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OBJECTIVE: Off-pump implantation of a valved stent into the mitral position has been in the focus of innovative research lately. This study presents the most recent results of transapical implantation of our newest mitral valved stent design in a porcine model one and two months after implantation.
METHODS: Eight pigs received a self-expanding valved stent with improved stent design (shape, size) into the mitral position via transapical approach. Hemodynamic stability, stent function and positioning were assessed before (n=8) and 1h after implantation (n=8), at one month (n=4) and at outstanding health of the animal at two months (n=1) using TEE, invasive pressure measurements, ventriculography, and cardiac CT.
RESULTS: Reliable stent stability and good positioning were achieved in all animals. One animal died of cardiac fibrillation during surgery and three animals died within the first month (7±3 days) due to endocarditis.
TEE evaluation showed normal gradients and echocardiographic parameters, but decreasing MAPSE after implantation (p=0.004). PA and PCWP pressure did not change throughout the observation period (p≥0.16). MAP decreased directly after implantation (p=0.002) and stabilized hereafter (p≥0.25; Table1). No paravalvular leackages (PVL) were detected directly after implantation. After one month no PVL were found in two animals, one animal had trace and one mild PVL. Central mitral regurgitation was observed in five of eight animals directly after implantation (n=1: none to trace, n=3: trace, n=1: mild) and in two of four animals after one month (n=1: trace, n=1 mild). Gross evaluation demonstrated correct stent position in all and no thrombus formation in all but one animal. Ingrowth within the native structures of the left atrium was 72±24 % after one month and 87% after two months.
CONCLUSIONS: Reliable stent stability, minimal gradients and adequate stent function were observed throughout the study at a high degree of reproducibility over a post-operative period of up to two months. In particular the occurrence of PVL was reduced with this newly developed prototype.

Table 1: Echocardiographic and hemodynamic results

	MAPSE[mm]	E/A[ ]	EF[%]	PGmean MV [mmHg]	PGmean AV[mmHg]	PCWP[mmHg]	PAP[mmHg]	MAP[mmHg]
Pre Implant (n=8)	1.2±0.1	1.1±0.3	62.5±5	0.7±0.4	1.7±0.7	8±4	14±4	77±14
Post Implant (n=8)	1.0±0.1	1.0±0.2	60.9±9	1.1±0.7	2.5±1.9	9±2	16±4	61±6
1 month (n=4)	1.1±0.3	0.9±0.3	49.1±13	4.1±1.5	1.9±0.9	17±3	24±7	75±24
2 months (n=1)	1.17	1.03	61.11	4.33	6.3	17	29	71
MAPSE: mitral annular plane systolic excursion; EF: ejection fraction; PGmean: mean gradient over the mitral valve (MV) and aortic valve (AV); PCWP: pulmonary capillary wedge pressure, PAP: pulmonary artery pressure; MAP: mean arterial pressure