IMPROVEMENT OF REPOLARIZATION ABNORMALITIES BY A K-QT SYNDROME( CHANNEL OPENER IN THE LQT1 FORM OF CONGENITAL LONG)

Background-This study used monophasic action potential (MAP) to examin e the effect of nicorandil, a K+ channel opener, on repolarization abn ormalities induced by epinephrine in the LQT1 form of congenital long- QT syndrome in which the KvLQT1 mutation underlies the defect in the c hannel responsible for the slowly activating component of the delayed rectifier potassium current. Methods and Results-MAPs were recorded si multaneously from two or three sites on the right ventricular and left ventricular endocardium in 6 patients with a congenital form of LQT1 syndrome with KvLQT1 defect (17 sites) and 8 control patients (24 site s). In LQT1 patients, epinephrine infusion prolonged the QT interval a nd 90% MAP duration (MAPD(50)) and increased the dispersion of MAPD(50 ). Epinephrine also induced early afterdepolarizations (EADs) as well as ventricular premature complexes (VPCs) in 2 of the 6 patients. Nico randil during epinephrine infusion abbreviated the QT interval and MAP D(50) decreased the dispersion of MAPD(50), and abolished the EADs as well as the VPCs in 1 patient. Addition of propranolol completely reve rsed the effect of epinephrine in prolonging the QT interval and MAPD( 50) and increasing the dispersion and eliminated the EADs and VPCs in another patient. In control patients, the effect of epinephrine and th at of additional nicorandil and propranolol on repolarization paramete rs were much less than in the LQT1 patients. Conclusions-Our results s uggest that nicorandil, a K+ channel opener, improves repolarization a bnormalities in the LQT1 form of congenital long-QT syndrome with KvLQ T1 defect.