The Prevalence of Microvascular Dysfunction, Its Role Among Men, and Links With Adverse Outcomes
Noninvasive Imaging Reveals the Tip of the Iceberg
Considerable evidence has accumulated to counter older concepts of a categorical definition of ischemic heart disease as simply the presence or absence of a flow-limiting stenosis. Revised concepts increasingly recognize ischemic heart disease as a continuous spectrum that is not limited to obstructive plaque seen by angiography in an epicardial coronary artery. Included in this spectrum are functional disorders of the large and smaller coronary blood vessels. These smaller vessels, collectively the coronary microcirculation, comprise most of the coronary blood vessels and control the volume and distribution of blood flow to the myocardium.
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Although not visualized by angiography, the coronary microcirculation may be indirectly assessed from the speed of radiographic contrast movement as the corrected thrombolysis in myocardial infarction (TIMI) frame count. This simple, objective, continuous index is accurate, reproducible, highly correlated with Doppler blood flow measurements, and provides information for risk stratification.1–3 The microcirculation can be directly assessed, in the absence of flow-limiting stenoses, by coronary flow reserve (CFR) and also by the index of microvascular resistance. Noninvasive methods, such as positron emission tomography (PET), Doppler echocardiography, and gadolinium perfusion cardiac magnetic resonance imaging, are also increasingly being used to evaluate microvascular function.
Patients with symptoms and signs of ischemia, referred for invasive coronary evaluation, increasingly appear without obstructive epicardial coronary artery disease (CAD).4,5 We and others identified that symptomatic patients with nonobstructive CAD may have an elevated risk of adverse outcomes compared with cohorts without symptoms or signs of ischemic heart disease.5 Unfortunately, because of lack of evidence-based results on treatment, management of these symptomatic patients is often frustrating for the patients and their physicians. As a result, these individuals consume medical resources rivaling those for patients with obstructive CAD.6 Approximately 45% to 60% of such …