Recurrent ventricular tachycardia associated with QT prolongation after mitral valve replacement and its association with intravenous administration of erythromycin

Abstract

A 65-year-old woman had severe mitral stenosis and trivial mitral regurgitation. There was no obstructive coronary disease. The mitral valve was replaced with a CarpentierEdwards xenograft. When transferred to the recovery ward she was in sinus rhythm and was receiving intravenous dopamine, the dose of which was gradually reduced. The infusion also contained 20 mEq/liter of potassium chloride. The patient's subsequent course is summarized in Figure 1. Erythromycin lactobionate, I g, and cloxacillin sodium, 500 rag, were given by intravenous injection. Within minutes of the injection VT developed, which reverted to sinus rhythm after the intravenous injection of calcium chloride, 5 ml of 10% solution, isoproterenol, 5 #g, and epinephrine, 2.5 ml of a I in 15,000 solution. During the next 24 hours, there were frequent ventricular premature contractions (VPCs ) with episodes of bigeminy and consecutive VPCs despite varying doses of lidocaine and mexiletine. There was sustained VT with hypotension on 3 further occasions, 2 of which immediately followed the administration of intravenous erythromycin and cloxacillin. The serum potassium level was measured several times during this period and was within the normal range on each measurement, the minimum value being 3. 7 mEq/liter. The serum magnesium concentration was 3.19 mg/lO0 ml and serum calcium 9.68 mg/lO0 ml; both values are above the lower limits for our laboratory. Twenty-four hours after the operation, a 12-lead electrocardiogram was recorded (Fig. 2). Compared with the preoperative ECG (Fig. 2a), sinus rhythm was present, the mean QRS axis had moved to the left and a new Q wave was present in lead A VL (Fig. 2b ). Anterior forces were less prominent than before. There was marked prolongation of the QT interval and there was widespread T-wave inversion. VPCs continued to occur frequently (Fig. 2c). Lidocaine and mexiletine treatment were discontinued. Potassium and calcium were given by intravenous injection and isoproterenol was infused in a dose sufficient to maintain the ventricular rate at 90 beats/rain. No further arrhythmias occurred for 6 hours, until the next injection of antibiotics was given. VT recurred and was successfully terminated by direct-current shock. Erythromycin treatment was then