Mitral Regurgitation Mitral regurgitation after STEMI occurs via 1 of 2 mecha- nisms: papillary muscle rupture or postinfarction LV remod- eling with displacement of the papillary muscles, leaflet tethering, and annular dilatation. Acute rupture affects the posteromedial papillary muscle more often than anterolateral papillary muscle because of its singular blood supply.470,471 Acute severe mitral regurgitation is characterized by pulmo- nary edema and/or shock; a systolic murmur may not always be appreciated. Suitable patients with papillary muscle rup- ture should be considered for urgent surgery while temporary stabilization with medical therapy and IABP is attempted. Mitral valve replacement rather than repair usually is required in this setting. Although emergency mitral valve replacement is associated with a relatively high mortality rate (20%), sur- vival and ventricular function are improved with surgery com- pared with medical therapy alone. Delay to operation appears to increase the risk of further myocardial injury, organ failure, Five-year survival rates after surgery average With ischemic (functional) mitral regurgitation, treatment is focused on timely reperfusion, diuretics, and afterload reduction. The severity of mitral regurgitation may improve in some patients with aggressive medical treatment, PCI, or both. The rate of long-term survival after STEMI declines as a function of residual mitral regurgitation severity. If surgery is required during the index hospitalization because of ongoing ischemia or HF, mitral valve repair with a downsized annu- loplasty ring usually is performed, though valve replacement may be preferred in many cases. In this regard, management of ischemic mitral regurgitation differs importantly from that of myxomatous mitral regurgitation. 9.4.3. Ventricular Septal Rupture Ventricular septal rupture usually is heralded by a loud sys- tolic murmur and HF or shock, depending on the size of the defect and the degree of RV and LV dysfunction. 