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CLINICAL RESEARCH: MYOCARDIAL INFARCTION

Predictive Value of the Index of Microcirculatory Resistance in Patients With ST-Segment Elevation Myocardial Infarction

Division of Cardiovascular Medicine, Stanford University Medical Center, Stanford, California.

Manuscript received June 12, 2007; revised manuscript received August 7, 2007, accepted August 27, 2007.

^_* Reprint requests and correspondence: Dr. William F. Fearon, Stanford University Medical Center, 300 Pasteur Drive, H3554, Stanford, California 94305. (Email: wfearon{at}stanford.edu).

Objectives: The objective of this study is to evaluate the predictive value of the index of microcirculatory resistance (IMR) in patients undergoing primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI).

Background: Despite adequate epicardial artery reperfusion, a number of patients with STEMI have a poor prognosis because of microvascular damage. Assessing the status of the microvasculature in this setting remains challenging.

Methods: In 29 patients after primary PCI for STEMI, IMR was measured with a pressure sensor/thermistor-tipped guidewire. The Thrombolysis In Myocardial Infarction (TIMI) myocardial perfusion grade, TIMI frame count, coronary flow reserve, and ST-segment resolution were also recorded.

Results: The IMR correlated significantly with the peak creatinine kinase (CK) (R = 0.61, p = 0.0005) while the other measures of microvascular dysfunction did not. In patients with an IMR greater than the median value of 32 U, the peak CK was significantly higher compared with those having values 32 U (3,128 ± 1,634 ng/ml vs. 1,201 ± 911 ng/ml, p = 0.002). The IMR correlated significantly with 3-month echocardiographic wall motion score (WMS) (R = 0.59, p = 0.002) while the other measures of microvascular function did not. The WMS at 3-month follow-up was significantly worse in the group with an IMR >32 U compared with 32 U (28 ± 7 vs. 20 ± 4, p = 0.001). On multivariate analysis, IMR was the strongest predictor of peak CK and 3-month WMS. The IMR was the only significant predictor of recovery of left ventricular function on the basis of the percent change in WMS (R = 0.50, p < 0.01).

Conclusions: Compared to standard measures, IMR appears to be a better predictor of microvascular damage after STEMI, both acutely and in short term follow-up.

Abbreviations and Acronyms   CFR = coronary flow reserve   CK = creatine kinase   cTFC = corrected Thrombolysis In Myocardial Infarction frame count   FFR = fractional flow reserve   IMR = index of microcirculatory resistance   PCI = percutaneous coronary intervention   STEMI = ST-segment elevation myocardial infarction   TIMI = Thrombolysis In Myocardial Infarction   TMPG = Thrombolysis In Myocardial Infarction myocardial perfusion grade   WMS = wall motion score

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