Structure and function of the ventricular tachycardia isthmus

Catheter ablation of postinfarction reentrant ventricular tachycardia (VT) has received renewed interest owing to the increased availability of high-resolution electroanatomic mapping systems that can describe the VT circuits in greater detail and the emergence and need to target noninvasive external beam radioablation. These recent advancements provide optimism for improving the clinical outcome of VT ablation in patients with postinfarction and potentially other scar-related VTs. The combination of analyses gleaned from studies in swine and canine models of postinfarction reentrant VT, and in human studies, suggests the existence of common electroanatomic properties for reentrant VT circuits. Characterizing these properties may be useful for increasing the specificity of substrate mapping techniques and for noninvasive identification to guide ablation. Herein, we describe properties of reentrant VT circuits that may assist in elucidating the mechanisms of onset and maintenance, as well as a means to localize and delineate optimal catheter ablation targets

Stabilization of cardiac ryanodine receptor prevents intracellular calcium leak and arrhythmias

Catecholaminergic polymorphic ventricular tachycardia is a form of exercise-induced sudden cardiac death that has been linked to mutations in the cardiac Ca(2+) release channel/ryanodine receptor (RyR2) located on the sarcoplasmic reticulum (SR). We have shown that catecholaminergic polymorphic ventricular tachycardia-linked RyR2 mutations significantly decrease the binding affinity for calstabin-2 (FKBP12.6), a subunit that stabilizes the closed state of the channel. We have proposed that RyR2-mediated diastolic SR Ca(2+) leak triggers ventricular tachycardia (VT) and sudden cardiac death. In calstabin-2-deficient mice, we have now documented diastolic SR Ca(2+) leak, monophasic action potential alternans, and bidirectional VT. Calstabin-deficient cardiomyocytes exhibited SR Ca(2+) leak-induced aberrant transient inward currents in diastole consistent with delayed after-depolarizations. The 1,4-benzothiazepine JTV519, which increases the binding affinity of calstabin-2 for RyR2, inhibited the diastolic SR Ca(2+) leak, monophasic action potential alternans and triggered arrhythmias. Our data suggest that calstabin-2 deficiency is as a critical mediator of triggers that initiate cardiac arrhythmias

Worldwide Survey of COVID-19-Associated Arrhythmias

Background: Coronavirus disease 2019 (COVID-19) has led to over 1 million deaths worldwide and has been associated with cardiac complications including cardiac arrhythmias. The incidence and pathophysiology of these manifestations remain elusive. In this worldwide survey of patients hospitalized with COVID-19 who developed cardiac arrhythmias, we describe clinical characteristics associated with various arrhythmias, as well as global differences in modulations of routine electrophysiology practice during the pandemic. Methods: We conducted a retrospective analysis of patients hospitalized with COVID-19 infection worldwide with and without incident cardiac arrhythmias. Patients with documented atrial fibrillation, atrial flutter, supraventricular tachycardia, nonsustained or sustained ventricular tachycardia, ventricular fibrillation, atrioventricular block, or marked sinus bradycardia (heart rate<40 bpm) were classified as having arrhythmia. Deidentified data was provided by each institution and analyzed. Results: Data were collected for 4526 patients across 4 continents and 12 countries, 827 of whom had an arrhythmia. Cardiac comorbidities were common in patients with arrhythmia: 69% had hypertension, 42% diabetes, 30% had heart failure, and 24% had coronary artery disease. Most had no prior history of arrhythmia. Of those who did develop an arrhythmia, the majority (81.8%) developed atrial arrhythmias, 20.7% developed ventricular arrhythmias, and 22.6% had bradyarrhythmia. Regional differences suggested a lower incidence of atrial fibrillation in Asia compared with other continents (34% versus 63%). Most patients in North America and Europe received hydroxychloroquine, although the frequency of hydroxychloroquine therapy was constant across arrhythmia types. Forty-three percent of patients who developed arrhythmia were mechanically ventilated and 51% survived to hospital discharge. Many institutions reported drastic decreases in electrophysiology procedures performed. Conclusions: Cardiac arrhythmias are common and associated with high morbidity and mortality among patients hospitalized with COVID-19 infection. There were significant regional variations in the types of arrhythmias and treatment approaches