Impact of Excessive Postural Tachycardia on Disability in Youth with Orthostatic Intolerance

To compare Functional Disability Inventory (FDI) between adolescents with chronic orthostatic intolerance (COI) and postural orthostatic tachycardia syndrome (POTS). This cross-sectional study included adolescents ≤19 years with orthostatic symptoms >3 months referred to a tertiary pediatric autonomic clinic (August 2024-March 2025) and classified as POTS or COI based upon active stand testing. Self- and parent-reported FDI scores were collected. Group comparisons used chi-square and Wilcoxon-Mann-Whitney tests. Univariable and multivariable linear regression models compared FDI scores, adjusting for age, sex, and body mass index. Adjusted means were estimated using post-fit marginal estimation. Ninety-two adolescents were included (46 POTS, 46 COI). Groups were similar in age, sex, and body mass index, but differed in heart rate response by definition. Self-reported FDI scores did not differ between COI and POTS in unadjusted (22.9 vs 22.4; P = .81) or adjusted analyses (adjusted mean difference 1.0, 95% CI -3.0 to 4.9; P = .63). Parent-reported FDI scores were also comparable in unadjusted (23.1 vs 22.3; P = .70) and adjusted analyses (adjusted mean difference 0.4, 95% CI -3.4 to 4.2; P = .85). Differences were well below the prespecified threshold for clinical significance. There was no evidence for a difference in functional disability in adolescents with COI, regardless of tachycardia-based POTS classification. This suggests that heart rate response is not associated with functional differences in pediatric orthostatic intolerance.