Overall, the study’s primary outcome of major adverse cardiovascular and cerebrovascular events (MACCE)—a composite of all-cause mortality, myocardial infarction, coronary revascularization and stroke four years after PCI—was seen in 19.3% of patients. The outcome was 19.8% more likely among patients who continued smoking after PCI compared to nonsmokers—and a similar difference was seen between current smokers and ex-smokers.

Perhaps the biggest takeaway from the team’s analysis was that patients who stopped smoking after PCI and had accumulated less than 20 “pack years” in their lives had cardiovascular outcomes comparable to patients who never smoked at all. However, when a patient had accumulated more than 20 pack years—a sign that they were a heavy smoker for a long period of time—it became harder for them to reverse the harm smoking had done to their health. These patients had a 20% higher MACCE rate than non-smokers, comparable to current smokers.

“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,” senior author Jung-Kyu Han, an internal medicine specialist with Seoul National University Hospital in South Korea, said in a prepared statement. “Yet, the revelation that this threshold lies around 20 pack years—not just five 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.”

Click here to read the full study in European Heart Journal, a publication of the European Society of Cardiology.