An uncommon cause of pacemaker malfunction

An intubated and ventilated patient was transferred from a hospital without full invasive cardiological services, to another hospital for insertion of a permanent pacemaker. The patient had presented 11 days previously for elective haemorrhoidectomy. The pre-operative ECG showed sinus rhythm and there was no history of cardiac disease. Immediately following induction of anaesthesia, the patient developed complete heart block with a ventricular rate of 30 beat.min−1. Intubation was carried out and the arrhythmia was treated with atropine and isoprenaline, whilst a transvenous pacing wire was inserted. The surgery was cancelled. Attempts to extubate the patient were unsuccessful and he was admitted to intensive care for ventilation. Unfortunately, at this stage the referring team did not perform serial ECGs and cardiac enzymes. He was treated with a temporary pacing wire but as there was no improvement in his intrinsic heart rate or rhythm, he was scheduled for insertion of a permanent pacemaker. His underlying rhythm was ventricular, rate 30–35 beat.min−1. He was paced in demand mode, with a threshold of 70 beat.min−1, output 1.4v and was fully paced on the ECG with no spontaneous beats. There had been no problems. Prior to transfer, he was sedated and ventilated, cardiovascularly stable with a heart rate of 70 paced beats and continuous invasive monitoring of arterial blood pressure recorded 130/85. Whilst lifting the stretcher up into the ambulance, it was noted that the rate of pacing dropped transiently and the heart rate registered as 50 beat.min−1. The stretcher was secured and the pacing box controls checked. These settings had not changed. Within seconds the pacing spontaneously reverted to a rate of 70 beat.min−1. Blood pressure was not affected. As the ambulance drove off, the rate of pacing then slowed immediately and progressively, allowing the emergence of spontaneous broad complex beats at a rate of 35 beat.min−1, and a noticeable drop in blood pressure to 90 mmHg systolic. The ambulance stopped while the situation was assessed. Once stationary, pacing reverted back to a rate of 70 beat.min−1 spontaneously and blood pressure recovered without any treatment. It was thought most likely that the pacemaker was sensing movement and vibration from the ambulance, and misinterpreting this as spontaneous cardiac beats of a rate sufficient to inhibit pacing. The pacemaker was changed from demand mode to fixed rate pacing at a rate of 70 beat.min−1and the transfer continued without further problems. A permanent pacemaker was inserted the next day. The patient was transferred back to his local hospital in the immediate postoperative period and went on to make an uneventful recovery. We suggest it is prudent to institute fixed rate pacing prior to ambulance transfer in patients dependent upon a temporary pacing wire.