Aortic Valve Replacement with a Homograft Valve

Operative Steps

Incision

1. A midline sternotomy is generally employed
2. A minimal approach using a lower ½ sternotomy may also be employed.

Cardiopulmonary bypass

1. The operation is performed on cardiopulmonary bypass using a single venous cannula (two stage) with oxygenated blood return to the ascending aorta. Two venous cannulae are employed in cases of extensive infection of the aortic root in case the right atrium or ventricle will be entered.
2. A vent catheter is inserted by way of right superior pulmonary vein to the left atrium and left ventricle.
3. The ascending aorta is occluded at the pericardial reflection and hypothermic cardioplegic solution is administered to assure total electro mechanical arrest and to protect the myocardium from ischemic injury. Retrograde perfusion of the myocardium via a catheter in the coronary sinus is the preferred method because of effectiveness even with aortic valve incompetence , simplicity, and the lack of cannulae in the aortic root.

Modified subcoronary valve replacement technique (Ross)

1. The ascending aorta is divided above the sinotubular junction. This provides optimal exposure while retaining the natural relationships of the aortic root.
2. The aortic valve is excised and the annulus and sinus aorta debrided of all calcareous deposits.
3. The diameter of the aortic root at the level of valve cusp attachment (annulus) is determined using standard sizing devices. This dimension must be accurately measured and clearly visualized. The valve chosen for replacement must be 1 - 2 mm smaller in internal diameter than the measured aortic annulus. Experience has shown that this amount of down-sizing is just about right to account for the anticipated minor shrinkage of the graft cusp tissues and for absorption of the septal myocardium. Greater down-sizing will likely result in aortic valve incompetence 3 or 4 months after operation.
4. The aortic homograft is removed from the liquid nitrogen freezer used for the valve bank and thawed out by protocol method. The septal muscle is excised with a finger placed inside the aorta to stabilize the graft and gauge the thickness of the trimmed graft.
5. The sinus aorta is trimmed away from the valve cusps leaving a 3-4 mm rim of aorta beyond the attachment of the cusps. Most of the sinus aorta will be removed from the right and left coronary sinuses. The noncoronary sinus aorta remains intact in order to fix the position of the two adjacent commissures. The aorta is shortened to approximately the same distance above the top of the commissural attachment between the left and right sinuses.
6. Three stitches are used to attach the valve to the outflow tract. The first is 3/0 polypropylene with two small strong needles (RB-1). This monofilament suture is chosen because of needle strength and because the suture loops slide easily without tendency to cut through the allograft tissue especially in the region of the septal myocardium. This suture is placed through the graft septal muscle below the appropriate commissure and then through the host aortic outflow tract below the medial commissure between the right and left coronary sinuses. The stitch is placed below the annulus of the host aortic valve. Two sutures are placed to aid in alignment of the homograft to the aortic root. These stitches are 4/0 polypropylene and will be removed as the primary suture line involves their position. These stitches are placed beneath the appropriate commissure of the graft and directly below the anterior and posterior commissures of the host aorta.
7. The allograft valve is lowered into position in the aortic root guided by the alignment sutures. The commissures of the graft are inverted through its annulus into the left ventricle of the host so as to expose the subvalvular edge of the graft. A knot is placed in the primary suture and the stay sutures tightened to align the graft with the aortic outflow tract.
8. Stitches are placed between the graft and the aortic outflow tract below the level of the annulus. Since the aortic annulus is not actually annular but in fact crescent or semilunar shaped, the stitches will be below the fibrous "annulus" in the sub-commissural region or interleaflet triangle and will come through this fibrous tissue at the mid-point of the aortic sinus. A real effort should be made to keep the plane of the suture line at an even level in the outflow tract. The stitches below the left coronary sinus are placed first. The suture line is taken to a point below the posterior commissure.
9. Using the opposite needle, the stitches between graft and aortic outflow tract are placed below the right coronary sinus and completed below the noncoronary sinus.
10. The commissures of the aortic homograft are pulled out of the left ventricle so that the valve assumes its normal position and configuration. The sinus aorta of the homograft are attached to the host aorta by continuous suture using 4/0 polypropylene. Separate stitches are used for the right and left aortic sinuses. The stitches are placed below the coronary ostia, deep in the sinus of Valsalva. As the suturing proceeds up the commissure, the stitches in the host aorta should be placed away from the actual fibrous commissure in the tissue of the aortic sinus so as to place the graft commissure flat against the host aortic wall. The final stitches securely fasten the commissure of the graft to the aortic wall.
11. Suturing proceeds in each aortic sinus until the graft is completely attached. Generally, the right coronary sinus is completed first, sewing from the center point of the sinus to each of the commissures using opposite ends of the suture. The left sinus follows. The noncoronary sinus aorta is trimmed level with the cut edge of the aorta so that the two edges may be approximated simply by over and over continuous stitch for a secure closure.
12. The repair is completed by anastomosis of the ascending aorta to the aortic root.

Complete aortic root replacement technique

1. The ascending aorta is divided above the sinotubular junction. The sinus aorta surrounding the coronary arteries is retained. All the rest of the sinus aorta is excised leaving only fibrous aortic valve attachments which are normal and uninvolved with the disease process which is being treated. An aortic homograft is selected. Sizing of the graft is of less importance than in freehand valve replacement because the graft will be free standing and not enclosed by host aorta. It is used intact and in natural orientation, with only the excess of septal myocardium and the anterior leaflet of the mitral valve removed. Before removing the mitral valve tissue, however, the pathologic defect should be evaluated to determine if the graft mitral valve will be of use in the reconstruction of the aortic root. The homograft is attached to the left ventricular outflow tract by simple interrupted stitches of 3/0 polypropylene suture. In many cases the stitches are placed through septal myocardium and the unsupported anterior leaflet of the mitral valve and roof of left atrium, because the annular connective tissue has been removed or destroyed by the disease process.
2. The key to a hemostatic proximal suture line is the use of a reinforcing collar. This collar will also support the proximal suture line and prevent dilation of the aortic allograft root. Teflon felt or pericardium is cut into a strip approximately 5 mm wide and the length sufficient to exceed the circumference of the aortic homograft. The felt strip will shorten as the sutures are tied over is and as it is compressed between the graft and the host aorta.
3. The homograft is slipped over the sutures into the outflow tract to the desired position. The sutures are then tied down, incorporating the felt or pericardial strip within the suture loops. This technique effectively seals up any potential leak points.
4. The coronary ostia of the graft are enlarged to create an opening to accommodate the coronary arteries of the patient by anastomosis. The sinus aorta surrounding the coronary ostia is anastomosed to the graft using continuous stitches of 4/0 or 5/0 polypropylene suture.
5. The repair is completed by end-to-end anastomosis of the distal end of the homograft to the patient aorta. Continuous stitches of 4/0 polypropylene are used. The patient aorta should be divided so that the posterior suture line can be constructed in the most secure fashion. Suturing to the intact posterior wall of the aorta and using of the aorta to cover the repair is not recommended

Preference Card

Devices

Aortic homografts in a variety of sizes, CryoLife Inc., Atlanta GA

Sutures

3/0, 4/0, 5/0 polypropylene on RB-1 needle, Ethicon Inc. Multipack (10) of 3/0 polypropylene RB-1 needle in alternating clear and blue color can be obtained by special order for ease of suture sorting (reference Dr. D.B. Doty, Ross procedure suture pack, Ethicon, Inc. Special Order D-9124).

Tips & Pitfalls

• Proper alignment of the three commissures and maintaining appropriate position at the sinotubular junction is essential in the subcoronary technique. Maintaining the noncoronary sinus makes this easier. Only the single free commissure needs to be properly positioned. Working within the intact aortic root with the aorta divided makes this easier. If the sinotubular junction of the patient is dilated, it can be narrowed by taking up excess aorta as the noncoronary sinus aorta of the patient is approximated to the graft. The sinotubular junction diameter should be 85% of that of the annulus, in other words, slightly smaller.
• As the sinus aorta is approximated to the aorta, stitches should be placed in radial fashion from the coronary ostia. The completed sinus repair suture line should be like a banjo head.
• There is argument as to whether the inflow suture line should be done by continuous suture with the graft inverted in the left ventricular outflow tract, or whether it should be done with interrupted stitches. Surgeon preference and familiarity should be followed in order to obtain a smooth approximation of the graft to the left ventricular outflow tract.
• There is argument as to whether the full root technique should be done by interrupted or continuous suture technique. Interrupted technique provides the most accurate anastomosis especially if there is size discrepancy. Continuous suture, on the other hand, is faster, and may be more hemostatic. If not carefully done, gathering or kinking the homograft will result in aortic valve incompetence. Continuous sutures placed with the graft separated from the left ventricular outflow tract may cut through the septal myocardium when the suture loops are pulled up.
• When complete root replacement technique is employed for aortic root infection, complete debridement of all infected tissues is the basic principle which should be followed for control of infection. No compromise should be made in excising all infected or necrotic tissue, even if it means deep incisions into the ventricular septum, left or right atrium, mitral or tricuspid valve. Large defects in the cardiac structure may be reconstructed using pericardium or the anterior leaflet of the mitral valve on the homograft. The graft description sheet should be checked carefully before thawing it out to be sure that the mitral leaflet is attached should it be required in the reconstruction. There is usually excess graft aorta which may also be useful in the reconstruction.
• Minimal incision (lower ½ sternotomy) provides good exposure of the aortic root. Dividing the aorta allows the aortic root to be rotated into full view and provides the intact aorta for optimal anatomic relationships. The ascending aorta, however, is not accessible beyond the lower ½.

References

1. Doty DB. Cardiac Surgery: Operative Technique. Mosby Inc., St Louis, 1997.
2. Doty JR, Salazar JD, Liddicoat JR, Flores JH, Doty DB. "Aortic valve replacement with cryopreserved aortic allograft: ten-year experience." J Thorac Cardiovasc Surg, 1998;115:371-80.
3. Doty JR, Flores JH, Millar RC, Doty DB. "Aortic valve replacement with Medtronic Freestyle bioprosthesis: operative technique and results." J. Cardiac Surgery, 1998; in press.
4. Doty DB, DiRusso GB, Doty JR."Full-spectrum cardiac surgery through a minimal incision: mini-sternotomy (lower half) technique." Ann Thorac Surg 1998;65:573-7.