Clinical characteristics and outcomes of patients with situational syncope compared to patients with vasovagal syncope

This study is a retrospective study that examined the prevalence, patient characteristics and outcomes of patients with situational syncope (SS) vs. vasovagal syncope (VVS) who presented at faint and fall clinic at the university of Wisconsin between January 2013 and December 2015.

1,401 consecutive patients were examined. SS was defined as syncope that occurred during or immediately after micturition, defecation, laughter, coughing, swallowing, or sneezing. VVS was diagnosed based on the presence of triggers such as heat, emotional stress, and prolonged standing or autonomic symptoms such as sweating, pallor, and nausea.

Out of the 1,401 patients, 55 patients (4.0%) were diagnosed with SS. 8 of the patients were lost to follow up. Out of 47 patients, the triggers were: defecation (n=16), micturition (n=15), cough (n=10), swallow (n=3), laughter (n=1), sneeze (n=1) and cough and laughter (n=1).

Over the same time period, 252 patients (18%) were diagnosed with VVS. Between the two populations, SS patients were older and more likely to be male, they had a higher prevalence of hypertension, higher baseline systolic BP and experienced more injuries due to syncope.

Pathophysiology: SS and VSS are both reflex mediated in the mechanism, but they differ in terms of the trigger and afferent part of the reflex arc. The central nervous processing and efferent signals are believed to be similar- both lead to bradycardia and vasodilation.

Presentation: VVS patients are younger, have a lower body mass index, and had more episodes of syncope when compared to patients with SS

Clinical outcome: the patients were instructed to avoid triggers when possible and to reduce or discontinue antihypertensive therapy when possible. The recurrence rate in SS patients was 20% at 1 year and 40% at 2 years. These rates were similar to the rates seen in VVS patients.

Conclusion: SS is an infrequent form of reflex syncope. Patients with SS have clinical features that distinguish them from VVS. The relative roles of cardio-inhibitory and vasodepressor reflexes in SS remains poorly understood and more research is needed to assess the potential benefit of pacing in this type of syncope.

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