Monday, December 12, 2005

Study: Patent Foramen Ovale Not a Risk Factor for Stroke ?

People and physicians interested in diving medicine are justifiably concerned by the presence of a patent foramen ovale, through which bubbles can flow from the right side of the heart into the left side during ascent from dives and causing unexpected decompression illness. There also have been associations drawn between stroke/TIAs and PFO. Here is a fairly large study of non-divers by the Mayo Clinic which fails to show a relationship between PFO and stroke.

*Note Dr. John Ross' letter below in which he notes that the study does not rule out a relationship.

See more about PFO on Scubadoc's Diving Medicine Online.

From Reuters Health Information as Printed in Medscape.

NEW YORK (Reuters Health) Dec 09 - Contrary to current thinking by some physicians, the findings from a new prospective study indicate that patent foramen ovale is not an independent risk factor for cerebrovascular events. Larger studies are needed to determine if this holds true with atrial septal aneurysm as well.

"We now see that a hole in the heart leading to stroke is not borne out in our study, the largest transesophageal echocardiogram-based study of the general population," study co-author Dr. Bijoy K. Khandheria, from the Mayo Clinic in Rochester, Minnesota, said in a statement. "Just because you have a hole, you don't automatically need to have it closed."

The findings, which appear in the Journal of the American College of Cardiology for December 9, are based on a study of 585 randomly selected subjects who lived in Olmsted County, Minnesota and were evaluated by transesophageal echocardiography and then followed for a median of 5.1 years.

Overall, 24.3% of subjects had a patent foramen ovale and 1.9% had an atrial septal aneurysm, the report indicates. The 11 subjects with atrial septal aneurysm included 6 with a patent foramen ovale and 5 without a patent foramen ovale.

During follow-up, stroke and other cerebrovascular events occurred in 41 subjects. As noted, patent foramen ovale was not an independent risk factor for such events. Atrial septal aneurysm, by contrast, raised the risk of cerebrovascular events nearly fourfold. However, possibly due to the small patient numbers, this association fell short of statistical significance.

"Our findings show that the hole is not always the guilty party in a stroke; it may be an innocent bystander," Dr. Khandheria concluded.

J Am Coll Cardiol 2005.

December 12, 2005

Dr. Omar Sanchez has generously sent us the following information about PFO and Stroke that was featured in the New England Journal of Medicine. This would seem to refute somewhat the article from the Journal of the American College of Cardiology.

"Dear Scubadoc.
About : - Patent Foramen Ovale Not a Risk Factor for Stroke.
Patent Foramen Ovale in Young Adults with Unexplained Stroke
J. R. Kizer and R. B. Devereux - Extract
The New England Journal of Medicine, Volume 353 - December 1, 2005 - Number 22

A 38-year-old man notes abrupt loss of vision in his right visual field while reading. He has no significant medical history and reports that he neither smokes nor uses alcohol or illicit drugs. Physical examination reveals right homonymous hemianopia but no other abnormalities. Magnetic resonance imaging reveals acute left occipital infarction and normal head and neck vessels. Transesophageal echocardiography shows a patent . . . [Full Text of this Article]

The Clinical Problem - Patent Foramen Ovale and the Risk of Stroke - Atrial Septal Aneurysm -

Strategies and Evidence - Evaluation - Treatment - Medical Therapy - Mechanical Closure - Areas of Uncertainty - Guidelines - Conclusions and Recommendations.

Dr. John Ross writes:

I read with interest the trial of pfo as a risk factor for stroke. The adjusted mean hazard ratio for an association was 1.4 (95% confidence interval 0.74-2.88). With this degree of variance, while the authors cannot say they have found an association, they can in no way rule one out. Bove's metanalysis of the relationship of PFO with decompression illness indicated that PFO more than doubled the risk. A similar relationship with stroke cannot be ruled out by this study.

Basically it is a numbers problem. I reckon that, in a balanced study design, 946 patients are required to have a 90% chance of detecting, as significant at the 5% level, an increase in the primary outcome measure (stroke) from 6% in the control group (no PFO) to 12% in the experimental group (PFO). That is 425 patients with PFO and 425 without. In terms of study design, you would identify the requisite number of PFO patients and then establish an age and gender matched control group. If a lesser increase of risk was though to be important, the numbers will be a lot higher.

This and other points are nicely highlighted by the editorial in the same edition of JACC.

Patent Foramen Ovale, Guilty But Only as a Gang Member and for a Lesser Crime * EDITORIAL
In Press, Corrected Proof, Available online 6 December 2005
Bernhard Meier


John Ross

Dr John A S Ross
Senior Lecturer, Hon. Consultant Department of Environmental and Occupational Medicine University of Aberdeen Medical School Aberdeen AB25 2ZP