Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiomyopathy and the leading cause of sudden death in young people and a major cause of heart failure symptoms at any age. Due to its genetic etiology, there is substantial heterogeneity in the phenotypic expression and clinical course of patients with HCM. Traditionally, two-dimensional echocardiography has been the easiest and reliable technique for establishing a diagnosis of HCM. However, cardiovascular magnetic resonance (CMR) has emerged as a novel, 3-dimensional tomographic imaging technique, which provides high spatial and temporal resolution images of the heart (not limited by thoracic or pulmonary parenchyma), in any plane and without ionizing radiation. As a result, CMR is particularly well suited to provide detailed characterization of the HCM phenotype, including a precise assessment of the location and distribution of LV wall thickening (as well as other myocardial structures such as the right ventricle and papillary muscles). In this regard, CMR has been demonstrated to provide a diagnosis of HCM in cases where the echocardiogram was non-diagnostic. Furthermore, CMR provides an accurate assessment of total LV mass which is a more robust marker of hypertrophy, with potential implications for risk stratification. In addition, with the intravenous administration of gadolinium, first-pass perfusion sequences can identify myocardial perfusion abnormalities, while late gadolinium enhancement sequences can identify areas of myocardial fibrosis/scarring. Although the clinical implications of late gadolinium enhancement in HCM are still uncertain this information may, in the near-future, have important implications with regard to identifying HCM patients at high risk of sudden death and progressive heart failure, including evolution into the end-stage phase of HCM. 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.
Cardiomyopathy, Hypertrophic ; diagnosis ; Humans ; Magnetic Resonance Imaging ; methods

Hypertrophic cardiomyopathy (HCM) is characterized by extreme clinical heterogeneity, ranging from sudden cardiac death to long-term disease progression and heart failure-related complications. Myocardial ischemia, occurring at the microvascular level, is a major determinant of clinical expression and outcome. Accordingly, the severity of this microvascular dysfunction has been shown to represent an early and powerful predictor of unfavorable outcome in HCM. The assessment of microvascular function in vivo is technically challenging, although critical to a truly comprehensive evaluation and risk stratification of HCM patients. Available technologies include positron emission tomography and cardiac magnetic resonance (CMR). Studies of regional myocardial blood flow using positron emission tomography have demonstrated that the vasodilator response to dipyridamole is impaired in most HCM patients, not only in the hypertrophied ventricular septum but also in the less hypertrophied or non-thickened left ventricular free wall. CMR also allows measurement of myocardial flow, although the technique is currently time-consuming and largely limited to research situations. CMR provides further insight into the effects of ischemia in HCM patients, by visualizing the distribution and extent of fibrosis at the intramyocardial level. Late gadolinium enhancement (LGE) is a potential predictor of risk in HCM patients, and is believed to largely reflect replacement fibrosis resulting from recurrent microvascular ischemia. LGE is associated with increased prevalence of ventricular arrhythmias, and associated with microvascular dysfunction. The present review is to provide a concise overview for the available evidence of microvascular ischemia and its consequences in HCM.
Cardiomyopathy, Hypertrophic ; diagnostic imaging ; pathology ; Humans ; Magnetic Resonance Imaging ; Myocardium ; pathology ; Positron-Emission Tomography