Calculation of the index of microcirculatory resistance without coronary wedge pressure measurement in the presence of epicardial stenosis

Andy S. Yong, Jamie Layland, William F. Fearon, Michael Ho, Maulik G. Shah, David Daniels, Robert Whitbourn, Andrew MacIsaac, Leonard Kritharides, Andrew Wilson, Martin K. Ng*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

113 Citations (Scopus)


Objectives: This study sought to investigate a novel method to calculate the index of microcirculatory resistance (IMR) in the presence of significant epicardial stenosis without the need for balloon dilation to measure the coronary wedge pressure (Pw). Background: The IMR provides a quantitative measure of coronary microvasculature status. However, in the presence of significant epicardial stenosis, IMR calculation requires incorporation of the coronary fractional flow reserve (FFRcor), which requires balloon dilation within the coronary artery for Pwmeasurement. Methods: A method to calculate IMR by estimating FFRcorfrom myocardial FFR (FFRmyo), which does not require Pwmeasurement, was developed from a derivation cohort of 50 patients from a single institution. This method to calculate IMR was then validated in a cohort of 72 patients from 2 other different institutions. Physiology measurements were obtained with a pressure-temperature sensor wire before coronary intervention in both cohorts. Results: From the derivation cohort, a strong linear relationship was found between FFRcorand FFRmyo(FFRcor= 1.34 × FFRmyo- 0.32, r2= 0.87, p < 0.001) by regression analysis. With this equation to estimate FFRcorin the validation cohort, there was no significant difference between IMR calculated from estimated FFRcorand measured FFRcor(21.2 ± 12.9 U vs. 20.4 ± 13.6 U, p = 0.161). There was good correlation (r = 0.93, p < 0.001) and agreement by Bland-Altman analysis between calculated and measured IMR. Conclusions: The FFRcor, and, by extension, microcirculatory resistance can be derived without the need for Pw. This method enables assessment of coronary microcirculatory status before or without balloon inflation, in the presence of epicardial stenosis.

Original languageEnglish
Pages (from-to)53-58
Number of pages6
JournalJACC: Cardiovascular Interventions
Issue number1
Publication statusPublished - 2013
Externally publishedYes


  • coronary intervention
  • coronary microvascular function
  • index of microcirculatory resistance
  • microcirculation


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