Wall stresses of early remodeled pulmonary autografts

Abstract

Objective: The Ross procedure is an excellent option for children or young adults who need aortic valve replacement because it can restore survival to that of the normal aged-matched population. However, autograft remodeling can lead to aneurysmal formation and reoperation, and the biomechanics of this process is unknown. This study investigated postoperative autograft remodeling after the Ross procedure by examining patient-specific autograft wall stresses.

Methods: Patients who have undergone the Ross procedure who had intraoperative pulmonary root and aortic specimens collected were recruited. Patient-specific models (n = 16) were developed using patient-specific material property and their corresponding geometry from cine magnetic resonance imaging at 1-year follow-up. Autograft ± Dacron for aneurysm repair and ascending aortic geometries were reconstructed to develop patient-specific finite element models, which incorporated material properties and wall thickness experimentally measured from biaxial stretching. A multiplicative approach was used to account for prestress geometry from in vivo magnetic resonance imaging. Pressure loading to systemic pressure (120/80) was performed using LS-DYNA software (LSTC Inc, Livermore, Calif).

Results: At systole, first principal stresses were 809 kPa (25%-75% interquartile range, 691-1219 kPa), 567 kPa (485-675 kPa), 637 kPa (555-755 kPa), and 382 kPa (334-413 kPa) at the autograft sinotubular junction, sinuses, annulus, and ascending aorta, respectively. Second principal stresses were 360 kPa (310-426 kPa), 355 kPa (320-394 kPa), 272 kPa (252-319 kPa), and 184 kPa (147-222 kPa) at the autograft sinotubular junction, sinuses, annulus, and ascending aorta, respectively. Mean autograft diameters were 29.9 ± 2.7 mm, 38.3 ± 5.3 mm, and 26.6 ± 4.0 mm at the sinotubular junction, sinuses, and annulus, respectively.

Conclusions: Peak first principal stresses were mainly located at the sinotubular junction, particularly when Dacron reinforcement was used. Patient-specific simulations lay the foundation for predicting autograft dilatation in the future after understanding biomechanical behavior during long-term follow-up.

Keywords: Ross procedure; computational modeling; dilatation; finite element analysis; pulmonary autograft; remodeling; wall stress.

Figure 1.

Representative 3D mesh models of pulmonary autograft and ascending aorta without(a) and with Dacron interposition graft(b); cross section of autograft and ascending aorta mesh showing the thickness variation without(c) and with Dacron interposition(d).

Figure 2.

a. First principal wall stress profiles (circumferential stresses) of patient-specific autograft and ascending aorta models (top) b. Second principal wall stress profiles (longitudinal stresses) of patient-specific autograft and ascending aorta models (bottom). First row and the first 3 of the second row had Dacron interposition graft to the ascending aorta and the remaining did not have Dacron graft. Each individual patient in left-to-right order in (a) is reflected in the same order in (b).

Figure 3.

Comparison of autograft subregions and ascending aorta: peak first (a) and second (b) principal wall stresses (solid markers=patients with Dacron interposition; unfilled markers=patients without Dacron interposition; black bar=median value). The first and second principal stresses on sinotubular junction, sinus, and autograft annulus were higher than ascending aorta. The second principal stresses on sinuses were larger than that in the annulus.

Figure 3.

Comparison of autograft subregions and ascending aorta: peak first (a) and second (b) principal wall stresses (solid markers=patients with Dacron interposition; unfilled markers=patients without Dacron interposition; black bar=median value). The first and second principal stresses on sinotubular junction, sinus, and autograft annulus were higher than ascending aorta. The second principal stresses on sinuses were larger than that in the annulus.

Figure 4.

Of 290 patients undergoing Ross procedure at Montreal Heart Institute, a subset of n=16 patients had autograft and aortic tissue removed during surgery for biaxial stretch testing for material properties and postoperative magnetic resonance imaging at 1 year. Patient-specific modeling of pulmonary autografts were performed using 3D patient-specific imaging and material properties. Finite element analyses were performed to determine wall stresses in the autograft and ascending aorta. Pulmonary autograft had significantly higher wall stresses than distal ascending aorta (native internal control) which could drive remodeling over time. Future clinical follow-up can provide understanding of autograft biomechanics in relation to clinical dilatation.

Central Figure

First principal stresses of representative patient-specific autograft, ascending aorta, and Dacron graft.