A Computational Study on Deformed Bioprosthetic Valve Geometries: Clinically Relevant Valve Performance Metrics.

Transcatheter aortic valves (TAV) are symmetrically designed, but they are often not deployed inside cylindrical conduits with circular cross-sectional areas. Many TAV patients have heavily calcified aortic valves, which often result in deformed prosthesis geometries after deployment. We investigated the effects of deformed valve annulus configurations on a surgical bioprosthetic valve as a model for TAV. We studied valve leaflet motions, stresses and strains, and analog hydrodynamic measures (using geometric methods), via finite element (FE) modeling. Two categories of annular deformations were created to approximate clinical observations: (1) noncircular annulus with valve area conserved, and (2) under-expansion (reduced area) compared to circular annulus. We found that under-expansion had more impact on increasing stenosis (with geometric orifice area metrics) than noncircularity, and that noncircularity had more impact on increasing regurgitation (with regurgitation orifice area metrics) than under-expansion. We found durability predictors (stress/strain) to be the highest in the commissure regions of noncircular configurations such as EllipMajor (noncircular and under-expansion areas). Other clinically relevant performance aspects such as leaflet kinematics and coaptation were also investigated with the noncircular configurations. This study provides a framework for choosing the most challenging TAV deformations for acute and long-term valve performance in the design and testing phase of device development.

Aortic Valve Cusp Coaptation Surface Area Using 3-Dimensional Transesophageal Echocardiography Correlates with Severity of Aortic Valve Insufficiency.

OBJECTIVE: The aim of this study was to test both in humans and using finite element (FE) aortic valve (AV) models whether the coaptation surface area (CoapSA) correlates with aortic insufficiency (AI) severity due to dilated aortic roots to determine the validity and utility of 3-dimensional transesophageal echocardiographic-measured CoapSA. DESIGN: Two-pronged, clinical and computational approach. SETTING: Single university hospital. PARTICIPANTS: The study comprised 10 patients with known AI and 98 FE simulations of increasingly dilated human aortic roots. INTERVENTIONS: The CoapSA was calculated using intraoperative 3-dimensional transesophageal echocardiography data of patients with isolated AI and compared with established quantifiers of AI. In addition, the CoapSA and effective regurgitant orifice area (EROA) were determined using FE simulations. MEASUREMENTS AND MAIN RESULTS: In the 10 AI patients, regurgitant fraction (RF) increased with EROA (R2 = 0.77, p = 0.0008); CoapSA decreased with RF (R2 = 0.72, p = 0.0020); CoapSA decreased with EROA (R2 = 0.71, p = 0.0021); and normalized CoapSA (CoapSA / [Ventriculo-Aortic Junction × Sinotubular Junction]) decreased with EROA (R2 = 0.60, p = 0.0088). In the 98 FE simulations, normalized CoapSA decreased with EROA (R2 = 0.50, p = 0.0001). CONCLUSIONS: In both human and FE AV models, CoapSA was observed to be inversely correlated with AI severity, EROA, and RF, thereby supporting the validity and utility of 3D TEE-measured CoapSA. A clinical implication is the expectation that high values of CoapSA, measured intraoperatively after AV repairs, would correlate with better long-term outcomes of those repairs.

Planar biaxial testing of heart valve cusp replacement biomaterials: Experiments, theory and material constants.

OBJECTIVES: Aortic valve (AV) repair has become an attractive option to correct aortic insufficiency. Yet, cusp reconstruction with various cusp replacement materials has been associated with greater long-term repair failures, and it is still unknown how such materials mechanically compare with native leaflets. We used planar biaxial testing to characterize six clinically relevant cusp replacement materials, along with native porcine AV leaflets, to ascertain which materials would be best suited for valve repair. METHODS: We tested at least six samples of: 1) fresh autologous porcine pericardium (APP), 2) glutaraldehyde fixed porcine pericardium (GPP), 3) St Jude Medical pericardial patch (SJM), 4) CardioCel patch (CC), 5) PeriGuard (PG), 6) Supple PeriGuard (SPG) and 7) fresh porcine AV leaflets (PC). We introduced efficient displacement-controlled testing protocols and processing, as well as advanced convexity requirements on the strain energy functions used to describe the mechanical response of the materials under loading. RESULTS: The proposed experimental and data processing pipeline allowed for a robust in-plane characterization of all the materials tested, with constants determined for two Fung-like hyperelastic, anisotropic strain energy models. CONCLUSIONS: Overall, CC and SPG (respectively PG) patches ranked as the closest mechanical equivalents to young (respectively aged) AV leaflets. Because the native leaflets as well as CC, PG and SPG patches exhibit significant anisotropic behaviors, it is suggested that the fiber and cross-fiber directions of these replacement biomaterials be matched with those of the host AV leaflets. STATEMENT OF SIGNIFICANCE: The long-term performance of cusp replacement materials would ideally be evaluated in large animal models for AV disease and cusp repair, and over several months or more. Given the unavailability and impracticality of such models, detailed information on stress-strain behavior, as studied herein, and investigations of durability and valve dynamics will be the best surrogates, as they have been for prosthetic valves. Overall, comparison with Fig. 3 suggests that CC and SPG (respectively PG) patches may be the closest mechanical equivalents to young (respectively aged) AV leaflets. Interestingly, the thicknesses of these materials are close to those reported for porcine and younger human AV leaflets, which may facilitate surgical implantation, by contrast to the thinner APP which has poor handling qualities. Because the native leaflets as well as CC, PG and SPG patches exhibit anisotropic behaviors, from a mechanistic perspective alone, it stands to reason that cardiac surgeons should seek to intraoperatively match the fiber and cross-fiber directions of these replacement biomaterials with those of the repaired AV leaflets.

Impact of aortic annular geometry on aortic valve insufficiency: Insights from a preclinical, ex vivo, porcine model.

OBJECTIVES: We sought to create a model of aortic insufficiency in a left heart simulator combined with 3-dimensional echocardiography and finite element modeling of the aortic valve. We examined the effects of aortic root geometry alteration on aortic insufficiency. METHODS: Porcine aortic roots were analyzed on a left heart simulator before (control, n = 8) and after intervention (n = 8). Intervention entailed 3 vertical incisions at the sinotubular junction with diamond-shaped patches incorporated into the defects to increase the sinotubular junction diameter. Hemodynamic parameters were assessed, including regurgitant volume and fraction. Video and echocardiography images evaluated aortic valve function, coaptation surface area, aortic insufficiency, and effective regurgitant orifice area. Finite element modeling corroborated relationships between root geometry and aortic insufficiency, and examined cusp stress. RESULTS: The intervention resulted in a sinotubular junction diameter increase of 55% ± 4%. The sinotubular junction to ventriculo-aortic junction diameter ratio was significantly higher in the intervention group (1.89 ± 0.16 vs 1.47 ± 0.04, P = .02). Increased sinotubular junction diameter resulted in aortic insufficiency assessed by regurgitant volume (28 ± 7 mL vs 5 ± 2 mL, P = .004), regurgitant fraction (36% ± 5% vs 7% ± 1%, P < .001), and effective regurgitant orifice (15 ± 5 mm(2) vs 0 mm(2), P = .016). Intervention coaptation surface area was smaller (1.03 ± 0.11 cm(2) vs 1.80 ± 0.08 cm(2), P < .001). There was a linear correlation between increased sinotubular junction/ventriculo-aortic junction ratio and regurgitant fraction (R(2) = 0.65, P = .003). The finite element modeling demonstrated a similar relationship between increasing sinotubular junction diameter and aortic insufficiency severity, and between end-diastolic cusp stresses and sinotubular junction diameters (R(2) = 0.98, P < .001). CONCLUSIONS: In this model, increasing sinotubular junction diameter is linearly related to reduced coaptation surface area and increasing aortic insufficiency severity. This model provides new insights into aortic insufficiency mechanisms and may be used to evaluate novel interventions for aortic valve repair.