Hidden Heart Risk: Microvascular Dysfunction Doubles Cardiac Event Rates
A landmark Lancet registry finds coronary microvascular dysfunction raises major cardiac event risk by 91%, even after treating visible blockages.
Summary
A large prospective Korean registry study published in The Lancet found that coronary microvascular dysfunction — disease in the heart's tiny blood vessels, not just the main arteries — is common and dangerous. Among 1,003 patients undergoing invasive heart procedures, about 21% of those with visible artery blockages also had microvascular dysfunction. Over roughly two years, patients with microvascular dysfunction were nearly twice as likely to experience death, heart attack, repeat procedures, or hospitalization for heart failure compared to those without it. This highlights that treating visible blockages alone may not address all cardiovascular risk, and that the small vessels of the heart deserve greater clinical attention in routine cardiac care.
Detailed Summary
Coronary artery disease is typically understood as blockages in the large, visible arteries of the heart. But a growing body of evidence suggests that disease in the heart's tiny microvasculature — vessels too small to see on standard angiography — may independently drive serious cardiac events. Despite this, the prevalence and prognosis of coronary microvascular dysfunction (CMD) in routine clinical practice have remained poorly characterized.
The Multicenter FLOW-CMD Registry enrolled 1,003 patients across seven South Korean tertiary hospitals who underwent clinically indicated invasive coronary angiography. Researchers used coronary flow reserve and the index of microcirculatory resistance to systematically identify CMD, independent of whether obstructive epicardial coronary artery disease (CAD) was present. This physiological approach goes beyond what standard imaging captures.
Key findings were striking. CMD was detected in 21.5% of patients who had obstructive epicardial CAD and in 9.3% of those without visible blockages. Over a median follow-up of 1.9 years, patients with CMD faced an 91% higher risk of the composite endpoint — all-cause death, myocardial infarction, repeat revascularization, or heart failure hospitalization — compared to those with preserved microvascular function (HR 1.91; 95% CI 1.22–2.99; p=0.0047). The 2-year event rate was 18.8% in CMD patients versus 10.5% in those without CMD.
The implications are significant for clinicians. Standard cardiac workups focus on identifying and treating epicardial blockages, but this registry demonstrates that a substantial proportion of high-risk patients have an additional, often unrecognized layer of disease. Physiological assessment of the microvasculature may need to become part of routine invasive cardiology practice.
Caveats include the relatively short follow-up period and the study's industry funding from Abbott Vascular and Boston Scientific, which supply the measurement tools used. Additionally, this summary is based on the abstract only, as the full text was not available.
Key Findings
- CMD found in 21.5% of patients with obstructive CAD and 9.3% of those without visible blockages.
- CMD was associated with a 91% higher risk of major cardiac events over ~2 years (HR 1.91).
- 2-year event rate: 18.8% with CMD vs. 10.5% with preserved microvascular function.
- CMD coexists with epicardial CAD, meaning treating blockages alone may leave significant risk unaddressed.
- Routine physiological assessment during angiography can identify this hidden, high-risk condition.
Methodology
Prospective, multicentre cohort study of 1,003 patients at seven South Korean tertiary hospitals enrolled between April 2022 and November 2024. CMD was defined as coronary flow reserve below 2.0 and index of microcirculatory resistance ≥25. The primary composite endpoint included all-cause death, MI, repeat revascularization, and heart failure hospitalization.
Study Limitations
This summary is based on the abstract only, as the full text is not open access; nuanced details of patient selection, statistical adjustments, and subgroup analyses are unavailable. Follow-up was relatively short at a median of 1.9 years, limiting conclusions about long-term outcomes. Industry funding from Abbott Vascular and Boston Scientific — makers of the physiological measurement tools used — represents a potential conflict of interest.
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