P0406 - Re-examining Physiologic Diagnostic Criteria: A Pilot Study using the Compensatory Reserve Index to Evaluate Individuals with Postural Orthostatic Tachycardia Syndrome

Background/Purpose:
Postural orthostatic tachycardia syndrome (POTS) can be associated with significant functional impairment and psychological distress. The diagnosis of POTS traditionally involves an orthostatic vitals evaluation (supine to standing), for which heart rate (HR) increases >30 beats per minute (Boris 2020). The Compensatory Reserve Index (CRI) is a noninvasive, FDA-cleared algorithm that analyzes photoplethysmogram or pulse oximetry waveforms in real-time to trend subtle waveform features that correspond with varying degrees of central volume loss, from normovolemia (CRI=1) to decompensation (CRI=0; SBP<80mmHg). We sought to: 1) examine the utility of using two physiologic parameters, HR criteria and CRI, as measures of true physiologic POTS, and 2) explore psychosocial factors associated with physiologic POTS.

Methods:
POTS patients 12-21 years old and healthy controls were prospectively enrolled from 2019-2020. Urine specific gravity values were used to assess hydration status. Orthostatic vitals and CRI values were assessed once patients had a urine specific gravity value of < 1.015. Optimal CRI cutoffs were determined using the Youden Index. Participants completed the Functional Disability Inventory (FDI), Revised Child Anxiety and Depression Scale (RCADS), Family Assessment Device General Functioning Scale (GFS), and investigator-created POTS Severity Scale (frequency of 10 physical symptoms). Adolescents were grouped for comparison based on whether they met HR criteria for POTS (physiologic POTS).

Results:
A total of 64 participants were enrolled, of which 44 (69%) had a pre-existing diagnosis of POTS. Most participants were female (46/64, 72%). Eleven patients met HR criteria for POTS, of which 8 had an existing POTS diagnosis. There were no significant differences in the rates of anxiety (64% vs 36%, p= 0.171) and depression (46% vs 25%; p= 0.300) in participants who met HR criteria (n=11) versus those who did not (n=53). Participants who met HR criteria for POTS had significantly greater supine to standing ∆CRI (0.67 vs 0.51; p<0.001) and lower median minimum standing CRI values (0.22 vs 0.32; p=0.006). The optimal cutoff for a ∆CRI to distinguish between participants with physiologic POTS versus those without was 0.63. For these same two groups, there were no significant differences in functional disability (15 vs 9; p= 0.368), family functioning (22 vs 22; p= 0.827), and symptom severity (22.5 vs 27; p= 0.551).

Conclusion:
The diagnosis of POTS is often difficult, because many of the associated symptoms are non-specific and can be affected by comorbidities, such as anxiety and depression. In our sample, only 18% (8/44) of previously diagnosed POTS patients met HR criteria. We found no significant differences in functional disability, family functioning and symptom severity in participants with physiologic POTS versus those without. These findings support the utility of objective physiologic measures, including the novel CRI method, to more accurately identify patients with true autonomic dysfunction.