Association between Smoking Habit Changes and the Risk of Myocardial Infarction in Ischemic Stroke Patients: A Nationwide Cohort Study.

Background: Smoking is a well-known risk factor for cardiovascular diseases, including myocardial infarction (MI) and ischemic stroke (IS). While the relationship between smoking and the risk of cardiovascular diseases is established, the impact of changing smoking habits post-IS on the risk of subsequent MI remains unclear. This study aims to elucidate the effects of alterations in smoking behavior following an IS diagnosis on the likelihood of experiencing an MI.

Methods: Utilizing data from the Korean National Health Insurance Services Database, this nationwide population-based cohort study included 199,051 participants diagnosed with IS between January 2010 and December 2016. Smoking status was categorized based on changes in smoking habits before and after IS diagnosis. The association between changes in smoking behavior and the risk of subsequent MI was analyzed using multivariable Cox proportional hazard regression models.

Results: During a median follow-up of 4.17 person-years, a total of 5,734 (2.88%) patients were diagnosed with MI after IS. Smoking quitters (2.93%) or former smokers (2.47%) have a similar or lower rate of MI than the average, even if they have smoked cigarettes, while sustained smokers (3.46%) or new smokers (3.81%) have much higher rates of MI. Among sustained and new smokers, the risk of incident MI was significantly higher than never smokers (new smoker adjusted HR [aHR]: 1.496, 95% CI: 1.262-1.774; sustained smoker aHR: 1.494, 95% CI: 1.361-1.641). Also, among the study participants, approximately two-thirds continued smoking after their IS diagnosis.

Conclusion: Changing smoking habits after an IS diagnosis significantly influences the risk of subsequent MI. Specifically, continuing or starting to smoke after an IS diagnosis is associated with a higher risk of MI. These results underscore the importance of targeted smoking cessation interventions for stroke patients to reduce the risk of subsequent MI.