Comparison of rigid and flexible rings for annuloplasty of the porcine mitral valve.

Seven rigid (Carpentier) and six flexible (Duran) annuloplasty rings were implanted in healthy pigs. First, in the intact pig, cinefluoroscopy was used to record movements of the anulus. Results were compared with data from three pigs instrumented with a continuous radiopaque marker on the anulus. Pump function of all hearts with annuloplasty rings and function of the mitral valve were studied 4-6 weeks after the operation, first in the exposed heart and then subsequently in the isolated heart in a perfusion chamber at maximal filling pressure and normal or low arterial pressure. Separation of the blood-perfused coronary circulation from the crystalline solution pumped by the left heart allowed videoendoscopy of the working valve. Flexible rings interfered less with normal movements of the mitral anulus than rigid rings and caused less impairment of filling of the basal part of the ventricle, and the unloaded stroke volume was 16% larger. For normal arterial pressures, the differences were smaller and will be difficult to detect in clinical situations. A stiff anulus was seen to be pushed underneath the aortic valve during systole, which caused a mild subvalvular obstruction. The mean diastolic pressure gradient across rigid annuloplasty rings was slightly larger than across flexible rings of the same or slightly smaller diastolic size. Rigid rings change the pattern of movement of the leaflets; the mural leaflet remains immobile throughout diastole. Although Duran rings interfere less with valvular function and filling of the basal part of the ventricle than do Carpentier rings, the differences are small and probably only of limited clinical importance.