Causes of impaired consciousness while driving a motorized vehicle.

T frequency of motor vehicle accidents in patients previously diagnosed with ventricular arrhythmias or vasovagal syncope has been reported.1–5 However, the converse, namely, the incidence of arrhythmias and vasovagal syncope in patients presenting with impaired consciousness while driving, has not been previously determined. This information is critical to help guide evaluation and management decisions and avoid future potentially lethal incidents. Our study examines the incidence of different etiologies of impaired consciousness while driving in motorists referred to the electrophysiologic service for evaluation. • • • We retrospectively reviewed the records of all patients who presented with impaired consciousness while driving personal or commercial vehicles between November 1985 and March 2000 at the Hospital of Saint Raphael, New Haven, Connecticut. Impaired consciousness was defined as syncope or presyncope. Patients were excluded if impaired consciousness was believed to be related to alcohol intoxication, illicit drug use, or as a secondary event as a result of the trauma of the accident. In all, 71 patients were identified with unexplained impaired consciousness while driving, and were referred to the electrophysiologic service for further evaluation. These 71 patients represent the study group. Medical history, physical examination, electrocardiogram, pertinent laboratory data, and chest x-ray were recorded in all patients. The results of Holter and electrocardiographic monitoring, echocardiography, carotid ultrasound, electroencephalography, and brain imaging were also collected and analyzed. All 71 patients underwent electrophysiologic evaluation in addition to routine workup for impaired consciousness. Electrophysiologic evaluation included tilt-table testing, electrophysiologic studies, and interrogation of implantable cardiac defibrillators, if present. Patients with structural heart disease underwent electrophysiologic study as the initial test, followed by tilttable testing if no etiology was convincingly demonstrated by the electrophysiologic study. Patients without evidence for structural heart disease underwent a tilttable test followed by electrophysiologic study; if they gave a cogent history of rapid palpitations accompanying the event, the electrophysiologic study was the initial diagnostic study. Patients who had a cardiac defibrillator had the device interrogated as the initial strategy, with further evaluation only if no tachyarrhythmic events in the device’s memory log were temporally correlated with the driving-related incident. The tilt-table test was performed by tilting the patients to 70° for 30 minutes. If the patient remained asymptomatic and had no known coronary disease, an isoproterenol infusion was begun and its rate titrated to increase the baseline heat rate by 25% for an additional 15 minutes. A tilt-table test was considered positive if syncope or presyncope was elicited with consistent hemodynamic changes and prodromal symptoms similar to the clinical event. During electrophysiologic study, a supraventricular tachycardia was considered the cause of impaired consciousness if a sustained supraventricular tachycardia could be induced, with or without isoproterenol, with accompanying adverse changes in hemodynamics. Ventricular tachycardia was only considered to be the cause of impaired consciousness if sustained monomorphic ventricular tachycardia could be elicited or if long bursts of symptomatic nonsustained ventricular tachycardia were seen. Advanced atrioventricular block was diagnosed if the block could be produced at paced cycle lengths 500 ms, or if spontaneous or procainamideinduced infra-Hisian block was noted. Baseline characteristics, cardiovascular history, and diagnostic testing of the study group are listed in Table 1.Three patients had 2 events while driving and 3 patients had 3 driving-related events. A presumptive diagnosis for impaired consciousness was made in 57 of 71 patients (80%) based on clinical findings and test results (Figure 1). Vasovagal syncope was diagnosed in 21 patients (30%) in whom a suggestive history was supported by a positive tilttable test result. Eighteen patients (25%) had supraventricular tachycardia induced during electrophysiologic study. Ventricular tachycardia was confirmed in 12 patients (17%). In 6 patients, ventricular tachycardia was found upon interrogation of their cardiac defibrillators after the accident. In another 6 patients, ventricular tachycardia was induced at electrophysiologic study. Advanced atrioventricular block was documented in 7 patients (10%), vestibular disease in 1 patient, and a seizure in 1 patient who had a negative electrophysiologic study result and a positive 24-hour ambulatory electroencephalograph. Three patients had a positive tilt-table test as well as inducible supraventricular tachycardia at electrophysiologic study and were included in both of the previously mentioned categories. Treatment based on these established diagnoses prevented recurrent episodes of impaired consciousFrom the Hospital of Saint Raphael and Yale University School of Medicine, New Haven, Connecticut. Dr. Schoenfeld’s address is: Cardiac Electrophysiology and Pacer Laboratory, Hospital of Saint Raphael, 330 Orchard Street, Suite 210, New Haven, Connecticut 06511. E-mail: Mschoenfeld@srhs.org. Manuscript received November 15, 2002; revised manuscript received and accepted February 12, 2003.