PURPOSE: The six-minute walk test (6MWT) is widely used to measure exercise capacity in pulmonary arterial hypertension (PAH) patients, and serves as the primary end point in many clinical trials. Although the 6MWT has been validated for use in idiopathic PAH, there has been no such validation in PAH patients with scleroderma or other connective tissue diseases (CTD), where unique co-morbidities exist. In this study, we compare the 6MWT in CTD-PAH patients to the gold standard for exercise evaluation, the cardiopulmonary exercise test (CPET), and identify baseline predictors of exercise capacity.
METHODS: Retrospectively, regression analysis was performed on the 6MWT vs. clinical, hemodynamic, and CPET variables in 28 CTD-PAH patients. PAH was diagnosed according to the Venice 2003 criteria. Unencouraged 6MWTs were performed as per previously published guidelines. Treadmill CPETs were performed according to ATS guidelines with breath-breath measurements of oxygen consumption (VO2), CO2 produced (VCO2), minute ventilation (VE), and estimation of anaerobic threshold (AT) by monitoring ventilatory equivalents for O2 (VE/VO2) and CO2 (VE/VCO2).
RESULTS: In the 28 CTD-PAH patients, significant correlations were made between the 6MWT and WHO/NYHA class (r=0.72, p<0.01). In 21 of the 28 patients who had echocardiographic right-ventricular systolic pressure (RVSP) measurements, the mean RVSP was 63+/−6 mmHg. However, there was no significant correlation (r=0.08) between the 6MWT and RVSP. For the various CPET parameters, significant correlations were made between the 6MWT and peak VO2 (r=0.50, p=0.01), VE/VO2 at AT (r=0.37, p=0.05), VE/VCO2 at AT(r=0.40, p=0.03), and peak HR (r=0.50, p<0.01).
CONCLUSION: 6MWT correlates significantly with PAH severity, as assessed clinically by WHO/NYHA criteria, but not with hemodynamic echocardiographic RVSP measurements. 6MWT also correlates well with both cardiac and pulmonary CPET variables.
CLINICAL IMPLICATIONS: The 6MWT is recommended for routine clinical follow-up for idiopathic PAH patients. It appears that the 6MWT may be a reliable indicator of exercise capacity in the CTD-PAH population as well.
DISCLOSURE: Sushmita Pamidi, None.