(Ivanhoe Newswire) – A common electrocardiogram (ECG) finding that
has largely been considered insignificant may actually pose significant
danger to the patient.
In their report in the Journal of the American Medical Association,
researchers from Massachusetts General Hospital (MGH) and Boston University
School of Medicine describe results of the first large-scale study looking
at the significance of a prolonged PR interval in a general population.
A common diagnostic test available in most physicians' offices, the
electrocardiogram records the heart's electrical activity and translates it
into waveforms that reflect how the contraction signal moves through the
heart muscle. A prolonged PR interval represents a delay in the time it
takes for the signal to move across the atria at the top of the heart, which
receive blood flowing in from the veins, into the ventricles at the bottom
of the heart, which pump blood out into the arteries.
The current study analyzed data from more than 7,500 participants in the
Framingham Heart Study, who were followed for more than three decades. A PR
interval of less than 200 milliseconds is considered normal, and
participants whose interval was longer than 200 milliseconds were found to
have twice the overall risk of developing atrial fibrillation, 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.
"Lengthening of the PR interval is commonly seen on routine
electrocardiograms, more often in older patients, and has been considered a
relatively harmless finding," Susan Cheng, MD, a cardiology fellow at MGH
and Brigham and Women's Hospital who is lead author of the JAMA paper is
quoted as saying. "But our results indicate that PR interval prolongation is
not as benign as previously thought."
Although a prolonged PR interval can signify conduction problems related to
serious conditions such as 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. But previous investigations
of the impact of PR prolongation were limited to younger, healthy
participants, such as members of the military.
"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," Thomas
Wang, MD, of the MGH Heart Center and assistant professor of Medicine at
Harvard Medical School, the study's senior author, is quoted as saying. "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."
SOURCE: JAMA, June 24, 2009
