Abnormal QT prolongation and psychotropic drug therapy in psychiatric patients: significance of bradycardia-dependent QT prolongation.

Because many psychotropic drugs have electrophysiological properties similar to antiarrhythmic drugs, they might lengthen QT interval and cause torsades de pointes. Electrocardiograms were obtained in 688 psychiatric patients receiving psychotropic drugs. A QTc interval >460 ms was observed in 96 (14%) patients. To elucidate the heart rate dependence of QT prolongation, we measured QT intervals and the preceding R-R intervals at various heart rates by 24-hour Holter electrocardiogram in 97 patients. We estimated the QT intervals at the heart rates of 80 beats/min and 50 beats/min by the regression curve. A QT interval at the heart rate of 80 beats/min exceeded 400 ms in 14 (15%) patients and that at the heart rate of 50 beats/min exceeded 480 ms in additional 12 (12%) patients. Therefore, additional attention is needed for bradycardia-dependent QT prolongation even when the QT interval was not prolonged at usual heart rates.