Maximilian Kuetting

Fluid-Structure Interaction Model of a Percutaneous Aortic Valve: Comparison with an In Vitro Test and Feasibility Study in a Patient-Specific Case.

Transcatheter aortic valve replacement (TAVR) represents an established recent technology in a high risk patient base. To better understand TAVR performance, a fluid–structure interaction (FSI) model of a self-expandable transcatheter aortic valve was proposed. After an in vitro durability experiment was done to test the valve, the FSI model was built to reproduce the experimental test. Lastly, the FSI model was used to simulate the virtual implant and performance in a patient-specific case. Results showed that the leaflet opening area during the cycle was similar to that of the in vitro test and the difference of the maximum leaflet opening between the two methodologies was of 0.42%. Furthermore, the FSI simulation quantified the pressure and velocity fields. The computed strain amplitudes in the stent frame showed that this distribution in the patient-specific case is highly affected by the aortic root anatomy, suggesting that the in vitro tests that follow standards might not be representative of the real behavior of the percutaneous valve. The patient-specific case also compared in vivo literature data on fast opening and closing characteristics of the aortic valve during systolic ejection. FSI simulations represent useful tools in determining design errors or optimization potentials before the fabrication of aortic valve prototypes and the performance of tests.

In vitro assessment of the influence of aortic annulus ovality on the hydrodynamic performance of self-expanding transcatheter heart valve prostheses

BACKGROUND Although CT-studies as well as intraoperative analyses have described broad anatomic variations of the aortic annulus, which is predominantly found non-circular, commercially available transcatheter aortic heart valve prostheses are circular. In this study, we hypothesize that the in vitro hydrodynamic function of a self-expanding transcatheter heart valve (Medtronic CoreValve) assessed in an oval compartment representing the aortic annulus will differ from the conventionally used circular compartment. METHODS Medtronic CoreValve prostheses were tested in specifically designed and fabricated silicone compartments with three degrees of defined ovalities. The measurements were performed in a left heart simulator at three different flow rates. In this setting, regurgitation flow, effective orifice area, and systolic pressure gradient across the valve were determined. In addition, high speed video recordings were taken to investigate leaflet kinematics. RESULTS The pressure difference across the prosthesis increased with rising ovality. The effective orifice areas were only slightly impacted. The analyses of the regurgitation showed minor changes and partially lower regurgitation when switching from round to slightly oval settings, followed by strong increases for further ovalization. The high speed videos show minor central leakage and impaired leaflet apposition for strong ovalities, but no leaflet/stentframe contact in any setting. CONCLUSION This study quantifies the influence of oval expansion of transcatheter heart valve prostheses on their hydrodynamic performance. While slight ovalities were well tolerated by a self-expanding prosthesis, more significant ovality led to worsening of prosthesis function and regurgitation.

In Vitro Evaluation of a Novel Hemodynamically Optimized Trileaflet Polymeric Prosthetic Heart Valve

Calcific aortic valve disease is the most common and life threatening form of valvular heart disease, characterized by stenosis and regurgitation, which is currently treated at the symptomatic end-stages via open-heart surgical replacement of the diseased valve with, typically, either a xenograft tissue valve or a pyrolytic carbon mechanical heart valve. These options offer the clinician a choice between structural valve deterioration and chronic anticoagulant therapy, respectively, effectively replacing one disease with another. Polymeric prosthetic heart valves (PHV) offer the promise of reducing or eliminating these complications, and they may be better suited for the new transcatheter aortic valve replacement (TAVR) procedure, which currently utilizes tissue valves. New evidence indicates that the latter may incur damage during implantation. Polymer PHVs may also be incorporated into pulsatile circulatory support devices such as total artificial heart and ventricular assist devices that currently employ mechanical PHVs. Development of polymer PHVs, however, has been slow due to the lack of sufficiently durable and biocompatible polymers. We have designed a new trileaflet polymer PHV for surgical implantation employing a novel polymer-xSIBS-that offers superior bio-stability and durability. The design of this polymer PHV was optimized for reduced stresses, improved hemodynamic performance, and reduced thrombogenicity using our device thrombogenicity emulation (DTE) methodology, the results of which have been published separately. Here we present our new design, prototype fabrication methods, hydrodynamics performance testing, and platelet activation measurements performed in the optimized valve prototype and compare it to the performance of a gold standard tissue valve. The hydrodynamic performance of the two valves was comparable in all measures, with a certain advantage to our valve during regurgitation. There was no significant difference between the platelet activation rates of our polymer valve and the tissue valve, indicating that similar to the latter, its recipients may not require anticoagulation. This work proves the feasibility of our optimized polymer PHV design and brings polymeric valves closer to clinical viability.

Review of Recent Patents on Foldable Ventricular Assist Devices

Abstract: Congestive heart failure accounts for a high morbidity worldwide. The only effective treatment for end-stage patients is heart transplantation or, in light of the shortage of suitable donors, an artificial heart or ventricular assist device (VAD). The newer-generation continuous-flow rotary VADs allow for a significant reduction in size and an improvement in reliability. However, the invasive implantation still limits this technology from being offered to critically ill patients. To benefit more heart failure patients, there is a need to develop a long-term VAD which can be implanted via minimally in-vasive procedure. Recently, expandable/deployable devices have been investigated as a potential solution. Such a device can be inserted percutaneously via the peripheral vessels in its collapsed form and operate in its expanded form at the de-sired location. This paper reviews significant patents on foldable VADs using mechanical and/or material means. Me-chanically folded structures adapt joints and links to facilitate the folding process whilst utilization of elastic materials al-lows the structure to be bent or twisted without permanent deformation. Current and future developments of foldable VADs are discussed. Foldable pumps could generate less blood damage and mechanical wear as compared to current miniature percutaneous VADs. Therefore, foldable VADs have the potential for longer-term application and minimally invasive insertion, providing a promising solution for heart failure patients.

Fluid–Structure Simulation of a Transcatheter Aortic Valve Implantation: Potential Application to Patient-Specific Cases

Valve diseases are more and more treated with transcatheter aortic valves. This work is based on an experimental setup with the corresponding fluid–structure interaction model to show the feasibility of performing accurate simulations which is able to capture the main behavior of a transcatheter valve both from structural and fluid dynamic points of view. The application of this methodology to patient-specific cases is also illustrated.

Right heart transcatheter valve therapies - a review of prostheses for the pulmonary and tricuspid positions

Minimally invasive, catheter-based treatment of valvular dysfunction has become an integral part of clinical routine. As left heart valvular disease is much more common and thus commercially of interest, transcatheter solutions for the treatment of aortic and mitral valvular defects were the first to become broadly clinically available, while even today options for the right heart valve are rare. This review looks at innovative attempts at developing effective transcatheter heart valve prostheses for the pulmonary and tricuspid heart valves, details their experience and highlights those that have made their way to application in humans.