By Michael H. Crawford, MD
Synopsis: A large, nationwide South Korean study of smokers undergoing percutaneous coronary intervention (PCI) has shown that electronic cigarette use and smoking cessation resulted in similarly lower subsequent major adverse cardiac events compared to continued smoking.
Source: Kang D, Choi KH, Kim H, et al. Prognosis after switching to electronic cigarettes following percutaneous coronary intervention: A Korean nationwide study. Eur Heart J. 2025;46(1):84-95.
Switching from combustible (C) cigarettes to electronic (E) cigarettes has been shown to improve vascular function in patients with coronary artery disease, but the effect of this intervention on cardiovascular outcomes in smokers following percutaneous coronary intervention (PCI) is unknown. Thus, these investigators from South Korea used the nationwide database from the National Health Insurance Service (NHIS) biannual evaluations of all Koreans to identify 216,566 adults who underwent PCI between 2018 and 2021, of whom 38,716 (26%) were smokers.
Among these patients, 22,787 had a health screening within three years after their PCI. Patients with cancer or stroke diagnosed before the study date were excluded. Also, to reduce the effect of additional events on smoking habits, those who developed acute myocardial infarction (MI) or underwent further revascularization before the post-PCI screening evaluation were excluded. In addition, to minimize reverse causality, those who died within the first three months post-PCI were excluded.
The final population of 17,973 patients were smokers as assessed by a self-reported questionnaire within three years before their PCI and were evaluated within three years post-PCI. Based on the post-PCI evaluation questionnaire, the patients were classified as smokers, quitters, E-cigarette users, or users of both E- and C-cigarettes.
The primary outcome was major adverse cardiac events (MACE) defined as all-cause death, MI, and repeat revascularization. Those free of MACE were followed for at least one year. C-cigarette use continued in 50% of the patients, 41% successfully quit smoking, and 9% switched to E-cigarettes. After a 2.4-year median follow-up, MACE was lower in the E-cigarette group (10%) and quitters (13%) than among the continued smokers (17%).
With C-cigarette users as the reference, the adjusted hazard ratio (HR) for E-cigarette switchers was 0.82 (95% confidence interval [CI], 0.69-0.98) and 0.87 (0.79-0.96) for quitters. Compared to dual C- and E-cigarette users, exclusive E-cigarette use was associated with lower MACE (HR, 0.71; 95% CI, 0.51-0.99). The authors concluded that E-cigarette use resulted in similar reductions in MACE as quitters compared to continued C-cigarette use in smokers who underwent PCI.
Commentary
E-cigarettes are believed to be a safer alternative to C-cigarettes for those who cannot quit smoking. However, the aerosols produced by these devices contain propylene glycol, glycerin, and particulate matter that can induce oxidative stress and inflammation, and impair vasodilation. These effects could be deleterious in patients with atherosclerotic cardiovascular disease. Thus, this first study of cardiac outcomes in post-PCI patients is of interest.
Half the study group continued smoking and 41% successfully quit. E-cigarettes were used by 9%. The researchers showed that E-cigarette users, after a 2.4-year median follow-up, had the lowest rate of MACE, followed by quitters. The highest rate of MACE was in the group that continued smoking, but the differences were small (4% to 7% difference). The researchers opined that E-cigarettes were a reasonable alternative for smokers post-PCI who could not quit smoking.
There are several limitations to this study. It was a retrospective observational study, so unmeasured confounding could be present, and causation cannot be inferred. Smoking behavior was self-reported and could be subject to recall bias and misclassification. We do not know if any changes in smoking status were made after the one post-PCI visit. There was no information regarding the use of other smoking cessation aids, such as nicotine and other drugs. Almost all the subjects in the study were men, so the results cannot confidently be applied to women. Finally, there was no information on biomarkers that may have informed the mechanism of the reported benefit of E-cigarettes.
Most health organizations recommend using E-cigarettes in those who cannot quit smoking, but only as part of a smoking cessation program that could involve other drugs and counseling. It is unclear in the Korean study whether there were any other interventions, but the low rate of quitting smoking suggests otherwise. Many are hesitant to recommend E-cigarettes because they could encourage C-cigarette use in nonsmokers. Some have opined that E-cigarettes, instead of an exit drug, have become a gateway drug to smoking, especially in young individuals. These concerns aside, E-cigarette use in high-cardiac risk subjects who cannot quit despite attending smoking cessation programs appears to be a relatively safe alternative. However, cessation of smoking and vaping should be the longer-term goal.
Michael H. Crawford, MD, is Professor of Medicine and Consulting Cardiologist, University of California Health, San Francisco.