Myocardial remodeling and arrhythmogenesis in moderate cardiac hypertrophyin rats

In 47 male adult Wistar rats with 4-wk aortic coarctation (AC) and 39 age-m atched sham-operated rats (SO) chronically instrumented for telemetry elect rocardiogram recording, we investigated the mechanisms of arrhythmogenesis in moderate cardiac hypertrophy, with an approach from "in vivo" toward the cellular level, analyzing 1) stress-induced cardiac arrhythmias in all rat s and 2) myocardial fibrosis in 35 animals and action potential duration an d density of hyperpolarization-activated current in 19 others at the ventri cular level. Aortic banding increased arterial blood pressure, cardiac weig ht, and ventricular myocyte volume by 11, 25, and 14%, respectively (P< 0.0 01-0.05). Ventricular arrhythmias occurred at similar rates in AC and SO ra ts throughout the stress procedure. Action potential duration and hyperpola rization-activated current were about twice as great and myocardial fibrosi s about four times greater in AC animals (P< 0.005-0.05). Electrocardiogram data also revealed more supraventricular arrhythmias in AC rats during the baseline period and after stress and fewer atrioventricular block episodes after stress (P< 0.05). Thus stress-induced supraventricular and atriovent ricular nodal, but not ventricular, arrhythmias were affected in moderate c ardiac hypertrophy when ventricular morphofunctional alterations were evide nt.