Nitrates and ectopic ventricular activity in mitral valve prolapse: clinical and experimental data

Three patients with mitral valve prolapse, high grade ventricular arrhythmias and a strong family history of sudden death were studied utilizing continuous Ecg monitoring and intracardiac stimulation and recording techniques. Analysis of 6-hour ambulatory Ecgs revealed frequent premature ventricular beats (PVBs) including repetitive and multiform PVBs in each patient. The electrophysiological studies demonstrated normal parameters of intracardiac conduction and refractoriness providing no evidence for reentrant mechanisms. Acute drug testing with 0.4 mg sublingual nitroglycerin completely suppressed all ventricular arrhythmias. During maintenance therapy antiarrhythmic nitrate efficacy was only partly confirmed monitoring the effects of 4 x20 mg isosorbide dinitrate on 6-hour ambulatory Ecgs. The electrophysiological parameters of intracardiac conduction and refractoriness were not significantly altered by 0.4 mg sublingual nitroglycerin. Experimental data obtained from isolated rabbit atria and canine ventricles revealed no significant action of nitroglycerin in the parameters of cardiac automaticity and conduction including transmembrane electrical activity of normal and hypoxically damaged SA nodal, atrial and ventricular fibers. It is concluded that a) PVBs in patients with mitral prolapse appear related to ectopic automaticity; b)nitrates may suppress ventricular ectopy in these patients; c) antiarrhythmic nitrate efficacy is not related to direct membrane effects.