Aortic Valve Area, Stroke Volume, Left Ventricular Hypertrophy, Remodeling, and Fibrosis in Aortic Stenosis Assessed by Cardiac Magnetic Resonance Imaging: Comparison Between High and Low Gradient and Normal and Low Flow Aortic Stenosis

Background—Recent works using echocardiography suggested that low gradient (LG), low flow (LF) aortic stenosis (AS) has more pronounced left ventricular (LV) concentric remodeling, smaller LV cavity size, and more interstitial fibrosis compared with high gradient (HG) normal flow (NF) AS. Therefore, we evaluated the accuracy of echocardiographic measurements and compared remodeling and fibrosis in different types of AS by cardiac magnetic resonance (CMR). Methods and Results—A total of 128 patients (73±11 years of age; 75 men) with aortic valve area (AVA) <0.6 cm2/m2 and ejection fraction >50% by echocardiography underwent CMR to measure planimetric AVA, phase-contrast indexed stroke volume, LV mass, and focal fibrosis. Using <40 mm Hg and indexed stroke volume <35 mL/m2 by echocardiography as criteria for LG and LF, 69 (54%) patients were HG/NF, 28 (22%) HG/LF, 17 (13%) LG/NF, and 14 (11%) LG/LF AS. LV outflow tract area, indexed stroke volume, and AVA correlated well between echocardiography and CMR (r=0.7, 0.61, and 0.65, respectively; P<0.001 for all). By CMR, however, planimetric AVA was larger in LF/LG (0.54±0.08 cm2/m2) and LG/NF (0.61±0.08 cm2/m2) than in HG/LF (0.46±0.07 cm2/m2; P<0.05) AS, and indexed LV mass was lower in LG/LF (75±12 g/m2) and LG/NF (81±18 g/m2) than in HG/LF (100±27 g/m2; P<0.05) AS. All groups of AS had similar LV volumes, predominantly concentric hypertrophy remodeling, and similar amounts of focal fibrosis. Conclusions—CMR confirmed overall accuracy of echocardiographic classification of AS but demonstrated that LG/LF and LG/NF AS have larger AVA, less LV hypertrophy, and similar focal fibrosis compared with HG/LF AS. This challenges the view that LG/LF AS is a more advanced state of AS.