Data and Common Sense – Powerful Predictors of the Future of AVBG

Dr. Gammie and his colleagues at the University of Maryland continue to present impressive data with regard to the clinical effectiveness of the AVBG procedure in high risk patients.  In a recent publication in the Annals of Thoracic Surgery (Ann Thor Surg 2010;90:136-43), lead author Dr. Crystal Vliek reviews hemodynamic data from 47 very high risk patients who underwent an AVBG procedure at Maryland between 2003 and 2009.  The conclusion is that the AVBG procedure effectively relieves the outflow obstruction created by aortic valve stenosis and that placement of the bypass graft halts the biologic progression of aortic stenosis.  The data is very convincing.

What I found to be even more interesting is the response Dr. Vliek gave to a question from Dr. John Kern in the Discussion section.  He asks what is the future of AVBG in light of “…soon to be widespread acceptance of transcatheter heart valves”.   I thought her answer  provides a great summary of why AVBG should be considered as a safer, more practical  way for surgeons to provide an off pump, less invasive aortic valve procedure.  I have reprinted her response below.

What is the future of this procedure going to be, seen 5 years from now and 10 years from now, given the transcatheter valve replacements? We feel there are some key differences between aortic valve bypass surgery and transcatheter valve replacements that may favor an aortic valve bypass approach.

Number one, our incision is the same size as is used in a transapical approach for a stent-mounted valve. Aggressive balloon aortic valvuloplasty is mandatory before implantation of a stent-mounted valve, and we know that there is a significant incidence of cerebral embolic injury associated with this maneuver; in contradistinction, the native aortic valve is never manipulated during aortic valve bypass surgery.

There is a clear risk of stroke associated with transcatheter and transapical stent-mounted aortic valve implantation, related to balloon aortic valvuloplasty as well as to manipulation of wires in the arch. In the longer term, we don’t know the embolic risk of a large stent in the ascending aorta. We do know that after conventional AVR, there is a 1% to 2% per year risk of stroke attributable to the presence of a prosthetic valve in the native position. We have shown that all cerebral blood flow after AVB surgery is supplied across the native valve; no blood traversing the prosthesis in the conduit reaches the brain; that may accrue a long-term benefit in terms of stroke prevention.

There is a significant risk of heart block requiring pacemaker implantation after stent-mounted aortic valve implantation; this is as high as 30% in some series. Since the native aortic valve is never manipulated in aortic valve bypass surgery, we have never seen heart block after this operation.

With aortic valve bypass surgery, there is no risk of damage (dissection, rupture) to the ascending aorta, nor a risk of obstruction of the coronary ostia. There is no risk of prosthesis malposition or embolization. There is no risk of peripheral vascular injuries. Although the incidence of paravalvular leak is significant after stent-mounted aortic valve implantation, we have, for obvious reasons, never seen paravalvular leak after aortic valve bypass surgery.

Clinical follow-up after stent-mounted valve implantation is limited to a few years; in contrast, there are a number of patients walking around today who have had an aortic valve bypass in place for more than a quarter of a century.

Aortic valve bypass surgery has not been widely performed because it has largely been under the radar screen, and in addition there is a certain “fear factor” associated with the insertion of a conduit in the apex of the left ventricle, particularly while the heart is beating. There are currently several surgical tools in development that will automate this process, making it rapid, bloodless, and reproducible. So we feel that this approach is very competitive with, and in many ways superior to, transcatheter (or transapical) stentmounted valve implantation.

We would suggest that future prospective studies comparing conventional AVR, medical therapy, and transcatheter valve implantation include an aortic valve bypass arm at a center experienced in this approach.

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