The Pulmonary Autograft (Ross Procedure) for Aortic Stenosis
Dateline: 06/22/97
In the previous weeks' articles, we discussed the different treatment options for Aortic Stenosis. This article is the last one of the series, and deals with the pulmonary autograft operation for aortic stenosis.
What is the Ross Operation ?
Donald Ross was one of the pioneers in cardiac surgery in the U.K. and along with Brian Barratt-Boyes in the early 1960s, was one of the first surgeons in the world to attempt the homograft procedure for aortic valve disease. In view of the uncertain longevity of aortic homografts in that era, Ross was trying to find a more durable and reliable alternative to replace the aortic valve when he struck upon the idea of using the very same patient's pulmonary valve ! In 1967, the first pulmonary autograft operation was performed.
The Ross operation involves removing the patient's diseased aortic valve, and replacing it with the patient's own pulmonary valve (the valve that guards the junction between the right ventricle and pulmonary artery). The pulmonary valve is then replaced with a homograft.
Some technical details:
The Ross operation is an open heart procedure performed with the assistance of the heart-lung machine. After the patient is hooked up onto the machine and the heart stopped, the surgeon evaluates the pathology for suitability for a pulmonary autograft. If it is feasible, the pulmonary valve is then harvested. Great care is taken not to injure branches of the coronary arteries that lie very close to this structure.
The diseased aortic valve is then excised, and the harvested pulmonary valve is implanted in a manner very similar to the aortic homograft implantation. The right ventricle outflow tract (from which the pulmonary valve was removed) is now reconstructed using a biologic tissue valve or human homograft valve. If the disease is more extensive and involves a part of the aortic root too, the operation can be modified to excise the damaged portion of the aortic valve and use the pulmonary valve and artery to replace it.
Why perform the Ross procedure ?
At first sight, it might seem that the Ross operation is in no way different from a homograft valve replacement of the aortic valve - indeed it seems more complex ! But consider these advantages of the Ross operation over the homograft procedure:
- The pulmonary valve is harvested just before implantation, and so there are no risks or costs involved with storage in a valve bank
- The pulmonary valve used as a graft is "viable" - that is, the cells are alive and continue to grow and divide even after implantation.
- The pulmonary valve that is used as a replacement device comes from the very same patient, and is therefore free from any risk of graft rejection.
- It has a very long durability, well over twenty years.
- There is almost no pressure gradient across the valve, which reflects it's excellent hemodynamic function after implantation.
- There is no risk of hemolysis (blood cell damage) and thromboembolism (blood clot fragmentation and entry into the blood stream).
What about the homograft valve used to reconstruct the right ventricle outflow ?
The Ross procedure involves removing the native pulmonary valve, and this then needs to be replaced. The choice lies between using a bioprosthetic valve (like porcine pericardium tissue valves), an aortic homograft (the aortic valve harvested from a human cadaver) or a pulmonary homograft. This last (pulmonary homograft) is today the preferred choice since it is nearly identical to the valve that was removed in the first place.
The use of a homograft valve in the pulmonary position is not as risky as using it in the aortic position because
- the right side of the heart is a low pressure circuit with lesser stress and strain on the valve
- any blood clots that form on the valve, and that may break away into the blood stream (embolise), will be filtered out in the lung, and not reach the general circulation.
What are the disadvantages with the Ross procedure ?
- It converts a single valve operation into a "two valve" procedure (aortic, as well as pulmonary)
- It is technically more complex and requires much training to perform well.
- It cannot be used in some situations like Marfan's disease and cystic medial necrosis, since the same disease process that affected the aortic valve may also affect the pulmonary valve.
- It cannot be used in certain emergency situations like infective endocarditis and bleeding problems.
Who is the ideal candidate for the Pulmonary Autograft operation ?
The pulmonary autograft has certain unique advantages - durability, resistance to infection, viability, excellent hemodynamics and autologous nature. These characteristics are most required for younger patients, particularly those with a life expectancy that exceeds twenty years (which is the expected average durability of the pulmonary autograft). The Ross procedure has become more popular in use for children with aortic valve disease for the reasons mentioned above.
This concludes the discussion of management options for aortic stenosis. In next week's article, we will discuss a more common condition, coronary artery disease. If there is anything you wish to have made clearer, or any way I can assist you, please e-mail me !
