Monophasic action potential studies in human subjects with prolonged ventricular repolarization and long QT syndromes.

In 58 human subjects monophasic action potentials (MAPs) were recorded with suction electrodes in several areas of the right ventricle (RV). Individual differences between the longest and the shortest RV MAP durations indicate that: normally (40 subjects) ventricular repolarization is almost synchronous; QT prolongation due either to bradycardia or to amiodarone treatment (eight cases) may be the result of a uniform lengthening of ventricular repolarization, when ventricular arrhythmias are not present; in long QT syndromes (LQTSs) of differing etiology (10 cases), in which severe ventricular arrhythmias are present, marked individual differences in RV MAP duration are present and correspond with pathological asynchrony of ventricular repolarization. Also observed in the LQTSs are morphological alterations (humps) in the terminal phase of the longest MAPs. Humps, interpreted as pathological delayed repolarization phenomena, may lead to focal re-excitation which seems to play a key role in the genesis of the arrhythmias complicating LQTSs.