Early- and delayed-afterdepolarizations as cellular promoter of ventricular fibrillation in hypertrophic cardiomyopathy
Authors: Santini L , Zocchi C , Olivotto I , Coppini R , Cerbai E 
Published: June 2022

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – EU funding. Main funding source(s): In Silico project

Background
Hypertrophic cardiomyopathy (HCM) represents the commonest inherited cardiac disease, with a prevalence of 1/500 in the general population. The most devastating consequence of HCM is sudden cardiac death (SCD) due to ventricular fibrillation, particularly common in children and young adults. The positive correlation between the extent of late gadolinium enhancement (LGE, reflecting myocardial fibrosis) and the arrhythmic risk suggests that ventricular arrhythmias are held to originate from the fibrotic regions, by a mechanism of electrical re-entry. However, recent data suggest that enhanced cellular automaticity (i.e. early- or delayed-afterdepolarizations, EADs or DADs-) may be clinically more relevant in promoting ventricular arrhythmias in patients.

Purpose
Aiming to better understand the cellular and molecular mechanisms of arrhythmogenesis in HCM and to establish a reliable arrhythmic risk stratification in patients, we performed a translational and retrospective study in 61 HCM patients who underwent surgical myectomy, by combining a clinical follow-up study with in vitro assessments of cellular arrhythmogenicity.

Methods
We retrospectively studied 61 HCM patients who underwent surgical interventricular-septum myectomy to relieve refractory obstruction-related symptoms. At the time of surgery, fresh ventricular tissue was collected and used to isolate single ventricular cardiomyocytes (CMs), which were used for patch-clamp measurements and Ca2+ imaging experiments to assess the occurrence of EADs and DADs. Patients were followed up for a median time of 8 years and the occurrence of non-sustained ventricular tachycardia (NSVT) or life-threatening arrhythmic events (LAE, including sustained VT and ventricular fibrillation, VF) was monitored. Moreover, data from ECG and cardiac magnetic-resonance studies were collected.

Results
EADs occurred in CMs from 36% of patients and were associated with prolonged action potential duration while DADs occurred in 24% of patients and correlated with abnormalities of intracellular Ca2+ handling. During follow up, NSVT events occurred in 19/61 patients while LAE occurred in 4/61 patients. Their combined occurrence (37%) strongly correlated with the presence of DADs in cardiomyocytes. Patients with NSVT/LAE were more likely to show specific "pro-arrhythmic" pathological ECG-patterns. Among patients with LGE, the presence of DADs in cells behaved as a necessary pre-requisite for NSVT/LAE, as none of the patients with evidence of fibrosis but negative for DADs had arrhythmic events.

Conclusions
The presence of pro-arrhythmic changes appears to be necessary for arrhythmia generation in HCM and seems to be related with specific alterations at ECG level, that might be used as clinical arrhythmia predictors in HCM patients. Fibrosis per se is not a major predictor of arrhythmias in HCM but may contribute to generate sustained arrhythmias in the presence of substantial cellular triggers (DADs).