Growth hormone decreases phase II ventricular tachyarrhythmias during acute myocardial infarction in rats

International audienceGrowth hormone administration during acute myocardial infarction (MI) ameliorates subsequent left ventricular (LV) dysfunction. In the present study, we examined the effects of such treatment on arrhythmogenesis. Fifty three Wistar rats (218±17g) were randomized into two intraperitoneal injections of either growth hormone (2IU/kg) (n=26) or normal saline (n=27), given 24 hours and 30 minutes, respectively, prior to MI, generated by left coronary artery ligation. A single-lead electrocardiogram was recorded for 24 hours post-MI, using an implanted telemetry system. Episodes of ventricular tachycardia (VT) and ventricular fibrillation (VF) during the first (phase I) and the following (phase II) hours of MI were analysed. Monophasic action potential was recorded from the lateral LV epicardium at baseline and 24 hours post-MI and signal duration at 90% of repolarization (APD90) was measured. Infarct size was calculated 24 hours post-MI. Infarct size and phase I VT+VF did not differ significantly between groups, but phase II hourly duration of VT+VF episodes was 82.8±116.6s/hour in the control group and 18.3±41.2s/hour in the growth hormone group (p=0.0027), resulting in a lower arrhythmic (p=0.016) and total (p=0.0018) mortality in treated animals. Compared to baseline, APD90 prolonged significantly 24 hours post-MI in the control group, displaying an increased beat-to-beat variation, but remained unchanged in the growth hormone group. We conclude that growth hormone decreases phase II ventricular tachyarrhythmias during MI in the rat. This finding may have implications in cardiac repair strategies