A tool for predicting the outcome of reperfusion in ST-elevation myocardial infarction using age, thrombotic burden and index of microcirculatory resistance (ATI score).

Aims: Restoration of effective myocardial reperfusion by primary percutaneous coronary intervention (PPCI) in patients with ST-elevation myocardial infarction is difficult to predict. A method to assess the likelihood of a suboptimal response to conventional pharmacomechanical therapies could be beneficial. We aimed to derive and validate a scoring system that can be used acutely at the time of coronary reopening to predict the likelihood of downstream microvascular impairment in patients with STEMI. Methods and results: A score estimating the risk of post-procedural microvascular injury defined by an index of microcirculatory resistance (IMR) >40 was initially derived in a cohort of 85 STEMI patients (derivation cohort). This score was then tested and validated in three further cohorts of patients (retrospective [30 patients], prospective [42 patients] and external [29 patients]). The ATI score (age [>50=1]; pre-stenting IMR [>40 and <100=1; >= 100=2]; thrombus score [4=1; 5=3]) was highly predictive of a post-stenting IMR >40 in all four cohorts (AUC: 0.87; p<0.001-derivation cohort, 0.84; p=0.002-retrospective cohort, 0.92; p<0.001-prospective cohort and 0.81; p=0.006-external cohort). In the whole population, an ATI score >= 4 presented a 95.1% risk of final IMR >40, while no cases of final IMR >40 occurred in the presence of an ATI score <2. Conclusions: The ATI score appears to be a promising tool capable of identifying patients during PPCI who are at the highest risk of coronary microvascular impairment following revascularisation. This procedural risk stratification has a number of potential research and clinical applications and warrants further investigation.