Reflux of oxygenated blood into the pulmonary artery in severe mitral regurgitation

A patient with severe mitral regurgitation secondary to ruptured chordae tendineae is described in whom there was a positive pulmonary arterial Kr 85 index and a step-up in oxygen saturation from right ventricle to pulmonary artery, in the absence of an abnormal communication between the systemic and pulmonary circulations. It was demonstrated that left atrial pressure exceeded pulmonary arterial pressure in late systole and early diastole, and the oxygen saturation in the pulmonary arterial bed increased with progressively more distal sampling sites. Following operative correction of the mitral regurgitation, cardiac catheterization showed a marked reduction in the left atrial pressure, and the step-up in oxygen saturation in the pulmonary artery, as well as the positive pulmonary arterial Kr 85 inhalation test, were abolished. It was concluded that the preoperative evidence of left-to-right shunting represented reflux of oxygenated blood into the pulmonary artery resulting from the severe mitral regurgitation.