Etiology of Syncope in Patients with Negative Electrophysiologic and Tilt Table Testing

Patients with syncope of unknown etiology (SUE) after electrophysiologic (EP) studies are said to have good prognosis but often suffer from recurrent disability. Syncopal episodes are often too infrequent for conventional ambulatory monitoring (AM) techniques to detect. We implanted long term subcutaneous monitoring device (Medtronic, Inc.) in 14 patients (m age 57 ± 21 yrs) with 7.3 ± 4.6 previous syncopal episodes and negative AM, head up tilt (HUT) and EP studies. The pacemaker-shaped device has 2 electrodes 3.2 cm. apart and is able to record 7.5 or 15 minutes of continuous ECG signal in circular buffer, which is triggered by magnet application by the patient or partner. The dat are then retrievable by telemetry. Eight patients had structural heart disease. Eleven patients developed recurrent syncope 4.1 ± 4.3 months after implantation. The etiology of syncope was bradycardic in 5 (sinus arrest in 3, complete heart block in 2), tachyarrhythmic in 2 (Supraventricular tachycardi in 1, ventricular tachycardi in 1), and non-arrhythmic in 4 (vasodepressor in 2, hemodynamic in 1, and psychogenic in 1). No further episodes of syncope have occurred over 10.3 ± 7.6 months follow-up after successful therapy was implemented in all 11 patients. The remaining 3 patients have not had recurrent syncope over mean of 8.7 months and continue to be followed. Conclusions: We conclude that patients with SUE after negative investigations have broad spectrum of etiologies, with bradycardi being the most common. The etiology of syncope is often not apparent from clinical variables. An implantable “loop recorder” is useful for making diagnosis when episodes are too infrequent for standard ambulatory monitoring techniques.