Orthostatic intolerance in adults with long COVID was not associated with postural orthostatic tachycardia syndrome

In this observational cross-sectional study, we investigated predictors of orthostatic intolerance (OI) in adults with long COVID. Participants underwent a 3-minute active stand (AS) with Finapres® NOVA, followed by a 10-minute unmedicated 70-degree head-up tilt test. 85 participants were included (mean age 46 years, range 25-78; 74% women), of which 56 (66%) reported OI during AS (OI_AS). OI_AS seemed associated with female sex, more fatigue and depressive symptoms, and greater inability to perform activities of daily living (ADL), as well as a higher heart rate (HR) at the lowest systolic blood pressure (SBP) point before the 1^st minute post-stand (mean HR_nadir: 88 vs 75 bpm, P=0.004). In a regression model also including age, sex, fatigue, depression, ADL inability, and peak HR after the nadir SBP, HR_nadir was the only OI_AS predictor (OR=1.09, 95% CI: 1.01-1.18, P=0.027). 22 participants had initial (iOH) and 5 classical (cOH) orthostatic hypotension, but neither correlated with OI_AS. 71 participants proceeded to tilt, of which 28 had OI during tilt (OI_tilt). Of the 53 who had a 10-minute tilt, 7 (13%) fulfilled hemodynamic postural orthostatic tachycardia syndrome (POTS) criteria, but 6 did not report OI_tilt. OI_AS was associated with a higher initial HR on AS, which after 1 minute equalized with the non-OI_AS group. Despite these initial orthostatic HR differences, POTS was infrequent and largely asymptomatic. <ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://ClinicalTrials.gov">ClinicalTrials.gov</ext-link> Identifier: <ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="clintrialgov" xlink:href="NCT05027724">NCT05027724</ext-link> (retrospectively registered on August 30, 2021).