The etiology of syncope in pacemaker patients.

A total of 46 patients with syncopal episodes after VVI pacemaker implantation were studied. Of these, 92% had one to three syncopal episodes and 8% more than three. All underwent a thorough clinical examination, which included chest X ray, echocardiogram, neurological exam, and the following protocol: 24-hour Holter monitoring, EEG, blood pressure (BP) measurement in three positions, Doppler exam of the carotid vessels, fasting blood glucose, and head-up tilt table test (60 minutes, 60 degrees). Holter monitoring showed exit block in two patients (4.3%) and failed sensing in one (2.1%). In two patients there was unilateral slowing on EEG. Orthostatic hypotension was found in four patients (8.6%), and hypoglycemia in three insulin-dependent diabetics. An occlusive atherosclerotic plaque in the carotid artery was found in three patients (6.5%). Syncope was induced in 17 patients (36.9%) by the tilt table test, after a mean standing time of 47 +/- 11 minutes. The mean resting systolic BP of these patients was 140 +/- 24 mmHg, and fell to a mean level of 56 +/- 8 mmHg (mean systolic BP drop was 79 +/- 8 mmHg). Sixteen of these 17 patients with positive tilt table were being paced at the time of syncope and one had a spontaneous heart rate of 73 beats/min. In 14 cases (30.4%) the cause of syncopal episodes after this extensive workup remained unexplained. These results indicate that pacemaker dysfunction is not a major cause of syncopal episodes in pacemaker patients and that these are most often due to vasovagal syncope. Long-term follow-up is warranted to determine the prognostic significance of various types of syncope in pacemaker patients.