Change in 6-minute walk distance (6MWD) has been used as a clinical marker in pulmonary hypertension. Determinants and worsening of 6MWD remain a matter of debate because nonpulmonary factors have an impact on the 6MWD. We hypothesized that future reduction of 6MWD in patients with systemic sclerosis (SSc) was more closely associated with cardiac dysfunction. We prospectively performed standard clinical and echocardiographic evaluations in SSc patients with the 6-minute walk test at enrollment. Features associated with the 6MWD were sought in a multiple linear regression analysis and compared using standardized β. Worsening of the 6MWD was defined as a 15% reduction and served as the primary outcome. Eighty-one patients were included. In the multivariate analysis, baseline 6MWD was related to SSc severity score (β = -0.250, p = 0.024), left atrial volume index (β = -0.222, p = 0.046), right ventricular fractional area change (β = 0.252, p = 0.025), and the ratio of mean pulmonary artery pressure and cardiac output (β = -0.31, p = 0.002). During follow-up, 20 patients reached the primary outcome. In sequential Cox models, a model based on right ventricular fractional area change at baseline (chi-square 4.8) was improved by left atrial volume index (chi-square 10.3, p = 0.007). In conclusion, determinants and worsening of 6MWD are explained by cardiac factors. When using the 6MWD as a clinical marker in pulmonary hypertension patients, their left ventricular diastolic function and right ventricular systolic function should be taken into consideration.
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