ACUTE EFFECTS OF THE ACE INHIBITOR LISINOPRIL ON CARDIAC ELECTROPHYSIOLOGICAL PARAMETERS OF ISOLATED GUINEA-PIG HEARTS

Angiotensin-converting enzyme (ACE) inhibitors are of benefit in life-threatening ventricular arrhythmias in patients with congestive heart failure and ventricular tachycardia caused by the onset of myocardial ischemia as well as by reperfusion of an ischemic area. The aim of the present study was to investigate whether direct electrophysiological effects are responsible for these observations. Therefore, we investigated the electrophysiological effects of lisinopril on the whole cardiac conduction and pacemaker system in isolated guinea pig hearts perfused by the method of Langendorff at concentrations of 0.01, 0.1, 1, and 10-mu-M. Lisinopril did not affect heart rate, atrioventricular, His bundle, or intraventricular conduction at any of the concentrations tested. Likewise the frequency-dependent QT duration was unchanged. At a concentration of 10-mu-M, lisinopril prolonged effective refractory period evaluated by premature beats (46 +/- 15%, n = 8, p < 0.01) as well as the rate-dependent effective refractory period (31 +/- 12, n = 8, p < 0.01) of the atrioventricular conduction. These effects can be explained by lisinopril's action as a minor calcium antagonist at a toxic concentration of 10-mu-M. The present results show that electrophysiological parameters are not substantially altered by lisinopril. Therefore, several other mechanisms such as the unloading of the left ventricle and/or the suppression of noradrenalin release and the electrolyte (potassium and magnesium) repletion and/or regression of left ventricular hypertrophy as long-term effects may play a major role in the antiarrhythmic efficacy of ACE inhibitors.