PFO and stroke - state of the evidence
Even on its face, PFO would seems an unlikely cause of stroke, since in order to have a stroke from a PFO many relatively unlikely events would have to take place all at the same time. The patient with a PFO would have to cough (or do some other maneuver to increase right atrial pressure, such as hold a high C note, or strain at the stool), at the precise moment that a blood clot is traversing the right atrium. That blood clot would then have to "decide" to go through the now-open PFO instead of following the major flow of blood (out the pulmonary artery and into the lungs). Once on the left side of the heart, the clot would then have to "decide" to join the 20% of the blood flow from the left heart that goes to the brain.
Proponents of the PFO-stroke theory point to non-randomized studies that appear to show an increased incidence of PFO in patients who have had strokes with no other likely cause - the so-called "cryptogenic" stroke. The problem with these studies are: A) They are non-randomized. In these studies, patients with known cryptogenic strokes had echocardiograms where pains were taken to find any possible PFO. As mentioned, the harder one looks, and the more liberal one is with criteria used for "diagnosing" a PFO, the more PFOs one will find. B) These studies tend to be conducted by doctors who have a vested interest in companies that make PFO-closure devices. I believe that these doctors are honest investigators who do not fudge data, but even honest investigators can be victims of a certain amount of self-deception, especially when the presence or absence of a PFO depends, to some extent, on how badly one wants to find one.
Recently (December 6, 2005), investigators reported in the Journal of the American College of Cardiology that PFO is indeed NOT an independent risk factor for stroke. In this first prospective, randomized trial yet conducted studying the relationship between PFO and stroke, investigators from the Mayo Clinic found 140 patients with PFO out of 585 individuals who were randomly screened. Over the next 5 years, 41 of these 585 patients had stroke. The rate of stroke was no higher for patients with PFO than for patients without PFO. (The rate of stroke did appear higher for those with ASA, but the results here were not statistically significant.) The authors concluded that there is no evidence that the presence of a PFO increases the risk of stroke, and that prior, non-randomized studies used flawed methodology.
One potential flaw in this new study is that the patients randomized in this trial were generally older than the patients studied in prior, non-randomized trials. It is still possible that PFO might be important in some younger patients (under 55) who have had cryptogenic strokes.
PFO and migraine - state of the evidence
While all the things that have to happen at once in order for a PFO to cause a stroke are very unlikely, it is at least possible that they could all occur simultaneously in some patients. This is not the case with migraine, where it is difficult to come up with a plausible theory as to how PFO might cause this condition. The only reason PFO is being invoked as a cause for migraine is that when patients with migraine have been carefully studied for the presence of PFO, an increased incidence of PFO was found. But as we have seen, when PFO is carefully sought in a population of patients, it is more likely to be found. The only reason PFO has not been associated with cancer, red hair, type A personality, or difficulty in memorizing the multiplication tables is that it has not been looked for. Until a blinded, randomized trial is done, even the suggestion that migraine is associated with an increased incidence of (let alone caused by) PFO needs to be greeted with great skepticism. (This situation is similar to that with mitral valve prolapse, another extremely common echocardiographic diagnosis that has been blamed for a host of symptoms.)
The poorly-supported allegation that PFO causes migraine is particularly unfortunate because some doctors, convinced of the association, have enthusiastically taken to "treating" migraine headaches by the invasive (and lucrative) step of closing PFOs. Migraine sufferers are particularly vulnerable to this and many other unproven therapies, since they are often disabled by their condition, and in many cases medical science (or medical ignorance) offers them no help. (For some real help with migraine headaches, check out Teri Robert's site at About.)
