A new prospective analysis has been published on the prevalence and prognosis of coronary microvascular dysfunction in Korea, the condition that affects the tiny vessels keeping the heart beating.
Samsung Medical Center announced Monday that a joint research team led by Professor Lee Joo-myung of the Cardiology Department at Samsung Medical Center and Professor Lee Seung-hun of the Cardiology Department at Chonnam National University Hospital published their findings in the prestigious medical journal The Lancet. The team analyzed the prevalence and treatment outcomes of coronary microvascular dysfunction in 1,003 patients who had undergone coronary angiography for suspected ischemic heart disease at seven medical institutions in Korea between April 2022 and November 2024.
The coronary arteries are three large blood vessels that supply oxygen and nutrients to the heart muscle itself. Originating from the aorta and surrounding the heart like a crown, they were named "coronary," meaning crown-shaped, after their appearance. Ischemic heart disease occurs when these coronary arteries narrow or become blocked, depriving the heart muscle of sufficient blood flow.
Coronary microvascular dysfunction is a condition in which the large coronary arteries appear normal, but the tiny capillaries within the heart muscle fail to dilate properly, resulting in insufficient blood flow to the myocardium. It is defined as a coronary flow reserve below 2.0 combined with an index of microcirculatory resistance of 25 units or higher. Coronary flow reserve (CFR) is a measure of how much blood flow can increase above baseline when vessels are maximally dilated. The index of microcirculatory resistance (IMR) quantifies the internal resistance to blood flow within vessels, with higher values indicating more severely impaired microvascular function.
Until now, diagnostic and treatment strategies for ischemic heart disease have focused on epicardial coronary artery disease, which accounts for the largest share of the coronary system. However, as coronary microvascular dysfunction has been identified as another important cause of ischemic heart disease, its significance has grown. The American College of Cardiology and American Heart Association (ACC/AHA) and the European Society of Cardiology (ESC) have recommended in their latest guidelines that microvascular function assessment using coronary flow reserve or the index of microcirculatory resistance be performed as a complementary test in patients without significant stenosis in the epicardial coronary arteries. This served as the backdrop for the team's investigation into the status of coronary microvascular dysfunction in Korean patients. The mean age of subjects included in this analysis was 65, and men accounted for 75.4 percent, roughly three times more than women.
According to the analysis, microvascular dysfunction was observed in a total of 163 of the 1,003 patients. This included 123 of 573 patients with coronary stenosis (21.5 percent) and 40 of 430 patients without coronary stenosis (9.3 percent). During a median follow-up period of 1.9 years, 26 of the 163 patients with microvascular dysfunction experienced the primary endpoints of the study, including all-cause death, myocardial infarction, repeat procedures for treatment purposes, and hospitalization for heart failure. The estimated two-year incidence based on Kaplan-Meier analysis was 18.8 percent.
By contrast, among the 840 patients without microvascular dysfunction, 70 (estimated two-year incidence of 10.5 percent) experienced all-cause death, myocardial infarction, repeat procedures for treatment purposes, or hospitalization for heart failure, confirming a statistically significant difference between the two groups. This suggests that coronary microvascular dysfunction is often accompanied by epicardial coronary stenosis. The research team's analysis indicates it is also associated with an increased risk of all-cause death, myocardial infarction, repeat procedures for treatment purposes, and hospitalization for heart failure.
The study was selected as one of the "most noteworthy clinical studies" at the recent annual conference of the European Association of Percutaneous Cardiovascular Interventions (EuroPCR) in Paris, France, where lead investigator Professor Lee Joo-myung presented the findings in person. The results overturn the prevailing view that coronary microvascular dysfunction primarily occurs in patients without observed stenosis in the epicardial coronary arteries, drawing attention to potential changes in future international guidelines.
"Existing guidelines mainly recommend physiological assessment of microvascular dysfunction in patients without coronary stenosis," Professor Lee Joo-myung said. "This study found that the prevalence of microvascular dysfunction was actually higher in patients who showed stenosis, and that the associated future risk was greater when microvascular dysfunction was present, so physiological assessment should also be recommended for patients with stenosis."
