Actigraphy Study Endpoints to Reduce Sample Size and Facilitate Drug Development for Pediatric Pulmonary Arterial Hypertension

Objective

To investigate the feasibility of using actigraphy to measure physical activity (pA) and heart rate variability (HRV) as study endpoints in pediatric pulmonary arterial hypertension (PAH) and to compare their performance to 6-minute-walk distance (6MWD), a common primary endpoint used in PAH clinical trials in adults and children who can walk and understand the test process.

Study design

We conducted a prospective, multicenter, noninterventional study in pediatric PAH patients and healthy children. Actiheart and Fitbit Charge 2 recorded pA and heart rate data. HRV was defined as SD of daily heart rate. Actigraphy pA and HRV and 6MWD from the same subjects were analyzed to compare children with PAH with controls, and Panama functional classification (FC) III vs II. Power/sample size simulations were conducted to detect hypothetical treatment effect equivalent to differences seen between FC III and FC II.

Results

We enrolled 116 children: 90 and 98 adhered with Actiheart and Fitbit, respectively. Actigraphy daily pA was ∼36% lower (P < .05) and daily HRV was ∼18% lower (P < .05) in children with PAH (n = 62) than healthy controls (n = 54). Daily pA and daily HRV trended ∼17% lower in FC III than FC II, whereas 6MWD showed little difference. Simulation at 80% power showed that pA required 175 subjects per group and HRV required 40 per group to detect the difference/effect, whereas 6MWD required over our maximum sample size of 200.

Conclusions

Actigraphy is a feasible measure in pediatric PAH. Compared with 6MWD, pA and HRV may be more sensitive in differentiating Panama FC III from II. HRV may improve actigraphy's utility in pediatric PAH.