A groundbreaking study has uncovered a new indicator that can identify patients with impaired function in their coronary microvessels, the tiny blood vessels that supply the heart with oxygen-rich blood. Notably, patients with low scores on this indicator also face a higher risk of major cardiovascular events, including heart attacks and heart failure.
Samsung Medical Center announced on Monday that Professor Lee Joo-myung from its Department of Cardiology, in collaboration with Professors Hong Young-jun, Lee Seung-heon, and Ahn Jun-ho from Chonnam National University Hospital, has published their multi-center research findings in the prestigious European Heart Journal. Their study evaluated coronary microvascular dysfunction using a novel metric called microvascular resistance reserve (MRR).
Coronary microvascular dysfunction (CMD) occurs when the heart’s tiny blood vessels fail to function properly, resulting in inadequate blood flow to the heart muscle. Even without significant blockages in the larger coronary arteries, dysfunction in these microvessels can trigger chest pain or myocardial ischemia.
The challenge lies in detecting issues within these minuscule vessels, as standard coronary angiography often falls short. Consequently, clinicians have relied on indicators such as coronary flow reserve (CFR) or the index of microvascular resistance (IMR) to assess microvascular function.
Recently, MRR has emerged as a promising new indicator, offering a more direct assessment of microvascular function. It measures the ability of microvessels to reduce resistance when the heart demands increased blood flow.
In layman’s terms, MRR gauges how effectively the small vessels dilate during periods of high blood flow demand. A lower MRR score indicates poorer microvascular function. The research team analyzed data from 1,003 patients who underwent coronary angiography or similar procedures for suspected ischemic heart disease at seven South Korean medical centers between April 2022 and November 2024.
The researchers defined microvascular dysfunction as an MRR of 2.5 or below. This condition was identified in 33.3% (334 patients) of the study cohort. After a follow-up period of approximately 1.9 years, the team discovered that patients with microvascular dysfunction faced a 1.94 times higher risk of experiencing major cardiovascular events compared to those without the condition.
Major cardiovascular events were assessed using a composite endpoint that included all-cause mortality, myocardial infarction, repeat revascularization procedures, and heart failure hospitalizations. The estimated two-year rate of major cardiovascular events was 18.2% in the microvascular dysfunction group, more than double the rate observed in the normal group (8.6%).
The research team emphasized that these findings suggest MRR’s potential extends beyond simply confirming reduced microvascular function. It could serve as a valuable tool for identifying patients at elevated risk for future cardiovascular diseases.
Professor Lee Seung-heon highlighted the study’s significance, stating that the research demonstrates the potential for a more streamlined evaluation of microvascular dysfunction using a single indicator – the microvascular resistance reserve – rather than relying on multiple metrics. Importantly, it has established a clear link between this novel assessment tool and real-world patient outcomes.
Professor Lee Joo-myung added that coronary microvascular dysfunction often eludes detection through standard coronary angiography, making it challenging to pinpoint the root cause of chest pain in some patients. It hopes this study will pave the way for new standards in diagnosing microvascular dysfunction and assessing cardiovascular risk with greater precision.
