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 (MAP_LR) and corresponding contributions of heart rate (HR_LR), stroke volume (SV_LR), and total peripheral resistance (TPR_LR) 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 MAP_LR 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 HR_LR, SV_LR, and TPR_LR to the drop in MAP_LR 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.