Predicting the cause of syncope from clinical history in patients undergoing prolonged monitoring

Syncope may be the result of primary bradycardia or tachycardia, vasovagal syncope, or noncardiac syncope. Risk factors and outcome scores to predict prognosis in patients with syncope have been developed. Although these correlate with morbidity and mortality in patients with syncope, their relationship with the mechanism of syncope has not been investigated.

The purpose of this study was to identify clinical predictors of primary bradycardia in a cohort of patients undergoing prolonged monitoring for unexplained syncope.

One hundred nineteen patients underwent prolonged monitoring with an implantable or external loop recorder after assessment at a single-center, tertiary care arrhythmia service. Fifty-two patients with recurrent syncope during monitoring were classified according to the mechanism of syncope (International Study on Syncope of Uncertain Etiology [ISSUE] classification). Clinical predictors of primary arrhythmic syncope were identified.

Twenty patients were classified with primary arrhythmia and 32 patients were classified with nonarrhythmic syncope. Five clinical variables were associated with primary arrhythmia: left bundle branch block, structural heart disease, and syncope without prodrome increased the likelihood of primary arrhythmia; a normal baseline ECG and history of syncope in childhood decreased the likelihood of primary arrhythmia. After multiple logistic regression, risk factors for the diagnosis of primary arrhythmia included syncope without warning symptoms and structural heart disease. The presence of left bundle branch block correlated perfectly with primary arrhythmia, whereas a normal ECG reduced the likelihood of primary arrhythmia.

Clinical predictors of primary arrhythmia in patients with recurrent syncope include normal ECG and structural heart disease. Left bundle branch block is an important finding in patients with unexplained syncope.