Mitral valve replacement in dogs. Surgical technique and postoperative management.

Although techniques for the perioperative management of patients undergoing mitral valve replacement have been well established in humans, the use of these techniques has not been widely accepted in veterinary practice. The purpose of this study is to demonstrate that low morbidity and mortality could be achieved in the dog undergoing mitral valve replacement. Nine mongrel dogs (25-45 kg body weight) were subject to left thoracotomy and mitral valve replacement using cardiopulmonary bypass (CPB). The average time on CPB was 1 hour with an aortic cross-clamping time of 40 minutes using chemically induced cardiac arrest. CPB was performed under conditions of moderate systemic hypothermia (28-30 degrees C) and hemodilution (hematocrit, 25-35%). Operative mortality was 22% (2/9) with one death from excessive bleeding and the other from cerebral air embolism. All other animals recovered and were clinically normal 3 weeks after surgery. The authors conclude that successful mitral valve replacement is possible in the large dog.

Is it important to preserve the chordae tendinae and papillary muscles during mitral valve replacement?

To evaluate the importance of preserving chordae tendinae and papillary muscles to left ventricular function after mitral valve replacement, 12 dogs had Carpentier-Edwards or Björk-Shiley mitral valves inserted. Cardiopulmonary bypass, systemic hypothermia at 25 degrees C and cold cardioplegia were used. The period of anoxic arrest was 30 minutes. In six dogs, mitral valve replacement was performed after complete excision of the mitral valve. In the other six dogs the anterior leaflet was partially excised but all chordae tendinae and papillary muscles were left intact. Hemodynamic measurements, including left ventricular function following volume loading, were made preoperatively and postoperatively. Left ventricular angiograms were obtained postoperatively in all dogs. Preoperatively there was no significant difference in the left ventricular function curves in the two groups, but postoperatively the curves showed significant differences. In the group with preserved chordae tendinae, left ventricular function improved with volume loading to a left ventricular end-diastolic pressure of 20 mm Hg while in the group with divided chordae tendinae, function improved more slowly and ceased to improve after loading to an end-diastolic pressure of 15 mm Hg. The mean left ventricular ejection fraction following mitral valve replacement with preserved papillary muscles was 0.62 +/- 0.01 and with divided papillary muscles was 0.45 +/- 0.05 (P less than 0.05). The authors conclude that it is important to preserve chordae tendinae and papillary muscles when carrying out mitral valve replacement.