DIAGNOSTIC-VALUE OF RECOVERY-TIME MEASURED BY BODY-SURFACE MAPPING INPATIENTS WITH CONGENITAL LONG QT SYNDROME

The QT interval of the resting 12-lead electrocardiogram is normal or borderline in some patients with congenital long QT syndrome (LQTS). R ecently, several in vivo experimental studies have shown that the time of maximum dV/dt in tire ST-T segment is correlated with the time of local ventricular recovery. The purpose of this study was to examine t he value of the body surface recovery time measured by 87-lead body su rface mapping for detecting LQTS. Body surface mapping and 12-lead ele ctrocardiography were performed simultaneously in 18 patients with LQT S and 40 controls of similar age and sex The recovery time (87), that is, the interval between QRS onset and the time of maximum dV/dt in th e ST-T segment, was measured automatically by computer from each of th e 87 mapping leads, and the corrected QT (QTc) was calculated by Bazet t's method. The QT interval was measured from each of the 12 standard electrocardiographic leads, and the corrected QT (QTc) interval was al so calculated. The maximum RC and RTc, the minimum RT and RTc, and the RC and RTc dispersions (difference between maximum and minimum RC and RTc in each patient) were significantly longer in the LQTS group than in the control group. In addition, a maximum RT of 390 msec, a maximu m RTc of 430 msec(1/2), an RT dispersion of 170 msec, and an QTc dispe rsion of 170 msec(1/2) separated the 2 groups completely (i.e., no ove rlap). The maximum QT and QTc, the minimum QT and QTc, and the QT and QTc dispersions (difference between maximum and minimum QT and QTc in each patient) were also significantly longer in the LQTS group than in the control group. However, the maximum QTc was normal (less than or equal to 440 msec(1/2) or borderline (less than or equal to 460 msec(1 /2)) in 5 of the 18 LQTS patients, and none of these parameters clearl y separated the 2 groups. These results suggest that measurement of RC by 87-lead body surface mapping is useful for diagnosing latent or bo rderline LQTS.