NEW YORK (Reuters Health) – People with a prolonged PR interval are at increased risk for atrial fibrillation, pacemaker implantation, and death at long-term follow-up, according to an analysis of data from the Framingham Heart Study.

With each 20-millisecond increase in the PR interval above normal, the odds of atrial fibrillation, pacemaker implantation, and death increased by 11%, 22%, and 8%, respectively, the findings in the Journal of the American Medical Association for June 24 indicate.

A prolonged PR interval is a common finding in clinical practice, but the impact, if any, on long-term outcomes was unclear, Dr. Thomas J. Wang, from Massachusetts General Hospital, Boston, and colleagues explain.

To investigate, the researchers analyzed data from 7575 adult subjects (mean age=47 years) who were followed from 1968-1974 to 2007 as part of Framingham Heart Study.

A total of 481 subjects developed atrial fibrillation, 124 underwent pacemaker insertion, and 1739 died, the authors note.

Subjects with a PR interval longer than 200 milliseconds, also known as first-degree atrioventricular block, had worse outcomes than those with shorter PR intervals. With atrioventricular block, the rates of atrial fibrillation, pacemaker insertion, and death per 10,000 person-years were 140, 59, and 334, respectively, compared with corresponding rates of 36, 6, and 126 with less severe PR prolongation.

Subjects with first-degree atrioventricular block were 2.06-, 2.89-, and 1.44-times more likely to develop atrial fibrillation, require pacemaker insertion, and die during follow-up, respectively, than were subjects without this ECG disturbance.

“These results suggest that the natural history of first-degree atrioventricular block is not as benign as previously believed,” the authors conclude. “Additional studies are needed to determine appropriate follow-up for individuals found to have prolongation of the PR interval on routine ECG.”

Reference:
JAMA 2009;301:2571-2577.