Volume 13, Issue 3 , Pages 148-160, Autumn 2008
Composite Root Replacement with a Mechanical Conduit
Article Outline
Composite valve graft replacement of the ascending aorta and aortic valve remains the gold standard operation against which all root replacement or valve-sparing procedures must be compared. Developed in 1968 by Bentall and DeBono, this procedure consists of root replacement with a conduit consisting of a Dacron tube graft and a prosthetic aortic valve.1 The procedure was originally described utilizing a graft inclusion technique. A homemade composite valve-graft was placed inside the dilated aortic root and, after attaching the coronary ostia, the native aneurysmal aorta was wrapped around a new root. Because Dacron grafts of that era were quite porous, the inclusion Bentall revolutionized surgery of the aortic root by dramatically reducing the incidence of life-threatening postoperative hemorrhage. Surgical results immediately improved and the perioperative mortality for ascending aneurysm repair fell from nearly 20% to less than 10%. However, with the inclusion technique, bleeding from the systemically pressurized suture lines was difficult to address and follow-up imaging often revealed pseudoaneurysm formation at the distal aortic and coronary anastomoses. A significant percentage of patients required high-risk reoperations.
Many of the perioperative and long-term complications of the original procedure were eliminated with the adoption of the exclusion composite valve-graft replacement.2 With this technique, the aorta is completely excised down to the annulus and the coronary ostia are mobilized and reattached on small buttons of native aortic tissue. Tension at these suture lines is nearly zero and the elimination of the inclusion wrap provides the surgeon the opportunity to evaluate all of the suture lines for bleeding before completing the operation. The availability of near zero-porosity collagen and gel-impregnated Dacron grafts has reduced the potential for surgical bleeding even further. All of these technical factors have improved the expectations for this once high-risk procedure. The operative mortality for elective composite root replacement is consistently less than 5% in centers with significant aortic experience.
The durability of the exclusion technique is obvious when examining long-term follow-up from a large cohort of patients with Marfan's syndrome.3 In 675 patients undergoing composite replacement of the aortic root, the operative mortality for elective cases was 1.5%. Only 3.4% of this cohort with a connective tissue disorder required reoperation on any part of the aorta for the remainder of their lives. The 10-year actuarial survival exceeded 90%. Despite the need for lifelong anticoagulation for the mechanical aortic valves, the freedom from thromboembolic or bleeding complications was in excess of 90% at 20 years of follow-up. Reoperation following composite replacement remains challenging but fortunately the need for such heroic efforts is rarely encountered when the exclusion technique is utilized.
Over the last 10 years we have performed more than 1000 procedures on the ascending aorta. Composite replacement utilizing an exclusion technique was necessary in 421 patients. A majority of our patients had elective root reconstruction for aneurysmal disease; however, our data also include those presenting with acute aortic catastrophes. Patients with connective tissue disorders such as Marfan's syndrome primarily presented with significant aortic insufficiency. However, we apply the same surgical principles to those patients with calcific aortic stenosis in the setting of both trileaflet and bicuspid aortic valves. The following figures illustrate the surgical procedures we utilize when performing aortic root replacement. We believe adherence to these basic concepts permit reproducible, low-risk, aortic root reconstruction for a majority of patients seen in current cardiac surgical practices.
Operative Technique
Figure 1.
Preoperative evaluation, ascending aortogram. Detailed anatomic information regarding aortic root anatomy is essential for a successful outcome with composite replacement of the aortic root. In patients with risk factors for coronary artery disease, cardiac catheterization is performed the day before the planned operation. Patients undergoing reoperations on the aortic root are also subjected to catheterization as part of their preoperative evaluation. In younger patients without significant risk factors, a 64-slice computed tomographic angiogram gives excellent images of the coronary anatomy and will identify any occult coronary artery disease or anomalous coronary anatomy. In patients with Marfan syndrome and severe kyphoscoliosis or pectus deformities, computed tomographic scanning is also useful in planning the sternotomy.
Figure 2.
Setup in the operating room. All patients are monitored with a right heart catheter and arterial line, usually in the nondominant hand. Epsilon-aminocaproic acid (amicar) is used as an antifibrinolytic. We put 10 g in the bypass circuit, give 10 g as a loading dose, and administer 2 g per hour as an infusion throughout the operation. For patients with pathologic problems isolated to the aortic root and ascending aorta, cannulation of the proximal arch is sufficient to completely resect the diseased aorta. The venous system is drained with a two-stage (46-Fr/36-Fr; Medtronic Corp., Minneapolis, MN) cannula inserted into the right atrial appendage. Placing the venous cannula in the appendage keeps it out of the aortic root. Exposure can be enhanced further by placing gentle traction on the venous cannula in a caudal direction during the procedure. A vent is placed through the right superior pulmonary vein into the left ventricle. Patients are systemically cooled to 28°C and the mean arterial pressure on bypass is maintained between 70 and 80 mm Hg. For those patients with disease extending into the aortic arch, the aortic aneurysm is cannulated at the junction of the ascending aorta and arch and bicaval cannulation (28 Fr for the superior vena cava, 32 Fr for the inferior vena cava) is performed in preparation for retrograde cerebral perfusion during the period of profound hypothermic circulatory arrest.4 In this case, aortic root exposure is greatly enhanced by bringing the cannulae in a caudal direction and placing all of the snares, as well as the vent, under the lower crossbar of the retractor. Once the arch is reconstructed, patients are placed back on bypass by placing a standard 20- or 22-Fr cannula into the prefabricated one-branch graft (Meadox Medical, Oakland, NJ). The adjustable flange is removed from the outflow end of the cannula before tying it into the one branch with heavy silk suture. IVC = inferior vena cava; LV = left ventricle; SVC = superior vena cava.
Figure 3.
To keep the one-branch graft out of the surgical field, the arch anastomosis is performed with the one-branch facing the main pulmonary artery. Myocardial protection is provided with cold blood potassium cardioplegia in an antegrade direction at 20- to 30-minute intervals, as well as topical iced saline slush. If the ascending aorta is too large or too friable to clamp, or if the patient has a patent mammary artery graft from a previous coronary artery bypass graft, cardioplegia can be given through the coronary sinus. Meticulous myocardial protection is essential for these sometimes prolonged operations, especially in patients with compromised cardiac function or extensive coronary artery disease, or those undergoing aortic root reoperations.
Figure 4.
Aneurysm and valve resection. An exclusion Bentall, as described by Kouchoukos and coworkers,2 is our preferred method of composite valve-graft (CVG) insertion. As such, identification of the root anatomy, and complete dissection of its components, is essential for a tension-free and hemostatic result. With the heart arrested, the aorta is resected down to the sinotubular junction and the coronary ostia and aortic valve are examined. If the valve leaflets are intact without significant thinning or fenestrations, the patient may be a candidate for a valve-sparing procedure. If the coronaries are not markedly displaced and the sinuses of Valsalva not significantly dilated, the patient may not require a CVG and, instead, a separate valve and tube graft may suffice. When the decision has been made to perform a CVG, the valve is excised and the annulus is debrided of all calcium. Meticulous debridement of the annulus is essential to achieving a watertight seal between soft annular tissue and the sewing ring of the CVG. In patients with bicuspid valves, this often includes debridement into the muscular septum under the right coronary sinus. Extreme caution must be exercised in this area to avoid creation of a ventricular septal defect. The coronary arteries are then mobilized on buttons of aortic tissue. If the coronary arteries are not particularly effaced and high in their respective sinuses, extensive mobilization from the surrounding connective tissue may be needed to attain sufficient length for tension-free coronary reimplantation. Additional length for the left main coronary can be attained by taking down the curtain of soft tissue between the pulmonary artery and the top of the left main coronary artery. When additional length is needed for the right coronary artery (RCA), one may have to sacrifice a small conal branch of the RCA on the pulmonary artery side of the RCA button. When administering subsequent doses of cardioplegia, the areas immediately under the buttons should be carefully examined for any venous or arterial bleeding. This is easily controlled with either small hemoclips or 6-0 polypropylene suture. These areas are extremely difficult to approach after bypass is discontinued and so absolute hemostasis in these areas is essential before removing the cross-clamp. Also, I try to leave some additional length of aortic tissue just above the commissure between the right and left sinuses. I often grasp this tissue to help expose the area between the two coronary button reattachment sites, an area very difficult to access once the heart is full and beating.
Figure 5.
Root reconstruction. Valve sutures (2-0 Ethibond with Gor-Tex pledgetts, Ethicon Corp., Somerville, NJ) are placed with the pledgetts on the supra-annular side, thus positioning the valve in an intra-annular position. Sutures are first placed at the three commissures and then each sinus is filled in with valve sutures alternating green and white colors. Each new stitch is placed in such a fashion that the needle exits the aortic root immediately under the last stitch placed. The travel stitch of each suture is no further away from the first suture than the width of the pledgett. It is particularly important to follow the curve of the needle through the annulus to avoid creating irregular needle holes that can lead to troublesome bleeding from the root at the end of the case. In areas where extensive calcium debridement has been required, especially when a prior prosthetic valve was excised, mitral valve sutures may be more useful than traditional aortic stitches as the larger needle more easily traverses the area in question. Care must be taken along the annulus in the area of the anterior leaflet of the mitral valve. Sutures that are placed too deep may create tension along the insertion of this part of the mitral that could lead to unwanted mitral insufficiency in the postoperative period. Suturing under the right coronary sinus must also be performed cautiously to avoid the conduction system.
Once all of the valve sutures are placed circumferentially around the annulus, mechanical valve sizers are used to choose an appropriate CVG. I usually do not downsize the valve, preferring to use one that corresponds to the sizer that fits snugly into the annulus. Do not size the root before placing the sutures as one will usually end up with a CVG that is oversized.
Figure 6.
Seating the composite valve graft. I like to orient a mechanical CVG with one of the pivot guards immediately under the commissure between the left and right sinuses. This places the opposite pivot guard into the midportion of the noncoronary sinus, an area that can be easily visualized as the valve is tied into position. Valve sutures are then brought through the sewing cuff of the CVG. The needles are passed through the bottom of the cuff and brought out through the highest point on the cuff to maximize the amount of sewing ring in the annular suture line. Skiving the cuff is not acceptable and is a setup for potential bleeding from the annular suture line. The valve sutures are then tied down beginning in the midportion of the left coronary sinus. The middle stitch of the right and noncoronary sinuses are then tied down, similar to securing the lug nuts of a car's spare tire. This seats the CVG in the annulus and insures that the pivot guards are in the left ventricular outflow tract. Once each middle stitch is tied, the remainder of the sutures are tied going sequentially from the left to the right to the noncoronary sinus. The annular suture line integrity is then checked for gaps with a small, pointed “baby” right-angle clamp. Any hints of a gap are repaired with additional valve stitches through the native annulus onto the sewing ring of the CVG.
Figure 7.
Cabrol reconstruction. In patients undergoing reoperations on the aortic root, especially in those in whom the original operation was performed with either biological glue or extensive Teflon felt, mobilizing the coronary arteries, especially the left main coronary, can be extremely difficult and hazardous. This also occurs in patients having aneurysms in the setting of inflammatory processes such as Takayasu's disease or inflammatory aneurysms. When this is encountered, extensive and repeated attempts at coronary mobilization should be abandoned in favor of a “modified” Cabrol reconstruction with a Dacron graft to the left main coronary artery. I am not enamored of the original Cabrol technique, whereby both coronaries are sutured to either end of a single graft that is then brought off the CVG in a side-to-side fashion.5 Rather, I prefer the modified technique described by Svennson, whereby a “Cabrol” graft is sewn to the left main ostia and the RCA button is reimplanted as with the exclusion method (A).6 After placing all of the annular pledgetted sutures, but before bringing them through the composite graft, a 10- or 12-mm graft is sewn around the ostium of the left main coronary with a running 5-0 Prolene suture. The graft should be beveled away from the surgeon's perspective to have the graft lay posterior to the CVG without tension or kinking. Suturing starts at the toe of the graft and substantial bites of aorta are taken to ensure hemostasis and reduce the potential for pseudoaneurysm formation. Care is taken to avoid passing the needle through the actual coronary artery as this can lead to bleeding behind the aorta that will be extremely difficult to control. Once this is completed, we perfuse down this graft with one arm of our octopus cardioplegia setup. This will identify any leaks as additional doses of cardioplegia are given down the left main. The composite valve-graft is then tied into the annulus and the distal suture line is completed. The RCA button is nearly always amenable to direct reattachment to the CVG. If mobilizing the RCA is deemed too hazardous, we prefer to sew a separate 10- or 12-mm graft to the ostium of the RCA. This is brought off of the anterior portion of the CVG 2 or 3 cm below the distal suture line. (B) The graft to the left main is then brought posterior to the main composite graft and off of the side of the CVG with a running 4-0 suture. When measuring this graft, we usually make it 1 or 2 cm longer than measured for a perfect fit to allow for the downward and posterior displacement of the CVG with the heart full and beating. a. = artery.
Figure 8.
Left main coronary artery reattachment. Once the CVG is seated into the annulus, the left main coronary button is reattached. The button is pulled up to the CVG and a handheld cautery is used to create a defect at the appropriate level on the CVG. The suture line to reattach the button is started with a 5-0 polypropylene suture at the most inferior point away from the surgeon's perspective. After the first stitch into the graft and button are completed, three throws are performed with the suture so that tension on this most important suture line is more easily maintained. The running suture line is then continued toward the surgeon in a forehand fashion, going from coronary button to the graft. Looking down through the CVG graft, one can see any potential sites of leak along the inferior-most portion of the suture line. These are taken care of with interrupted 6-0 suture. A second layer of running 5-0 suture ensures hemostasis on the left main button. Cardioplegia is then administered through a Foley catheter with a 30 mL balloon that is placed into the CVG.
Figure 9.
Once the graft is full, the balloon is inflated and the left main button is inspected for any potential leaks. These, too, are repaired with 6-0 suture.
Figure 10.
Distal and RCA button anastomoses. Many times, especially in patients with Marfan's syndrome, the distal ascending aorta is significantly smaller than the annulus and there is tremendous mismatch between the size of the Dacron graft of the CVG and the recipient native aorta. In a majority of cases, careful suturing will compensate for this discrepancy. At times, however, the mismatch is too great and a tailored “V-plasty” of the Dacron graft is necessary to make a more acceptable distal anastomosis. The distal anastomosis is then performed with a running 3-0 polypropylene suture starting at the furthest point away from the surgeon along the back wall and sewing toward the patient's right side. This suture line is then reinforced with interrupted, pledgetted 3-0 horizontal mattress polypropylene sutures.
The right coronary button reattachment is the last portion of the procedure, performed after completing the distal suture line. This allows for more accurate placement of the button on the anterior wall of the graft and gives a better estimate of how it will sit when the graft and heart are full. If the RCA is attached before the distal is done, the button may be placed too low on the CVG and the RCA will kink once the distal suture line is complete. The button should be placed as high as possible on the CVG to avoid this problem. Frequently, additional mobilization of this button is necessary to eliminate any tension between the button and the graft. This should be done with care as there are frequently small conus branches of the RCA that travel toward the right ventricular outflow tract. On occasion, these may be killed to gain the additional length necessary. The reattachment is started on the most inferior portion of the button to toward the patient's left and working toward the right side with a running 5-0 polypropylene. The LV vent is turned off as you begin the superior-most portion of the suture line to allow the heart to begin filling. Any gaps or “dog ears” are closed with interrupted 5-0 sutures. Once this is complete, an 18-gauge needle is placed in the Dacron graft to assist in removing air before coming off of bypass. This site is oversewn with 5-0 polypropylene at the completion of the case.
Figure 11.
Bioprosthetic CVG. It may be more appropriate for some patients to have their aortic root replaced with a bioprosthetic-based composite valve-graft. In this case, I use a standard bovine pericardial or porcine aortic valve (Edwards Lifesciences, Orange County, CA) and a Hemashield Dacron graft to create the CVG. Bioprosthetic sizers are used to determine the size of the valve required. When a porcine valve is chosen, a graft 3 mm larger than the valve is chosen. For example, a 28-mm Dacron graft would be sewn onto a 25-mm porcine valve. If a bovine valve is preferred, a graft 5 mm larger than the size of the valve is necessary because the bovine valves are slightly larger than their porcine counterparts. In either situation, the graft is lowered down over the valve and sewn to the sewing ring of the valve with a running 3-0 polypropylene suture. Care must be taken to pull the graft taut as you are sewing the two together to avoid running out of graft as you complete the CVG. When completed, look through the graft to ensure that none of the running suture line impinges on the valve leaflets in any way. The valve sutures are then brought through the sewing ring of the valve and up through at least one or two rings of the Dacron graft. This makes the connection between the valve and Dacron absolutely watertight. If extra valve sutures are needed to close potential gaps in the annular suture line, extra care must be taken with a bioprosthetic valve to avoid any damage to the delicate bioprosthetic leaflets.
Results for Composite Valve-Graft Root Replacement
Over the last 10 years we have performed 421 consecutive composite valve-graft replacements of the ascending aorta and aortic valve. A majority of the patients required root replacement for an ascending aneurysm (364/421, 86.4%). However, 28 (6.7%) patients had a CVG placed for an acute type A dissection and an additional 29 patients (6.9%) had surgery in the setting of chronic dissection. Greater than 30% required circulatory arrest to entirely excise the diseased aorta. The mean age of our patient population was 53 years and 83% were male. Seventy-one (16.9%) had Marfan's syndrome. The mean diameter of the aortic root was 63 mm.
A majority of the patients received full Hammersmith dose aprotonin as their antifibrinolytic therapy (85%, 358/421), whereas the remaining 15% were treated with epsilon-aminocaproic acid. Ninety percent were placed on cardiopulmonary bypass through either the ascending aorta or the arch, whereas 10% required femoral cannulation (43/421). Axillary artery cannulation was never necessary in any of our patients regardless of the pathologic aortic disease or the urgency of the surgery.
There were no intraoperative deaths. Our in-hospital and 30-day mortality was 1.2% (5/421). Just over 5% of the patients (22/421, 5.3%) required reexploration for bleeding in the immediate postoperative period. This includes patients having prolonged periods of cardiopulmonary bypass for arch reconstructions requiring profound hypothermic circulatory arrest. Two patients (0.4%) experienced embolic CVAs and a similar number (2/421, 0.4%) required temporary hemodialysis for acute renal failure. Three patients (3/421, 0.7%) developed respiratory failure and required a tracheostomy.
There have not been any reoperations for pseudoaneurysm formation or valve failure, including the 165/421 (39%) having CVG replacement with a bioprosthetic valve. The 10-year actuarial freedom from reoperation on any part of the aorta including the root was 96.5%. The 1-, 3-, 5- and 10-year actuarial survival for the entire cohort of 421 patients was 97, 95, 94.4, and 75.3%, respectively. This was not significantly different when patients having mechanical valves were compared with their bioprosthetic counterparts.
Conclusions
In summary, we believe the mechanical composite valve-graft replacement is the gold standard operation for aortic root reconstruction. Even when a bioprosthetic valve is needed, the results are reproducible and durable.
References
- . A technique for complete replacement of the ascending aorta. Thorax. 1968;23:338–339
- . Eleven-year experience with composite graft replacement of the ascending aorta and aortic valve. J Thorac Cardiovasc Surg. 1986;92:691–705
- Replacment of the aortic root in patients with Marfan's Syndrome. New Engl J Med. 1999;340:1307
- . Retrograde cerebral perfusion via a superior vena caval cannula for aortic arch aneurysm operations. Ann Thorac Surg. 1994;57:1668–1669
- Complete replacement of the ascending aorta with reimplantation of the coronary arteries. J Thorac Cardiovasc Surg. 1980;79:388–410
- . Approach to the insertion of composite valve graft. Ann Thorac Surg. 1989;54:76–78
PII: S1522-2942(08)00039-1
doi:10.1053/j.optechstcvs.2008.06.004
© 2008 Elsevier Inc. All rights reserved.
Volume 13, Issue 3 , Pages 148-160, Autumn 2008
