Acute myocardial infarction: association with time since stopping smoking in Italy. GISSI-EFRIM Investigators. Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto. Epidemiologia dei Fattori di Rischio dell'Infarto Miocardico.

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Abstract
STUDY OBJECTIVE--The study aimed to investigate the relationship between years since stopping smoking and the risk of acute myocardial infarction. DESIGN--This was a hospital based, multicentre, case-control study conducted in Italy between September 1988 and June 1989 within the framework of the GISSI-2 clinical trial. SETTING--Over 80 coronary care units in various Italian regions participated. SUBJECTS--A total of 916 incident cases of acute myocardial infarction, below age 75 years, and with no history of ischaemic heart disease, and 1106 control subjects admitted to the same hospitals for acute, non-neoplastic, cardiovascular or cerebrovascular conditions that were not known or suspected to be related to cigarette smoking took part in the study. MAIN OUTCOME MEASURES AND RESULTS--Measures were relative risk (RR) estimates of acute myocardial infarction according to the time since stopping smoking and adjusted for identified potential confounding factors. Compared with never smokers, the multivariate RRs were 1.6 (95% confidence interval (CI) 0.8,3.2) for subjects who had given up smoking for one year; 1.4 (95% CI 0.9,2.1) for those who had stopped for two to five years; 1.2 (95% CI 0.7,2.1) for six to 10 years; and 1.1 (95% CI 0.8,1.8) for those who had not smoked for over 10 years. The estimated RR for current smokers was 2.9 (95% CI 2.2,3.9). The risks of quitters were higher for heavier smokers and those below age 50 years, while no difference emerged in relation to the duration of smoking, sex, and other risk factors for myocardial infarction. CONCLUSIONS--These results indicate that there is already a substantial drop in the risk of acute myocardial infarction one year after stopping. The risk in ex-smokers, however, seemed higher (although not significantly) than that of those who had never smoked, even more than 10 years after quitting. This could support the existence of at least two mechanisms linking cigarette smoking with acute myocardial infarction--one involving thrombogenesis or spasms that occurs over the short term, and another involving atherosclerosis that is a long term effect.