Cardiovascular risk of smoking in patients without obstructive coronary artery disease

Background Smoking increases risk of cardiovascular disease by increasing atherosclerosis and thrombogenesis. Purpose We examined the impact of smoking on cardiovascular risk in patients without obstructive coronary artery disease (CAD) after coronary angiography. Methods We conducted a cohort study in patients without obstructive CAD examined by coronary angiography from 2003–2016 in Western Denmark and no previous history of MI or coronary revascularization. Smokers were compared with non-smokers (former/never smokers) and with an age- and sex matched comparison group sampled from the Western Denmark general population without a history of CAD. The main outcome was myocardial infarction (MI). Other outcomes were ischemic stroke and death. Maximum follow-up was 10 years. Adjusted hazards ratios (aHRs) were estimated using Cox regression. Results We identified 46,462 patients without obstructive CAD, of whom 10,879 (23%) were active smokers and 35,583 (77%) were non-smokers at the time of angiography. Patients were matched with 234,648 individuals from the general population with no previous MI or coronary revascularization. Median follow-up was 7.0 years. Smokers had higher risks of MI (aHR 1.65, 95% CI: 1.41–1.93), ischemic stroke (aHR 1.49, 95% CI: 1.28–1.74), and death (aHR 1.77, 95% CI: 1.67–1.87) compared to non-smokers undergoing CAG. As shown in the Figure, the MI risk increased immediately after start follow-up and the curves continued to diverge. Compared to the general population, smokers without obstructive CAD had a similar risk of MI (aHR 0.96, 95% CI: 0.83–1.10), but an increased risk of ischemic stroke (aHR 1.36, 95% CI: 1.19–1.56) and death (aHR 1.49, 95% CI: 1.41–1.56), while non-smokers had reduced risks of MI (aHR 0.57, 95% CI: 0.51–0.63), ischemic stroke (aHR 0.85, 95% CI: 0.78–0.93), and death (aHR 0.78, 95% CI: 0.75–0.81). Conclusions In patients without obstructive CAD by coronary angiography, active smoking was associated with a 65% increased 10-year risk of MI compared to non-smokers, suggesting a prothrombotic effect of smoking. Compared to a general population, with unknown CAD and smoking status, smokers examined by CAG had a similar or higher risk of cardiovascular events despite the absence of CAD, while non-smokers had a lower risk. Figure 1 Funding Acknowledgement Type of funding source: Public hospital(s). Main funding source(s): Department of Cardiology, Aarhus University Hospital