A new approach to interventional atrioventricular valve therapy

Transcatheter mitral valve replacement with the NaviGate stent in a preclinical model

AIMS

The aim of this study was to test the feasibility of transcatheter mitral valve implantation of the NaviGate device in acute and chronic preclinical models.

METHODS AND RESULTS

We evaluated NaviGate valved stent implantation in the mitral position in an acute swine model (n=24, ≤5 days) through three different approaches - transatrial, transapical, and transseptal - and in a chronic swine model (n=12, >10 days) through a transatrial approach. The NaviGate implantation procedures were successful in 83% of the acute model studies (n=20) and 83% of the chronic model studies (n=10). Echocardiographic assessment showed low gradient across the valved stent (mean gradient <3 mmHg) and the left ventricular outflow tract (mean gradient <6 mmHg). Post implantation, there was no mitral regurgitation (MR) in 75% (n=15) of the acute studies and mild MR in 25% (n=5). In the chronic model, there was no MR in 60% (n=6) and mild MR in 40% (n=4). The implantation procedure was aborted in four acute studies due to inferior vena cava injury and in two chronic studies due to prosthesis-annulus mismatch.

CONCLUSIONS

In preparation for clinical application, transcatheter mitral implantation of the NaviGate valved stent was proved feasible in acute and chronic preclinical models. The three featured delivery approaches are of particular value for high-risk patients with functional MR and challenging vascular access.

A comparative study of the morphology of mammalian chordae tendineae of the mitral and tricuspid valves

It is assumed that the human heart is almost identical to domestic mammalian species, but with limited literature to support this. One such area that has been underinvestigated is that of the subvalvular apparatus level. The authors set out to examine the morphology of the subvalvular apparatus of the mammalian atrioventricular valves through gross dissection and microscopic analysis in a small-scale pilot study. The authors examined the chordae tendineae of the mitral and tricuspid valves in sheep, pig and bovine hearts, comparing the numbers of each of these structures within and between species. It was found that the number of chordae was up to twice as many for the tricuspid valve compared with the mitral valve. The counts for the chordae on the three valve leaflets of the tricuspid valve, as well as the two mitral valve leaflets, were almost identical between species. However, the chordae attaching onto the posterior papillary muscle were almost double compared with the septal and anterior papillary muscles. Histological analysis demonstrated an abrupt transitional zone. In conclusion, the authors have shown that there is no gross morphological difference between, or within, these species at the subvalvular apparatus level.

The MitraClip experience and future percutaneous mitral valve therapies

Mitral regurgitation is the most common valve abnormality worldwide and its prevalence is expected to increase in the future due to aging of the population. Percutaneous mitral valve repair therapies may offer an opportunity to treat severe MR in the elderly or other high-risk groups who would otherwise be ineligible for surgery. The MitraClip system uses edge-to-edge coaptation of the mitral leaflets to create a double-orifice valve and reduce MR. It has been performed in over 10 000 patients to date, and as experience has improved, procedural times have shortened from over 200 minutes to less than 100 minutes, with increasing numbers of patients being left with ≤ grade 2+ MR. This review will focus on the literature available on MitraClip and other novel percutaneous techniques that are being developed for the treatment of severe MR.

A personalized approach to interventional treatment of tricuspid regurgitation: experiences from an acute animal study

OBJECTIVES

Interventional treatment of tricuspid valve disease has so far received little attention due to the anatomical challenges in a thrombogenic surrounding. In the present study, we present an imaging-based, personalized interventional approach to the therapy of tricuspid regurgitation.

METHODS

In our porcine model, we used rapid prototyping to build a matrix reproducing the geometry of the right atrium that was previously derived from computer tomography (CT) scans. Over this matrix, a braided nitinol device fitting almost completely the right atrium was crafted. An additional tubular stent component was developed to carry a tissue valve prosthesis. This part was designed to be connectable to the annular portion of the main device. In our feasibility study, the crimped device was implanted via jugular access into the right atrium of 12 pigs and expanded subsequently. Following isolated implantation of the device without the valve-carrying component, further procedures included implantation of the whole composite device, including the mentioned tissue valve. Representing a only feasibility study, all implantations were performed under full bypass and direct sight. On-site visualization was performed by both echocardiography and fluoroscopy. Additional imaging was realized by postoperative CT scans.

RESULTS

Following implantation, 9 of 12 animals were weaned from cardiopulmonary bypass. Correct positioning of the device and orthodromic blood flow as maintained by the valve prosthesis were demonstrated by echocardiography and fluoroscopy. Postoperative contrast CT evaluation demonstrated proper fitting of the device into the right-sided heart cavities without obstruction of the outflow tract. Autopsy additionally confirmed its correct positioning without major trauma to surrounding structures.

CONCLUSIONS

We demonstrated the feasibility in principle of a personalized interventional treatment for tricuspid regurgitation using a braided stent, based on individual cardiac imaging, with anchoring forces mainly exerted on the venae cavae and on the inner surface of the right atrium. The design process of this device is a good indicator of the growing potential of an imaging-based personalized simulation and production approach for the treatment of tricuspid valve disease.

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.