ECG changes during long-term minoxidil therapy for severe hypertension.

A prospective assessment of the effects of minoxidil on the ECG was carried out in a series of 80 patients with severe hypertension, representing an observation of 139.6 patient years. In combination with beta-adrenergic blocking agents and diuretics, minoxidil resulted in substantial reductions in blood pressure at rest and during exercise. Concomitant with the initiation of minoxidil treatment, ECG changes consisting of flattening or inversion of the T waves, ranging from slight to very marked, were observed in 90% of the patients. While these changes may be potentially disconcerting, the observations of this study show that they are not related to changes in heart rate or other clinical criteria associated with myocardial ischemia. They are not influenced by exercise or beta-blockade and they generally revert to control appearance during chronic treatment, at which time accompanying improvement in preexisting abnormalities of the T wave was frequently seen. During long-term treatment, a substantial reduction of increased QRS voltages was observed.