Antiarrhythmic uncoupling

Antiarrhythmic drug classifications and the clinician: a gambit in the land of chaos

Several classifications of antiarrhythmic drugs have appeared and all suffer considerable limitations. Recently a Task Force of the Working Group on Arrhythmias of the European Society of Cardiology proposed a novel classification of antiarrhythmic drugs (the so-called Sicilian Gambit) based on their action on the most vulnerable parameter of an arrhythmogenic mechanism. The present article attempts a critical reappraisal of the antiarrhythmic drug actions and the relationship of vulnerable parameters with cellular mechanisms such as ion channels. The clinical applicability of these concepts, the implications of the new classification in the pharmacologic therapy of arrhythmias, and its potential limitations are discussed.

Effects of sotalol on the signal-averaged electrocardiogram in patients with sustained ventricular tachycardia: relation to suppression of inducibility and changes in tachycardia cycle length

OBJECTIVES

This study examines the effects of sotalol on the signal-averaged electrocardiogram (ECG) in patients with spontaneous and inducible sustained ventricular tachycardia and correlates these findings with the effect of sotalol on tachycardia inducibility and tachycardia rate.

BACKGROUND

Standard electrocardiography generally does not detect any change in the duration of the QRS complex resulting from sotalol therapy. However, the signal-averaged ECG is more sensitive than the standard ECG for detecting changes in QRS duration induced by antiarrhythmic drugs and can also detect changes in late potential duration.

METHODS

Signal-averaged electrocardiography was performed before therapy in 30 patients with spontaneous and inducible ventricular tachycardia, and both electrophysiologic study and a signal-averaged ECG were repeated during therapy with d,l-sotalol.

RESULTS

During sotalol therapy the signal-averaged QRS duration decreased by 2.6 +/- 6.6 ms in the 11 patients with no inducible tachycardia during therapy, whereas it increased by 3.8 +/- 5.8 ms (p = 0.01) in the 19 patients with inducible tachycardia during therapy. In the latter group there was a significant positive correlation between prolongation of tachycardia cycle length and prolongation of late potential duration by sotalol (r = 0.56, p = 0.01).

CONCLUSIONS

Sotalol can alter QRS and late potential duration as measured by the signal-averaged ECG. Prolongation of QRS duration or late potential duration may reflect a slowing of conduction by sotalol that may interfere with this agent's antiarrhythmic efficacy and slow ventricular tachycardia.

Preferential effect of procainamide on the reentrant circuit of ventricular tachycardia

Transient entrainment was used to test the hypotheses that 1) procainamide prolongs the cycle length of ventricular tachycardia in patients with coronary artery disease because it has a preferential effect on the reentrant tachycardia circuit, and 2) regions of slow conduction in the reentrant circuit are more susceptible to the effect of procainamide than are other areas of the ventricles. In five patients with prior myocardial infarction, sustained ventricular tachycardia with identical QRS configuration was inducible before and after intravenous infusion of procainamide. Transient entrainment of ventricular tachycardia was demonstrated at two or more cycle lengths by rapid pacing in the baseline state and after procainamide. Rapid pacing was performed from the same site during sinus rhythm at the cycle lengths that demonstrated transient entrainment of ventricular tachycardia. The conduction interval to the transiently entrained site during ventricular tachycardia (orthodromic interval) was compared with the conduction interval to the same site during pacing in sinus rhythm (antidromic interval). The mean tachycardia cycle length increased by 27% after procainamide administration (p = 0.002). The antidromic conduction intervals were prolonged by 9% (p = 0.06) compared with a 28% increase in the mean orthodromic conduction interval (p = 0.002). The difference between the orthodromic and antidromic conduction intervals increased by 40% (p = 0.003). Prolongation of the tachycardia cycle length after procainamide administration correlated positively with increases in the orthodromic conduction intervals (r = 0.94, p = 0.02) but not with changes in the antidromic intervals (r = -0.08, p = NS). The effect of procainamide on the difference between correlated strongly with changes in the cycle length of ventricular tachycardia (r = 0.97, p = 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)