March 28, 2026European Heart Journal
Coronary autoregulation: the complex interplay between epicardial and microvascular resistance
Key result
Coronary microvascular resistance determines resting coronary blood flow by dynamically adapting to epicardial resistance.
Why the study?
Despite its fundamental role in coronary physiology, coronary autoregulation remains complex, often overlooked, and poorly understood.
Key Points
- This review aims to clarify the role of coronary autoregulation and the factors influencing coronary blood flow.
- Review of animal and human studies on coronary autoregulation.
- Assessment techniques including nuclear imaging, Doppler, and thermodilution.
- Development of an integrative model of coronary resistance during different physiological states.
- Coronary autoregulation maintains stable blood flow despite changes in myocardial perfusion pressure.
- Microvascular resistance plays a critical role in determining coronary blood flow.
- Understanding the interplay between epicardial and microvascular resistance is essential for clinical assessments in coronary artery disease.
Design
Review
Discussion
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Key expert perspectives
Captured external expert commentary on this paper, strongest first. Original sources are linked where available.
“At rest, coronary autoregulation maintains stable flow despite the presence of epicardial disease through a compensatory background decrease in microvascular resistance. During hyperaemia, autoregulation is eliminated and the true haemodynamic effect of a stenosis is revealed.”
“This is a textbook demonstration of coronary autoregulation showing normal adaptive microvascular vasodilatation in response progressive epicardial stenosis.”
“I was struck by the fact that flow was absolutely maintained despite major stenoses. Because of the vasodilation of the microcirculation.... I, maybe you too, don't think about the microcirculation that much. Modern cardiology focuses on the epicardial stenoses. We can stent those.... It's not just about those epicardial stenoses that we cosmetically improve with PCI.”
Implication
Requires microvascular compensation in epicardial physiology interpretation; reinforces textbook coronary autoregulation.
Abstract
Coronary autoregulation is the intrinsic ability of the coronary circulation to maintain stable blood flow despite fluctuations in myocardial perfusion pressure, provided that metabolic demands remain constant. Central to this process is the dynamic modulation of microvascular resistance within the coronary microcirculation, which acts as the main determinant of coronary blood flow. This regulatory mechanism enables the coronary vasculature to adapt to variations in aortic pressure and epicardial resistance, preserving myocardial perfusion. Historically, the study of coronary autoregulation relied on animal models using implanted flow probes. In humans, modalities such as nuclear imaging and intracoronary Doppler have been employed. Most recently, continuous intracoronary thermodilution has emerged as a robust technique, allowing simultaneous and accurate assessment of absolute coronary blood flow, epicardial resistance, and microvascular resistance. Yet, despite its fundamental role in the understanding of coronary physiology, coronary autoregulation remains complex, often overlooked, and poorly understood. This review focuses on the pivotal role of the coronary microcirculation, specifically microvascular resistance, in maintaining stable resting flow in the context of epicardial coronary artery disease. It provides a theoretical framework, summarizes key animal and human data, and presents an integrative model illustrating the haemodynamic transition from rest to maximal hyperaemia from the perspective of coronary resistance. Finally, it highlights the importance of understanding coronary autoregulation and the interplay between epicardial and microvascular resistance when interpreting not only the clinical presentation of patients with epicardial disease but also the results of the coronary physiological assessment.
Cite This Study
Mahendiran et al. (2026) studied this question. Coronary microvascular resistance acts as the primary determinant of coronary blood flow, dynamically adapting to epicardial resistance to preserve stable myocardial perfusion at rest.