Stroke is one of the leading causes ofdisability and death, and its prevalence and morbidity tend to increase as we enteran aging society. It is also known that myocardial infarction (MI) occurs notinfrequently after ischemic stroke (IS) and both diseases share risk factorsand similar strategies for secondary prevention. There are continuousdevelopments in secondary prevention methods for MI and IS, emphasizing usingmedication and lifestyle modification, including smoking cessation. However, whetherchanges in smoking habits before and after the diagnosis of IS affects the riskfor myocardial infarction remain unclear. Thus, we aimed to investigate theimpact of smoking habit change on the risk of myocardial infarction in theischemic stroke population using the Korean National Health InsuranceServices(K-NHIS) Database.

The K-NHIS cohort used for this study consisted of people who underwent a nationwide health checkup between January 2010 and December 2016. We identified 1,005,879 patients newly diagnosed with acute IS in this period. After exclusion according to the following criteria,199,051 patients with IS with no history of MI were included in the study (Figure1).The main exposure was the status of the smoking habit changes. Study participants were categorized by changes in smoking status before and after IS diagnosis. We categorized the patients into five groups: never-smokers, former smokers, smoking quitters after IS, new smokers, or current(sustained) smokers. Never-smokers were defined as participants who never smoked. Former smokers were subjects who quit smoking before the first health examination and remained non-smoking state at the next health examination. Smoking quitters after IS are those who were current smokers in the first health examination but became ex-smokers after IS diagnosis at the following health examination. New smokers were current smokers in the second examination while responded as never smokers in the first examination. And current smokers continuously kept smoking from the first and second health examinations.

199,051 patients with IS with no history of MI (mean ischemic stroke age 64.2±10.5 years; male, 45.1%) were finally included in the diagnosis. Median follow-up duration was 4.17 person-years(interquartile range 2.61-5.93) and 63,868 (32.1%) patients had a smoking history; median pack-years was 24.03. Patients in the never-smokers group were more likely to be female (78.49%), older, non-diabetic, and consume less alcohol. Out of 26,463 patients who were sustained smokers before the diagnosis of ischemic stroke, 23,472 (85.2%) continued to smoke even after the diagnosis of ischemic stroke. During a median follow-up of 4.17person-years, a total of 5,734 (2.88%) patients were diagnosed with MI afterIS. The rate of IS events tends to be higher in smokers than in non-smokers. Also, smoking quitters (2.93%) or former smokers (2.47%) have a similar or lower rate than the average, even if they have smoked cigarettes, while those who continue to smoke (3.46%) or new smokers (3.81%) have a much higher rate of MI. The results that smoking habit affects MI after IS remained significant after adjusting for covariates including age, sex, alcohol intake, physical activity, economic status, history of hypertension, diabetes, dyslipidemia, and CKD, in the group of new and current smokers when compared to never-smokers. (new smoker adjusted HR [aHR]: 1.496, 95% CI 1.262-1.774; current smoker aHR 1.494,95% CI 1.361-1.641). This result remained consistent after adjusting the number of cigarettes (new smoker aHR 1.375, 95% CI 1.151-1.642, current smoker aHR 1.344, 95% CI 1.202-1.504).The Kaplan-Meier curve in the overall population shows that the difference in the incidence of MI is significantly different between never-smokers and smoking quitters after IS, and those who continue to smoke or start smoking (Figure 2). While the Kaplan-Meier curve in men is not significantly different from the curve in the overall population, whereas the curve for women who quit smoking after an ischemic stroke does not differ significantly compared to those who continue to smoke or start smoking.

This study is conducted with the largest population regarding the reports on the incidence of MI in a single race‐ethnic group over a relatively long period of time after IS using a KNHIS big database. In conclusion, smoking quitters or former smokers have a similar or lower rate of MI after IS than the average. Otherwise, current and new smokers had a significantly higher risk of incident myocardial infarction after ischemic stroke. Our results have a crucial clinical suggestion that physicians should actively advise patients to stop smoking, not just to prevent stroke recurrence but to reduce the risk of myocardial infarction.