The effects of direct current countershock on ventricular late potentials.

Signal averaging is a noninvasive method of recording ventricular late potentials. These late potentials are present in many patients with sustained ventricular tachycardia. Analysis of ventricular late potential characteristics may develop as a useful marker of antiarrhythmic drug efficacy. Often antiarrhythmic drugs are tested acutely in the electrophysiology laboratory after direct current countershock (DC shock). The purpose of this study was to investigate the effects of DC shock delivered for cardioversion of sustained ventricular tachycardia or fibrillation on ventricular late potentials. Signal averaged electrocardiograms (SAEKGs) were recorded before and after 13 DC shocks. There was no significant change in QRS duration, duration of the high frequency filtered QRS, or duration of the high frequency signal under 40 microvolts. There was a small increase in the root mean square amplitudes of the terminal 40 milliseconds (41 microV to 49 microV). This degree of change is felt to be clinically insignificant. Except for one trial, no late potential appeared or disappeared after electrical cardioversion. We have shown that ventricular late potentials are only slightly altered by programmed ventricular stimulation, induced sustained ventricular tachycardia or ventricular fibrillation, and DC countershock. To analyze changes in ventricular late potentials after antiarrhythmic drug administration in the electrophysiology laboratory, in those patients requiring DC countershock, comparisons should be made to postshock SAEKGs rather than those obtained prestudy.