Initial orthostatic hypotension among patients with unexplained syncope: An overlooked diagnosis?

Initial orthostatic hypotension (IOH) is a clinical syndrome of transient orthostatic hypotension that is defined as a drop in blood pressure of >40 mm Hg systolic and/or >20 mm Hg diastolic within 15 s after standing, accompanied by symptoms of cerebral hypoperfusion, but without sustained orthostatic hypotension (blood pressure decrease >20/10 mm Hg after 1-3 min of standing). As the etiology of syncope remains unknown in a large proportion of patients, we hypothesized that IOH is highly prevalent among patients with unexplained syncope.

We studied 250 consecutive outpatients with unexplained syncope that were evaluated in the syncope-unit of our tertiary referral hospital. We measured hemodynamic changes in response to active standing using a beat-to-beat blood pressure measurement device, first after lying supine for >5 min and then after squatting for 30 s.

11.2% of the patients were diagnosed with syncope due to IOH, with a mean fall in blood pressure of 47.4 ± 12.5/29.0 ± 10.7 mm Hg within 15 s after standing up. Therefore, IOH was the second commonest cause of syncope in our cohort. 46.2% of the patients diagnosed with syncope due to IOH used antihypertensive drugs, mostly betablockers (41.6%) and/or tamsulosin (24.9%). The squatting-to-standing-test in addition to the lying-to-standing-test resulted in only 3 additional patients diagnosed with syncope due to IOH.

IOH is highly prevalent among patients with previously unexplained syncope. Therefore, beat-to-beat blood pressure measurement should be considered in patients with unexplained syncope.