INTRACORONARY ACETYLCHOLINE-INDUCED PROLONGATION OF MONOPHASIC ACTION-POTENTIAL IN LONG QT SYNDROME

Two patients with long QT syndrome, who bad episodes of syncope, under went recordings of the monophasic action potential (MAP) from the righ t ventricle. Intracoronary administration of acetylcholine (ACh) induc ed prolongation of MAP duration and caused Torsade de Pointes (Tdp) in both patients. In one patient, intravenous atropine administration di d not induce any change in MAP duration. In the other patient, ACh was administered after atropine. According to the results of the present study, abnormal regulation of the muscarinic receptor-mediated K-chann el may be involved in the mechanism causing prolongation of MAP durati on caused by ACh administration.