The influence of free hand suturing technique and zero pressure fixation on the hydrodynamic function of aortic root and aortic valve leaflets.

OBJECTIVE

There is increasing interest in the use of stentless porcine bioprostheses implanted by the free hand suturing technique. However, preservation of the normal valve geometry and function is a matter of concern. This study has been conducted to investigate the influence of free hand insertion on the hydrodynamic function of the aortic valve. In particular, free sewn valves have been compared to whole root replacements for both fresh valves and zero pressure fixed bioprostheses.

METHODS

Four sets of porcine aortic roots with six aortic roots in each set consisting of (A) fresh aortic roots, (B) fresh aortic valve inserted by free hand suturing technique in fresh aortic valve fixed in glutaraldehyde under zero pressure, inserted by free hand suturing technique in fresh aortic roots, and (D) aortic roots fixed in glutaraldehyde under zero pressure, were studied. Hydrodynamic function and leaflet bending deformations were analysed in a modified pulsatile flow simulator which incorporates the elastic aortic roots.

RESULTS

The glutaraldehyde-treated roots were found to be less distensible than the fresh aortic roots, with a mean dilatation of only 8% compared with 43% for the fresh roots at 120 mmHg pressure. The other two groups of free sewn valves showed reasonably good dilatation of 38%. There was no significant difference between the two sets. The hydraulic effective orifice area (EOA) of the valve, which was derived from the flow and pressure measurements, was divided by the actual orifice area for the annulus to arrive at the performance index. The performance index for glutaraldehyde-fixed aortic root was the lowest, with an index of 0.47 compared with 0.91 for that of fresh roots, 0.61 for the fresh valve in fresh root and 0.50 for the glutaraldehyde-treated valve in fresh root. The mean pressure difference during the peak flow also associated the same order with 12 mmHg for the glutaraldehyde-fixed roots, 1.8 mmHg for the fresh roots, 5.3 mmHg for the fresh valve in fresh root and 7.7 mmHg for the glutaraldehyde-treated valve in fresh root. The free hand suturing technique altered the leaflet geometry and caused increased open leaflet bending deformations compared to the fresh root. Both groups of free sewn valves behaved better than the zero pressure fixed root.

CONCLUSIONS

Alteration in leaflet biomechanics is likely to influence long-term valve durability.