Influence of previous aspirin treatment and smoking on the electrocardiographic manifestations of injury in acute myocardial infarction

Objective-To examine demographic and clinical characteristics of patients w ith acute myocardial infarction in order to identify factors affecting the electrocardiographic evolution of injury. Methods-Prospective cohort study of 1399 consecutive patients with a first myocardial infarction. Baseline clinical data associated with ST elevation and Q wave development were identified and 12 month survival was estimated. Results-Smoking had complex effects on the evolution of injury, increasing the odds of ST elevation (odds ratio (OR) 1.61; 95% confidence interval (CI ) 1.08 to 2.36), but reducing the odds of Q wave development (OR 0.69, 95% CI 0.49 to 0.96). The effects of previous aspirin treatment were more consi stent with reductions in the odds of ST elevation (OR 0.57, 95% CI 0.35 to 0.94) and Q wave development (OR 0.53, 95% CI 0.34 to 0.84). ST elevation a nd Q wave development were both associated with an adverse prognosis, with estimated 12 month survival rates of 80.6% (95% CI 78.2% to 83.1%) and 80.0 % (95% CI 77.5% to 82.5%), respectively, compared with 86.5% (95% CI 81.2% to 91.9%) and 89.9% (95% CI 86.2% to 93.7%) for patients without these ECG changes. Conclusions-The thrombogenicity of the blood may be a major determinant of infarct severity. Smoking increases thrombogenicity and the likelihood of S T elevation, but because coronary occlusion is relatively more thrombotic i n smelters, responses to both endogenous and exogenous thrombolysis are bet ter, reducing the risk of Q wave development. Previous aspirin treatment re duces thrombogenicity, protecting against ST elevation and Q wave developme nt.