Incidence and Prognosis of Syncope

Abstract & Commentary

Synopsis: Patients with cardiac syncope constitute a high-risk group predisposed to morbidity and premature mortality from cardiovascular disease.

Source: Soteriades ES, et al. N Engl J Med. 2002;347: 878-885.

In this report from the Framingham study, Sote-riades and colleagues report the incidence, causes, and prognosis of syncope among participants in the study. The Framingham Heart Study is a longitudinal epidemiologic study of residents of Framingham, Mass. Middle aged men and women were enrolled in the study and were followed periodically with an emphasis on the development of cardiovascular diseases. Of the 7814 study participants who were followed long term, 822 reported syncope. In each case, the cause of syncope was assigned a clinical diagnosis by 2 physicians based on available documentation. For this analysis, the causes of syncope were classified into 8 categories: cardiac, unknown, stroke or transient ischemic attack, seizure disorder, vasovagal, orthostasis, medication-induced, and other. For each patient with syncope, 2 study participants without syncope matched for age and gender were randomly selected as a comparison group.

During the study, 7814 participants were followed for an average of 17 years. The mean age of entry was 51.1 ± 14 years. A total of 822 participants reported syncope. However, patients who reported syncope only at their most recent visit were excluded since no follow-up data were available. Data from 727 participants with syncope who had adequate follow-up times were included in this report.

The overall incidence rate of a first report of syncope was 6.2 per 1000 patient years. There was a sharp increase in the incidence rate among patients in their eighth and ninth decades. For men and women between ages 70 and 79, the incidence rates were 11.1 and 11.1 per 1000 person years and for men and women older than 80 years of age, the rates were 16.9 and 19.5 per 1,000 patient years. Syncope was more frequent among men and women of all ages in whom cardiovascular disease was known to be present. A cardiac cause for syncope was assigned to only 9.5% of the total episodes but 26% of the episodes among men with cardiovascular disease and 16.8% of the episodes among women with known cardiovascular disease were believed to be of cardiac origin. Vasovagal syncope was thought to be the mechanism in 21.2% of cases. No specific cause could be assigned to 36.6% of cases. Participants with cardiac syncope had a lower survival than those without syncope. Even after statistical adjustment for other variables, the risk of death was increased by 31% among all participants with syncope and was doubled among patients with cardiac syncope. Syncope of unknown cause and neurologic syncope were associated with an increased risk of death from any cause and neurologic syncope was associated with a threefold increased risk of stroke. Vasovagal syncope, medication-induced syncope, and other situational causes of syncope were not associated with increased risk of either stroke or death.

Soteriades et al conclude that patients with cardiac syncope constitute a high-risk group predisposed to morbidity and premature mortality from cardiovascular disease. Patients with syncope of unknown cause appear to constitute a mixed group at increased risk of death presumably since some of these episodes were cardiac in origin. Vasovagal and situational syncope appear to have a benign prognosis.

Comment by John P. DiMarco, MD, PhD

Syncope is one of the most frustrating conditions with which physicians must deal. By its very nature, syncope is a transient symptom and the patient frequently appears well when he presents for evaluation. This paper from the Framingham Heart Study provides further evidence that syncope is a worrisome symptom, but several factors limit our ability to use these data to improve practice.

Soteriades et al assigned causes for syncope based on data in the patients’ medical records. Unfortunately, they do not provide data about the criteria they used. Since only a minority of patients are reported to have recurrent syncope, one must assume that a diagnosis was inferred based on the data obtained at time of the episode. It is likely that a cardiac cause was assigned to patients with more advanced cardiovascular disease who are likely to have lower ejection fractions, intraventricular conduction defects, and atrial and ventricular tachyarrhythmias that may suggest, but certainly are not definite evidence for the cause of a past syncopal episode. It would have been interesting to include such factors as left ventricular ejection fraction and heart failure functional class in the multivariate analysis but these parameters were not used.

One also should remember that treatments for specific cardiac causes of syncope are available. Pacemakers effectively treat bradyarrhythmias. Antiarrhythmic drugs and implantable cardioverter defibrillators (ICDs) should decrease cardiovascular deaths due to tachyarrhythmias. However, any influence of therapy in this paper cannot be assessed since we are not told what, if any, steps were taken to treat the identified causes.

The paper provides valuable evidence about the incidence of syncope in the general population. However, in the absence of certainty about the identified cause and information about treatment, it doesn’t provide much new information about prognosis associated with individual events. The data presented do reinforce the impression that syncope in patients with established cardiovascular disease warrants investigation for reversible and treatable causes. In many cases, in patients who are thought to be at increased risk for either bradyarrhythmias or ventricular tachyarrhythmias based on their clinical profile, empiric implantation of either a pacemaker or an ICD should be considered.

Dr. DiMarco is Professor of Medicine Director, VAMC Cardiac Catherization Laboratory University of New Mexico Health Sciences Center Albuquerque, NM.