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The index of microcirculatory resistance in the physiologic assessment of the coronary microcirculation
Gonzalo J Martínez1, Andy S C Yong, William F Fearon
1aDepartment of Cardiology, Royal Prince Alfred Hospital bSydney Medical School, The University of Sydney cDepartment of Cardiology, Concord Hospital, Sydney, New South Wales, Australia dDivision of Cardiovascular Medicine, Stanford University Medical Center, Stanford, California, USA eDepartment of Cardiology, Catholic University School of Medicine, Santiago, Chile.
Insights
The index of microcirculatory resistance (IMR) offers a reliable method to assess coronary microcirculation function. This invasive technique aids in predicting outcomes for myocardial infarction and stable coronary artery disease.
Area of Science:
- Cardiovascular Physiology
- Interventional Cardiology
Background:
- Coronary microcirculation is vital for cardiac function and disease.
- Evaluating microvascular function has faced technical challenges.
- The index of microcirculatory resistance (IMR) is a novel invasive assessment tool.
Purpose of the Study:
- To review the theoretical and practical basis of IMR.
- To discuss clinical studies supporting IMR.
- To explore future research directions for IMR in microcirculation interventions.
Main Methods:
- Utilizes a pressure-temperature sensor guidewire.
- Relies on thermodilution theory.
- Measures minimum achievable microcirculatory resistance.
Main Results:
- IMR provides quantitative assessment of microvascular integrity.
- IMR is reproducible and independent of hemodynamic changes.
- IMR predicts myocardial recovery, mortality, and periprocedural myocardial infarction.
Conclusions:
- IMR is a valuable tool for assessing coronary microcirculation.
- IMR-guided interventions aim to treat microcirculatory dysfunction.
- Further research will expand the clinical application of IMR.
Abstract:
The coronary microcirculation plays a critical role in normal cardiac physiology as well as in many disease states. However, methods to evaluate the function of the coronary microvessels have been limited by technical and theoretical issues. Recently, the index of microcirculatory resistance (IMR) has been proposed and validated as a simple and specific invasive method of assessing the coronary microcirculation. By relying on the thermodilution theory and using a pressure-temperature sensor guidewire, IMR provides a measurement of the minimum achievable microcirculatory resistance in a target coronary artery territory, enabling a quantitative assessment of the microvascular integrity. Unlike indices such as coronary flow reserve, IMR is highly reproducible and independent of hemodynamic changes. In ST-elevation myocardial infarction, IMR predicts myocardial recovery and long-term mortality, whereas in patients with stable coronary artery disease, preintervention IMR predicts the occurrence of periprocedural myocardial infarction. Increasingly, research has focused on IMR-guided interventions of the microcirculation, with the aim of preventing and/or treating the microcirculatory dysfunction that commonly accompanies the epicardial coronary disease. In the present review, we will discuss the theoretical and practical basis for IMR, the clinical studies supporting it, and the future lines of research using this novel tool.
