Stentless bioprosthetic valve

Stentless bioprosthetic valve

Stentless bioprosthetic valves do not have supporting framework so that they can have a higher effective valve orifice area. This is an advantage in avoiding patient prosthesis mismatch, especially in aortic stenosis. In isolated aortic stenosis, the aortic annulus is not dilated and often only a small sized prosthesis can be implanted unless one goes for aortic root widening procedures with added morbidity and potential mortality. The relatively smaller size of stented aortic prosthesis leads to patient prosthesis mismatch and poor regression of transvalvar gradient and left ventricular hypertrophy.

This can be avoided to some extent by using stentless bioprosthesis which has higher effective valve orifice area compared to stented bioprosthesis due to the absence of a supporting framework. But implanting stentless bioprosthetic valve is technically more demanding for the surgeon and can prolong operating times causing higher morbidity. Stentless bioprosthetic valves aim at maximizing the effective orifice area to tissue annulus ratio for better hemodynamic and clinical outcomes.

Stentless bioprosthetic valve produces better exercise hemodynamics and greater regression of left ventricular hypertrophy when used in the aortic position. They have a better orifice size for a given annular size. Hence they are suited for those patients with aortic stenosis and a small aortic annulus. The other option in case of small annular size in aortic stenosis is aortic root widening procedure.

Six year results of Toronto SPV (stentless porcine valve) bioprosthesis was reported in 1999 [1]. There were 635 patients in the age range of 33 to 93 years. At 6 years, the actuarial survival was 82.6%. The mean systolic gradient was only 5 mmHg and 81% were free of cardiac symptoms. 85% did not have aortic regurgitation and there were no primary tissue failures.

An early meta analysis compared the regression of left ventricular mass between stented and stentless aortic prosthetic valves [2]. After evaluating ten studies which involved a total of over nine hundred patients, they concluded that stentless aortic prosthesis give better regression of left ventricular mass, lower trans aortic gradients and better effective orifice index. But the aortic cross clamp times and cardiopulmonary bypass times were higher because of the complexity of the replacement process of stentless aortic bioprosthesis.

Long term data on Freestyle stentless bioprosthesis is also available [3]. Between 1993 and 2013, 531 patients underwent implantation of Freestyle stentless bioprosthesis either with or without aortic root reconstruction. Freedom from reoperation for structural valve degeneration was 94.6% and 76.7% at 10 and 15 years, respectively, in those who did not undergo aortic root reconstruction. In those who underwent aortic root reconstruction also, it was 98.9% and 88.1% at 10 and 15 years, indicating a better result for those who underwent aortic root reconstruction as well. But the difference in techniques did not influence in hospital or long term mortality.

Bach DS et al [4] have also reported on the long results (15 years) of Freestyle stentless bioprosthesis. 402 males and 323 women had a total follow up of 5,491.2 patient-years. Ten and 15 year survivals were around 46% and 26% respectively. Freedom from valve related death was around 95% and 93% respectively. Increased age was associated with higher mortality, but lower risk of reoperation and explant due to structural valve degeneration, as expected.

References

1. David TE. The Toronto SPV bioprosthesis: clinical and hemodynamic results at 6 years. Ann Thorac Surg. 1999 Sep;68(3 Suppl):S9-13.
2. Babu Kunadian, Kunadian Vijayalakshmi, Andrew R Thornley, Mark A de Belder, Steven Hunter, Simon Kendall, Richard Graham, Michael Stewart, Jeetendra Thambyrajah, Joel Dunning. Meta-analysis of valve hemodynamics and left ventricular mass regression for stentless versus stented aortic valves. Ann Thorac Surg. 2007 Jul;84(1):73-8.
3. Mohammadi S, Kalavrouziotis D, Voisine P, Dumont E, Doyle D, Perron J, Dagenais F. Bioprosthetic valve durability after stentless aortic valve replacement: the effect of implantation technique. Ann Thorac Surg. 2014 Jun;97(6):2011-8.
4. Bach DS, Kon ND. Long-term clinical outcomes 15 years after aortic valve replacement with the Freestyle stentless aortic bioprosthesis. Ann Thorac Surg. 2014 Feb;97(2):544-51.