912-42 Dynamics of Ventricular Repolarization in Relation to Heart Rate in Patients with CongenitalLong QT Syndrome

Abstract

Several clinical studies have shown that patients with congenital long QT syndrome (LQTS) have primary ventricular repolarization abnormalities, which are characterized by prolongation and increased dispersion of ventricular repolarization. Recently, efficacy of pacemakers has been reported as a therapy for LQTS patients in addition to β -adrenergic blocking drugs. The present study was performed to evaluate the influence of different heart rate on ventricular repolarization in LQTS patients. We recorded monophasic action potentials (MAPs) with a contact electrode during right atrial pacing. MAPs were obtained simultaneously from two to four sites at the right and left ventricular endocardium in 9 LQTS patients (28 sites) and 7 control patients (17 sites). Heart rate was changed from 70/min to 140/min by using right atrial pacing, then MAP duration at 90% repolarization (MAPD90) and dispersion of MAPD90 (difference between the longest MAPD90 and the shortest MAPD90 in each patients) in relation to heart rate were examined at steady state. 70/min 80/min 100/min 120/min 140/min MAPD90(ms) (LQTS; n = 28) 392 ± 58 *** 347 ± 56 *** 316 ± 44 *** 284 ± 31 *** 239 ± 17 ** (Control; n = 17) 303 ± 16 275 ± 22 249 ± 24 234 ± 19 199 ± 10 Δ 89 72 67 50 40 70/min 80/min 100/min 120/min 140/min Dispersion of MAPD90 (ms) (LQTS; n = 9) 79 ± 18 ** 59 ± 20 * 39 ± 19 34 ± 17 25 ± 21 (Control; n = 7) 27 ± 6 28 ± 8 21 ± 7 21 ± 7 15 ± 14 Δ 52 31 18 13 10 Δ; difference between mean value in LQTS patients and that in control patients at each heart rate * P < 0.05 ** P < 0.005 *** P < 0.0005 v.s. control patients Repolarization abnormalities were attenuated gradually by increasing heart rate in LQTS patients, which supported the efficacy of pacemaker therapy in this syndrome.