The coronary circulation and blood flow in left ventricular hypertrophy

Two distinct types of left ventricular hypertrophy (LVH) have been described: the so called “physiologic” hy- 21 pertrophy, which is normally found in professional athletes, and “pathologic” LVH which is found in patients 22 with inherited heart muscle disease such as hypertrophic cardiomyopathy (HCM) or patients with cardiac 23 and systemic diseases characterized by pressure or volume overload. Patients with pathologic LVH have 24 often symptoms and signs suggestive of myocardial ischemia despite normal coronary angiograms. Under 25 these circumstances ischemia is due to coronary microvascular dysfunction (CMD). The abnormalities of 26 the coronary microcirculation may be unrelated to the degree of LVH and cause a reduction in maximum 27 myocardial blood flow which, in the absence of epicardial stenoses, is suggestive of CMD. There is no tech- 28 nique that enables direct visualization of coronary microcirculation in vivo in humans. Therefore, its assess- 29 ment relies on the measurement of parameters which reflect its functional status, such as myocardial blood 30 flow and coronary flow reserve which is an integrated measure of flow through both the large epicardial cor- 31 onary arteries and the microcirculation. In this review article we discuss the pathophysiological mechanisms 32 responsible for CMD in patients with primary and secondary LVH and how the recognition of this phenom- 33 enon is providing new important information on patient stratification and prognosis. Finally, we discuss 34 how assessment of CMD may be used as a valuable surrogate marker to test the efficacy of old and new 35 drugs. This article is part of a Special Issue entitled ‘Coronary Blood Flow SI’.