Vasodilatory capacity of the coronary microcirculation is preserved in selected patients with non-ST-segment-elevation myocardial infarction

Background-The use of fractional flow reserve in patients with non-ST-segment-elevation myocardial infarction (NSTEMI) is a controversial issue. We undertook a study to assess the vasodilatory capacity of the coronary microcirculation in patients with NSTEMI when compared with a model of preserved microcirculation (stable angina [SA] cohort: culprit and nonculprit vessel) and acute microcirculatory dysfunction (ST-segment-elevation myocardial infarction [STEMI] cohort). We hypothesized that the vasodilatory response of the microcirculation would be preserved in NSTEMI. Methods and Results-A total of 140 patients undergoing single vessel percutaneous coronary intervention were included: 50 stable angina, 50 NSTEMI, and 40 STEMI. The index of microvascular resistance (IMR), fractional flow reserve, and coronary flow reserve were measured before stenting in the culprit vessel and in an angiographically normal nonculprit vessel in patients with SA. The resistive reserve ratio, a measure of the vasodilatory capacity of the microcirculation and calculated using the equation: baseline resistance index (Tmn_Base×Pa _Base[Pd_Base-Pw/Pa_Base-Pw])-IMR/IMR, where TmnBase referred to nonhyperemic transit time; Pa_Base and Pd _Base, the nonhyperemic aortic and distal coronary pressures, respectively; and Pw referred to the coronary wedge pressure, was also measured. Troponin was also measured =24 hours after percutaneous coronary intervention. The resistive reserve ratio was significantly lower in the STEMI patients compared with the stable angina patients both culprit and nonculprit vessel (STEMI, 1.7 versus SA culprit, 2.8; P=0.001 and SA nonculprit, 2.9; P<0.0001) and compared with NSTEMI patients (NSTEMI, 2.46; P=0.001). The resistive reserve ratio was similar in stable angina and NSTEMI patients (P=0.6). IMR was significantly higher pre-PCI in STEMI compared with SA and NSTEMI (IMR STEMI, 36.51 versus IMR NSTEMI, 22.73 [P=0.01] versus IMR SA, 18.26 [P<0.0001]). However, there was no significant difference in IMR pre-PCI between NSTEMI and SA (IMR NSTEMI, 22.73; IMR SA, 18.26 [P=0.1]). Conclusions-The vasodilatory capacity of the microcirculation is preserved in selected patients with NSTEMI. The clinical use of fractional flow reserve in the culprit vessel may be preserved in selected patents with NSTEMI.