国际循环网版权所有，谢绝任何形式转载，侵犯版权者必予法律追究。

<International Circulation>: Improvements in heathcare actually leads to the increase in the incidence of some conditions， such as aortic valve calcification. Aortic valve calcification in elderly patients can cause aortic stenosis and because age has increased risk for all kinds of complications and multiple organ dysfunctions， the risk of surgery is very high. Recently， percutaneous aortic valve implantation has presented itself as an appropriate therapy for these special patients. Can you outline the indications and contraindications for the procedure?