Cardiac MRI evaluation of hypertrophic cardiomyopathy: Left ventricular outflow tract/aortic valve diameter ratio predicts severity of LVOT obstruction

Purpose: To evaluate if left ventricular outflow tract/aortic valve (LVOT/AO) diameter ratio measured by cardiac magnetic resonance (CMR) imaging is an accurate marker for LVOT obstruction in patients with hypertrophic cardiomyopathy (HCM) compared to Doppler echocardiography. Materials and Methods: In all, 92 patients with HCM were divided into three groups based on their resting echocardiographic LVOT pressure gradient (PG): <30 mmHg at rest (nonobstructive, n = 31), <30 mmHg at rest, >30 mmHg after provocation (latent, n = 29), and >30 mmHg at rest (obstructive, n = 32). The end-systolic dimension of the LVOT on 3-chamber steady-state free precession (SSFP) CMR was divided by the end diastolic aortic valve diameter to calculate the LVOT/AO diameter ratio. Results: There were significant differences in the LVOT/AO diameter ratio among the three subgroups (nonobstructive 0.60 ± 0.13, latent 0.41 ± 0.16, obstructive 0.24 ± 0.09, P < 0.001). There was a strong linear inverse correlation between the LVOT/AO diameter ratio and the log of the LVOT pressure gradient (r = -0.84, P < 0.001). For detection of a resting gradient >30 mmHg, the LVOT/AO diameter ratio the area under the receiver operating characteristic (ROC) curve was 0.91 (95% confidence interval [CI] 0.85-0.97). For detection of a resting and/or provoked gradient >30 mmHg, the LVOT/AO diameter ratio area under the ROC curve was 0.90 (95% CI 0.84-0.96). Conclusion: The LVOT/AO diameter ratio is an accurate, reproducible, noninvasive, and easy to use CMR marker to assess LVOT pressure gradients in patients with HCM. J. Magn. Reson. Imaging 2012;36:598-603.