New estimate of valvuloarterial impedance in aortic valve stenosis: A cardiac magnetic resonance study

Purpose Valvuloarterial impedance (Z VA ), estimating left ventricle (LV) afterload, has been proposed in transthoracic echocardiography (TTE) as a predictor of mortality in aortic valve stenosis (AVS). However, its calculation differs from arterial characteristic impedance (Z C ). Our aim was to apply the concept of Z C calculation to estimate Z VA from MR with carotid tonometry and to evaluate these indices through their associations with symptoms, LV diastolic function and aortic stiffness. Materials and Methods In 40 patients with AVS (76 ± 13 years), Z VA‐TI derived from velocity time integral and E/Ea were estimated by TTE. Z VA‐INS , based on Z C formula, calculated as the instantaneous pressure gradient to peak flow ratio and aortic compliance were estimated by using MRI at 1.5 Tesla. Results Both Z VA estimates were higher in symptomatic than asymptomatic patients (707 ± 22 versus 579 ± 53 dyne.s/cm 5 , P  = 0.031 for Z VA‐INS and 4.35 ± 0.16 versus 3.33 ± 0.38 mmHg.m 2 /mL, P  = 0.018 for Z VA‐TI ). Although they were both associated with aortic compliance (r = ‐0.45; P  = 0.006 for Z VA‐INS and r = ‐0.43; P  = 0.008 for Z VA‐TI ) only Z VA‐INS was associated with E/Ea (r = 0.50; P  < 0.001). In multivariate analysis to identify determinants of E/Ea, a model including age, mean blood pressure, LV ejection fraction, LV mass, and aortic valve area was performed (R 2  = 0.41; P  < 0.01). When Z VA‐INS was added to the model, its overall significance was higher R 2  = 0.56 ( P  < 0.01) and Z VA‐INS and LV mass were the only significant determinants. Conclusion Z VA‐INS was more strongly associated with diastolic dysfunction than usual parameters quantifying AVS severity. This new Z VA estimate could improve LV afterload evaluation. Level of Evidence: 1 J. Magn. Reson. Imaging 2017;45:795–803.