Transcatheter mitral valve implantation: supra-annular and subvalvular fixation techniques

Transcatheter mitral valved stent implantation provides an off-pump treatment option for mitral valve regurgitation, especially for secondary mitral valve regurgitation. The aim of this study was to evaluate novel fixation strategies: direct fixation (SUPRA) and subvalvular fixation (sub-VALV) to successfully implement alternative fixation methods at the mitral annulus and to reduce radial stent and apical tether forces.

Specific concepts were developed for the supra-annular hook-shaped fixation (SUPRA) and the subvalvular fixation (sub-VALV). These prototypes were compared with the sole apical tether fixation (AP) methods. Thirty-three pigs underwent mitral valved stent implantation accompanied by standardized transoesophageal echocardiographic and haemodynamic evaluation of heart function and the stent performance 1 h after implantation. Additionally, animals were followed up for 3 months.

Secure deployment and correct positioning with low transvalvular gradients were achieved in all cases with mitral valved stent implantation. Nevertheless, 2 pigs died due to rhythm disturbances during dissection and pre-transcatheter mitral valve implantation. Paravalvular leakages were trace or less in prototypes with supra-annular fixation and sole apical fixation. In contrast, moderate paravalvular leakages were observed in the sub-VALV group (P < 0.001). In addition, the effect of a specific stent design on heart function was demonstrated: an increased rate of ischaemia and arrhythmia (P = 0.037) and a small left ventricular ejection fraction reduction (P < 0.05) were observed in the group with subvalvular fixation. In all but 1 case, gross evaluation demonstrated a good ingrowth of the valved stents of between 36% and 100% tissue coverage after a follow-up of 1 month or longer.

The low degree of paravalvular leakages in the supra-annular and apical fixation groups and the normal longitudinal function highlight the good alignment of these new mitral valved stent designs within the native anatomy. The novel, hook-shaped, supra-annular fixation elements were well tolerated in the hearts resulting in excellent health of the animals at long-term follow-up times of up to 3 months.