The surgical removal of some portion of diseased aorta is called aortic resection. A polyester graft is used to replace the diseased aortic tissue. The polyester grafts (such as Dacron) are an excellent example of successful substitution of a synthetic material within the human body. Dacron is so completely compatible with the body that rejection and calcification do not occur. With the passage of time the body deposits its own tissue into the Dacron graft. Today's modern Dacron grafts are strong, flexible and collagen impregnated, making them impervious to blood. The durability of these grafts exceeds that of the human life span.
Surgery on the thoracic aorta is in some respects similar to other types of open-heart surgery. Particular details regarding the size and location of the incision, the use of the heart-lung machine and specialized techniques used to provide neurologic protection vary depending on the type of aortic surgery being performed.
Surgical Procedures on the aortic valve, root, ascending aorta and arch
Aortic disease often simultaneously affects some combination of the aortic valve, root, ascending aorta and arch. The arteries that branch from these aortic segments require special consideration during surgery. This includes the coronary arteries, which supply blood to the heart, as well as the arteries branching from the arch, which supply blood to the head and upper body. A combination of procedures may be used in one surgery. For example, a single operation might address the aortic valve and root with either the Bentall or David procedure and use open anastomsis with hypothermic circulatory arrest (HCA) for the ascending aorta and arch.
There are several different procedures from which aortic surgeons may choose based on their assessment of an individual patient. Procedures and techniques include:
- Button Bentall with Bioprosthesis or Prosthesis
- David Valve-Sparing Re-Implantation Procedure
- Yacoub Remodeling Procedure
- Ross Procedure
- Porcine Root Replacement (Freestyle)
- Homograft Technique
The condition of the aortic valve, root, ascending aorta and arch taken together with the patient's overall health determine the surgical procedure that will be performed. Prior to surgery a strategy is developed based on what has been revealed by diagnostic testing. However, in some instances the final decision regarding the best approach is made during surgery itself.
The surgical procedures described here are the result of the continued pursuit of excellence in surgeries that may begin with the aortic valve and reach to the arch, or be limited to some subset of these structures. Generally, in order for a surgical procedure to be successful it must lend itself well to widespread usage across many surgeons and centers. Procedures that are too difficult to duplicate will not be widely adopted and will be replaced by a procedure that is easier to perform while maintaining good results. For example, if a brilliant valve-sparing operation cannot be duplicated easily, it will not be a viable procedure for use in a majority of patients.
Bentall with Bioprosthesis or Prosthesis
This procedure, a variation of the original Bentall procedure, is a simultaneous replacement of the aortic valve, root and the entire ascending aorta. A composite Dacron graft, which includes the new valve bioprosthesis or prosthesis, is put in place. Then the coronary arteries are implanted in the Dacron graft using aortic buttons. This procedure is typically required in severe connective tissue disorders such as the Marfan syndrome. It is also indicated whenever there is a combined dilation of the aortic root and annulus, as well as the ascending aorta.
David Valve-Sparing Aortic Root replacement
As its name indicates, this procedure is used for the replacement of the aortic root and ascending aorta only. The aortic valve is not replaced. However, it is re-implanted inside the Dacron tube graft, and both coronary arteries are re-attached to the Dacron. This procedure is primarily suitable for patients with trileaflet aortic valves with minimal aortic insufficiency. It may also be used in Marfan syndrome patients if their aortic annulus is not too dilated. Some patients with bicuspid aortic valve may also undergo this operation, if the leaflets are normal.
Yacoub Remodeling Procedure
The Yacoub remodeling procedure uses a scalloped design to create a new aortic root out of Dacron. This scalloped shape was thought to experience less shear force and, therefore, might be expected to add more longevity and competence to valve-sparing operations. While the long-term outcomes of the original procedure have varied across centers, data regarding the latest modification to this technique is still emerging and requires careful analysis. This procedure is indicated for use in the same group of patients as the David valve-sparing re-implantation procedure, but does not have the same endurance as the David repair.
The pulmonary valve is very similar to the aortic valve, and it has been found that a patient's own pulmonary valve may successfully be substituted for a diseased aortic valve. The surgical procedure to accomplish this is called the Ross procedure. Essentially a pulmonary valve autograft is placed in the aortic valve position, and a homograft (human donor) valve replaces the pulmonary valve. This could be an ideal operation for a young or middle-aged patient who requires aortic valve replacement. It has particular significance for children, meeting their need for a new aortic valve that will grow with them. An additional benefit of the Ross procedure is resistance to infection. However, the extensiveness of the surgery may be beyond the tolerance of those patients who are already septic and experiencing multi-organ failure secondary to infection.
The Ross procedure is more complex and technically challenging than a single valve surgery. Up to 20 percent of patients will require re-operation for degeneration of the homograft within 10 to 15 years. This procedure is appropriate in selected young patients who do not have Marfan's syndrome or a connective tissue disorder.
Porcine Root Replacement (Freestyle)
The aortic root is replaced with a preserved pig aorta. The porcine root is not long enough to address the ascending aorta. Therefore, added Dacron graft is required for replacement of the ascending aorta. This can be a reasonable replacement for the same indications as a homograft, as well as for a replacement of a short segment of aorta (aortic root).
Homografts are the most resistant to infection, making this the preferred technique for the treatment of aortic root infection and endocarditis at the Aortic Program. The major disadvantages of a homograft include issues with the longevity, the size and the length. Since homografts depend on human donor availability, there is no assurance that there will be a sufficient quantity of the different sizes and lengths that may be needed. Regarding the longevity of this solution, chronic rejection causes severe calcification of the aortic wall, which becomes like a "lead pipe". To a lesser degree, the aortic valve leaflets also degenerate. Homografts may be considered for use in an elderly patient with a life expectancy less than 15 years for treatment of a heavily calcified (porcelain or egg shell) aorta in lieu of aortic valve replacement and endarterectomy of the aorta. A major draw back is the lack of overall availability.
Valve Repair Versus Replacement
The decision to repair versus replace the aortic valve is based on complex factors, as well as the experience and results of the particular treatment center. At the Aortic Program, a repaired valve is expected to have a life of ten years or more (comparable to the minimum expectation for a bioprosthesis). If the repaired valve is not projected to last at least that long, the valve is replaced rather than repaired. A repaired valve could last a lifetime. Therefore, in feasible cases, aortic valve repair is always the first choice at this institution.
There are factors unique to each patient that must be evaluated regarding valve repair. The anatomy of the aortic valve, nature of the tissue and comfort level of the surgeon in performing the repair all are factors in the resulting durability of the repaired valve. Careful scrutiny is required for bicuspid aortic valves. In young patients where the bicuspid valve functions well with minimal calcification, or if there is localized prolapse of only one leaflet, a durable repair may be possible. When a normal trileaflet aortic valve is present, there is greater potential for repair. Particularly during surgery for ascending aortic dissection involving a normal aortic valve, lifetime durable repairs are often possible.
Surgical procedures on the descending and thoracoabdominal aorta
Surgery for aneurysm of the descending and thoracoabdominal aorta typically involves older, higher risk patients who may have hypertension, atherosclerosis, pulmonary obstructive disease (COPD), a history of smoking and some degree of existing kidney disease.
There are several techniques for surgery on this segment of the aorta. The "clamp and sew" method is the simplest, fastest approach, but has higher neurologic complication rate. Currently for elective surgery of the descending and thoracoabdominal aorta, the Aortic Program involves sequential aortic clamping with or without hypothermic circulatory arrest. Regardless of the technique used, the main consideration in surgery of the descending and thoracoabdominal aorta is always spinal cord and kidney protection.
- "Clamp and Sew" Method
- Partial Cardiopulmonary Support (Partial Heart-Lung Machine)
- Left Heart Bypass
- Total Circulatory Arrest Technique
"Clamp and Sew" Method
This technique has the advantages of simplicity, and there is less chance of coagulation problems. It is the fastest technique, but also has the highest complication rate for paraplegia, renal failure and embolization of sclerotic material to the visceral organs, lower extremities and kidneys. This is especially true if the ischemia time is above 30 minutes. Therefore,this technique is offered for a short-segment aortic pathology, when the operation is typically completed within 25 minutes.
Partial Cardiopulmonary Support (Partial Heart-Lung Machine)
With this technique cannula are placed through the femoral vein and artery. A full dose of heparin is used, and the aorta is still clamped. This approach provides some protection to the spinal cord and kidneys. This technique may be used in combination with sequential aortic clamping technique.
Left Heart Bypass
In this approach the patient's own lungs continue to function. Only the heart is bypassed. This technique can therefore be done with a low dose of heparin. Similar to the partial cardiopulmonary approach, there is risk of atherosclerotic embolization. This technique may be used in combination with sequential aortic clamping technique.
Hypothermic Circulatory Arrest Technique
At the Aortic Program, the hypothermic circulatory arrest technique has been used since 1994. This technique has minimized the risk of embolization while also providing maximum spinal cord protection. Through the use of this technique, renal failure became extremely unlikely, and the risks of paraplegia and postsurgical mortality dramatically reduced. However, there is an increased risk of bleeding or pulmonary complications.