnormalities in the RYR2-hiPSC-CMs. Expression of the mutant RYR2 allele was confirmed at the mRNA level and partial silencing of the mutant allele resulted in a reduction in calcium handling abnormalities at baseline. The nonsense variant behaves similarly to other gain of function variants in RYR2. Carvedilol and nebivolol may be suitable treatments for patients with gain of function RYR2 variants.

Characterization of heart failure patients with reverse left ventricular remodelling post-angiotensin receptor blockers/neprilysin inhibitors therapy.

AIMS: To assess the effect of angiotensin receptor blockers/neprilysin inhibitors (ARNI) on left ventricular (LV) ejection fraction (LVEF) and LV dimensions in a real-life cohort of heart failure and reduced ejection fraction (HFrEF) patients, while analysing patient characteristics that may predict reverse LV remodelling. METHODS AND RESULTS: The ARNI-treated HFrEF patients followed at a single tertiary medical centre HF-outpatient clinic were included in the study. Clinical and echocardiographic parameters were evaluated prior to ARNI initiation, and while on ARNI therapy, assessing patient characteristics associated with reverse LV remodelling. The cohort included 91 patients (mean age 60.5 years, 90% male) and 47 (52%) patients exhibited ARNI responsiveness, defined as an increase in LVEF during therapy. Overall, LVEF increased by 19% post-ARNI (23.8 to 28.4%, P < 0.001). Subgroup analysis revealed several parameters associated with significant LVEF improvement, including baseline LVEF <30%, non-ischaemic HF aetiology, lack of cardiac resynchronization therapy (CRT), better initial functional class and ARNI initiation within 3 years from HF diagnosis (P ≤ 0.001 for all). Significant reduction in LV dimensions was noted in patients with lower initial LVEF, non-ischaemic HF and no CRT. Further combined subgrouping of the study population demonstrated that patients with both LVEF <30% and a non-ischaemic HF gained most benefit from ARNI with an average of 51% improvement in LVEF (19.9 to 30%, P < 0.001). CONCLUSIONS: The ARNI treatment response is not uniform among HFrEF patient subgroups. More pronounce reverse LV remodelling is associated with early ARNI treatment initiation in the course of HFrEF, and in those with LVEF <30%, non-ischaemic HF and no CRT.

Female gender is associated with a worse prognosis amongst patients hospitalised for de-novo acute heart failure.

BACKGROUND: Recent evidence showed that new-onset (de-novo) acute heart failure (AHF) is a distinct type of AHF. However, the prognostic implication of gender on these patients remains unclear. AIMS: We aimed to investigate the impact of gender on both short and long-term mortality outcomes after hospitalisation for de-novo AHF. METHODS: We analysed the data of 721 patients with de-novo AHF, who were enrolled in the HF survey in Israel between March and April 2003 and were followed until December 2014. RESULTS: Fifty-four percent (N = 387) of the patients were men. In comparison to women, men patients were more likely to be younger, smokers, and with ischemic HF aetiology. At 30 days, mortality rates were higher in women (12% vs 7%, P = .013). Survival analysis showed that at 1 and 10 years the all-cause mortality rates were significantly higher in women (28% vs 17%, and 78% vs 67%, 1 and 10 years, P < .001, respectively). Consistently, multivariable analysis showed that women had an independently 82% and 24% higher mortality risk at 1 and 10 years, respectively, (1-year hazard ratio = 1.82; 95% confidence interval = 1.07 to 3.11, P = .03; 10-year hazard ratio = 1.24; 95% confidence interval = 1.03 to 1.48, P = .02). CONCLUSIONS: Amongst patients with de-novo AHF, women had higher mortality rates compared with men. The observed gender-related differences in de-novo AHF patients highlight the need for further and deeper research in this field.

Patient-Specific Drug Screening Using a Human Induced Pluripotent Stem Cell Model of Catecholaminergic Polymorphic Ventricular Tachycardia Type 2.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia type 2 (CPVT2) results from autosomal recessive CASQ2 mutations, causing abnormal Ca2+-handling and malignant ventricular arrhythmias. We aimed to establish a patient-specific human induced pluripotent stem cell (hiPSC) model of CPVT2 and to use the generated hiPSC-derived cardiomyocytes to gain insights into patient-specific disease mechanism and pharmacotherapy. METHODS AND RESULTS: hiPSC cardiomyocytes were derived from a CPVT2 patient (D307H-CASQ2 mutation) and from healthy controls. Laser-confocal Ca2+ and voltage imaging showed significant Ca2+-transient irregularities, marked arrhythmogenicity manifested by early afterdepolarizations and triggered arrhythmias, and reduced threshold for store overload-induced Ca2+-release events in the CPVT2-hiPSC cardiomyocytes when compared with healthy control cells. Pharmacological studies revealed the prevention of adrenergic-induced arrhythmias by ß-blockers (propranolol and carvedilol), flecainide, and the neuronal sodium-channel blocker riluzole; a direct antiarrhythmic action of carvedilol (independent of its α/ß-adrenergic blocking activity), flecainide, and riluzole; and suppression of abnormal Ca2+ cycling by the ryanodine stabilizer JTV-519 and carvedilol. Mechanistic insights were gained on the different antiarrhythmic actions of the aforementioned drugs, with carvedilol and JTV-519 (but not flecainide or riluzole) acting primarily through sarcoplasmic reticulum stabilization. Finally, comparable outcomes were found between flecainide and labetalol antiarrhythmic effects in vitro and the clinical results in the same patient. CONCLUSIONS: These results demonstrate the ability of hiPSCs cardiomyocytes to recapitulate CPVT2 disease phenotype and drug response in the culture dish, to provide novel insights into disease and drug therapy mechanisms, and potentially to tailor patient-specific drug therapy.

Monitoring Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes with Genetically Encoded Calcium and Voltage Fluorescent Reporters.

The advent of the human-induced pluripotent stem cell (hiPSC) technology has transformed biomedical research, providing new tools for human disease modeling, drug development, and regenerative medicine. To fulfill its unique potential in the cardiovascular field, efficient methods should be developed for high-resolution, large-scale, long-term, and serial functional cellular phenotyping of hiPSC-derived cardiomyocytes (hiPSC-CMs). To achieve this goal, we combined the hiPSC technology with genetically encoded voltage (ArcLight) and calcium (GCaMP5G) fluorescent indicators. Expression of ArcLight and GCaMP5G in hiPSC-CMs permitted to reliably follow changes in transmembrane potential and intracellular calcium levels, respectively. This allowed monitoring short- and long-term changes in action-potential and calcium-handling properties and the development of arrhythmias in response to several pharmaceutical agents and in hiPSC-CMs derived from patients with different inherited arrhythmogenic syndromes. Combining genetically encoded fluorescent reporters with hiPSC-CMs may bring a unique value to the study of inherited disorders, developmental biology, and drug development and testing.

Modeling of arrhythmogenic right ventricular cardiomyopathy with human induced pluripotent stem cells.

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a primary heart muscle disorder resulting from desmosomal protein mutations. ARVC is characterized pathologically by fibrofatty infiltration and clinically by arrhythmias and sudden cardiac death. We aimed to establish a patient-/disease-specific human induced pluripotent stem cell (hiPSC) model of ARVC. METHODS AND RESULTS: Dermal fibroblasts were obtained from 2 patients with ARVC with plakophilin-2 (PKP2) mutations, reprogrammed to generate hiPSCs, coaxed to differentiate into cardiomyocytes (CMs), and then compared with healthy control hiPSC-derived CMs (hiPSC-CMs). Real-time polymerase chain reaction showed a significant decrease in the expression of PKP2 in the ARVC-hiPSC-CMs. Immunostainings revealed reduced densities of PKP2, the associated desmosomal protein plakoglobin, and the gap-junction protein connexin-43. Electrophysiological assessment demonstrated prolonged field potential rise time in the ARVC-hiPSC-CMs. Transmission electron microscopy identified widened and distorted desmosomes in the ARVC-hiPSC-CMs. Clusters of lipid droplets were identified in the ARVC-CMs that displayed the more severe desmosomal pathology. This finding was associated with upregulation of the proadipogenic transcription factor peroxisome proliferator-activated receptor-γ. Exposure of the cells to apidogenic stimuli augmented desmosomal distortion and lipid accumulation. The latter phenomenon was prevented by application of a specific inhibitor of glycogen synthase kinase 3ß (6-bromoindirubin-3'-oxime). CONCLUSIONS: This study highlights the unique potential of the hiPSC technology for modeling inherited cardiac disorders in general and ARVC specifically. The hiPSC-CMs were demonstrated to recapitulate the ARVC phenotype in the dish, provide mechanistic insights into early disease pathogenesis, and provide a unique platform for drug discovery and testing in this disorder.

Modeling of catecholaminergic polymorphic ventricular tachycardia with patient-specific human-induced pluripotent stem cells.

OBJECTIVES: The goal of this study was to establish a patient-specific human-induced pluripotent stem cells (hiPSCs) model of catecholaminergic polymorphic ventricular tachycardia (CPVT). BACKGROUND: CPVT is a familial arrhythmogenic syndrome characterized by abnormal calcium (Ca(2+)) handling, ventricular arrhythmias, and sudden cardiac death. METHODS: Dermal fibroblasts were obtained from a CPVT patient due to the M4109R heterozygous point RYR2 mutation and reprogrammed to generate the CPVT-hiPSCs. The patient-specific hiPSCs were coaxed to differentiate into the cardiac lineage and compared with healthy control hiPSCs-derived cardiomyocytes (hiPSCs-CMs). RESULTS: Intracellular electrophysiological recordings demonstrated the development of delayed afterdepolarizations in 69% of the CPVT-hiPSCs-CMs compared with 11% in healthy control cardiomyocytes. Adrenergic stimulation by isoproterenol (1 µM) or forskolin (5 µM) increased the frequency and magnitude of afterdepolarizations and also led to development of triggered activity in the CPVT-hiPSCs-CMs. In contrast, flecainide (10 µM) and thapsigargin (10 µM) eliminated all afterdepolarizations in these cells. The latter finding suggests an important role for internal Ca(2+) stores in the pathogenesis of delayed afterdepolarizations. Laser-confocal Ca(2+) imaging revealed significant whole-cell [Ca(2+)] transient irregularities (frequent local and large-storage Ca(2+)-release events, broad and double-humped transients, and triggered activity) in the CPVT cardiomyocytes that worsened with adrenergic stimulation and Ca(2+) overload and improved with beta-blockers. Store-overload-induced Ca(2+) release was also identified in the hiPSCs-CMs and the threshold for such events was significantly reduced in the CPVT cells. CONCLUSIONS: This study highlights the potential of hiPSCs for studying inherited arrhythmogenic syndromes, in general, and CPVT specifically. As such, it represents a promising paradigm to study disease mechanisms, optimize patient care, and aid in the development of new therapies.

Modelling the long QT syndrome with induced pluripotent stem cells.

The ability to generate patient-specific human induced pluripotent stem cells (iPSCs) offers a new paradigm for modelling human disease and for individualizing drug testing. Congenital long QT syndrome (LQTS) is a familial arrhythmogenic syndrome characterized by abnormal ion channel function and sudden cardiac death. Here we report the development of a patient/disease-specific human iPSC line from a patient with type-2 LQTS (which is due to the A614V missense mutation in the KCNH2 gene). The generated iPSCs were coaxed to differentiate into the cardiac lineage. Detailed whole-cell patch-clamp and extracellular multielectrode recordings revealed significant prolongation of the action-potential duration in LQTS human iPSC-derived cardiomyocytes (the characteristic LQTS phenotype) when compared to healthy control cells. Voltage-clamp studies confirmed that this action-potential-duration prolongation stems from a significant reduction of the cardiac potassium current I(Kr). Importantly, LQTS-derived cells also showed marked arrhythmogenicity, characterized by early-after depolarizations and triggered arrhythmias. We then used the LQTS human iPSC-derived cardiac-tissue model to evaluate the potency of existing and novel pharmacological agents that may either aggravate (potassium-channel blockers) or ameliorate (calcium-channel blockers, K(ATP)-channel openers and late sodium-channel blockers) the disease phenotype. Our study illustrates the ability of human iPSC technology to model the abnormal functional phenotype of an inherited cardiac disorder and to identify potential new therapeutic agents. As such, it represents a promising paradigm to study disease mechanisms, optimize patient care (personalized medicine), and aid in the development of new therapies.

Linguistic history of posterior reversible encephalopathy syndrome: mirror of developing knowledge.

BACKGROUND: the term posterior reversible encephalopathy syndrome (PRES) was first proposed in 2000. Since then, the acronym PRES has become very popular in imaging and clinical literature as it is short, easy to say and remember, and neatly couples the frequent localization of neuroimaging findings along with the typical outcome of this syndrome. Another possible reason for the popularity of this acronym in clinical circles is the connotation of PRES with (elevated blood) PRESsure, as a majority of cases are believed to be associated with hypertension. However, problems exist with the interpretation and common understanding of PRES, questioning the appropriateness of "P" and "R" in the acronym. The linguistic issues related to the acronym of PRES are interesting. OBJECTIVES: the aim of this work is to analyze the controversies related to the acronym of PRES. RESULTS: in 2006, modifying the meaning of the acronym was suggested, renaming it Potentially Reversible Encephalopathy Syndrome in order to adjust to the cases when posterior involvement is not prominent and emphasize that the reversibility is not spontaneous. This meant the creation of a backronym, where the new phrase is constructed by starting with an existing acronym. CONCLUSION: this new backronym indicates that the original acronym of PRES has become a misnomer.