PROGNOSIS AFTER SYNCOPE - IMPACT OF LEFT-VENTRICULAR FUNCTION

A cardiac cause of syncope has been associated with increased sudden death risk, whereas unexplained syncope has a benign prognosis. However, in patients who have depressed left ventricular function, the accuracy of diagnostic tests and the efficacy of therapy, such as antiarrhythmic drugs, are reduced. Previous studies of patients with syncope have not evaluated the contribution of left ventricular performance in risk stratification for sudden death. The purpose of our study of a large population of patients with syncope was to determine the impact of left ventricular dysfunction on sudden death risk if syncope is caused by a cardiac cause or remains unexplained after electrophysiologic testing. We retrospectively evaluated the relationship of left ventricular ejection fraction to sudden death prognosis in 88 consecutive patients referred for electrophysiologic testing to determine a cause of syncope. The mean age was 57 +/- 18 years, left ventricular ejection fraction was 0.41 +/- 0.20, and 66 patients (75%) had structural heart disease. In 49 patients (56%) a cardiac cause of syncope was diagnosed, and in 39 patients (44%) the cause of syncope remained unexplained after evaluation. Cardiac syncope was attributed to ventricular tachycardia in 27 patients, bradyarrhythmia in 11 patients, and supraventricular tachyarrhythmia in 11 patients. By logistic regression only structural heart disease was independently associated with cardiac cause of syncope (p = 0.003). After a mean follow-up of 790 +/- 688 days, nine patients had died suddenly, eight (89%) of whom had left ventricular ejection fraction less than 0.30. In 51 patients who had left ventricular ejection fraction greater than 0.30, 3-year actuarial sudden death risk was similarly low for patients who had cardiac compared with unexplained causes of syncope (0 vs 8%, p = NS). In 47 patients who had ejection fraction less than 0.30, sudden death risk was substantial for both patients who had cardiac syncope (58%) and for those who had unexplained syncope (50%, p = NS). In the Cox multivariate analysis reduced left ventricular ejection fraction (p < 0.0001) was the only independent predictor of sudden death. In summary, prognosis is excellent for patients with syncope who have preserved left ventricular function, even if the cause of syncope is cardiac. In contrast, when left ventricular function is markedly depressed, sudden death risk is high in patients who have cardiac or unexplained causes of syncope. More sensitive diagnostic tests and perhaps greater use of nonpharmacologic therapies may be needed in this high risk group.