Determinants and functional significance of myocardial perfusion reserve in severe aortic stenosis

Objectives: The purpose of this study was to assess the functional significance of cardiac magnetic resonance (CMR) measures of left ventricular (LV) remodeling and myocardial perfusion reserve (MPR) in patients with severe aortic stenosis (AS), without obstructive coronary artery disease.

Background: Measures of stenosis severity do not correlate well with exercise intolerance in AS. LV remodeling in AS is associated with myocardial fibrosis and impaired MPR. The functional significance and determinants of MPR in AS are unclear.

Methods: Forty-six patients with isolated severe AS were prospectively studied before aortic valve replacement. The following investigations were undertaken: cardiopulmonary exercise testing to measure aerobic exercise capacity (peak VO(2)); CMR to assess left ventricular mass index (LVMI), myocardial fibrosis with late gadolinium enhancement (LGE), myocardial blood flow (MBF), and MPR; and transthoracic echocardiography to assess stenosis severity and diastolic function.

Results: Peak VO(2) was associated with sex (β = -0.41), age (β = -0.32), MPR (β = 0.45), resting MBF (β = -0.53), and septal transmitral flow velocity to annular velocity ratio (E/E') (β = -0.34), but not with LVMI, LGE, or echocardiographic measures of AS severity. On stepwise regression analysis, only MPR was independently associated with age- and sex-corrected peak VO(2) (β = 0.46, p = 0.001). MPR was also inversely related to New York Heart Association functional class (p = 0.001). Univariate associations with MPR were sex (β = 0.38, p = 0.02), septal E/E' (β = -0.30, p = 0.03), peak aortic valve velocity (β = -0.34, p = 0.02), LVMI (β = -0.51, p < 0.001), and LGE category (β = -0.46, p = 0.002). On multivariate analysis, LVMI and LGE were independently associated with MPR.

Conclusions: CMR-quantified MPR is independently associated with aerobic exercise capacity in severe AS. LV remodeling appears to be a more important determinant of impaired MPR than stenosis severity per se. Further work is required to determine how CMR assessment of MPR can aid clinical management of patients with AS.