A lengthening of the PR interval is commonly seen on routine ECGs and represents a delay in the time it takes for the electrical signal to move across the atria to the ventricles.
This latest study found that patients who showed a prolonged PR interval longer than 200ms were twice as likely to develop AF.
Lead researcher Dr Susan Cheng, from the Brigham and Women's Hospital in Boston, said: 'The results indicate that PR interval prolongation is not as benign as had been previously thought.'
The researchers propose that a prolonged PR interval could be a marker for progressive problems with the heart's electrical conduction system.
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