964-9 Prospective Assessment of Quinidine-induced QT Prolongation and Proarrhythmia in Hospitalized Patients

Abstract

In retrospective studies, quinidine-induced proarrhythmia and excessive lengthening of the OT interval have been described to occur in 5–10% of patients (pts). There are, however. no prospective studies. Therefore, the purpose of this study was to prospectively assess the acute effects of quinidine on the QT interval and on the incidence of proarrhythmic events in hospitalized pts. using daily 12-lead ECG's and continuous telemetric monitoring. Clinical data included gender, age, body surface area, left ventricular ejection fraction (LVEF), etiology of heart disease, congestive heart failure class, Q-wave infarction pattern, indication for quinidine, quinidine and potassium serum levels, and use of a diuretic, digoxin or an antiarrhythmic agent. Pts were followed until time of discharge. Quinidine was initiated in 35 pts (18 M; 17 F) for supraventricular (n = 22) or ventricular (n = 13) arrhythmias 19 pts had an ischemic, 6 had a nonischemic, and 3 had a valvular cardiomyopathy; 5 had hypertensive and 2 had no heart disease. The mean age was 63 ± 13 years. the mean LVEF was 0.38 ± 0.15 and the mean functional class was 2.0 ± 1.1. The mean quinidine level was 2.7 ± 1.2 μg/ml. The QT interval increased from 388 ± 61 to 499 ± 70 msec (p < 0.01) and the QTc increased from 445 ± 61 to 543 ± 60 msec (p < 0.005). 11 pts (31%) developed a QTc > 550 msec. Torsade de pointes (n = 3) or other ventricular proarrhythmic events (n = 3) occurred in 6 pts (17%). The pts experiencing torsade de pointes were female pts with a mean LVEF of 0.24 and a QTc of 610 to 650 msec. Female gender (p = 005), younger age (p = 0.04), lower LVEF (p = 0.01). and an increased baseline QTc interval (p < 0.005) were statistically associated with proarrhythmia. Proarrhythmic events occurred on day 2.3 ± 1 of quinidine therapy (range: 1–4). in this prospective study of hospitalized pts, quinidine resulted in lengthening of the QTc inteNal beyond 550 msec in 31% of the pts and in a 17% incidence of clinically significant ventricular proarrhythmia. Proarrhythmia was statistically associated with female gender, decreased LVEF and increased baseline QTc interval. The results of this prospective study indicate that the incidence of quinidine-induced proarrhythmia and excessive QT prolongation may be higher than the 5–10% incidence previously reported in retrospective studies.