Acute myocardial infarction - consequences of new treatment modalities and smoking status : Observations from two prospective cohort studies

Abstract

This thesis is based upon a comparison of two cohorts of consecutive patients admitted with chest pain suspected to be acute coronary syndrome (ACS) in 2003 (n = 755) and 2006 (n = 934). In 2003 the predominant reperfusion strategy for patients with ST-segment elevation myocardial infarction (STEMI) was prehospital fibrinolysis. Patients with non-ST-segment elevation myocardial infarction (NSTEMI) and unstable angina pectoris (UAP) were managed with an ischemia-driven approach for invasive procedures. In September 2005, following the introduction of new European guidelines on invasive treatment, an early invasive strategy was implemented. Patients with STEMI were transported 100 km to Rikshospitalet University Hospital in Oslo for primary percutaneous coronary intervention. Those with NSTEMI or UAP were routinely transported for invasive management within 48-72 hours in the absence of contraindicating factors. In 2003, 48% of patients qualified for a diagnosis of ACS as compared with 39% in 2006 (p<0.001). In both cohorts NSTEMI patients were older and had greater co-morbidity than patients with STEMI. From 2003 to 2006 the incidence rate for STEMI decreased from 100 to 77 cases per 100,000 personyears, whereas for NSTEMI this decrease was 147 to 143 cases per 100,000 person-years. The oneyear all-cause mortality for NSTEMI decreased from 32% in 2003 to 19% (p = 0.002) in 2006. The corresponding figures for STEMI were 20% and 11% (p = 0.086). After adjustment for age, sex, previous acute myocardial infarction (AMI), previous stroke, diabetes, smoking status, previous left ventricular dysfunction and serum creatinine on admission, patients with AMI in the 2006 cohort had a significantly lower risk for one-year mortality than those managed for AMI in 2003 (hazard ratio 0.54, 95% confidence interval 0.38-0.78, p = 0.001). In a post-hoc analysis, smokers with NSTEMI seemed to be a subset of patients with a particular survival benefit of early invasive management, but smoking on admission was still an independent predictor of death. In a systematic literature search on studies addressing the occurrence of the “smoker’s paradox” in ACS (i.e. that smokers have lower adjusted case fatality than non-smokers), we found that studies supporting the existence of the paradox were from the pre-thrombolytic and thrombolytic era. No studies of patients with contemporary management found support for the paradox. The “smoker’s paradox” most probably represents a historical phenomenon without relevance for today’s practice. In conclusion, the implementation of routine early invasive management for unselected patients with AMI was followed by a 41% reduction in one-year total mortality. For NSTEMI this survival benefit was especially pronounced for smokers, but smoking was still an independent predictor of one-year mortality.