Effect of the sinus of valsalva on the closing motion of bileaflet prosthetic heart valves

Novel insights by 4D Flow imaging on aortic flow physiology after valve-sparing root replacement with or without neosinuses

OBJECTIVES

This study was undertaken to evaluate the flow dynamics in the aortic root after valve-sparing root replacement with and without neosinuses of Valsalva reconstruction, by exploiting the capability of 4D Flow imaging to measure in vivo blood velocity fields and 3D geometric flow patterns.

METHODS

Ten patients who underwent valve-sparing root replacement utilizing grafts with neosinuses or straight tube grafts (5 cases each) were evaluated by 4D Flow imaging at a mean of 46.5 months after surgery. We used in-house processing tools to quantify relevant bulk flow variables (flow rate, stroke volume, peak velocity and mean velocity), wall shear stresses and the amount of flow rotation characterizing the region enclosed by the graft and the aortic valve leaflets.

RESULTS

Despite bulk flows with similar peak velocities, flow rates and stroke volumes (P = 0.31-1.00), the neosinuses graft was associated with a lower mean velocity (P < 0.03) and magnitude of wall shear stress along the axial direction of the vessel wall (P < 0.05) at the proximal root level but remained comparable along the circumferential direction (P = 0.22-1.0) to the straight tube graft. Flow rotation was evidently and systematically higher in the neosinuses grafts, characterized by streamline rotations higher than 270°, nearly triple that of tubular grafts (10.3 ÷ 14.0% of all aortic streamline vs 2.2 ÷ 5.7%, P = 0.008).

CONCLUSIONS

Recreation of the sinuses of Valsalva during valve-sparing root replacement is associated with significantly lower wall shear stress and organized vortical flows at the level of the sinus that are not evident using the straight tube graft. These findings need confirmation in larger studies and could have important implications in terms of aortic valve durability.

Time-Resolved PIV Technique for High Temporal Resolution Measurement of Mechanical Prosthetic Aortic Valve Fluid Dynamics

Prosthetic heart valves (PHVs) have been used to replace diseased native valves for more than five decades. Among these, mechanical PHVs are the most frequently implanted. Unfortunately, these devices still do not achieve ideal behavior and lead to many complications, many of which are related to fluid mechanics. The fluid dynamics of mechanical PHVs are particularly complex and the fine-scale characteristics of such flows call for very accurate experimental techniques. Adequate temporal resolution can be reached by applying time-resolved PIV, a high-resolution dynamic technique which is able to capture detailed chronological changes in the velocity field. The aim of this experimental study is to investigate the evolution of the flow field in a detailed time domain of a commercial bileaflet PHV in a mock-loop mimicking unsteady conditions, by means of time-resolved 2D Particle Image Velocimetry (PIV). The investigated flow field corresponded to the region immediately downstream of the valve plane. Spatial resolution as in “standard” PIV analysis of prosthetic valve fluid dynamics was used. The combination of a Nd:YLF high-repetition-rate double-cavity laser with a high frame rate CMOS camera allowed a detailed, highly temporally resolved acquisition (up to 10000 fps depending on the resolution) of the flow downstream of the PHV. Features that were observed include the non-homogeneity and unsteadiness of the phenomenon and the presence of large-scale vortices within the field, especially in the wake of the valve leaflets. Furthermore, we observed that highly temporally cycle-resolved analysis allowed the different behaviors exhibited by the bileaflet valve at closure to be captured in different acquired cardiac cycles.

By accurately capturing hemodynamically relevant time scales of motion, time-resolved PIV characterization can realistically be expected to help designers in improving PHV performance and in furnishing comprehensive validation with experimental data on fluid dynamics numeric modelling.

Development of a completely autologous valved conduit with the sinus of Valsalva using in-body tissue architecture technology: a pilot study in pulmonary valve replacement in a beagle model

BACKGROUND

We developed autologous prosthetic implants by simple and safe in-body tissue architecture technology. We present the first report on the development of autologous valved conduit with the sinus of Valsalva (BIOVALVE) by using this unique technology and its subsequent implantation in the pulmonary valves in a beagle model.

METHODS AND RESULTS

A mold of BIOVALVE organization was assembled using 2 types of specially designed silicone rods with a small aperture in a trileaflet shape between them. The concave rods had 3 projections that resembled the protrusions of the sinus of Valsalva. The molds were placed in the dorsal subcutaneous spaces of beagle dogs for 4 weeks. The molds were covered with autologous connective tissues. BIOVALVEs with 3 leaflets in the inner side of the conduit with the sinus of Valsalva were obtained after removing the molds. These valves had adequate burst strength, similar to that of native valves. Tight valvular coaptation and sufficient open orifice area were observed in vitro. These BIOVALVEs were implanted to the main pulmonary arteries as allogenic conduit valves (n=3). Postoperative echocardiography demonstrated smooth movement of the leaflets with trivial regurgitation. Histological examination of specimens obtained at 84 days showed that the surface of the leaflet was covered by endothelial cells and neointima, including an elastin fiber network, and was formed at the anastomosis sides on the luminal surface of the conduit.

CONCLUSIONS

We developed the first completely autologous BIOVALVE and successfully implanted these BIOVALVEs in a beagle model in a pilot study.

Preparation of in-vivo tissue-engineered valved conduit with the sinus of Valsalva (type IV biovalve)

A novel autologous valved conduit with the sinus of Valsalva-defined as a type IV biovalve-was created in rabbits by "in-body tissue-architecture" technology with a specially designed mold for the valve leaflets and the sinus of Valsalva and a microporous tubular scaffold for the conduit. The mold included 2 rods composed of silicone substrates. One was concave shaped, with 3 projections resembling the sinus of Valsalva; the other was convex shaped. The connection between the rods was designed to resemble the closed form of a trileaflet valve. The 2 rods were connected with a small aperture of 500-800 microm, which bound membranous connective tissue obtained from the dorsal subcutaneous layer of a rabbit. The rods were placed in a polyurethane scaffold that had many windows in its center. Both ends of the scaffold were tied with thread for fixation, and this assembly was embedded for 1 month in a subcutaneous pouch in the same Japanese white rabbit from which the connective tissue was obtained. After 1 month, all the surfaces of the implant were found to be completely covered with newly developed connective tissue. The substrates were removed from both sides of the harvested cylindrical implant, and homogenous well-balanced trileaflet-shaped membranous tissue was found inside the developed conduit with 3 protrusions resembling the sinus of Valsalva. The trileaflet valve closed and opened rapidly in synchrony with the backward and forward flow of a pulsatile flow circuit in vitro.

Expanded polytetrafluoroethylene valved conduit and patch with bulging sinuses in right ventricular outflow tract reconstruction

OBJECTIVES

No specific prosthetic material is currently recognized as being the most suitable for right ventricular outflow tract reconstruction for congenital heart defects. Prosthetic valves are subject to wear and stress because they do not create vortex flow, which helps natural valves to close. We designed a fan-shaped expanded polytetrafluoroethylene valved conduit and patch with bulging sinuses that create vortex flow, making them more reliable over the long term.

METHODS

Bulging sinuses were formed on a sheet of expanded polytetrafluoroethylene using a specially designed mold. Fan-shaped expanded polytetrafluoroethylene sheets (0.1 mm thick) were anastomosed to the edge of the bulging sinuses as valve leaflets, creating monocuspid, bicuspid, or tricuspid valves. These valves were implanted in 157 patients undergoing right ventricular outflow tract reconstruction (age 16 days to 45.4 years, median 2.0 years), in 48 patients as a conduit, and in 109 patients as a patch. Valve function was followed up by echocardiography for 5.6 to 63.7 months (mean 20.8 months).

RESULTS

There was no mortality or morbidity, and no patients required reoperation during follow-up. No patients had stenosis, and regurgitation was less than mild in all patients with conduits and moderate in 15 patients (13.8%) with patches, but moderate regurgitation did not further develop during follow-up. Valve motion was fully maintained in all patients.

CONCLUSIONS

The expanded polytetrafluoroethylene valved conduits and patches with bulging sinuses showed excellent early-to-midterm results. The valved conduits and patches seem to be promising alternatives to homografts in right ventricular outflow tract reconstruction. Their function will be followed up further.

The Closing Behavior of Mechanical Aortic Heart Valve Prostheses

Mechanical artificial heart valves rely on reverse flow to close their leaflets. This mechanism creates regurgitation and water hammer effects that may form cavitations, damage blood cells, and cause thromboembolism. This study analyzes closing mechanisms of monoleaflet (Medtronic Hall 27), bileaflet (Carbo-Medics 27; St. Jude Medical 27; Duromedics 29), and trileaflet valves in a circulatory mock loop, including an aortic root with three sinuses. Downstream flow field velocity was measured via digital particle image velocimetry (DPIV). A high speed camera (PIVCAM 10-30 CCD video camera) tracked leaflet movement at 1000 frames/s. All valves open in 40-50 msec, but monoleaflet and bileaflet valves close in much less time (< 35 msec) than the trileaflet valve (>75 msec). During acceleration phase of systole, the monoleaflet forms a major and minor flow, the bileaflet has three jet flows, and the trileaflet produces a single central flow like physiologic valves. In deceleration phase, the aortic sinus vortices hinder monoleaflet and bileaflet valve closure until reverse flows and high negative transvalvular pressure push the leaflets rapidly for a hard closure. Conversely, the vortices help close the trileaflet valve more softly, probably causing less damage, lessening back flow, and providing a washing effect that may prevent thrombosis formation.