Eosinopenia is considered a surrogate of inflammation in several disease settings. Following ST-segment elevation myocardial infarction, eosinopenia is presumed to be a marker of infarct severity. We sought to study the relationship between eosinopenia and infarct severity and how this relationship determined the long-term outcomes following ST-segment elevation myocardial infarction.

Six hundred and six consecutive patients undergoing primary percutaneous coronary interventions from a large volume single center were enrolled. Low eosinophil count was defined as < 40 cells/mL from samples within 2 hours after reperfusion. Primary endpoint was defined as composite of death, myocardial infarction, stroke, unplanned revascularization, and readmission for heart failure over 3.5 years’ follow-up.

Sixty-five percent of the patients had eosinopenia. Patients in the low eosinophil group had larger infarct size as measured by troponin value (2934 vs 1177 ng/L, P < .001) and left ventricle systolic function on echocardiography (48% vs 50%, P = 0.029). There was a weak correlation between eosinophil count and both troponin (r = -0.25, P < 0.001) and ejection fraction (r = 0.10, P = .017). The primary endpoint was higher in eosinopenic patients (28.8% vs. 20.4%; hazard ratio [HR] 1.49, 95% confidence interval [CI] 1.05 to 2.13, P = .023). A discordance between eosinopenia and severe left ventricle systolic dysfunction was observed in 55.6% of cases. Compared with normal count, eosinopenia was associated with worse clinical outcomes in patients with non-severe left ventricle dysfunction (24.1% vs 16.2%; HR 1.58, 95% CI 1.01 to 2.45, P = .044) but not in those with severe left ventricle dysfunction (42.3% vs. 38.9%; HR 1.10, 95% CI 0.59 to 2.03, P = .77) (P < .01 for interaction).

Eosinopenia is an easily determined marker that reflects worse clinical outcomes over long-term follow-up.