Appropriate implantable cardioverter defibrillator therapy in hypertrophic cardiomyopathy: What happens on Sunday afternoons in May?

Abstract

This editorial refers to ‘The relation of ventricular arrhythmia electrophysiological characteristics to cardiac phenotype and circadian patterns in hypertrophic cardiomyopathy’ by C. O'Mahony et al ., on page 724 Hypertrophic cardiomyopathy (HCM) is a clinically and genetically heterogeneous disease. Sudden cardiac death (SCD) is the most devastating complication of HCM. The substrate for potentially life-threatening ventricular arrhythmias (VA) in HCM is complex. The hypertrophy causes dispersion of repolarization and refractoriness, which increases the vulnerability to triggered arrhythmia. Myocardial disarray, the histological hallmark of the disease leads to a disruption of cell-to-cell alignment and together with the expansion of the interstitial compartment and replacement fibrosis creates unidirectional conduction block that predispose to re-entry arrhythmia. Sarcomeric protein gene mutations influence calcium homeostasis, and abnormalities in ion fluxes during repolarization can cause after-depolarization and triggered activity. This unpredictable, complex arrhythmogenic substrate is further influenced by maladaptive autonomic responses, myocardial ischaemia, left ventricular outflow tract obstruction, and currently unknown factors.1 Although these characteristics are to some extent present in most HCM patients, risk of SCD in the general HCM population is low.2 The risk of sudden death increases in the presence of the following clinical risk factors: positive family history of SCD, unexplained syncope, abnormal blood pressure response to exercise, left ventricular wall thickness ≥30 mm, …