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

doi:10.1016/j.jbiomech.2014.01.024

Journal of Biomechanics

Volume 47, Issue 5, 21 March 2014, Pages 957-965

https://doi.org/10.1016/j.jbiomech.2014.01.024 Get rights and content

Abstract

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.

Introduction

Percutaneous heart valve implantation is the therapy of choice for patients with severe symptomatic aortic valve stenosis who cannot undergo surgery (Vahanian et al., 2013). In the context of preprocedural planning, the assessment of various anatomic factors is essential. Although CT-studies as well as intraoperative analyses have described broad anatomic variations of the aortic annulus, which is predominantly non-circular (Tops et al., 2008, Zegdi et al., 2008, Schultz et al., 2009), transcatheter heart valves (THV) are round-shaped. While this mismatch can be reshaped surgically in open heart valve implantation, transcatheter heart valve prostheses anchor in the native anatomy. Deformation of these devices due to annulus anatomy or heavily calcified valve leaflets can lead to an oval valve orifice and associated poor function (Schultz et al., 2011). Intra-procedurally, this finding can be addressed by post-dilatation of the prosthesis in most of the cases (Daneault et al., 2013). However, post-dilatation can be associated with relevant complications, such as aortic annular rupture and cerebrovascular events (Schultz et al., 2011) and may potentially impair leaflet function. Published data on post-implantation visualization of the implanted prosthesis indicate that non-circular expansion of percutaneous heart valves occurs frequently, especially in self-expanding prostheses (Schultz et al., 2009). To date, no studies on the influence of an oval annulus and thus an oval heart valve opening area on the hydrodynamic performance of a transcatheter heart valve have been published.

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.

Section snippets

Methods

In this study, we investigate the Medtronic CoreValve^® transcatheter prosthesis in two commercially available sizes (26 mm and 29 mm). This heart valve consists of a self-expanding nitinol frame with porcine pericardial leaflets and has been evaluated in multiple clinical settings (Gilard et al., 2012, Ussia et al., 2012).

Compartment design

To achieve reproducible testing conditions, silicone compartments resembling aortic roots were designed using CAD [ProEngineer Wildfire 5.0, PTC, USA]. The outline of the aortic roots was defined by the equations determined by Reul et al. to describe the shape of the human aortic root (Reul et al., 1990). In order to include the influence of ovality in the created models, the curve defining the annulus could be altered to resemble an ellipsis with two defined axes. The relation between the two

Hydrodynamic measurements

The prostheses were positioned in the oval compartments and heated to a physiological temperature of 37 °C to ensure proper stent expansion (Fig. 3). Radial positioning was maintained throughout all measurements, with one commissure lining up with the ridge between two sinuses, which in turn was lined up with the rest of the pulse duplicator. The shape of the valve and compartment were examined by caliper to confirm the degree of ovality following device expansion. The implantation height was

Results

The results of the hydrodynamic tests are listed in Table 2.

Systolic pressure gradient

With the use of the 26 mm CoreValve^® prosthesis, we found increasing systolic pressure gradients with increasing ovality (Fig. 7). The pressure gradient also was found to increase with increased flow rate. The rate of increase was comparable for all prosthesis/compartment pairings and flow conditions. The measurements with the 26 mm prosthesis in the A3 compartment all showed a pressure gradient which is approximately twice that of the round A1 compartment. The increase from B1 to B3 for the 29 mm

Effective orifice area (EOA)

ISO 5840-3 requires an effective orifice area of 1.25 cm³ for the 23 mm compartments and 1.575 cm³ for the 26 mm compartments. This requirement was met in all measurements (Fig. 8). The effective orifice was slightly lower in the oval compartments, with the exception of the 3 l/min measurement points. An increase was observed for each prosthesis/compartment pairing with increasing flow rate.

Regurgitation

The amount of regurgitation was analyzed in volume and in percent of the total stroke volume (forward flow volume including regurgitation) (Fig. 9). The regurgitation volume is made up of the closure volume and the leakage volume. The closure volume was largely unaffected when switching from a round to a slightly oval compartment for all flow rates. Further increases in ovality of the compartment led to an increase in the closure volume for all prosthesis/compartment pairings. The amount of

Leaflet kinematics

The high-speed video recordings of the prosthesis revealed differences in the opening characteristics for the different ovalities (Fig. 11a–c). These were reflected mainly in shapes of the orifices of the valves during opening. All prostheses opened completely, with stronger ovalities showing more leaflet motion during mid-to-end systole. No leaflet stentframe contact was observed for any of the measurements. In the measurements performed in the A3 and B3 compartments, incomplete leaflet

Discussion

To our knowledge, this study is the first to describe the in vitro impact of an oval aortic annulus on the hydrodynamic performance of transcatheter heart valves. Although transcatheter heart valves are round in design, implantation of these valves commonly results in an elliptical/oval fashion. Such deformation is of special interest in self-expanding heart valves, but has also been described with balloon-expandable heart valves (Allam et al., 2012). In our study, we found an increase of

Limitations

The valve/annulus pairings chosen for this study were at the upper end of their range, meaning that the amount of valve oversizing was minimal. For example, performing the same measurements with a 26 mm in a 21 mm or 22 mm annulus might have led to the prosthesis exerting a higher radial force and achieving a better seal. In general, the regurgitation volumes in our study were high which is particularly visible for the 29 mm CoreValve^® in the 26 mm compartments at the 3 l/min and 5 l/min measurement

Future outlook

The influence of annulus ovality needs to be further evaluated and will need to be considered within the planning of transcatheter heart valve replacement procedures as well as the development and approval testing of future devices.

Our in vitro data suggests that the definition of a maximum ovality as a cut off for transcatheter heart valve implantation might be beneficial in order to ensure that transcatheter valve implantation remains an effective form of therapy for treated individuals. A

Conclusion

In this study, we were able to demonstrate a difference of hydrodynamic valve function of a self-expanding transcatheter heart valve, namely the CoreValve^® prostheses, when in an oval configuration. In this scenario, slight ovality does not result in significant worsening of hydrodynamic function. However, in stronger ovality, relevant increases in regurgitation and pressure gradients are observed. We assume these effects to be relevant for all transcatheter heart valves prostheses.

Conflict of interest statement

The authors declare no conflict of interest.

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¹: Contributed equally to this manuscript.

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

Abstract

Background

Methods

Results

Conclusion

Introduction

Section snippets

Methods

Compartment design

Hydrodynamic measurements

Results

Systolic pressure gradient

Effective orifice area (EOA)

Regurgitation

Leaflet kinematics

Discussion

Limitations

Future outlook

Conclusion

Conflict of interest statement

J. Thorac. Cardiovasc. Surg.

JACC Cardiovasc. Interv.

J. Thorac. Cardiovasc. Surg.

Am. J. Cardiol.

JACC Cardiovasc. Interv.

J. Biomech.

J. Am. Coll. Cardiol.

J. Biomech.

J. Thorac. Cardiovasc. Surg.

J. Am. Coll. Cardiol.

J. Am. Coll. Cardiol.

J. Biomech.

JACC. Cardiovasc. Imaging

JACC Cardiovasc. Interv.