Papillary muscle ischemia with patent coronary arteries

Intermittent murmurs of insufficiency (MI) associated with left atrial "V waves" often are ascribed to papillary muscle (PM) ischemia in coronary artery disease but their cause is not clear with unobstructed coronary arteries. In 49 open-chest dogs, left atrial, left ventricular, and aortic pressures and regional coronary flow (microsphere method) were measured. Subendocardial (SE) ischemia (endocardial/epicardial flow ratios less than 1.0, ischemic intracavitary electrocardiograms) was produced by lowering the SE supply/demand ratio (diastolic pressure time index times O2 content per tension time index) to below 12 with either arteriovenous fistulas, anemia, or aortic stenosis. In nonischemic hearts, O2 delivery to the PM was 20 percent more than to the SE (P less than 0.01) and rose with increasing demands. When ischemia occurred, O2 delivery per unit demand fell 35 percent (p less than 0.01) to the SE muscle, and PM O2 delivery decreased more strikingly (55 percent, p less than 0.01). This reduction in PM and SE O2 delivery often was associated with a "V wave" in the left atrium which disappeared when the intervention impairing the adequacy of O2 delivery was discontinued. We conclude that PM ischemia (1) is the probable cause of intermittent MI, and (2) can be predicted from readily obtained measurements of blood pressure and O2 content.