South Korea Study Evaluates Role of Smoking on Outcomes After PCI

September 27, 2023—The European Society of Cardiology (ESC) announced the publication of a study that found patients who quit smoking after undergoing percutaneous coronary intervention (PCI) for narrowed arteries have similar outcomes as nonsmokers during 4 years of follow-up after the procedure. However, if they had been heavy, long-term smokers, no improvement was seen.

According to ESC, the study of 74,471 patients who underwent PCI between 2009 and 2016 is the first, large population-based study to examine the impact of smoking on cardiovascular outcomes, such as death, heart attack, and stroke, since drug-eluting stents were first approved for use in PCIs in Europe in 2002 and in the United States in 2003.

The study was led by Professor Jung-Kyu Han, MD, with Seoul National University Hospital in Seoul, South Korea. You-Jeong Ki, MD, et al published the findings online in European Heart Journal.

According to ESC, the investigators analyzed data from the Korean National Health Insurance System nationwide database to investigate patient outcomes during 4 years after PCI. They looked at the rates of major adverse cardiovascular and cerebrovascular events (MACCE), which include heart attacks, strokes, repeated procedures to widen arteries, and deaths from any cause.

Additionally, the investigators collected information on factors that could affect the results, such as medications and socioeconomic status, as well as information on whether or not the patients were current smokers, never-smokers, or ex-smokers.

They found that during 4 years of follow-up, current smokers had a 19.8% higher rate of MACCE than patients who had never smoked; ex-smokers had a comparable rate as never-smokers.

The investigators also analyzed data from 31,887 patients with information on their smoking habits before and after PCI to further assess the impact of quitting smoking after PCI. They assessed how much patients smoked by placing them in four groups: < 10 pack years, 10-19 pack years, 20-29 pack years, and ≥ 30 pack years. “Pack years” indicates a person’s accumulated exposure to tobacco. This was reached by multiplying the number of cigarettes smoked a day by the number of years the person had smoked.

According to ESC, the investigators found that quitters who stopped smoking after PCI and who had smoked < 20 pack years had a comparable rate of MACCE as people who had never smoked. However, those who had smoked > 20 pack years before quitting had a 20% higher rate of MACCE, similar to the rate for persistent smokers.

“Patients who quit smoking after undergoing PCI, with a cumulative smoking exposure of 20 pack years, had cardiovascular risks similar to those of nonsmokers,” commented Prof. Han in the ESC press release. “Notably, this finding was observed within a relatively short interval after smoking cessation—a median of 628 days between pre- and post-PCI-health checkups.”

The ESC press release noted that one of the reasons Prof. Han and colleagues conducted the study was because most previous research did not consider changes in smoking habits before and after PCI, leaving the effects of quitting smoking after PCI largely unexplored.

Prof. Han continued, “From the beginning of this study, my colleagues and I, as clinical researchers, suspected that there could be a threshold for irreversible harm resulting from smoking. Yet, the revelation that this threshold lies around 20 pack years—not like just 5 or 10 pack years—was an encouraging discovery. It suggests that smokers undergoing PCI, who have not reached a cumulative smoking exposure of 20 pack years, may still have an opportunity to evade the lasting detrimental effects on their cardiovascular outcomes caused by smoking.”

He stated further, “Patients undergoing PCI should be encouraged to quit smoking as soon as possible, and smoking cessation may improve their cardiovascular outcomes even within a relatively short period of time. This emphasizes the paramount importance of clinicians’ attention to their patients’ smoking status, along with the combined efforts of clinicians, patients, and policymakers in promoting smoking cessation.”

The study also contributes to debunking what is known as the “smokers’ paradox”;some previous studies seemed to suggest that smokers who had a heart attack had a better prognosis after PCI, advised the ESC press release.

Prof. Han explained, “A subgroup analysis of our study, which included 28,266 patients with myocardial infarction, refuted this paradox by demonstrating that current smokers had a significantly higher rate of adverse cardiovascular events compared to nonsmokers. Notably, the positive impact of smoking cessation in patients with myocardial infarction was not as pronounced as in the overall study population. This may be due to insufficient numbers of patients and events in the subgroup analyses, or because the synergistic effects of heart attack and smoking resulted in more irreversible damage to the myocardium.”

The ESC press release summarized the study’s strengths and weaknesses as follows:

• A strength is that the study is based on the Korean National Health Insurance System, which covers 97% of the Korean population and is one of the most comprehensive sources of data on people’s health.
• Limitations include that whether or not a person smoked and how much a person smoked was self-reported in a questionnaire and may not reflect the true status, other unknown factors might affect the findings, the findings cannot be generalized to all races, and pack years cannot differentiate between the impact of long-term smoking at low doses from short-term smoking at high doses.