Therapeutic Hypothermia-Related Torsade de Pointes
A 79-year-old woman suddenly collapsed at the emergency department triage counter. She had a history of diabetes and coronary heart disease and had received coronary artery bypass graft surgery 8 years earlier. She had begun regular hemodialysis 1 month prior for end-stage renal disease. Just before cardiac arrest happened, the hemodialysis was interrupted because of low blood pressure, and she was immediately referred to the emergency department. Her sudden collapse occurred after she walked into the emergency department. Cardiopulmonary resuscitation was started immediately after she collapsed. The initial cardiac rhythm presented as ventricular fibrillation and was converted to a sinus rhythm after a single DC shock with monophasic energy of 360 J. Ventricular tachycardia appeared during resuscitation and was again converted with the same shock energy. The return of spontaneous circulation (ROSC) was achieved after 7 minutes of resuscitation. She remained comatose and was unresponsive to verbal command, although the hemodynamic status had stabilized 1 hour after ROSC with a blood pressure of 152/110 mm Hg and a heart rate of 125 beats/min. Therapeutic hypothermia was performed after obtaining informed consent from the patient’s family. Her initial body temperature was 37.5°C. Hypothermia was induced with an endovascular catheter (Icy catheter and CoolGard 3000 Thermal Regulation System, Aurora BioScience, Baulkham Hills, Australia) at a maximal rate of about 1.0°C per hour. Midazolam (0.5 mg/kg per hour) was administered for sedation and cisatracurium (1 mg/kg per hour) for neuromuscular blocking. The induction of hypothermia began 5 hours after achieving ROSC, and the target temperature of 32°C was achieved at 10 hours. A QTc interval prolongation was noted after this hypothermia treatment. The maximal QT interval was 390 ms (maximal QTc=549 ms) before commencing the hypothermia (Figure 1a) and was prolonged to 720 ms (maximal QTc=686 ms) after reaching the target temperature (Figure 1b). Ventricular ectopic beats appeared. Rewarming at a rate of 0.3°C per hour was started after 12 hours of therapeutic hypothermia, or 22 hours after resuscitation. Rewarming to 37°C was completed at 39 hours after resuscitation. The QTc prolongation persisted, with a maximal QT of 620 ms (maximal QTc=688 ms) at the termination of the rewarming process (Figure 1c). Torsade de pointes ventricular tachycardia occurred with hemodynamic collapse at 41 hours after resuscitation, at which point the body temperature was 37.5°C (Figure 2). Termination of the torsade de pointes was achieved by a single DC shock of 360 J. Lidocaine was administered at a loading dose of 1 mg/kg with an infusion rate of 0.5 mg/min for 3 hours. Electrocardiographic rhythm monitoring and recordings showed frequent multifocal ventricular ectopic beats and a R-on-late-T event preceding torsade de pointes. The QTc prolongation gradually shortened after maintaining the temperature in 37°C (Figure 1d) for 24 hours, 63 hours after resuscitation. The patient regained consciousness 4 days after ROSC. Her left ventricular ejection fraction was 24% as evaluated by an echocardiogram. The coronary angiographic examination showed total occlusion of the proximal portion of the previous saphenous vein graft. There was adequate flow from the left internal mammalian artery to the left anterior descending artery. A cardioverter-defibrillator was successfully implanted.