I was born with a CHD, TOF, (2 vsds), absent pulmonary valve syndrome. I am now 56 years old, and the valve was replaced with a biological valve 18years ago. At that time my surgeon was very concerned, as the valve the previous valve was in it s 17th year, and in poor condition. He had stated that it should be replaced within 10 to 15 years max. What is the life expectancy of this valve?