Extent of size, shape and systolic variability of the left ventricular outflow tract in aortic stenosis determined by phase-contrast MRI

PURPOSE:Left ventricular outflow tract (LVOT) dimensions are important for calculation of aortic valve areas and planning of valve repair. Mostly, LVOT areas are calculated from echocardiographic longitudinal measurements with the assumption of a round shape. Here, orthogonal phase contrast (PC) MRI with dynamic assessment of LVOT was compared to standard longitudinal cine MRI and 2D echocardiography. METHODS:In 19 patients with aortic stenosis (5 female; 69±10years), LVOT areas were determined on orthogonal PC images, either by planimetry (Aplan) or by two-diameter measurement (Aellip). Data were analyzed in early, middle and late systole (t1/t2/t3). Additionally, standard diameter-based calculation (A3CV) of LVOT on longitudinal three-chamber view (3CV) MRI images and 2D echocardiography was performed. RESULTS:Calculated PC LVOT areas strongly correlated to planimetry (r=0.95; p<0.001) with almost identical areas (Aplan 5.1±1.1cm2 vs. Aellip 5.3±1.0cm2). In PC changes of LVOT-eccentricity during systole were most pronounced in late systole (t1 vs. t3plan -7.4±18%). Cine 3CV calculation resulted in lower LVOT areas compared to Aplan (A3CV 3.7±0.9cm2; p<0.001), yet correlating to Aplan (r=0.66; p=0.002). 3CV LVOT areas correlated to echocardiography (r=0.56; p=0.014). CONCLUSIONS:Calculated LVOT areas seem to be sufficient for daily routine. Compared to the orthogonal view, standard long-axis 3CV underestimates the LVOT size and overestimates the systolic reduction of LVOT-size. Systolic changes are most pronounced in late systole.