The case for myocardial ischemia in hypertrophic cardiomyopathy.

Since its original description 50 years ago, myocardial ischemia has been a recognized but underappreciated aspect of the pathophysiology of hypertrophic cardiomyopathy (HCM). Nevertheless, the assessment of myocardial ischemia is still not part of routine clinical diagnostic or management strategies. Morphologic abnormalities of the intramural coronary arterioles represent the primary morphologic substrate for microvascular dysfunction and its functional consequence-that is, blunted myocardial blood flow (MBF) during stress. Recently, a number of studies using contemporary cardiovascular imaging modalities such as positron emission tomography (PET) and cardiovascular magnetic resonance (CMR) have led to an enhanced understanding of the role that myocardial ischemia and its sequelae fibrosis play on clinical outcome. In this regard, studies with PET have shown that HCM patients have impaired MBF after dipyridamole infusion and that this blunted MBF is a powerful independent predictor of cardiovascular mortality and adverse LV remodeling associated with LV systolic dysfunction. Stress CMR with late gadolinium enhancement (LGE) has also shown that MBF is reduced in relation to magnitude of wall thickness and in those LV segments occupied by LGE (i.e., fibrosis). These CMR observations show an association between ischemia, myocardial fibrosis, and LV remodeling, providing support that abnormal MBF caused by microvascular dysfunction is responsible for myocardial ischemia-mediated myocyte death, and ultimately replacement fibrosis. Efforts should now focus on detecting myocardial ischemia before adverse LV remodeling begins, so that interventional treatment strategies can be initiated earlier in the clinical course to mitigate ischemia and beneficially alter the natural history of HCM.