Association Between Coronary Microvascular Dysfunction and Exercise Capacity in Dilated Cardiomyopathy.

Background: Aerobic exercise capacity is an independent predictor of mortality in dilated cardiomyopathy (DCM), but the central mechanisms contributing to exercise intolerance in DCM are unknown.

Objectives: Characterize coronary microvascular function in DCM and determine if cardiovascular magnetic resonance (CMR) measures are associated with aerobic exercise capacity.

Methods: Prospective case-control comparison of adults with DCM and matched controls. Adenosine-stress perfusion CMR to assess cardiac structure, function and automated inline myocardial blood flow quantification, and cardiopulmonary exercise testing (CPET) to determine peak VO₂, were performed. Pre-specified multivariable linear regression, including key clinical and cardiac variables, was undertaken to identify independent associations with peak VO₂.

Results: Sixty-six patients with DCM (mean age 61 years, 71% male) were propensity-matched to 66 controls (mean age 59 years, 71% male) based on age, sex, body mass index and diabetes. DCM patients had markedly lower peak VO₂ (19.8±5.5 versus 25.2±7.3mL/kg/min; P<0.001). The DCM group had greater left ventricular (LV) volumes, lower systolic function, and had more fibrosis compared to controls. In the DCM group, there was similar rest but lower stress myocardial blood flow (1.53±0.49 versus 2.01±0.60mL/g/min; P<0.001) and lower MPR (2.69±0.84 versus 3.15±0.84; P=0.002). Multivariable linear regression demonstrated that LV ejection fraction, extracellular volume fraction and MPR, were independently associated with percentage predicted peak VO₂ in DCM (R²=0.531, P<0.001).

Conclusions: In comparison to controls, DCM patients have lower stress myocardial blood flow and MPR. In DCM, MPR, LV ejection fraction and fibrosis are independently associated with aerobic exercise capacity.