DDD/DDT pacemakers in the treatment of ventricular tachycardia

The possibility of adapting multimode dual-chamber pacemakers for programmed and burst stimulation was explored in a group of patients with ventricular tachycardia. The potential usefulness and pitfalls of these pacemakers were exemplified in one patient, presented in detail. The implanted DDD pacemaker was programmed to an all-synchronous mode (DDT), permitting programmed ventricular stimulation through synchronization with chest wall stimulation provided by a standard external programmable stimulator. With the ventricular sensing refractory period shortened to 200 ms, both programmed electrical stimulation and burst pacing for termination of induced tachycardias were possible. When medications failed to offer protection against the patient's tachycardias, the ventricular sensing refractory period (and minimum stimulation interval) was increased to 300 ms, thereby permitting burst pacing at up to 200 beats/minute for termination of spontaneous episodes. After many trials to confirm the efficacy of such stimulation, and the lack of muscle potential triggering, the patient was discharged home with the pacemaker in the DDT mode. He was instructed to go to his local emergency room, and was equipped with a portable device to trigger his implanted unit. Subsequently, the patient had successful termination of several spontaneous episodes of ventricular tachycardia in an emergency room. Later, he began to experience palpitations during certain exercises, and it was found that the implanted unit was being triggered by pectoral myopotentials. The unit was therefore reprogrammed to decrease the sensitivity, and the patient was again discharged. The need for careful evaluation and close follow-up is emphasized to maximize the benefits and to minimize the very serious potential risks of this pacing mode.