People who were exposed to secondhand smoke during gestational development and early childhood were at a higher risk of having atrial fibrillation later in life, according to a cross-sectional analysis of an Internet-based, cardiovascular cohort study.

After adjusting for multiple variables and confounding factors, the researchers from the University of California, San Francisco, found having had a smoking parent during gestational development or having lived with a smoker during childhood were significantly associated with atrial fibrillation. They published their results online in HeartRhythm on Sept. 1.

“That was a bit of a surprise,” Gregory M. Marcus, MD, a study author, told Cardiovascular Business. “I think that does require validation, but it is very interesting that exposure in utero could have an effect on the atrium decades later. That, to my knowledge, has not been demonstrated."

In the U.S., more than 2.7 million adults have atrial fibrillation, which is one of the most common causes of stroke. Previous research found that exposure to secondhand smoke increases nonsmokers’ coronary artery disease risk by 25 percent to 30 percent. In addition, studies showed that smoking appeared to be associated with atrial fibrillation.

In this analysis, the researchers analyzed data obtained between March 8, 2013, and Nov. 13, 2014, from the Health eHeart Study, an ongoing, Internet-based study open to any English-speaking adult with a working email address. Nearly 30,000 people from more than 90 countries and every state in the U.S. have enrolled in the study.

“Our goal is to enroll one million people and to really make this an international movement that can enhance the understanding of cardiovascular disease and therefore help us determine how to best predict it, prevent it and treat it,” Marcus said.

Participants completed a 22-question survey about secondhand smoke exposure and self-reported whether they had atrial fibrillation. The researchers also reviewed electronic medical records from 42 participants who gave them consent. Participants who said they had atrial fibrillation completed an additional survey asking about their symptoms, diagnosis and treatment.

“When people took this survey, they didn’t necessarily know that we were going to be looking for associations with atrial fibrillation,” Marcus said. “They were doing a bunch of surveys. In one of them, we asked about a bunch of medical things, one of them being a-fib. In that sense, we think that mitigates against recall bias, for example, a little bit.”

Of the 4,976 participants, 11.9 percent had atrial fibrillation. Of those with atrial fibrillation, 45.7 percent had persistent atrial fibrillation and 46.4 percent had paroxysmal atrial fibrillation.

The researchers found that participants with atrial fibrillation were more likely to have been exposed to secondhand smoke in utero, as a child, as an adult, at home and at work. They were also more likely to have been exposed to secondhand smoke for a longer period of time at work, but participants without atrial fibrillation were more likely to have visited social environments with significant secondhand smoke.

The relationship between secondhand smoke exposure and atrial fibrillation was significantly stronger in participants who were 60 years old or younger and had no known hypertension, diabetes, coronary disease or heart failure.

“Assuming this is true and there’s no some other confounder that we weren’t able to account for, it suggests that there’s some direct effect on the atrium or on the pulmonary vein that is responsible for this relationship,” Marcus said.