June 23 (HealthDay News) -- A slight abnormality in an electrocardiogram (EKG), until now thought to be insignificant, can be a warning sign of future cardiac problems and an increased risk of early death, a new study indicates.
Lengthening of what is called the PR interval, the right-hand portion of the jagged blip that records electrical activity as the heart contracts and expands, was associated with a doubled risk of developing the abnormal heartbeat called atrial fibrillation, three times the risk of needing a pacemaker, and one-and-a-half times the risk of early death, according to a report in the June 24 issue of the Journal of the American Medical Association.
"Historically, this has been viewed as benign," said study senior author Dr. Thomas Wang, associate director of heart failure and heart transplantation at Massachusetts General Hospital. "The main message of this paper is that there is an association between this EKG finding and future risk of heart rhythm abnormalities and death."
The PR interval records the time that the electrical activity of the heart moves across the atria, the two upper chambers of the heart that receive blood flowing from the body, into the ventricles, the lower blood-pumping chambers. EKG activity is recorded in thousandths of seconds, and a PR interval is said to be prolonged if it is greater than 200 milliseconds. Such a prolonged PR interval is generally seen in healthy adults, middle-aged and older, with the incidence increasing with age.
Analysis of EKGs of 7,500 participants in the Framingham Heart Study found a prolonged PR interval in 124 of them, and the increased risk was detected in a long-term follow-up.
"It is not known exactly why it happens," Wang said. "It could be scarring and other abnormalities in the electrical system of the heart."
When the abnormality is detected on an EKG, "there is no need to be panicked," Wang said. "But physicians should follow these patients more closely. There is no evidence that such patients should be treated differently, but future studies may show otherwise."
The 200-millisecond threshold was set rather arbitrarily, he said. The degree of risk seen in the study was directly associated with the length of the PR segment prolongation -- the longer the interval, the greater the risk.
And the amount of prolongation was directly associated with age -- the older the person, the longer a prolonged PR interval was likely to be. The association with age is no surprise, Wang said. It's also seen in those with cardiac risk factors such as high blood pressure.
"Lengthening of the PR interval is commonly seen on routine electrocardiograms, more often in older patients, and has been considered a relatively harmless finding," Dr. Susan Cheng, a cardiology fellow at Massachusetts General Hospital and Brigham and Women's Hospital and a member of the research team, said in a statement. "But our results indicate that PR interval prolongation is not as benign as previously thought."
The event rates seen in the study "are pretty low, even over 20 years of follow-up," said Dr. Daniel Lloyd-Jones, associate professor of preventive medicine and cardiology at the Northwestern University Feinberg School of Medicine.
"And from a clinician's point of view, I wouldn't do an electrocardiogram just to look for a prolonged PR interval," Lloyd-Jones said. "But we do electrocardiograms for all sorts of reasons, and it is reasonable to look for prolonged PR intervals because it is a modest marker of risk."
The most intriguing association is with the increased risk of atrial fibrillation, he added. "The atrial fibrillation study is really an interesting one," Lloyd-Jones said.
SOURCES: Thomas Wang, M.D., assistant professor, medicine, Harvard Medical School, and associate director, heart failure and heart transplantation, Massachusetts General Hospital, Boston; Daniel Lloyd-Jones, associate professor, preventive medicine and cardiology, Feinberg School of Medicine, Northwestern University, Chicago; June 24, 2009, Journal of the American Medical Association