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Background Inflammation is an indicator of worse clinical outcomes following acute myocardial infarction. Eosinopenia was identified as a surrogate of inflammation in sepsis and obstructive airway disease. Whether this readily-available marker has any impact on long term outcomes following ST-segment elevation myocardial infarction (STEMI) is yet to be determined. Purpose We sought to study the incidence and relationship between eosinopenia and infarct severity and whether low eosinophil had impact on clinical outcomes following STEMI. Methods 606 consecutive STEMI patients undergoing primary PCI from a large volume single centre were enrolled. Low eosinophil count was defined as <40 cells/ml from samples within 2 -hours post reperfusion. Primary endpoint was defined as composite of death, MI, stroke, unplanned revascularisation, re-admission for heart failure over 3.5 years follow up. Results 65% of patients had eosinopenia. Patients in the low eosinophil group had larger infarct size as measured by troponin value [2934 vs. 1177ng/L, P<0.001] and left ventricle (LV) systolic function on echocardiography [48% vs. 50%, P=0.029]. Thehre was a modest correlation between eosinophil count and both troponin (r=−0.25, P<0.001) and ejection fraction (r=0.10, P=0.017). The primary endpoint was higher in eosinopenic patients (28.8% vs. 20.4%, HR 1.49, 95% CI 1.05 to 2.13, P=0.023) (Figure). The difference was mainly driven from higher percentage of unplanned revascularisations (8.2% versus 2.9%, P=0.012) (Table). Low eosinophil count was an independent predictor of adverse cardiovascular events, beyond infarct severity, in elderly, non-diabetic patients (HR 2.04, 95% CI 1.04 to 4.01, P=0.038). Incidence rate of major clinical Clinical characteristics Low eosinophil Normal eosinophil P value Long term clinical events 28.8% (112) 20.4% (42) 0.026 Long term mortality 14.1% (55) 11.1% (23) 0.31 Long term MI 6.9% (27) 4.9% (10) 0.32 Long term unplanned revascularisation 8.2% (32) 2.9% (6) 0.012 Long term re-admission CCF 6.7% (26) 4.9% (10) 0.37 Long term stroke 2.6% (10) 1% (2) 0.19 Conclusions Eosinopenia is a readily-available marker which was associated with a larger infarcts and worse clinical outcomes over long term follow up.

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