Lower Daily Activity Tracks With Clinical Worsening in PAH

Key Takeaways

• In adults with pulmonary arterial hypertension (PAH), lower accelerometer-measured daily activity at baseline was associated with a higher risk of clinical worsening over 12 months.
• Activity was lower among patients in WHO functional class III and fell over the course of follow-up.
• More daily activity was associated with better PAH-specific quality of life and higher hip and femoral bone mineral density.

The 6-minute walk distance (6MWD) is the standard measure of exercise capacity in PAH. Because it is a single test done in clinic, it may miss the activity limits patients face in daily life. Wearable devices can record real-world movement continuously, but whether those measurements reflect disease severity and outcomes has not been well defined.

Investigators conducted a longitudinal analysis of daily physical activity in PAH using data from PHANTOM, a multicenter randomized trial of anastrozole at 7 U.S. centers. The trial enrolled 84 men and postmenopausal women with PAH on stable therapy. Participants wore hip-based accelerometers during waking hours for 7 days at baseline and at 3, 6, and 12 months. Mixed-effects models examined how active time related to clinical characteristics, quality of life, 6MWD, and bone mineral density. Cox models assessed time to clinical worsening, defined as death, PAH-related hospitalization, or treatment escalation.

Adherence was high, with 2,182 patient-days of data collected. Participants spent about 11.9 hours a day sedentary, with minimal moderate-to-vigorous activity. Compared with baseline, active time fell by 15 minutes a day at follow-up visits. Patients in functional class III were 50 minutes a day less active than those in class I or II. Activity also declined with age and was lower in fall and winter than in spring and summer.

Each additional hour of daily activity was associated with a 1.5-point better emPHasis-10 quality-of-life score at baseline, though the differences did not reach the minimal clinically important difference. At baseline, each hour of daily activity was associated with a 22-meter longer 6MWD. Each additional hour of daily activity was associated with hip bone mineral density 0.14 g/cm² higher.

During follow-up, 20 clinical worsening events occurred, including 3 deaths, 10 hospitalizations, and 7 treatment escalations. Lower baseline activity was associated with a higher risk of worsening (hazard ratio 1.06 per hour per week less active; 95% confidence interval [CI] 1.03–1.10). In time-dependent models, declining activity was also linked to a shorter time to worsening.

This was an observational analysis within a trial, so causality cannot be inferred. The number of events was modest, and the authors described the outcome findings as hypothesis-generating. Hip-worn devices may miss upper-body movement. Trial participants may also have been more motivated than patients in routine care.

The authors concluded that accelerometer-derived activity reflects disease severity and is associated with quality of life, bone health, and clinical worsening, offering a patient-centered complement to traditional assessments.