Influence Of Mitral Valve Area On Left Ventricular Function

Objectives:To validate the strategy for selection of prosthesis size during mitral valve replacement.Methods:75 adult male New Zealand white rabbits were selected, weighing between 2.00 kg and 2.20 kg. The mitral annulus diameter of all rabbit hearts was calculated as 9mm. Metal rings with diameter of 10mm,9mm,8mm, and 7mm were prepared. The isolated rabbit working heart model was established with pre-load of 10 mmHg and after-load of 50 mmHg. The whole system was maintained at 37℃with a circulating water bath. The left ventricular pressure, aortic flow and the coronary flow were recorded. After the maintenance of working mode for 30 minutes, the heart was infused with cardioplegic solution (10ml/kg body weight) at 4℃through aortic canula, and immersed into ice-cold normal saline for 25 minutes, during which metal ring implantation can be performed. The rabbit hearts were randomly assigned to one of the following groups: control (n=15),10mm (n=15),9mm (n=15),8mm (n=15),7mm (n=15). The group name means the size of metal ring which was implanted on the mitral annulus except the control group. Then the working heart model was re-established and the left ventricular pressure, aortic flow and coronary flow were recorded.Results:Rate-pressure product (RPP) and+dP/dt max had no statistically significant change after annuloplasty in all groups (P>0.05). Cardiac output (CO) and Aortic flow (AF) had statistically significant decrease after annuloplasty in all groups except the controls (P<0.001). Coronary flow (CF) had no statistically significant change after annuloplasty in all groups (P>0.05). End diastolic pressure of left ventricle (LVEDP) had statistically significant increase after annuloplasty in groups of 10mm and 9mm (P<0.05), but had no statistically significant change in the other groups (P>0.05). Both cardiac output recovery rate and aortic flow recovery rate of control group had significant difference to all other groups (P<0.05), while those of 8mm group had significant difference compared with other treatment groups (P<0.05). End diastolic pressure of left ventricle (LVEDP) recovery rate had no significant difference among all the groups (P>0.05). Conclusion:Implantation of mitral ring with about 80% of normal area showed better heart performance (cardiac output and aortic flow) than other groups (including the bigger one), which might provide us clue for strategy of selection of prosthesis size during mitral valve replacement.