Patients who have syncope or presyncope while driving represent a diagnostic problem; electrophysiologic studies may identify a cause. Blitzer and associates retrospectively reviewed the records of 71 persons who had unexplained impaired consciousness while driving and were referred for electrophysiologic testing.

All patients had tilt-table testing, electro-physiologic studies, and evaluation of implantable cardiac defibrillators, if present. Results of all other testing on these patients also were collected. Using commonly recognized test end points, a presumptive diagnosis was made in 57 patients (80 percent). Vaso-vagal syncope was diagnosed in 21 patients (30 percent) who had a suggestive history and a positive tilt-table test. Eighteen patients (25 percent) had an inducible supraventricular tachycardia on electrophysiologic study. Twelve patients (17 percent) had ventricular tachycardia, either inducible on electrophysiologic study or found on evaluation of their cardiac defibrillators.

Advanced atrioventricular block was noted in seven patients (10 percent). One patient (1 percent) was diagnosed with vestibular disease, and one patient was diagnosed with a seizure. Treatment based on these diagnoses prevented any further episodes of impaired consciousness during the follow-up period (range, three months to 15 years). One patient had a recurrence after ablation of supraventricular tachycardia; tilt-table testing showed that the correct diagnosis was vasovagal syncope. This patient was treated successfully with beta blockers.

The authors conclude that vasovagal syncope is a common cause of impaired consciousness while driving. Electrophysiologic testing can detect arrhythmias in these patients. A combination of tilt-table testing and electrophysiologic studies results in a high yield of diagnoses, allowing a greater likelihood of preventing further episodes through proper treatment.