Aetiology and haemodynamic patterns of orthostatic hypotension in a tertiary syncope unit

Orthostatic hypotension (OH) is an important differential diagnosis in unexplained syncope. Neurogenic OH (nOH) has been postulated to differ from non-neurogenic OH (non-nOH), yet pathophysiological differences are largely unexplored. We aimed to investigate aetiology and tilt table test (TTT)-induced haemodynamic responses in symptomatic OH patients.

We performed a retrospective study analysing patients referred for unexplained syncope or highly symptomatic orthostatic intolerance with TTT-verified classical OH (cOH). Medical records were analysed for the presumptive aetiology of cOH. Fifty-two patients (mean age 73 ± 9 years, 46% women) with good quality TTT recordings were divided into three groups on clinical grounds: nOH, non-nOH, and mixed OH. The log-ratio (LR) method was applied to compare the decrease in mean arterial pressure (MAPLR) and corresponding contributions of heart rate (HRLR), stroke volume (SVLR), and total peripheral resistance (TPRLR) during the upright phase of TTT. The prevalence of cOH was 12 (23%) nOH, 14 (27%) non-nOH, and 26 (50%) mixed OH. No difference in MAPLR was observed among the three groups during the 4th upright minute of TTT (nOH: -0.10 ± 0.04 vs. non-nOH: -0.07 ± 0.05 and vs. mixed OH: -0.06 ± 0.05, P = 0.10). The contributions of HRLR, SVLR, and TPRLR to the drop in MAPLR did not differ between groups (all P > 0.05).

One-half of highly symptomatic OH patients had mixed OH, whereas one-quarter had either pure neurogenic or non-neurogenic OH, respectively. Different forms of OH were indifferentiable based on haemodynamic responses during TTT, questioning the clinical utility of such classification. Larger studies are needed to confirm these findings.