Background: The 6-minute walk distance (6MWD) is a useful measure of functional class and has been shown to predict mortality in patients with pulmonary hypertension (PH). Determinants of functional class in PH are incompletely understood. We hypothesized that cardiovascular structure and function, as determined by cardiac magnetic resonance (CMR) imaging, and cardiac hemodynamics, as determined by right heart catheterization (RHC), would predict 6MWD in adult patients with PH.
Methods: Forty-three patients (32 women) with PH underwent RHC, CMR and 6MWD testing within a 3-month period. The 6MWD was correlated with RHC and CMR variables using Spearman rho (r) coefficients. These relationships were further evaluated using linear regression analysis.
Results: Median 6MWD was 233.2 (interquartile range 161.6 to 338.4) meters. The 6MWD was correlated with pulmonary artery (PA) elasticity (r = 0.42, p = 0.006), PA average blood flow velocity (r = 0.38, p = 0.014), right ventricular stroke volume index (RVSVI; r = 0.41, p = 0.008), left ventricular SVI (LVSVI; r = 0.36, p = 0.018) and RV stroke work index (RVSWI; r = 0.37, p = 0.017). These associations remained significant after adjustment for age, gender, body mass index and the presence of lung disease. Exercise performance did not correlate with commonly measured indices such as ventricular volume, ejection fraction or pulmonary pressure.
Conclusions: Stroke volume index, PA elasticity and PA average blood flow velocity are novel CMR parameters associated with functional class in PH. CMR can provide insights into determinants of exercise performance and may be a useful tool to non-invasively monitor cardiovascular status in patients with PH.