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

Selected in EuroIntervention by S. Brugaletta

S. Brugaletta reviews an article from EuroIntervention on a tool using age, thrombotic burden and index microcirculatory resistance to predict the outcome of reperfusion.

References

Authors

De Maria GL, Fahrni G, Alkhalil M, Cuculi F, Dawkins S, Wolfrum M, Choudhury RP, Forfar JC, Prendergast BD, Yetgin T, van Geuns RJ, Tebaldi M, Channon KM, Kharbanda RK, Rothwell PM, Valgimigli M, Banning AP

Reference

EuroIntervention. 2016 Nov 20;12(10):1223-1230

Published

November 2016

Link

Read the abstract

My Comment

What is known 

Prompt revascularisation using primary percutaneous coronary intervention (PPCI) has reduced in-hospital and six-month mortality for patients with ST-elevation myocardial infarction (STEMI). However, even prompt opening of the epicardial coronary artery may not restore optimal myocardial reperfusion in the infarcted territory. This condition, referred to as slow flow or no-reflow, is a reflection of residual coronary microvascular injury. The index of microcirculatory resistance (IMR) is a parameter that is readily measurable in the catheterisation laboratory during the revascularisation procedure and reflects the status of coronary microvasculature when measured at the end of PPCI and predicts the final infarct size and extent of microvascular obstruction observed by cardiac magnetic resonance imaging (MRI). A post-procedural IMR >40 predicts mortality and/or readmission for heart failure at one year post PPCI. The present study aimed to derive and validate a simple risk score to predict a final IMR value greater than 40, in a large population of STEMI patients.

Major findings 

  • 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.

My comment

This paper analyses the problem of microvascular obstruction after primary PCI, which has been related to long-term outcome. The authors developed a simple score in order to predict microvascular obstruction. Age, thrombus score and pre-stenting IMR are the variables considered. The paper is interesting because it applies the TRIPOD statement, which should be used when a score is developed. Moreover, it potentially allows identification of those high-risk patients who could benefit from additional or alternative therapeutic strategies.

However, it is noteworthy that whereas age and thrombus score are easy to measure, pre-stenting IMR would require a specific evaluation before implanting stent, which is not user-friendly. This limits the wide applicability of this score. A successful score should be simply to calculate in seconds and would not require anything out of clinical practice.

Does someone have a suggestion on how to identify those STEMI patients at risk of microvascular obstruction and how to treat them?

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