Undiagnosed syncope: search for an arrhythmic etiology.

Patients with recurrent, unheralded syncope are often suspected of having intermittent cardiac bradyarrhythmias or tachyarrhythmias. However, syncopal episodes may be infrequent and investigations may yield few or non-specific etiological clues. Therapy may be entirely empirical (pacing or antiarrhythmic drugs) or guided by an abnormality detected that suggests a particular diagnosis. Intracardiac electrophysiological studies may detect conduction abnormalities or provoke arrhythmias but the relationship between these findings and clinical symptoms may be difficult to establish. The recording of the ECG during syncope by repeated ambulatory monitoring or other methods remains the only unequivocal diagnostic technique to establish an arrhythmic etiology.