Cardiac angina is a major source of morbidity, affecting more than 5% of the U.S. population.2 It leads to more than 1.5 million hospitalizations and $190 billion in costs yearly.3 Obstructive coronary artery disease (CAD) is the most common cause of angina. However, no obstructive CAD is found on elective coronary angiography in more than 50% of cases.4, 5 These patients with angina but no obstructive CAD are a heterogeneous group. Some have noncardiac explanations for their angina or nonobstructive epicardial abnormalities such as coronary spasm. However, many patients with angina and no obstructive CAD have microvascular dysfunction from endothelial dysfunction or microvascular obstructive disease as the cause. These patients have microvascular angina.

The coronary microvasculature is responsible for more than 70% of coronary resistance and thus plays a key role in regulating blood flow to match demand.6 Microvascular dysfunction can occur in the setting of dilated, hypertrophic, and restrictive cardiomyopathies. However, it is commonly seen in the setting of atherosclerotic risk factors or can be idiopathic.6, 7 Microvascular dysfunction is manifest as insufficient stress myocardial blood flow and/or reduced myocardial perfusion reserve (MPR), the ratio of stress flow to rest flow, in response to a stress such as vasodilator administration. Absolute myocardial blood flow and MPR can be assessed noninvasively with high precision and accuracy by cardiac magnetic resonance (CMR) imaging Reduced MPR in patients with angina is associated with significant morbidity, including a high risk of cardiac events, high medical costs, and a decreased quality of life.Despite the poor prognosis of this population, therapeutic options to reduce angina and improve MPR have not been well studied. Preliminary analysis shows that statins may improve endothelial function. ACE-inhibitors and beta-blockers improve symptoms in Syndrome X, a related disorder in which patients have angina, no obstructive CAD, and ischemic changes but a better prognosis. Therapeutic exercise has also been used in the Syndrome X population, improving exercise tolerance and endothelial function and reducing symptom severity.Improvements in MPR could be expected with exercise due to the reduced resting flow and increased MPR seen in healthy volunteers and improved endothelial function from increased nitric oxide bioactivity in patients with probable microvascular dysfunction. However, no studies have examined the effect of these medications or their synergism with exercise on MPR, aerobic capacity, anginal symptoms, or quality of life in patients with angina and reduced MPR. Identification of an effective therapy that improved symptoms and prognosis would have dramatic impact on this highly prevalent patient population.

The primary goal of this study is to characterize which patients with angina but no obstructive CAD have reduced MPR and test the effectiveness of intensive medical therapy plus a 12-week supervised exercise program versus intensive medical therapy alone to improve MPR, aerobic capacity, and the patient-centered outcomes of cardiac events, angina severity, and quality of life in this population with microvascular angina.