In a recent retrospective study published in the Journal of Interventional Cardiology, results indicate that loading of third-generation P2Y12 inhibitors before primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI) was linked with a decrease in the index of microcirculatory resistance.

In the study involving 160 STEMI patients, the average age was 56±11 years with 88.1% men. The index of microcirculatory resistance (IMR) was measured using a pressure sensor/thermistor-tipped guidewire immediately after primary PCI. High IMR was defined as values ≥66th percentile of IMR in enrolled patients (IMR >30.9 IU).  

The researchers noted that all 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. The researchers found that clinical factors for Killip class (P = .006), postponed hospitalization from symptom onset (P = .004), peak troponin-I level (P = .042), and multivessel disease (P = .003) were correlated with elevated IMR. They also indicated that attaining final thrombolysis in myocardial infarction myocardial perfusion grade 3 had a propensity to be linked with low IMR (P = .119), while the presence of distal embolization was substantially linked with high IMR (P = .034). With regard to therapeutic strategies that involved adjusting clinical and angiographic factors associated with IMR, preloading of third-generation P2Y12 inhibitors correlated with decreasing IMR value (Beta = 10.30, P <.001). 

Researchers also noted that at follow-up, seven patients were lost. Among the remaining 153 patients, 11.1% had major advanced cardiac events and three patients had cardiovascular death, all of whom had elevated IMR (P = .038). Instances of heart failure, nonfatal myocardial infarction, stroke, target lesion revascularization, stent thrombosis, or major bleeding did not vary between patients with high versus low IMR. 

After adjusting for covariates, the only effective therapeutic strategy for lowering IMR after STEMI was the preloading of third-generation P2Y12 inhibitors (P <.013). Jang et al indicated that mechanical therapeutic strategies, including stent diameter/length, preballoon dilatation, direct stenting, and thrombectomy, were not linked with low IMR value (all P >.05), and postballoon dilatation was correlated with elevated IMR (Beta = 8.30, P = .020). 

In their conclusion, Jang et al noted, “Mechanical 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. 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.”
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