Heart rate monitoring improves clinical assessment during 6‐min walk

Abstract

Right ventricular (RV) function is a predictor of outcomes in pulmonary arterial hypertension (PAH). The 6-minute walk test (6MWT) is likely an indirect measure of RV function during exercise, but changes in absolute walk distance can also be influenced by factors like effort and musculoskeletal disease. Paired 6MWT with continuous electrocardiogram monitoring were performed in stable PAH patients, patients adding PAH therapies, and healthy controls. Heart rate expenditure (HRE) was calculated (integrating pulse during 6MWT) and then divided by walk distance (HRE/d). We also evaluated changes in peak heart rate, time above age adjusted maximum predicted heart rate, and heart rate at 6 minutes. HRE/d was compared to invasive hemodynamic measures in patients who had right heart catheterization performed within seven days, WHO functional class assessment, and Emphasis 10 questionnaire. We measured two 6MWT in 15 stable PAH patients, 13 treatment intensification patients, and 8 healthy controls. HRE/d was reproducible in the stable PAH group (median difference, -0.79%), while it decreased (median difference, 23%, p =0.0001) after adding vasodilator therapy. In 11 patients with right heart catheterization, HRE/d correlated strongly with stroke volume, r=-0.72, p=0.01. Peak heart rate decreased after adding vasodilator therapy. HRE/d also correlated with WHO functional class and Emphasis 10 score. Continuous heart rate monitoring during 6MWT provides valuable physiologic data accounting for effort. HRE/d appears to enhance test reproducibility in stable patients while detecting change after adding therapy as compared to walk distance alone.

Cardiac Effort to Compare Clinic and Remote 6-Minute Walk Testing in Pulmonary Arterial Hypertension

“…All clinic 6MWTs were performed according to the American Thoracic Society criteria 22 without masks to minimize confounders between in-clinic and remote walks. As previously described, 7 two BioStamp nPoint sensors (MC10) were placed on the chest to record acceleration and…”

“…16 Cardiac effort was calculated as previously described. 7 Adhesive reaction, falls, syncope, and other injuries were recorded during this 3-week observation period. We also collected baseline demographic and clinical information.…”

“…Beyond equipment for assessing vital signs, the 6MWT requires only an unobstructed walking space (preferably 30 m). The initial 6MWT validation study, 1 as well as subsequent follow-up studies, 6,7 have shown variability in repeat 6MWT distance for stable participants whose walks were > 400 m. This variability complicates interpreting changes in walk distances and, especially, in identifying a clinically meaningful improvement (the minimal clinically important difference 8 ). Variability has made some speculate about a ceiling effect in PAH therapy trials despite the fact that walks > 500 m are routinely recorded.…”

“…This measure was less variable than 6MWT distance and sensitive to changes in therapy; it also correlated with two different assessments of right ventricular function. 7,11 The SARS-CoV-2 pandemic has exposed the limitations of gauging objective exercise tolerance testing in patients with PAH. The difficulty of doing in-clinic hallway walks complicated efforts to restart therapeutic research after the first wave, and the absence of 6MWT data made risk assessment in clinical practice less meaningful.…”

Cardiac effort and 6‐min walk distance correlate with stroke volume measured by cardiac magnetic resonance imaging

“… 15 , 16 , 17 Cardiac Effort is more reproducible than 6MWD 16 , 17 and correlates strongly with resting stroke volume (SV) measured by nuclear ventriculography and indirect Fick during right heart catheterization. 15 , 16 …”