Coronary microvascular disease (CMD) can exist independently or coexist with obstructive epicardial coronary artery disease. In earlier years, patients presenting with angina or angina-like symptoms, objective evidence of myocardial ischemia, and normal coronary angiography (without epicardial coronary artery stenosis) were diagnosed with cardiac syndrome X. This condition accounts for 10%-30% of patients undergoing coronary angiography due to chest pain. The exact etiology remains unclear, but it may be related to endothelial dysfunction and microvascular abnormalities. Currently, it is believed that both functional and structural abnormalities of the coronary microvasculature can lead to myocardial ischemia. Most patients present with stable angina, though some may exhibit unstable angina, making CMD one of the causes of myocardial infarction with non-obstructive coronary arteries (MINOCA).
This condition is more common in premenopausal women. The ECG may appear normal or show nonspecific ST-T changes, and approximately 20% of patients may have a positive result on exercise stress testing. During exercise stress testing or atrial pacing, an increase in coronary sinus lactate concentration can be detected. Intravascular ultrasound (IVUS) and Doppler flow studies may reveal abnormalities such as intimal thickening, early atherosclerotic plaque formation, reduced coronary flow reserve, and an elevated coronary resistance index.
The prognosis of CMD is generally favorable. However, the presence of clinical symptoms often leads to frequent medical visits, excessive diagnostic testing, increased medication use, reduced quality of life, and impaired daily functioning.
There is currently no specific treatment for CMD. Nicorandil, a selective microvascular vasodilator, is considered the first-line therapy. Other anti-ischemic medications, such as beta-blockers, nitrates, calcium channel blockers, and trimetazidine, may alleviate symptoms in some patients, though the overall efficacy is limited. ACE inhibitors (ACEIs) and statins may improve endothelial function, but their effectiveness remains uncertain.