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smokers — so-called ever smokers — had a 21 percent higher risk. For former smokers, the relative risk was 9 percent. "One impor ta nt f inding wa s the i ncrea sed r i s k w a s s ubs t a nt i a l ly attenuated a mong 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- qua r ters of t he excess r isk ca n be avoided by quitting smoking. Further studies need to look at the duration of smoking cessation in relation to atria l fibrillation to clarify if the risk decreases to the level of never smokers at some point." L i ke Dr. Sol i m a n's g roup, Au ne and his co-authors believe smoking 's significant role in the development of several chronic diseases that increase atria l fibrillation risk may account for the a ssociation bet ween smok- ing and atria l fibrillation. They a lso point to nicotine's role in increasing resting heart rate, blood pressure and hy per tension, a mong other factors, as elements that could contribute to the association. MORE EVIDENCE OF SMOKING'S DELETERIOUS EFFECTS Aune ack nowledges t hat smok i ng increases risk for atria l 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 P ublic Hea lt h at Emor y 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 a s 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-ana lysis could have an impact on the smoking habits of certain groups of patients. "[C ]l i n ic a l pr a c t ic e g u ide l i ne s 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 atria l fibrillation to stop smoking or avoid starting smoking." n 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." SPECIAL CLINICAL SECTION: CARDIOLOGY M D N E W S . C O M /// M D N E W S L O N G I S L A N D ■ 2 019 1 9