Coronary microvascular dysfunction is best described as:

• A. A spectrum of alterations that results in an inability to increase blood flow relative to myocardial metabolic demand
• B. A disease limited to epicardial arteries
• C. An issue limited to capillary perfusion with no impact on flow
• D. The same as obstructive coronary artery disease

Answer: (A)

The key idea is that coronary microvascular dysfunction is a failure of the small coronary vessels to enlarge blood flow to meet the heart’s increased metabolic needs. When demand rises, the microvasculature should dilate to boost perfusion, but in CMD this response is blunted, leading to a reduced coronary flow reserve and possible ischemia even though the major (epicardial) arteries show no obstructive disease. This helps explain why symptoms can occur with nonobstructive arteries (INOCA) and why the problem is about flow regulation in the microvasculature, not fixed narrowing of the large arteries. It’s not limited to epicardial arteries, it doesn’t imply capillary perfusion is unaffected with no flow impact, and it’s distinct from obstructive coronary artery disease, which involves a structural blockage of the major arteries.