In vitro hemodynamic testing of Amplatzer plugs for paravalvular leak occlusion after transcatheter aortic valve implantation

Distensibility of Deformable Aortic Replicas Assessed by an Integrated In-Vitro and In-Silico Approach

The correct estimation of the distensibility of deformable aorta replicas is a challenging issue, in particular when its local characterization is necessary. We propose a combined in-vitro and in-silico approach to face this problem. First, we tested an aortic silicone arch in a pulse-duplicator analyzing its dynamics under physiological working conditions. The aortic flow rate and pressure were measured by a flow meter at the inlet and two probes placed along the arch, respectively. Video imaging analysis allowed us to estimate the outer diameter of the aorta in some sections in time. Second, we replicated the in-vitro experiment through a Fluid-Structure Interaction simulation. Observed and computed values of pressures and variations in aorta diameters, during the cardiac cycle, were compared. Results were considered satisfactory enough to suggest that the estimation of local distensibility from in-silico tests is reliable, thus overcoming intrinsic experimental limitations. The aortic distensibility (AD) is found to vary significantly along the phantom by ranging from 3.0 × 10⁻³ mmHg⁻¹ in the ascending and descending tracts to 4.2 × 10⁻³ mmHg⁻¹ in the middle of the aortic arch. Interestingly, the above values underestimate the AD obtained in preliminary tests carried out on straight cylindrical samples made with the same material of the present phantom. Hence, the current results suggest that AD should be directly evaluated on the replica rather than on the samples of the adopted material. Moreover, tests should be suitably designed to estimate the local rather than only the global distensibility.

Numerical Models Can Assist Choice of an Aortic Phantom for In Vitro Testing

(1) Background: The realization of appropriate aortic replicas for in vitro experiments requires a suitable choice of both the material and geometry. The matching between the grade of details of the geometry and the mechanical response of the materials is an open issue that deserves attention. (2) Methods: To explore this issue, we performed a series of Fluid–Structure Interaction simulations, which compared the dynamics of three aortic models. Specifically, we reproduced a patient-specific geometry with a wall of biological tissue or silicone, and a parametric geometry based on in vivo data made in silicone. The biological tissue and the silicone were modeled with a fiber-oriented anisotropic and isotropic hyperelastic model, respectively. (3) Results: Clearly, both the aorta’s geometry and its constitutive material contribute to the determination of the aortic arch deformation; specifically, the parametric aorta exhibits a strain field similar to the patient-specific model with biological tissue. On the contrary, the local geometry affects the flow velocity distribution quite a lot, although it plays a minor role in the helicity along the arch. (4) Conclusions: The use of a patient-specific prototype in silicone does not a priori ensure a satisfactory reproducibility of the real aorta dynamics. Furthermore, the present simulations suggest that the realization of a simplified replica with the same compliance of the real aorta is able to mimic the overall behavior of the vessel.

Valve-in-valve transcatheter aortic valve replacement to treat multijet paravalvular regurgitation: A case series and review

Treatment advances for severe symptomatic aortic stenosis including transcatheter and open surgical valve replacement have improved patient survival, length of stay, and speed to recovery. However, paravalvular regurgitation (PVR) is occasionally seen and when moderate or greater in severity is associated with an at least 2-fold increase in 1 year mortality. While several treatment approaches focused on single-jet PVR have been described in the literature, few reports describe multijet PVR. Multijet PVR can successfully be treated with a variety of catheter-based options including valve-in-valve (ViV) transcatheter aortic valve replacement (TAVR). We present two patients with at least moderate PVR following aortic valve replacement who were successfully treated with ViV TAVR along with a review of literature highlighting our rationale for utilizing each management approach. Multijet PVR can be treated successfully with ViV TAVR, but additional options such as self-expanding occluder devices and bioprosthetic valve fracture have a role as adjunctive treatments to achieve optimal results. The etiology of multijet PVR can differ between patients, this heterogeneity underscores the paucity of data to guide treatment strategies. Therefore, successful treatment of multijet PVR requires familiarity with available therapeutic options to achieve optimal results and, by extension, decrease patient mortality.

In Vitro and Ex Vivo Hemodynamic Testing of an Innovative Occluder for Paravalvular Leak After Transcather Aortic Valve Implantation

This study aims at achieving a proof-of-concept for a novel device designed to occlude the orifices that may form between transcatheter valves and host tissues after TAVI. The device effect on the performance of a SAPIEN XT with a paravalvular gap was assessed into an in vitro and ex vivo pulse duplicator. The in vitro tests were performed complying with the standard international regulations, measuring the trasvalvular pressure and regurgitant volumes with and without the paravalvular gap, and with the occluder correctly positioned into the gap. In the second series of tests, the leakage reduction due to the presence of the occluder was assessed for the same setup, into a beating swine heart. The occluder implantation decreased the regurgitant fraction of about 50% for the in vitro assessment and 75% for the ex vivo test, under rest operating conditions. These results suggest that suitably designed occluders can lead to important benefit in the PVL treatment.

Complete Unsteady One-Dimensional Model of the Net Aortic Pressure Drop

Background:

A large amount of engineering and medical research has been devoted to the assessment of aortic valve stenosis severity in the past decades. The net transvalvular pressure drop has been recognized as one of the parameters that better reflect stenosis effects on left ventricle overload, and its adoption in clinical assessment of stenosis has been proposed. Flow unsteadiness has been shown to have a non-negligible impact on the net drop; however, a simple formulation for net drop calculation that includes not only flow pulsatility but also the effects of valve dynamics is still lacking.

Objective:

The present contribution is hence aimed at developing a complete unsteady one-dimensional model of the net aortic transvalvular pressure drop that just requires non-invasive data to be implemented.

Methods:

Transvalvular flow is described as a jet of incompressible viscous fluid through a circular orifice placed in a concentric rigid circular tube. The classical one-dimensional mass and total head conservation equations are applied. The effective orifice area and transvalvular flow rate are assumed to vary with time throughout the ejection period.

Results:

The model is found to capture pressure drop oscillations occurring when the valve opens/closes and/or leaflets flutter, thanks to the inclusion of valve dynamics effects. The model is also proposed as a numerical tool for the calculation of the instantaneous effective orifice area once net pressure drop and flow rate are known.

Conclusion:

The model may contribute to the improvement of non-invasive aortic stenosis assessment.

In vitro assessment of pacing as therapy for aortic regurgitation

Background and objective

Clinical evaluation of pacing therapy in mitigating the aortic insufficiency after transchateter aortic valve implantation often gives contradictory outcomes. This study presents an in vitro investigation aimed at clarifying the effect of pacing on paravalvular leakage.

Methods

A series of in vitro tests reproducing the heart operating changes clinically obtained by pacing was carried out in a 26 mm Edwards Sapien XT prosthesis with mild paravalvular leakage. The effect of pacing on the regurgitant volumes per cycle and per minute was quantified, and the energy and power consumed by the left ventricle were calculated.

Results

Results indicate that though pacing results in some reduction in the total regurgitation per cycle, the volume of fluid regurgitating per minute increases substantially, causing overload of left ventricle.

Conclusions

Our tests indicate no effective haemodynamic benefit from pacing, suggesting a prudential clinical use of this therapy for the treatment of postoperative aortic regurgitation.

Valve-in-Valve Transcatheter Aortic Valve Implantation: A Novel Approach to Treat Paravalvular Leak

Enlarging or "cracking" a surgical stented bioprosthetic valve during valve-in-valve transcatheter aortic valve implantation (TAVI) increases orifice area, reducing transvalvular energy losses. We demonstrate that TAVI with valve cracking can be used to treat paravalvular leak (PVL) while providing optimal aortic valve physiology. A 61-year-old woman with a history of aortic valve replacement with a stented bioprosthesis presented with heart failure. Transthoracic echocardiography revealed severe prosthetic aortic valve stenosis with PVL and severe regurgitation. The patient underwent valve-in-valve TAVI with valve cracking. This successfully treated both the stenosis and the PVL with regurgitation.

Percutaneous Closure of Paravalvular Regurgitation After Transcatheter Aortic Valve Implantation: A Systematic Review

Paravalvular regurgitation (PVR) remains one of the drawbacks of transcatheter aortic valve implantation (TAVI). Details of percutaneous closure (PCC) of PVR after TAVI remain obscure. We aimed to explore the patient characteristics, procedural details, closure devices used, and outcomes of PCC after TAVI. A systematic search of the MEDLINE/PubMed and Embase databases from January 2002 to September 2015 was conducted. Reports considered to include same patient were excluded and only the studies with largest cohorts were included. A total of 14 studies including 58 patients (61 cases) were included in the study. A balloon-expandable (BE) valve was used more frequently compared with a self-expandable (SE) valve (72.6% vs 27.4%, respectively). The mean success rate was 86.9% (100% and 77.8%, respectively; P = 0.097). The median number of closure devices used was 1 (range, 1-4) and did not differ between SE and BE valves (P = 0.71). Mean time from index procedure to PCC did not differ between SE and BE valves (295 ± 380 days vs 379 ± 353 days; P = 0.71). Seven patients had history of valve-in-valve and 6 patients had procedural success. Among the patients with available follow-up data (94.8%), there were 15 deaths (27.3%). Percutaneous closure of PVR after TAVI had a high success rate in selected patients in both BE and SE valves. The success rate, timing, and number of closure devices were similar between BE and SE valves. However, prognosis remains fairly poor.