The influence of size mismatch on the hemodynamic performance of the pulmonary autograft in vitro

Objectives: We established an in vitro model to investigate the effect of s ize mismatch between the aortic and pulmonary root on the hydrodynamic perf ormance and leaflet motion of the pulmonary autograft. Methods: Ten fresh p orcine pulmonary roots (annulus diameter: 19-25 mm) were tested in a pulsat ile flow simulator. The autografts then were implanted in fresh porcine aor tic roots (annulus diameter: 19-30 mm) and retested in the flow simulator. Three roots were oversized by 21-39%, three were undersized by 32-45% and t here were four size for size implantations. The external diameter of the ro ots and autografts was measured at the sinotubular junction at hydrostatic pressures of 0-120 mmHg. The transvalvular gradient and regurgitation were also measured and the effective orifice area was calculated. The leaflet mo tion was recorded on video. Results: The fresh pulmonary roots were more co mpliant than the fresh aortic roots (46 +/- 8.4% vs. 35 +/- 7.8% dilatation from 0 to 120 mmHg). The group of matching size autografts dilated by 43 /- 4.9% in the same pressure ranger The external diameter of the undersized autografts was 10 +/- 2.1% bigger than before implantation at 0 pressure a nd then the dilatation was 40 +/- 5.3% at 120 mmHg. The oversized implantat ion made the autografts 11 +/- 9.4% smaller in their relaxed state, but the n they dilated by 65 +/- 11% as the pressure increased to 120 mmHg, resulti ng in a net dilatation of 54% over the original undilated state. The under or oversizing had little effect on the pressure gradient measured across th e valves (5.6 +/- 2.57 mmHg before, 6.3 +/- 3.27 mmHg after implantation). Only the oversized valves showed significantly higher gradients than the na tive pulmonary valves. The effective orifice area of the undersized autogra fts was slightly bigger and the oversized autografts was slightly smaller a fter implantation, although the differences were not significant. The size mismatch did not cause regurgitation on the valves. The video images showed very low-open leaflet-bending deformation, both on the fresh pulmonary and the autograft valves. Conclusion: Under or oversizing the pulmonary autogr aft up to 40% of the annulus diameter did not affect the hydrodynamic param eters significantly. The compliance of the autograft root was able to compe nsate for the size mismatch without adversely influencing the valve perform ance. (C) 1999 Elsevier Science B.V. All rights reserved.