Slow conduction and spatial dispersion of repolarization are intrinsic properties of cardiomyocyte electrophysiology that contribute to proarrhythmia in an iPSC model of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited heart muscle disease; characterised by left ventricular wall thickening, cardiomyocyte disarray, and fibrosis, and is associated with arrhythmias, heart failure and sudden death. However, it is unclear to what extent the electrophysiological disturbances that lead to sudden death occur secondary to the structural changes in the myocardium, or as a result of intrinsic properties of the HCM cardiomyocyte. In this study, we used an induced pluripotent stem cell model of the Arg403Gln variant in myosin heavy chain 7 ( MYH7 ) to study ‘tissue level’ electrophysiological properties of HCM cardiomyocytes. For the first time, we show significant slowing of conduction velocity and an increase in local spatial dispersion of repolarisation - both well-established substrates for arrhythmia - in monolayers of HCM cardiomyocytes. Analysis of rhythmonome protein expression in R403Q cardiomyocytes revealed dramatically reduced connexin-43, sodium channels, and inward rectifier channels – a three-way hit that combines to reduce electrotonic coupling between HCM cardiomyocytes and slow cardiac conduction. Our data therefore represent a novel, biophysical basis for arrhythmia in HCM, that is intrinsic to cardiomyocyte electrophysiology. Later in the progression of the disease, these proarrhythmic electrical phenotypes may be accentuated by fibrosis and myocyte disarray to contribute to sudden death in HCM patients.