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

OBJECTIVE: To compare Functional Disability Inventory (FDI) between adolescents with chronic orthostatic intolerance (COI) and postural orthostatic tachycardia syndrome (POTS). STUDY DESIGN: 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. RESULTS: 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. CONCLUSION: 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.