Smokers are at risk for sudden cardiac death, but quitting can reduce that risk over time to levels seen among those who never smoked, an analysis of the Nurses’ Health Study showed.

Through a follow-up of 30 years, the risk of sudden cardiac death was significantly greater among smokers when compared with those who never smoked (HR 2.44, 95% CI 1.80 to 3.31), according to Roopinder Sandhu, MD, of the University of Alberta in Edmonton, and colleagues from Brigham & Women’s Hospital and the Harvard School of Public Health, Boston.

Past smokers also had an elevated risk overall (HR 1.40, 95% CI 1.10 to 1.79), although it steadily declined with an increasing duration of cessation, reaching a level of risk within 20 years that was comparable to risk of those who never smoked, the researchers reported online in Circulation: Arrhythmia and Electrophysiology.

“Our data reinforces the important concept that sudden cardiac death risk associated with cigarette smoking is modifiable,” they wrote, adding that “this suggests efforts to prevent sudden cardiac death among women should include aggressive strategies for smoking cessation.”

Although smoking is a well-known risk factor for sudden cardiac death and coronary heart disease, few studies have examined the relationships between risk and quantity of cigarettes smoked, smoking duration, and smoking cessation. Sandhu and colleagues explored those issues using data from the Nurses’ Health Study on 101,018 women without known coronary heart disease, stroke, or cancer at baseline in 1980; 29.1% were current smokers, 26.4% were past smokers, and 44.5% had never smoked at baseline. The researchers accounted for changes in smoking status during the study. Through 2010, there were 351 sudden cardiac deaths confirmed through medical records, autopsy reports, and interviews with family members. In addition to smoking status, both quantity of cigarettes smoked each day and smoking duration were associated in a linear fashion with sudden cardiac death risk after adjustment for several coronary heart disease risk factors, including age, diabetes, hypertension, hypercholesterolemia, body mass index, alcohol use, physical activity, menopausal status and postmenopausal hormone use, use of aspirin, multivitamins, and vitamin E, and family history of MI (P<0.0001 for both trends). Even a small-to-moderate amount of smoking -- one to 14 cigarettes a day -- was associated with a higher risk compared with never smoking (HR 1.84, 95% CI 1.16 to 2.92). Every 5 years of continued smoking was associated with an 8% greater risk of sudden cardiac death (HR 1.08, 95% CI 1.05 to 1.12). Quitting, however, was associated with a declining risk. Within 20 years of quitting, the risk of sudden cardiac death -- compared with continuing smokers -- was similarly reduced in both past smokers (HR 0.45, 95% CI 0.31 to 0.64) and those who had never smoked (HR 0.40, 95% CI 0.30 to 0.54). That reduction in risk after quitting was more rapid among the women who did not develop coronary heart disease during follow-up compared with those who did (less than 5 years versus 15 to 20 years). In women with coronary heart disease, the authors explained, "severe and/or vulnerable coronary atherosclerotic plaques and resultant myocardial fibrosis and scarring may confer a residual sudden cardiac death risk which persists for some time after smoking cessation." "In contrast," they wrote, "the more immediate ... risk reduction observed among women without coronary heart disease may, in part, be explained by alleviation of acute pro-arrhythmic effects of nicotine such as reductions in catecholamine release, alteration of potassium handling, and lowering of ventricular fibrillation threshold caused by transient enhanced platelet adhesion." The researchers acknowledged some limitations of the study, including possible misclassification of cigarette consumption based on self-report, possible error in determining sudden cardiac death, the lack of information about the severity of coronary heart disease events during follow-up, and potential residual or unmeasured confounding. In addition, the study population was mostly white, female nurses, and the findings may not apply to other groups.