Which statement best describes coronary microvascular dysfunction?

• A. CMD is a spectrum of alterations leading to inability to increase blood flow relative to metabolic demand
• B. CMD is identical to epicardial artery disease
• C. CMD only occurs in diabetics
• D. CMD is not related to coronary flow regulation

Answer: (A)

Coronary microvascular dysfunction means the small vessels of the heart fail to appropriately increase blood flow as the heart’s demand grows, even when the major coronary arteries appear unobstructed. This reflects a spectrum of functional and structural changes—endothelial dysfunction, abnormal smooth muscle reactivity, and microvascular remodeling—that together reduce coronary flow reserve. Because of this impaired regulation, ischemia can occur during stress or exercise despite no large-vessel blockages.

This description is the best match because it emphasizes the range of microvascular problems that limit flow when it’s needed, rather than pointing to a single lesion. The other statements miss key aspects: CMD is not the same as epicardial artery disease, since it involves the small vessels; it is not confined to diabetics—though diabetes increases risk, CMD also occurs in other populations; and CMD is intrinsically tied to how coronary flow is regulated at the microvascular level, not independent of flow regulation.