In the outpatient setting, differentiation of cardiac syncope (CS) from other more common forms of syncope is difficult, particularly in the elderly. We examined the frequency of the different types of syncope in a clinic population and estimated missed CS cases.

We retrospectively examined the relevant data for patients assessed in our Christchurch Hospital syncope clinic over a 5-year study period (1 January 2011–31 December 2015). Patients who were later found to have cardiac syncope (and were not initially diagnosed in our clinic) were counted as “missed” cases.

Eight hundred thirty-nine (839) patients (median age 57, interquartile range: 35–73 years, 56% female) were assessed during the study period. Vasovagal syncope (VVS) was the most frequent diagnosis (42.8%) followed by drug-related postural hypotension (DRPH) (26.6%). Cardiac syncope was initially diagnosed in only 3.1%. Of 30 CS patients initially assessed in syncope clinic who later required pacing, 18 (2.1%) were missed CS. In this group, 12-lead electrocardiograph (ECG) was normal in 50% and the majority (n=10) were tilt-positive. The 2.5-year mortality was 5.7% (n=48) including three sudden unexpected cardiac deaths.

Vasovagal syncope and DRPH were by far the most frequent diagnoses. Cardiac syncope was less frequent because patients were selected mainly from an outpatient population, not the emergency department. In a small number of patients, CS was missed for the following reasons: (1) coexistence of cardiac conduction system disease with VVS and DRPH in the elderly, and (2) insensitivity of 12-lead ECG, in-hospital telemetry and out-of-hospital Holter monitoring for detecting conduction system disease early in its development.