Coronary microvascular dysfunction in patients with cardiomyopathies.

Anginal symptoms and electrocardiographic changes suggestive of myocardial ischemia, despite angiographically normal coronary arteries, are common in patients with cardiomyopathies and those with left ventricular hypertrophy secondary to pressure overload. Studies using positronemission tomography (PET) to measure regional myocardial blood flow have demonstrated that maximum myocardial blood flow and coronary flow reserve are severely blunted in patients with hypertrophic as well as dilated cardiomyopathy.1,2 In the absence of epicardial stenoses, blunted maximum myocardial blood flow and coronary flow reserve are suggestive of coronary microvascular dysfunction.3,4 Furthermore, it has been demonstrated that in both hypertrophic and dilated cardiomyopathy, the severity of coronary microvascular dysfunction, assessed by measuring myocardial blood flow with PET, is an independent predictor of prognosis.2,5 In patients with cardiomyopathies, coronary microvascular dysfunction can be sustained by a number of different pathogenetic mechanisms. These include structural and functional abnormalities of the intramural arterioles as well as extravascular mechanisms (eg, increased extramural compression).4