The current and emerging role of cardiovascular magnetic resonance imaging in hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiomyopathy with substantial heterogeneity in phenotypic expression and clinical course. Traditionally, two-dimensional echocardiography has been the easiest and most reliable technique for establishing a diagnosis of HCM. However, cardiovascular magnetic resonance (CMR) has emerged as a novel, three-dimensional tomographic imaging technique, which provides high spatial and temporal resolution images of the heart in any plane and without ionizing radiation. As a result, CMR is particularly well suited to provide detailed characterization of the HCM phenotype, including precise assessment of the location and distribution of left ventricular (LV) wall thickening. In this regard, CMR can identify hypertrophy (particularly in the anterolateral free wall and apex), not well appreciated (or underestimated) by two-dimensional echocardiography, with important implications for diagnosis. CMR can also provide detailed characterization of other myocardial structures such as the papillary muscles, which may impact on preoperative management strategies for patients who are candidates for surgical myectomy. Furthermore, CMR enables an accurate assessment of total LV mass, a robust marker of the overall extent of hypertrophy, which may have implications for risk stratification. In addition, a subgroup of HCM patients have normal LV mass (with focal hypertrophy), suggesting that a limited extent of hypertrophy is consistent with a diagnosis of HCM. Finally, following the intravenous administration of gadolinium, first-pass perfusion sequences can identify myocardial perfusion abnormalities, while late gadolinium enhancement (LGE) sequences can characterize areas of myocardial fibrosis/scarring. LGE is associated with systolic dysfunction and likelihood for ventricular tachyarrhythmias on ambulatory Holter monitoring in patients with HCM. However, the precise clinical implications of myocardial perfusion abnormalities and LGE in HCM are still uncertain; this information may have important implications with regard to identifying HCM patients at risk of sudden death and adverse LV remodeling associated with systolic dysfunction. Therefore, at present, CMR provides important information impacting on diagnosis and clinical management strategies in patients with HCM and will likely have an expanding role in the evaluation of patients with this complex disease.