Daily Step Counts Are Associated with Hospitalization Risk in Pulmonary Arterial Hypertension

Abstract

To the Editor: Patients with pulmonary arterial hypertension (PAH) often have decreased exercise capacity, which is consistently associated with adverse outcomes and reduced right ventricular (RV) function. The 6-minute-walk distance (6MWD) is associated with clinical outcomes in PAH but has important limitations as a clinical tool and trial endpoint (1, 2). In contrast, little is known about the relationship between uncoached daily activity (e.g., step counts) and clinical outcomes in PAH (3). Step counts and 6MWD correlate only moderately, suggesting the two measures capture different, nonoverlapping information about activity. We hypothesized that decreased step counts would be associated with adverse PAH outcomes, including decline in RV function and increased risk of hospitalization. Some results were presented at the American Thoracic Society 2021 Scientific Sessions (4). We recruited adult patients with idiopathic, heritable, or associated PAH between October 2017 and January 2020 and followed them until March 15, 2021. Functional class I–III patients on stable PAH therapy for 3 months were included. Participants wore a Fitbit Charge 3 device for a 2-week run-in period of a behavioral intervention trial. Average step counts for this study were determined by taking the mean daily step count for Week 2 of the run-in. Week 1 steps were discarded to account for a possible observer effect. 6MWD and echocardiography were performed at the conclusion of the activity monitoring period. Subsequent 6MWD and RV function measurements were obtained as part of routine clinical care. To examine how baseline step counts and 6MWD associated with outcomes during follow-up, we used ordinary least regressions for continuous outcomes and logistic regression for binary outcomes. We performed time-to-event analyses for the first hospitalization and medication escalation during follow-up. All regressions included baseline step counts (or 6MWD) as the main predictor and were adjusted for age and sex. The ordinary least and logistic regressions were also adjusted for baseline outcome level and the time elapsed between baseline and follow-up measures. To improve interpretability of the results, hazard ratios, odds ratios, and estimated differences reflect a comparison between patients at the 75th and 25th percentiles of baseline step counts (or 6WMD). Medication escalation was defined as either an unplanned increase in the dosage or addition of a new PAH-targeted therapy.

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