Higher Neutrophil Counts Associated with Poorer Outcomes Following MI

Higher baseline neutrophil counts in patients undergoing fibrinolytic therapy following ST-elevation myocardial infarction (STEMI) are associated with worse angiographic findings, higher mortality, and a diminished response to clopidogrel, according to a new study.

Researchers from Brigham and Women's Hospital (Boston, MA, USA) measured baseline neutrophil count in 2865 patients participating in a randomized trial of clopidogrel versus placebo in STEMI patients undergoing fibrinolysis. Angiography was performed at 2-8 days following enrollment. Analyses were adjusted for demographics, time from symptom onset, Killip class, peak Creatine Kinase–MB (CK-MB), and therapies received. The primary composite endpoint was thrombolysis in myocardial infarction (TIMI) flow grade 0/1, or death, or MI prior to angiography.

The study results showed that a higher baseline neutrophil count was directly related to the risk of cardiovascular death in the first 30 days following MIi, ranging from 1.4% for patients with neutrophil counts in the lowest quartile to 7.4% for those in the highest quartile. Higher baseline neutrophil counts were also independently associated with significantly higher risk of congestive heart failure (CHF), lower likelihood of complete ST-segment resolution following fibrinolytic therapy, and lower odds of myocardial microvascular perfusion at the time of angiography. The study also found that patients with baseline neutrophil counts above the median derived less benefit from clopidogrel treatment than did those with lower neutrophil counts. Clopidogrel reduced the odds of the primary composite endpoint by 54% in patients with lower neutrophil counts, but only by 17% in patients with higher neutrophil counts. The study was published in the April 2008 edition of the European Heart Journal.

"We were initially surprised to see that those patients with a lower baseline neutrophil count were those who appeared to have the greater benefit from adjunctive therapy with clopidogrel,” said lead author Michelle O'Donoghue, M.D. "This finding is not immediately intuitive since pathways between thrombosis and inflammation are widely overlapping.”

"We believe the current analysis confirms a strong and independent association between neutrophil count and the risk of death and CHF in a very large population of patients with STEMI undergoing fibrinolysis,” concluded Dr. O'Donoghue. "The current study also provided us with the unique opportunity to examine the association between cell count and angiographic outcomes in the largest angiographic dataset for this study population to date.”


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