Children have a much bigger chance of developing atrial fibrillation (AF) later in life if their parents smoke, a new study has found.

AF causes irregular and rapid heartbeats, which can make the heart less efficient at pumping blood around the body. It is a major risk factor for stroke.

Smoking has already been established as a risk factor for AF, however US researchers decided to look into the potential impact of secondhand (passive) smoke.

They analysed data relating to over 5,100 children who were under the age of 18 at the start of the study. The children and their parents were regularly monitored by doctors between 1971 and 2014.

Among the participants in which smoking status was known, 82% of the children were exposed to secondhand smoke. Parents smoked an average of 10 cigarettes per day.

Almost 15% of the children went on to develop AF over the follow-up period of more than 40 years and the researchers found that and for each pack per day increase in parental smoking, children had an 18% increased risk of developing the heart condition.

The study also found that almost one in five children of smokers were more likely to smoke themselves, which suggests another way that parental smoking could predispose children to developing AF later in life.

"Our observations provide new information pertinent to smoking cessation, highlighting the harms that may be associated not only to others, but to close and the most vulnerable members of the family. With the rising prevalence of AF, it is imperative to address modifiable risk factors such as cigarette smoking to reduce its global burden," commented one of the study's senior authors, Dr Gregory Marcus, of the University of California, San Francisco.

The researchers said that while some of the link between parental smoking and AF in children was explained by the children becoming smokers too, "the results indicate that secondhand smoke exposure in childhood is a risk factor for future development of AF".

Details of these findings are published in the Journal of the American College of Cardiology.