The Relationship between Microcirculatory Resistance and Fractional Flow Reserve in Patients with Acute Myocardial Infarction

Background and Objectives: It was demonstrated that the fractional flow reserve (FFR) with partial balloon obstruction may have implications for assessing viable myocardium. In a different way, the index of microcirculatory resistance (IMR) was introduced as a useful indicator for assessing microvascular function. We evaluated the relationship between the FFR0.8 and the IMR. Subjects and Methods: We studied 48 consecutive patients who had undergone coronary intervention for acute myocardial infarction (AMI). After revascularization using stent(s), an undersized short balloon was positioned inside the stent and inflated to create a specific normalized pressure drop of FFR (distal coronary/aortic pressure=0.80) at rest. The FFR0.8 was obtained during hyperemia with the fixed state balloon-induced partial obstruction. IMR was measured by three injections of saline. The association between the FFR0.8 and the IMR was investigated. Results: The mean age of the patients was 60 +/- 12 years and 36 (75%) overall presented with ST-segment elevation myocardial infarction. The mean FFR0.8 was 0.68 +/- 0.06. A statistically significant correlation between the FFR0.8 and the log-transformed IMRtrue (LnIMR(true)) was found through a multivariable linear regression analysis (beta=0.056, p<0.001). Both the FFR0.8 and the LnIMR(true) had a positive correlation with the log-transformed peak troponin I (TnI) with statistical significance (r(2)=0.119, p=0.017; r(2)=0.225, p=0.006, respectively). Conclusion: There was a positive correlation between the LnIMR(true) and the FFR0.8. Both of the values were associated with peak TnI. Those values may be used as appropriate surrogate measures of microvascular function after AMI.