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

GH (growth hormone) administration during acute MI (myocardial infarction) ameliorates subsequent LV (left ventricular) dysfunction. In the present study, we examined the effects of such treatment on arrhythmogenesis. A total of 53 Wistar rats (218 +/- 17 g) were randomized into two groups receiving two intraperitoneal injections of either GH (2 international units/kg of body weight; n = 26) or normal saline (n = 27), given at 24 h and 30 min respectively, prior to MI, which was generated by left coronary artery ligation. A single-lead ECG was recorded for 24 h post-MI, using an implanted telemetry system. Episodes of VT (ventricular tachyarrhythmia) and VF (ventricular fibrillation) during the first hour (phase I) and the hours following (phase II) MI were analysed. Monophasic action potential was recorded from the lateral LV epicardium at baseline and 24 h post-MI, and APD90 (action duration at 90% of repolarization) was measured. Infarct size was calculated 24 h post-MI. Infarct size and phase I VT + VF did not differ significantly between groups, but phase 11 hourly duration of VT + VF episodes was 82.8 +/- 116.6 s/h in the control group and 18.3 +/- 41.2 s/h in the GH group (P = 0.0027), resulting in a lower arrhythmic (P = 0.016) and total (P = 0.0018) mortality in GH-treated animals. Compared with baseline, APD90 was prolonged significantly 24 h post-MI in the control group, displaying an increased beat-to-beat variation, but remained unchanged in the GH group. We conclude that GH decreases phase II VTs during MI in the rat. This finding may have implications in cardiac repair strategies.