Monophasic Action Potential Studies in Human Subjects with Prolonged Ventricular Repolarization and Long QT Syndromes

Abstract

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.

A New Look at Torsades de Pointesa

“…In addtion, measurements performed in several places in the right ventricle showed an increased Qspersion in cases of TDP. 32 The results of Bonatti et al in hmilial long QT syndrome are in agreement with our data obtained in the acquired form of the long QT syndrome, showing a prolonged RVERP.…”

“…MAP were studled both during spontaneous rhythm and during ventricular pacing. 32 In all cases, the length of ventricular repolarization was longer in patients with prolonged w without ventricular arrhythmias as compared with patients without abnormality of ventricular repolarization. This prolongation was even more marked in patients with prolonged QT complicated by TDP.…”

Torsades de pointes and early afterdepolarizations

“…7. Recordings of monophasic action potentials with catheter electrodes in patients with a prolonged QT and ventricular arrhythmias, including torsades de pointes, show prolonged durations and second upstrokes that strongly resemble early afterdepolarizations with second upstrokes [18][19][20].…”

Differential response to right and left ansae subclaviae stimulation of early afterdepolarizations and ventricular tachycardia induced by cesium in dogs.

“…13,14 Although it is possible that early afterdepolarizations are important in the acquired long QT syndrome, for example, caused by quinidine,5 they may be important also in the idiopathic long QT syndrome.] 5 The constant prolonged QT interval may be due to early afterdepolarizations, augmented by sympathetic stimulation to produce arrhythmias.…”