Remote 6-minute-Walk Testing in Patients with Pulmonary Hypertension: Further Validation Needed?

To the Editor:

The 6-minute-walk test (6MWT) provides insight on functional status, disease severity, and therapeutic efficacy in people with chronic lung disease. The need for digital-technology enabled healthcare provisions that mitigate in-clinic patient visits accelerated during the coronavirus disease (COVID-19) pandemic. Accordingly, the report of LaPatra and colleagues (1) in the April 1 issue of the Journal on the feasibility, safety, and accuracy of performing “remote” 6MWTs in nonclinical settings for pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) is timely and promising. Using and incorporating locations chosen by study participants, audiovisual guidance from study personnel, and companion “support” for each participant, the authors found “no systematic difference” in average 6MWT distance (6MWD) between in-clinic versus remote settings, with excellent concordance between the in-clinic and remote walks. Other than in one patient (lightheadedness, tinnitus), no adverse events were reported during the remote walks. The authors did, however, find that 6MWD was shorter (∼20 m) in masked versus unmasked participants during remote walks. While acknowledging that their findings require replication, the authors conclude that remote 6MWTs may be feasible and valid in stable patients with PH. We applaud the authors for their work; however, two aspects of their conclusions warrant further consideration.

Observing that facemasks were associated with decreased 6MWD (remote setting), the authors suggest that repeat, unmasked studies may be warranted when masking is associated with a reduction in in-clinic 6MWD. Recently, however, we found that facemask wearing had no effect on arterial oxygen saturation, perceptual responses to exercise, or 6MWD in 45 group 1 PAH patients in-clinic (2), which is consistent with reports in healthy individuals (3) and those with lung disease (4). Although not clear why, it is possible that the impact of facemask wearing on 6MWD may be different in-clinic versus remote settings. Based on the available evidence, we would not at this time endorse repeat 6MWT without versus with face-masking in the clinic setting.

Second, LaPatra et al. suggest that 6MWD is not different in-clinic vs. remote settings but that wearing a facemask negatively impacts 6MWD. However, closer inspection of the data reveals that 6MWD differed by ⩾50 m in ∼10 patients (40% of cohort) and by ⩾100 m in ∼5 patients (20% of cohort) in-clinic versus remote settings. By comparison, the difference in 6MWD with versus without a facemask was ⩾50 m and ⩾100 m in only ∼5 (23% of cohort) and ∼2 (9% of cohort) patients, respectively. Comparison of the Deming regression fit to the perfect concordance line for 6MWD in-clinic versus remote settings suggests that patients with a shorter 6MWD distance “perform better” in-clinic whereas patients with a longer 6MWD “perform better” in remote settings. This does not appear to be as true for 6MWD with versus without a facemask, with better clustering of datapoints around the perfect concordance line (see Figure 2 in original report) (1). Two questions arise: 1) do patients with lower exercise capacity (presumably sicker patients) perform better during in-clinic versus remote walk tests; and 2) despite no difference in group mean 6MWD in-clinic versus remote settings, could substantial intra-individual heterogeneity exist in the concordance between in-clinic and remote 6MWTs? Speculatively, it is possible that sicker patients with more impairment “perform better” in clinical settings secondary to direct supervision from healthcare professionals, making remote-based 6MWTs less appropriate in such individuals. Also, given that 6MWD differed by ⩾50 m in-clinic compared with remote settings in ∼40% of patients, we suggest that the applicability of remote-based 6MWT as an accurate and valid marker of functional status, disease severity, and therapy efficacy requires further validation.