Syncope is a relatively common problem with a favorable prognosis in most patients. In one subgroup of patients, however, syncope denotes increased risk for serious cardiac or neurologic disease. Soteriades and coworkers used data from the Framingham Heart Study to provide some specific population-based numbers on the causes of syncope and its long-term outcomes.

The authors scanned records for 7,814 Framingham participants and found 822 subjects with reported syncope; follow-up data were available for 727 of these patients. Based on chart reviews, a physician committee excluded 120 other reported syncope cases as equivocal. To minimize recall bias, they also excluded 101 cases in which patients had not had a clinical examination in the previous four years. Other exclusions included 47 cases of syncope associated with head trauma and seven cases with incomplete records.

Four diagnostic groups were established for describing the cause of syncope: cardiac cause (e.g., ischemia, arrhythmias); neurologic cause (e.g., transient ischemic attack, stroke, seizure); unknown cause; and vasovagal or other cause (e.g., vasovagal syncope, orthostatic syncope, medication-induced syncope, syncope from cough or micturition, situational syncope).

The average age of the 822 study subjects reporting syncope was 65.8 years. The overall incidence of syncope was 6.2 cases per 1,000 person-years; the incidence increased with age and nearly doubled in the cohort of patients older than 70 years. The authors found that the most common diagnostic group was the group with vasovagal or other cause of syncope (44.9 percent), followed by the groups with unknown cause (36.6 percent), cardiac cause (9.5 percent), and neurologic cause (9.0 percent).

The average duration of follow-up available for review after a first report of syncope was 8.6 years (n = 2,181). After adjustments for age, sex, smoking, hypertension, diabetes, cardiovascular disease, use of cardiac medications, and several other relevant clinical variables, the overall risk of death from any cause was found to be 31 percent higher in the patients with syncope than in those without the diagnosis (i.e., hazard ratio of 1.31). Patients with a cardiac etiology of syncope had double the risk of death from any cause compared with patients who did not have syncope. The overall risk of death in patients with a neurologic or unknown cause of syncope was elevated to a lesser degree (hazard ratios of 1.54 and 1.32, respectively). Risk of death, myocardial infarction, or stroke was not found to be significantly elevated in the patients with vasovagal or other cause of syncope.

The authors noted that their findings supported a benign prognosis for syncope with a vasovagal cause. Their findings suggested that the small group of patients with cardiac causes of syncope should be closely monitored because of their high risk of morbidity and mortality. In addition, patients with syncope from an unknown cause may require further testing.

editor's note: In an accompanying editorial, Maisel and Stevenson noted that the mortality rate in this study was more than 10 percent in the first six months of follow-up after syncope in patients with a cardiac etiology. They recommended expeditious evaluation of these patients, including a history, a physical examination, and electrocardiography. They also thought that echocardiography might be prudent, because patients with syncope, structural heart disease, or a depressed ejection fraction are much more likely to have life-threatening arrhythmias and sudden death.—b.z.