Left ventricular outflow tract obstruction in hypertrophic cardiomyopathy : presurgical and postsurgical evaluation by computed tomography magnetic resonance imaging

Along with hypertrophy of the left ventricle (LV), hypertrophic cardiomyopathy (HC) is characterized by LV outflow tract (LVOT) obstruction, partly from systolic anterior motion (SAM) of the anterior mitral leaflet ; if obstruction is significant, excision of excess subaortic septal myocardium may be indicated. In this study, the ability of computed tomography magnetic resonance imaging (Cine MRI) to provide information about LVOT obstruction was assessed in a series of 37 HC cases undergoing evaluation, including echocardiography (0 to 14 days before), for possible septal myectomy ; in 4 cases, Cine MRI was used postsurgically (5 to 25 months after). Blinded to echocardiography results, 3 reviewers analyzed by consensus the Cine-MRI LVOT-long-axis image-loops for SAM grade (none, mild, severe) and aorta :LVOT signal ratio (intensity in descending aorta/intensity in LVOT at maximum systolic-flow disturbance). Resting LVOT flow velocities were separately determined using Doppler analysis, permitting differentiation between insignificant (<30 mm Hg) and significant (≤30 mm Hg) gradients. With echocardiography, significant resting obstruction was found in 62% of cases, including 92% treated surgically. A significant association between SAM grade and obstruction was found ; all cases with a SAM grade of none had insignificant ([-] predictive value : 100%) and most with a severe grade had significant ([+] predictive value : 78%) obstruction. Signal ratio in the absence of a significant gradient was significantly lower than in its presence ; a significant linear relationship between aorta :LVOT signal ratio and resting gradient was found : LVOT gradient = ([2.9 x [signal ratio]) + 22.8. SAM grade did not contribute significantly in obstruction categorization when signal ratio was known. In all cases studied after surgery, SAM grade had decreased from severe to insignificant levels and aorta : LVOT signal ratio had been significantly reduced. Insights into the dynamic nature of the LVOT in HC patients can be provided by Cine MRI, either during their evaluation for surgery or after their septal myectomy.