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Updated: Aug 23, 2025
Evaluation of Coronary Flow Reserve After Myocardial Ischemia Reperfusion in Rats
Published on: June 28, 2019
Impact of the downstream myocardial mass on values of coronary microvascular resistance
Tadashi Murai1, Hiroyuki Hikita1, Tim P van de Hoef2
1Cardiovascular Center, Yokosuka Kyosai Hospital, Yokosuka, Japan.
Insights
Hyperemic microvascular resistance (HMR) assessment is influenced by measurement location and downstream myocardial mass (PMM). Proximal assessment sites with >35g PMM provide reliable HMR values, minimizing location-based variability.
Area of Science:
- Cardiovascular Physiology
- Interventional Cardiology
- Myocardial Perfusion Imaging
Background:
- Hyperemic microvascular resistance (HMR) is a key indicator of coronary microvascular function.
- Previous assessments suggest HMR values may vary based on the measurement site within the coronary artery and the amount of distal myocardial mass.
- Understanding these variations is crucial for accurate interpretation of HMR in clinical practice.
Purpose of the Study:
- To investigate the impact of assessment location (distal vs. proximal) on HMR values.
- To examine the relationship between HMR and the amount of partial myocardial mass (PMM) distal to the assessment site.
- To identify optimal assessment locations for reliable HMR measurements.
Main Methods:
- Intracoronary physiological assessments, including Doppler flow velocity, were performed in 29 vessels from 26 patients.
- Measurements were taken at both distal and proximal thirds of the same coronary arteries.
- Hyperemic microvascular resistance (HMR) and partial myocardial mass (PMM) were calculated for each site.
Main Results:
- Distal HMR values (2.08 ± 0.75 mmHg/cm/sec) were significantly higher than proximal values (1.19 ± 0.33 mmHg/cm/sec) (p < 0.001).
- Smaller distal PMM was significantly associated with higher distal HMR (r = -0.544, p = 0.002) and was the strongest factor influencing HMR.
- This association was not observed at proximal sites, and the impact of PMM on HMR diminished when PMM exceeded 35g.
Conclusions:
- A small distal myocardial mass can lead to artificially high HMR values.
- Assessing HMR in the proximal coronary artery, where distal myocardial mass is >35g, minimizes the influence of assessment location.
- Proximal assessment sites with substantial myocardial mass are recommended for accurate HMR evaluation.
Abstract:
The assessment of hyperemic microvascular resistance (HMR) may be dependent on the assessment location in the coronary artery and the amount of partial myocardial mass (PMM) distal to the assessment locations. The aim of this study was to investigate the differences in HMR values between the distal and proximal sites in the same coronary arteries as well as the relationship between HMR and PMM. Twenty-nine vessels from 26 patients who had undergone intracoronary physiological assessments including Doppler flow velocity at the distal third part and the proximal third part in the same vessels were assessed. The mean values of HMR and PMM at the distal sites were 2.08 ± 0.75 mmHg/cm/sec and 22.2 ± 10.4 g, respectively. At the proximal sites, the values of HMR and PMM were 1.19 ± 0.33 mmHg/cm/sec and 59.9 ± 18.3 g, respectively. All HMR values at the distal sites were significantly higher than those at the proximal sites (p < 0.001). Smaller PMM at the distal sites was significantly associated with higher HMR (r = -0.544, p = 0.002) and was the strongest factor affecting the HMR values (p = 0.009), while this relationship was not observed at the proximal sites (r = -0.262, p = 0.17). The impact of PMM on HMR was diminished at assessment locations where PMM was greater than 35 g. In conclusion, a small amount of downstream myocardial mass could be related to high HMR values. The assessment location around the proximal coronary artery with over 35 g of myocardium would be appropriate to assess HMR because it minimizes the influence of the assessment location.
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