Common ECG Finding May Indicate Serious Cardiac Problems

A common electrocardiogram (ECG) finding that has largely been considered insignificant may actually signal an increased risk of atrial fibrillation (AT), according to a new study.

Researchers at Massachusetts General Hospital (MGH; Boston, USA) and Boston University School of Medicine (MA, USA) conducted a large-scale study that analyzed data from more than 7,500 participants in the Framingham Heart Study to determine the significance of a prolonged PR interval on the ECG. The researchers found that although only 124 of those participants showed a prolonged PR interval on the ECG (taken when they entered the study), the prolongation proved to be a significant risk factor; participants whose PR interval was longer than 200 ms had twice the overall risk of developing AT, three times the risk of needing a pacemaker, and almost one and a half times the risk of early death. Further prolongation of the PR interval led to even greater risk. The study was published in the June 24, 2009, issue of the Journal of the American Medical Association (JAMA).

"Lengthening of the PR interval is commonly seen on routine electrocardiograms, more often in older patients, and has been considered a relatively harmless finding,” said lead author Susan Cheng, M.D., a cardiology fellow at MGH. "But our results indicate that PR interval prolongation is not as benign as previously thought.”

"We do not yet know why a subtle finding such as a prolonged PR interval is associated with such serious adverse outcomes, but it may be a marker for progressive problems with the heart's electrical conduction system,” said senior author Professor Thomas Wang, M.D., of the MGH Heart Center. ‘We need to learn more about how a prolonged PR interval is linked to these serious events and what should be done to prevent them. Right now, clinicians might consider that their patients with PR prolongation may be at increased risk of these problems and follow their electrocardiograms more closely.”

A prolonged PR interval (longer than 200 ms) represents a delay in the time it takes for the signal to move across the heart atria. Although a prolonged PR interval can signify conduction problems related to serious conditions such as a heart attack, a prolonged PR interval is most commonly seen in generally healthy, middle-aged to older adults and has been thought to reflect normal age-related changes. However, these conclusions were based on previous investigations of PR prolongation that were limited to younger, healthy participants, such as members of the military.

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Massachusetts General Hospital
Boston University School of Medicine