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OBJECTIVE: In this study three different fixation designs of a mitral valved stent are presented: apical fixation, sub-annular fixation and supra-annular fixation.
METHODS: Mitral valved stents were implanted in the porcine model via transapical approach in the beating heart. The stents were comprised of an atrial element and a tubular body accommodating a bioprosthetic heart valve. The first prototype was solely anchored apically with neo-chords attached to the ventricular rim of the stent (AP;n=10). Additional sub-annular fixation elements were included in the body of the second design (SUB;n=10). In the third design (SUPRA), hook-shaped fixation elements were attached to the atrial element to achieve a supra-annular fixation (n=6).
2D and 3D transesophageal echocardiographic (TEE) and hemodynamic evaluations following standardized protocols were conducted pre- (n=26) and post implantation (n=24) and at monthly intervals during the follow up.
RESULTS: Three animals were excluded due to ventricular fibrillation prior to stent deployment (SUB:n=2, SUPRA:n=1). Secure deployment and stent positioning was reproducibly achieved in all remaining cases. The mean gradients across the mitral valved stent and the LVOT were slightly increased in group AP and SUB (p≤0.018), but remained within a physiological range in all groups. The mitral-annular-plane-systolic-excursion remained within physiological ranges. The pulmonary capillary wedge pressure was higher in group SUPRA (p=0.043).
No paravalvular regurgitation (PVL) was detected in the group of design AP following implantation. In group SUPRA the fixation elements caused shunts in 2/5 and multiple stent fractures in all cases. The concept was hence abandoned. The overall well-being was best in the group AP.
CONCLUSIONS: Three prototypes following different fixation technologies were successfully tested in vivo. Low gradients and a normal longitudinal LV function were achieved. Improvement potential (e.g. sizing of fixation elements) has been identified for the sub-annular design. Stents with sole apical fixation showed the most promising outcome so far with no PVL, normal longitudinal function and good health of the animals for up to three months.

Table 1: Echocardiographic and hemodynamic evaluation

Parameter	Pre-Implant	Apical Fixation	Sub-Annular Fixation	Supra-Annular Fixation
EF [%]	63±4	52±10*	48±10*	60±8*
Pmean MV [mmHg]	0.3±0.4	1.1±0.5	2.6±2.0	1.2±0.8
Pmean LVOT [mmHG]	1.2±0.8	3.4±0.5	2.6±2.6	1.2±0.8
Pmean AV [mmHg]	1.6±1.4	3.4±3.1	4.4±2.8	1.6±0.8
E/A []	1.3±0.4	1.1±0.2*	1.0±0.2*	0.9±0.3*
E/E` []	8.4±2.3	14.0±3.4	17.4±5.9	9.8±2.4
MAPSE [cm]	1.2±0.1	1.0±0.1	1.0±0.1	1.0±0.1
PCWP [mmHg]	8±4	11±4	9±4*	16±6*
EF: left ventricular ejection fraction, Pmean: mean gradient over the MV: mitral valve, LVOT: left ventricular outflow tract, AV: aortic valve, E/A: left ventricular filling index , E/E´: hhh,MAPSE: mitral annular plane systolic excursion, PCWP: pulmonary capillary wedge pressure; *: statistical significant difference with p≤0.05