CORRESPONDENCE: LETTER TO THE EDITOR
Patent Foramen Ovale and Stroke Risk: The Devil Is in the Detail
Markus Schwerzmann, MD* and
Bernhard Meier, MD, FACC, FESC
* Cardiology, University Hospital Inselspital, Bern CH-3010, Switzerland (Email: markus.schwerzmann{at}insel.ch).
The risk of stroke due to a patent foramen ovale (PFO) is real. Case reports document venous thrombi slipping through a foramen ovale to the left atrium and causing a stroke (1). The absolute risk for ischemic strokes in the presence of a PFO is unknown. The report of Di Tullio et al. (2) in a recent issue of the Journal may not shed more light on this question, because some "minor" details could end up seriously biasing their results.
As the investigators point out in their discussion, the prevalence of a PFO in the general population is close to one-quarter (3). The prevalence of a PFO in the current study is 15%. The most likely reason for this low PFO prevalence is underdiagnosis of interatrial shunts by transthoracic echocardiography (4). Otherwise, the researchers have to argue for a lower PFO prevalence in citizens from northern Manhattan compared to other cities of the U.S. Missing 4 of 10 PFOs would lower the hazard ratio (HR) for stroke in the PFO group compared to the non-PFO group, because these nondiagnosed shunts may increase the risk for stroke in the latter group. The results of the Cox regression models as presented would underestimate the actual hazard. In addition to the problem of underdiagnosis, a question arises regarding the patients studied. The mean age of patients participating in this project was 68 to 69 years. The association of a PFO and stroke has been demonstrated for patients <55 years (5) and is probably weaker in the elderly with competing conventional cardiovascular risk factors as hypertension, diabetes, and dyslipidemia.
Last but not least, Di Tullio et al. (2) should provide not only the HR for a stroke in the setting of a PFO, but also the corresponding HRs for other cardiovascular risk factors they corrected for.
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References
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- Sibbing D, Overbeck M, Schmidt R, Gaa J, Barthel P. Patent foramen ovale with a riding vermicular thrombus causing paradoxical and massive pulmonary embolism Eur Heart J 2006;272724.
- Di Tullio MR, Sacco RL, Sciacca RR, Jin Z, Homma S. Patent foramen ovale and the risk of ischemic stroke in a multiethnic population J Am Coll Cardiol 2007;49:797-802.[Abstract/Free Full Text]
- Hagen PT, Scholz DG, Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts Mayo Clin Proc 1984;59:17-20.[ISI][Medline]
- Hara H, Virmani R, Ladich E, et al. Patent foramen ovale: current pathology, pathophysiology, and clinical status J Am Coll Cardiol 2005;46:1768-1776.[Abstract/Free Full Text]
- Lechat P, Mas JL, Lascault G, et al. Prevalence of patent foramen ovale in patients with stroke N Engl J Med 1988;318:1148-1152.[Abstract]
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