Patent foramen ovale: a cause of significant post-coronary artery bypass grafting morbidity.

We describe two patients who underwent coronary artery bypass grafting complicated by postoperative hypoxemia due to a patent foramen ovale with right-to-left shunting. We discuss different hypotheses to explain the shunt: decreased right ventricular compliance, right atrial geometric changes due to septal distension or ischemia, exceeding filling pressure and localised haemorragic pericardial tamponade and low atrial pressure when correcting aortic stenosis. We emphasize the close interplay of pericardectomy and the four cardiac chambers including the distortion of the heart axis. The contrast echo produced by microbubbles of air is the safest and the most accurate procedure to detect the shunt. The two patients progressed positively with an extracorporeal circulation of short duration and without complications linked to the intervention. We conclude that postoperative unexplained hypoxemia must always exclude diagnosis of right-to-left shunting due to a patent foramen ovale (PFO).