Meta-Analysis: As Smoking Increases, So Does Atrial Fibrillation Risk

By Thomas Crocker
Friday, December 7, 2018
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Risk for atrial fibrillation, the most common heart rhythm disorder, increases with every cigarette a person smokes per day, according to a meta-analysis of nearly 30 prospective studies.

Smoking is a well-established risk factor for cardiovascular disease, but an association between smoking and atrial fibrillation is less settled. Neither the CDC nor the Heart Rhythm Society names smoking as a risk factor for atrial fibrillation. Studies investigating a possible association have produced conflicting results.

Most researchers would agree that smoking is associated with atrial fibrillation risk, says Elsayed Z. Soliman, MD, Professor of Public Health Sciences at Wake Forest Baptist Medical Center and co-author of a 2017 study in the Journal of Cardiology that examines the relationship between smoking and atrial fibrillation risk. His research team concluded that smoking may affect atrial fibrillation risk through its influence on other risk factors, such as hypertension and obesity, and that variance in the strength of the smoking-atrial fibrillation association among subgroups in the 2017 study may help explain previous studies’ diverging results.

“[T]here was no association [between smoking and atrial fibrillation] when we adjusted for many confounders,” Dr. Soliman says. “When we adjusted only for age or sex, we saw an association, but when we adjusted for more confounders, the association disappeared. Once we started to look at differences between subgroups, we found the association was [stronger] in some groups compared to others. The association was stronger in younger people compared to older, and stronger in people with cardiovascular disease compared to those without. In black people, the association was significant, but not in whites.”

A Dose-Response Relationship

To shed more light on smoking’s effect on atrial fibrillation risk, Dagfinn Aune, PhD, Associate Professor at Bjørknes University College in Oslo, Norway, and a postdoctoral researcher at Imperial College London, and three colleagues conducted a systematic review of the literature and a meta-analysis of 29 cohort studies published through July 20, 2017.

The authors found a dose-response relationship between smoking and atrial fibrillation risk. Compared with smoking zero cigarettes per day, the relative risk for atrial fibrillation rose steadily when individuals smoked five, 10, 15, 20, 25 and 29 cigarettes per day. Smoking 10 cigarettes per day increased the relative risk of atrial fibrillation 14 percent, and smoking 10 pack-years — a pack-year is the number of cigarette packs smoked per day multiplied by the number of years a person has smoked — heightened the risk 16 percent. Compared with people who had never smoked, current smokers were 32 percent more likely to develop atrial fibrillation, and current and former smokers — so-called ever smokers — had a 21 percent higher risk. For former smokers, the relative risk was 9 percent.

“One important finding was the increased risk was substantially attenuated among former smokers, suggesting that much of the increased risk can be avoided simply by quitting smoking,” Aune says. “The relative risk increased 32 percent among current smokers but 9 percent among former smokers, suggesting that nearly three-quarters of the excess risk can be avoided by quitting smoking. Further studies need to look at the duration of smoking cessation in relation to atrial fibrillation to clarify if the risk decreases to the level of never smokers at some point.”

Like Dr. Soliman’s group, Aune and his co-authors believe smoking’s significant role in the development of several chronic diseases that increase atrial fibrillation risk may account for the association between smoking and atrial fibrillation. They also point to nicotine’s role in increasing resting heart rate, blood pressure and hypertension, among other factors, as elements that could contribute to the association.

More Evidence of Smoking’s Deleterious Effects

Aune acknowledges that smoking increases risk for atrial fibrillation relatively modestly compared with the increased risk smokers face for heart attack, stroke and aortic aneurysm, but he believes his group’s findings help fill in the picture of smoking’s overall effects on health.

Alvaro Alonso, MD, PhD, Associate Professor of Epidemiology at the Rollins School of Public Health at Emory University, who was not involved in the study, says it is important to expand understanding of smoking’s population-level impact, and studies like Aune’s help do that.

“I wouldn’t consider smoking as one of the main risk factors [for atrial fibrillation],” Dr. Alonso says. “We know other things, like hypertension and obesity, are much stronger predictors of atrial fibrillation and stronger risk factors for it, but that does not diminish the importance of smoking cessation because [smoking] is a risk factor for many other cardiovascular diseases.”

Aune says the meta-analysis could have an impact on the smoking habits of certain groups of patients.

“[C]linical practice guidelines already encourage smoking cessation among smokers and avoiding tobacco smoking among nonsmokers,” he says. “Nevertheless, ... the findings might encourage patients [at] particularly high risk of atrial fibrillation to stop smoking or avoid starting smoking.”

Unanswered Questions

Dagfinn AUne, PhD, Associate Professor at Bjørknes University College in Oslo, Norway, and a postdoctoral researcher at Imperial College London, says questions remain about the association between smoking and atrial fibrillation following the recent publication of a meta-analysis he co-authored on the topic.

“There are still quite a number of large-scale cohort studies that have not yet published about smoking and atrial fibrillation,” he says. “[S]ome of the issues that could be clarified in future studies are how the dose-response relationships are at more extreme levels of smoking exposure, whether passive smoking increases risk of atrial fibrillation, whether risk of atrial fibrillation approaches that of never smokers with longer duration of smoking cessation and potential confounding by alcohol or other risk factors.”

Alvaro Alonso, MD, PhD, Associate Professor of Epidemiology at the Rollins School of Public Health at Emory University, wants to know what impact smoking cessation may have in the progression of atrial fibrillation in individuals who have been diagnosed with it.

“Are people with atrial fibrillation going to do better when they quit smoking?” Dr. Alonso asks. “Probably ... but it will be nice to have studies about that.”