Feb. 21 (HealthDay News) -- Increased pulse pressure -- the difference between the high and the low numbers that designate blood pressure -- is an important indicator of the risk of developing the dangerous abnormal heartbeat called atrial fibrillation, data from a major heart study show.

"The normal value of pulse pressure is about 40," explained cardiologist Dr. Gary F. Mitchell, president of Cardiovascular Engineering, a private company that does research funded by the U.S. National Institutes of Health. "When you get into the 50 range, the risk of atrial fibrillation starts to go up substantially."

Mitchell's team tracked more than 5,300 participants in the Framingham Heart Study for an average of 16 years.

Reporting in the Feb. 21 issue of the Journal of the American Medical Association., they found that a 20-point rise in pulse pressure was associated with a 34 percent increase in the risk of developing atrial fibrillation.

In atrial fibrillation, the upper chambers of the heart tend to quiver, rather than beat steadily. The condition can lead to formation of blood clots that travel to the brain, causing stroke. It is also associated with other major problems, including heart failure. An estimated 2.3 million Americans are diagnosed with atrial fibrillation, and the incidence is expected to increase as the population grows older.

Stiffness of the arteries is an indicator of atrial fibrillation risk, Mitchell said. "We have been doing various measurements of arterial stiffness, and it occurred to us that pulse pressure was a very good measure of arterial stiffness that is frequently ignored," he said.

Determining pulse pressure is a simple matter of subtraction. For example, someone with a blood pressure reading of 120 over 80 (the top number is the systolic pressure, the bottom number diastolic pressure) has a pulse pressure of 40. If systolic pressure goes up to 130 and diastolic pressure remains the same, the pulse pressure reading is 50.

"The key here is that if you can identify people at high risk of atrial fibrillation because of stiffening of the arteries, you can intervene and prevent such problems as atrial fibrillation," Mitchell said.