The PFO gets blamed again…perhaps this time it is real.

Patent foramen ovale (PFO) closure is the thing to do these days in the interventional laboratory. Closures are done for strokes, migraine headaches, and postural cyanosis, and for divers who are at risk for decompression sickness. Atrial septal defect closures are also done in the interventional laboratory, but these are known to reduce the significant left-to-right intracardiac shunt that eventually, when large enough, results in pulmonary hypertension, an Eisenmenger syndrome, and permanent lung injury. We have seen the image of a thrombus partially protruding through the PFO, threatening a major stroke (1), and seen the retrospective data indicating that there is a higher incidence of PFOs in patients with cryptogenic strokes, and in some forms of decompression sickness (2). But, the Reverend Bayes continually reminds us that an increased incidence of PFO in a stroke population is not the same as an increased incidence of stroke in a PFO population, particularly with the high incidence of PFO in the general population (3) or, in Bayesian terms, the high prior probability of PFO