A study of people born with a common cardiac defect shows that they may have less to be concerned about than previously thought,

Patent foramen ovale, or PFO, is a congenital anomaly in which a small hole between the left and right atria - the upper chambers of the heart - fails to seal shut, as it should, at birth.

The hole is normally used strictly during fetal circulation. The fetus does not use its own lungs to breathe; instead it pulls oxygen-saturated blood from the mother through the placenta. It's unnecessary for it to pump blood from its heart to its lungs. For efficiency's sake, the fetal heart shuttles blood directly from the right atrium to left atrium via the foramen ovale. In adults, blood flows from the right atrium to the right ventricle, from which it is then pumped to the lungs. In the lungs, blood cells load up on oxygen before returning to the left atrium.

The foramen ovale, in other words, serves as a bypass mechanism for fetal circulation.

At birth, increased blood pressure on the left side of the heart, which comes with the infant's first breath, causes a flap over the atrial hole to seal shut over time. A patent foramen ovale occurs when the hole is not completely sealed shut.

Some cardiac experts have worried that increased blood pressure may, in certain cases, cause blood to travel from the right atrium into the left atrium in adults with PFO. The concern is that blood clots from the right side of the heart could end up on the left side, and then, with a simple pump of the left ventricle, be sent to the brain, where it might cause a stroke.

The Mayo Clinic study, published in the Journal of the American College of Cardiology and led by neurologist Irene Meissner, M.D., shows this concern is unfounded, despite evidence that some stroke victims do indeed have patent foramen ovales.

The study looked at 585 adults age 45 and older. The researchers used echocardiography, a heart imaging technique, to determine that 140 of the subjects had patent foramen ovales. They then followed all participants for more than five years.

The results: Those with PFO were no more likely than their normal-hearted counterparts to have a stroke.

Meissner surmises the supposed link between PFO and stroke arose when some stroke patients were found to have patent foramen ovales. But, she explains, "If you detect patent foramen ovale in someone who has already had a stroke, one cannot immediately assume that the patent foramen ovale is causative."

The researchers conclude that surgery to close patent foramen ovales in patients who are otherwise healthy is unnecessary if the goal is to reduce stroke risk.

Mike Watkins, M.D., a member of myDNA's Medical Advisory Board, says not to discount PFO impacts on stroke.

"This is indeed good news, but stay tuned for further debate and other studies to clarify this important issue. We have other data which suggests that a patent foramen ovale can be involved in the causation of stroke in certain patients, and this study of 585 patients does not support the prior contention," he says. "The truth probably lies somewhere in the middle, and the clinical problem will be to sort out which specific patients might actually have a problem caused by a patent foramen ovale," Watkins says.

"From an anatomical and physiological standpoint, from some detailed case studies and from clinical experience, some strokes do occur in a 'paradoxical' fashion, with clots from the venous system crossing to the arterial circulation via a defect in the atrial septum," he says.

"The value of the current study is most likely going to be that this type of event is not as likely or frequent as has been previously postulated. That is fortunate, since strokes are quite common. If the medical profession was forced to evaluate every stroke patient of whatever cause to see if they have a patent foramen ovale, and then to potentially have to close it, the process would be quite costly and involved."

© 2006 mydna.com