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Percutaneous Patent Foramen Ovale Closure Impact on Migraine
Patent Foramen Ovale
Galen already knew of the foramen ovale and its normal postnatal closure, but it was Leonardo Botallo, an Italian surgeon after whom the aorto–pulomonary duct was named, who described in the 16th Century the persistence of a foramen ovale after birth, without understanding its function in the fetus. In a contemporary study with 965 autopsy specimens from patients without known cardiac disease, the foramen ovale was patent in 27% of cases. In this often-cited necropsy study, the incidence of a PFO decreased with the patient's age, suggesting that spontaneous PFO closure after birth may be possible or that selective mortality may offer an alternative explanation. The PFO incidence was 34% during the first three decades of life, 25% during the 4th through 8th decades and up to 20% during the 9th and 10th decades. In a recent letter from the Cleveland Clinic, an incidental PFO was found on an intraoperative transesophageal echocardiogram in 17% of 13,261 patients undergoing cardiac surgery, and this incidence was constant with age, suggesting that there may be no decrease in PFO incidence with age.
Discrepancies in the PFO prevalence among different studies depend on the methods used to diagnose this intracardiac shunt. In vivo, transthoracic or transesophageal echocardiography and transcranial Doppler studies, all with contrast bubbles, are used to detect this intermittent right-to-left shunt. In a comparative study in patients with a previous ischemic stroke, transesophageal contrast echocardiography was more sensitive than a transcranial Doppler examination in detecting a PFO, especially in cases of minimal right-to-left shunts. Transthoracic contrast echocardiography was the least sensitive test. Diagnosing a PFO depends not only on the imaging method, but also on the ability of the patient to perform a Valsalva maneuver. The temporary raise in venous return and the concomitant increase in right atrial pressure after release of the Valsalva strain phase are decisive for the opening of the flap valve in most patients with a PFO. Sedation, often necessary to perform a transesophageal echocardiogram, can compromise an effective Valsalva maneuver and may be one of the reasons for a false negative exam. Cubital administration of contrast bubbles is another reason for missing some PFOs. Due to the cardiac anatomy, especially the eustachian valve, inferior and not superior vena cava blood is preferentially directed to the fossa ovalis. In some patients, a real washout effect impedes the contrast bubbles arriving from the superior vena cava to cross the foramen ovale, even when it is widely open. Therefore, it is not surprising that the PFO prevalence is lower with imaging methods compared with necropsy studies.
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