Effects of antiarrhythmic drugs on the repetitive extrasystole threshold and the ventricular fibrillation threshold.

The effects of class 1 antiarrhythmic drugs on the repetitive extrasystole threshold (RET) and the ventricular fibrillation threshold (VFT) were studied in 32 anesthetized dogs with localized transmural necrosis. All four drugs significantly increased VFT. Although lidocaine and mexiletine increased RET, procainamide and disopyramide did not. We conclude that class 1b antiarrhythmic agents prevent ventricular fibrillation by suppressing the initiation of reentry, and that class 1a drugs decrease the vulnerability by preventing the reentrant repetitive excitation from degenerating into chaotic multiple reentries.