Electrocardiographic follow-up of patients with demand pacemakers

Changes in rhythm and degree of block, and evidence of pacemaker failure were determined in the first 30 patients with permanent implantation of Medtronic 5841 transvenous demand pacemaker. Standard 12-lead electrocardiograms and ten-hour Holter continuous electrocardiograms were obtained up to 16 months after surgery. In symptomatic patients, the supporting electrocardiographic indication for pacemaker insertion consisted of sinus arrest or sinus bradycardia in six, second-degree heart block in 10, complete heart block in 7, atrial flutter or fibrillation, rate 45 to 50 beats per minute, in 2, and bilateral bundle branch block in 5. No patient had a recent myocardial infarction. A change from the preoperative electrocardiogram in supraventricular rhythm was noted in 7, and a change in the degree of heart block in 13 patients. These changes did not appear to have been produced by the pacemaker and did not produce symptoms in patients with functioning pacemakers. In 3 patients, only the postoperative electrocardiogram disclosed the probable preoperative arrhythmia responsible for dizziness or syncope. There were 7 instances of pacing failure due to catheter malposition in 3, increased myocardial threshold in 2, and battery failure in 2, as evidenced on the electrocardiogram as either pacemaker artifact not followed by a QRS complex or absence of pacemaker artifact. Three of these patients were symptomatic. There were three deaths, the first from intractable congestive heart failure, the second from an acute myocardial infarction, and the third occurred suddenly nine months after pacemaker implantation. Protection during changes in rhythm and block and during the administration of antiarrhythmic drugs, in addition to absence of competition between the natural and artificial pacemaker, suggests advantages of the demand pacemaker.