Loading of third-generation P2Y12 inhibitors before primary percutaneous coronary intervention for ST-segment elevation myocardial infarction (STEMI) was associated with a reduction in the index of microcirculatory resistance (IMR), according to a retrospective study published in the Journal of Interventional Cardiology.

Patients (n=160; mean age, 56±11 years; 88.1% men) who underwent PCI between 2009 and 2016 at Inha University Hospital in South Korea within 12 hours of experiencing STEMI, as assessed by the presence of myocardial ischemia with ST-segment elevation during electrocardiography examination, were included. ST elevation was defined as a new ST elevation at J point in 2 contiguous leads ≥2 mm in men and ≥1.5 mm in women. Patients were preloaded before primary PCI with 300 mg aspirin plus 600 mg clopidogrel, 180 mg ticagrelor, or 60 mg prasugrel. All patients underwent a transthoracic echocardiography within 24 hours of primary PCI.

Patients with high vs low IMR at admission differed significantly in age (60±11 vs 54±11 years, respectively; P =.001), symptom onset to hospital time (144 min vs 95 min, respectively; P =.003), symptom onset to balloon time (235 min vs 162 min, respectively; P =.001), left ventricle ejection fraction (44.7±6.8% vs 47.3±7.0%, respectively; P =.028), E/e’ (10.5 vs 9.8, respectively; P =.024), wall motion score index (1.7 vs 1.5, respectively; P =.040), creatine kinase peak (3102.0 IU/L vs 2020.0 IU/L, respectively; P =.028), and creatine kinase muscle/brain peak (289.4 vs 188.0, respectively; P =.010).

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During coronary angiography and physiologic assessment, patients with high vs low IMR differed significantly for the following factors: multivessel angiographic parameters (53.7% vs 30.2%, respectively; P =.006), thrombolysis in myocardial infarction myocardial perfusion (grade 2, 50.0% vs 17.0%, respectively; P <.001; grade 3, 46.3% vs 82.1%, respectively; P <.001), distal embolization (31.5% vs 8.5%, respectively; P <.001), mean transit time at rest (0.7 s vs 0.4 s, respectively; P <.001), hyperemia mean transit time (0.6 s vs 0.2 s, respectively; P <.001), coronary flow reverse (1.3 vs 1.8, respectively; P <.001), and corrected index of microcirculatory resistance (40.2 U vs 16.4 U, respectively; P <.001).

At follow-up, 7 patients were lost. Among the remaining 153 patients, 11.1% had major advanced cardiac events and 3 patients had cardiovascular death, all of whom had high IMR (P =.038). Instances of heart failure, nonfatal myocardial infarction, stroke, target lesion revascularization, stent thrombosis, or major bleeding did not differ between patients with high vs low IMR.

After adjusting for covariates, the only successful therapeutic strategy for reducing IMR after STEMI was the preloading of third-generation P2Y12 inhibitors (P <.013).

Study limitations include selection bias. In the univariate, but not in the multiple regression analysis, mechanical therapies (eg, larger stent diameter or shorter stent size) had a significant effect on reducing the IMR, which may be due to the choice of interventional approach decided by each individual physician.

“[M]echanical strategies were suboptimal in achieving myocardial salvage. Only preloading of third generation P2Y12 inhibitors was associated with low IMR value which represents a trend of [microvascular dysfunction] prevention in [patients with] STEMI,” noted the study authors. “Therefore, it is necessary to use third generation P2Y12 inhibitors according to the current guidelines, and novel procedural techniques should be developed to reduce [microvascular dysfunction] in patients with STEMI.”


Jang J H, Lee M J, Ko K Y, et al. Mechanical and pharmacological revascularization strategies for prevention of microvascular dysfunction in ST-segment elevation myocardial infarction: Analysis from index of microcirculatory resistance registry data. J Interv Cardiol. 2020;2020:5036396. doi:10.1155/2020/5036396