Determining the causes of syncopal episodes can be difficult. Methods that would distinguish between cardiac, reflex-mediated, neurogenic, and idiopathic etiologies would be helpful. Brain natriuretic peptide plasma concentrations are being used widely to identify patients with myocardial dysfunction.

Tanimoto and associates measured brain natriuretic peptide levels on the morning after admission in 118 adult patients who were admitted to the hospital for syncope. The cause of syncope was determined using a diagnostic algorithm suggested by the American College of Physicians. Patients were classified into one of four etiologic categories; a majority (52 percent) had cardiac etiologies for the syncopal episode. The cause of syncope was unknown in 25 percent of the patients.

Brain natriuretic peptide was significantly higher in the cardiac group (118 ± 42 pg per mL) than in the other groups. The highest levels occurred in patients with organic cardiac disease, followed by those with tachycardia and then by those with bradycardia. Using a cutoff of 40 pg per mL, the sensitivity and specificity of brain natriuretic peptide levels in identifying cardiac syncope were 82 and 92 percent, respectively.

The authors conclude that cardiac causes for syncope are much more likely in patients with a brain natriuretic peptide level greater than 40 pg per mL. Electrocardiography and echocardiography are helpful in identifying specific cardiac causes. Because some patients in the unknown-cause group had elevated levels of brain natriuretic peptide, it is likely that these patients had cardiac syncope but that the specific cardiac disorder was not identified.