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Aortic valve replacement


Aortic valve replacement is usually required when operative intervention is performed for aortic valve stenosis or incompetence in older patients. Several replacement devices are available, but all operations share a common approach and principles.

Morphology

Figure 31-1, A Operative image of aortic valve stenosis, degenerative type. Normal three-leaflet architecture is maintained. Commissures are not fused. Leaflets are held in a closed position due to diffuse, nodular calcific deposits. Calcification, often described as “eggshell,” may involve the sinuses of Valsalva. This morphology is presumed to be atheromatous. B Operative image of aortic valve stenosis, degenerative type. There are three leaflets and no commissural fusion. The degeneration is advanced, with marked nodular calcification. As aortic valve degeneration progresses, the aortic valve area decreases at a rate of 0.12 cm 2 /year. C Operative image of aortic valve stenosis, congenital type. The valve is bicuspid, with fusion of the commissure between the left and right coronary leaflets. There is heavy dystrophic calcification of the leaflets. The valve orifice is eccentric and slit-like. D Operative image of aortic valve stenosis, congenital type. There is only one open commissure, that between the left and noncoronary leaflets. The other two commissures are completely fused. This may be called a unicuspid valve. Calcification is not as severe as in Part C . E Operative image of the ascending aorta in aortic valve stenosis. The aorta is frequently abnormal in patients with bicuspid aortic valve. This image shows dilation of the ascending aorta. F Aortic valve stenosis and regurgitation, rheumatic type, in an excised valve specimen. Normal three-leaflet structure is retained. There is scarring and shortening of the leaflets with rolling of the free edges, resulting in central regurgitation due to a lack of leaflet coaptation. The thickened leaflets also obstruct left ventricular outflow (aortic valve stenosis). G Operative image of aortic valve regurgitation. The noncoronary leaflet of the aortic valve is redundant and prolapsed. Many cases of aortic valve regurgitation are caused by an abnormality of the aorta, primarily dilation, producing secondary changes in otherwise near-normal aortic valve leaflets. These cases are often amenable to repair by correcting the aortic morphology.

Valve excision and débridement

Figure 31-2, A The operation is performed with the patient on cardiopulmonary bypass using a single venous cannula (two stages), with oxygenated blood returned to the ascending aorta. A vent catheter is inserted by way of the right superior pulmonary vein to the left atrium and left ventricle. The aorta is occluded, and hypothermic cardioplegic solution is administered to ensure total electromechanical 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 its effectiveness, even with aortic valve incompetence, its simplicity, and the absence of cannulae in the aortic root. The coronary arteries can also be perfused in an antegrade fashion through a cannula in the wall of the aorta to perfuse the aortic root or, if there is aortic valve regurgitation, directly in the coronary ostia using coronary perfusion cannulae. A transverse incision is made in the ascending aorta and extended into the noncoronary sinus of Valsalva. This is the classic incision for operations on the aortic valve. An alternative incision (inset) makes implantation of aortic valve bioprostheses or aortic homografts easier and more anatomic in the aortic root. The aorta is completely divided above the sinotubular junction, leaving the noncoronary sinus intact. Exposure of the intact aortic root is enhanced by traction sutures placed at the apex of each aortic valve commissure or the remnant thereof. Traction sutures rotate the aortic root inferiorly, achieving the excellent views demonstrated in Figure 31-1 , A–D and G . This approach requires anastomosis of the aorta following aortic valve replacement, but this suture line is actually more secure than incisions deep into the noncoronary sinus, which may lead to troublesome bleeding from the apex of the incision as pressure is restored to the aorta. B Excision of the aortic valve is begun at the commissure between the right and noncoronary sinuses, where there is little danger of extending the incision outside the heart. The commissure is excised from the aortic wall, and the right coronary cusp is excised at the annulus. Careful and deliberate excision of the valve cusp, with attention to removing as much of the annular calcification as possible, hastens the procedure. Curved Mayo scissors are ideal for excision of the valve; their relatively blunt tips and strong blades allow the calcium deposits to be squeezed away from the annulus and aortic sinuses, with little risk of aortic perforation. C The commissure between the left and right coronary cusps is removed from the aortic wall, and the left coronary cusp is excised. D The noncoronary cusp is excised toward the commissure between the left and noncoronary cusps, completing the excision posteriorly. Extreme caution must be used during excision of the aortic valve in the area of the commissure between the left and noncoronary cusps and in the left cusp because the risk of extending the incision outside the heart is greatest in this area. E Any remaining nidus of calcium is removed from the aortic annulus. A vascular forceps is used to grasp and remove the pieces of calcium with a twisting motion. This technique preserves all the connective tissue of the aortic annulus, preventing overexcision and perforation of the aorta. The forceps technique is gentler and more controlled, making it preferable to other techniques. Rongeurs or other instruments that cut the tissues must be used with caution. During this portion of the procedure a small bit of gauze should be placed in the left ventricular outflow tract below the aortic valve annulus to catch any bits of calcium that fall away as the débridement proceeds. With patience and attention to detail, essentially all the calcium deposits can be removed from the aortic annulus to allow better seating and healing of the valve prosthesis. F Traction stitches are placed at the sinotubular junction (sinus rim) above each of the commissures. These stitches are pulled up tightly to provide maximal exposure of the aortic annulus. The annulus is calibrated, and an appropriately sized prosthesis is selected for replacement of the aortic valve. There is no advantage in choosing an oversized prosthesis, which risks mechanical malfunction. If the aortic annulus is too small to accommodate a prosthesis that will provide adequate hemodynamic performance, the annulus should be enlarged.

Continuous suture technique

Continuous suture technique for aortic valve replacement has some distinct advantages over the more standard pledget-reinforced mattress suture technique. A larger prosthesis can be accommodated in the aortic outflow tract with the continuous suture technique because the tissues are not compressed, as they are with the mattress suture technique. The tension on each suture can also be adjusted and made uniform with the continuous suture technique. In addition, there are fewer knots, which can act as potential nidi for clot formation.

Figure 31-3, A Retraction stitches are placed just above the commissures. The aortic annulus is divided into three segments by the commissures. During the valve replacement procedure the annulus is subdivided at the midpoint on the annulus between the commissures to create six subsegments. A double-needle 2/0 polypropylene suture with a compressed Teflon pledget in the center of the suture is used. An initial mattress stitch is placed at the center of the sinus of Valsalva, through the aortic annulus, and brought through the sewing ring of the prosthesis. The prosthetic valve is held away from the annulus and positioned and retracted for added exposure. Exactly three stitches are placed between the initial pledget-reinforced stitch and the commissure on each side of the sinus. The final stitch at each end is secured to the wound drapes by a hemostat. A loop of 0 silk suture is placed around the polypropylene suture as the first suture loop is completed through the prosthesis in each subsegment. This silk loop is held by a hemostat and is later used to adjust tension on the suture line. B Sutures in the right coronary annulus are placed from the center toward the commissures in the first and second subsegments. The initial stitch in the left coronary sinus passes through the sewing ring of the prosthesis, opposite the last stitch of the second subsegment. Working from the center to the commissures in the left coronary sinus, the surgeon attaches the third and fourth subsegments to the prosthesis. Last, sutures are placed in the fifth and sixth subsegments in the noncoronary sinus. C Traction is placed on the six 0 silk loop sutures to pull the prosthesis into the annulus of the aortic valve. The pledget must be tightly approximated because this is the lowest point in the annulus and has the most tension when drawn up to the prosthesis. This is accomplished by pulling up on the loop sutures adjacent to the pledget to seat it firmly. Care must be taken not to draw the pledget beneath the prosthesis. D The silk traction suture loops are removed sequentially, and the ends of the polypropylene suture are pulled up tightly to approximate the sewing ring of the prosthesis precisely to the annulus of the aortic valve. The occluder of the prosthesis is opened, and the surgeon checks to ensure that there are no loose suture loops beneath the aortic prosthesis in the outflow tract of the left ventricle. This traction suture loop technique, which was devised by Dr. Russell M. Nelson, makes it easy to pull the prosthesis into the annulus of the aortic valve and tighten the continuous sutures. E A final check is performed to verify approximation of the sewing ring of the aortic prosthesis to the annulus of the aortic valve. Special attention is paid to accurate placement of the pledget, which should be above the annulus at the point of maximal stress, deep in the center of the sinus of Valsalva. The suture ends are then joined by a knot at the three commissures.

Interrupted suture technique

Interrupted suture technique is standard for replacement of the aortic valve. This method offers maximal strength of prosthetic attachment and has the lowest incidence of perivalvular leak.

Figure 31-4, A A double-needle suture of synthetic material with a centrally placed, compressed Teflon pledget is used for the repair. Using sutures of two different colors (green or blue and white) simplifies intraoperative identification of the suture pairs. In this way, the sutures from each annulus repair beneath each sinus of Valsalva can be held together as a group. Mattress stitches are taken through the annulus of the aortic valve, beginning at the commissure between the left and right coronary cusps. Stitches are placed in the right coronary annulus in a clockwise fashion, working toward the commissure between the right and noncoronary sinuses. Separate stitches are placed close to one another, and the space along the aortic annulus is taken beneath the pledget of the mattress stitch. The prosthesis is held away from the aortic annulus until all stitches have been placed. B The annulus of the left coronary sinus of Valsalva is then approximated to the sewing ring of the aortic valve prosthesis. The sutures are placed in a counterclockwise fashion, beginning at the commissure between the left and right coronary cusps. C The annulus of the noncoronary sinus of Valsalva is approximated to the valve prosthesis, working in a clockwise fashion from the commissure between the right and noncoronary cusps toward the commissure between the left and noncoronary cusps. The needles are passed through the annulus in a backhand fashion. The three groups of sutures are then strongly retracted so that the prosthesis can be slid over the suture loops into the aortic annulus. The position of the occluder mechanism can be adjusted before the valve holder is removed. D The sutures are sorted and tied down in a specific order. First the sutures in the noncoronary sinus are tied down in a counterclockwise fashion. The first suture in the left coronary sinus closest to the commissure between the left and right coronary cusps is tied directly across the annulus from those sutures already tied in the noncoronary sinus, to ensure that the prosthesis is securely seated. The sutures of the left coronary sinus are then tied down in a counterclockwise fashion. To complete the repair, the sutures are tied in the right sinus in a clockwise fashion. If a portion of the valve prostheses projects below the sewing ring and is thus positioned partially below the annulus in the left ventricular outflow tract, the order of suture tying is altered so that those portions of the prosthesis below the annulus are secured first. E An alternative technique for placement of the pledget-reinforced stitches is used in cases of a small aortic annulus. The pledgets are placed below the annulus in the left ventricular outflow tract by placing a mattress stitch with a center pledget via a double-needle suture; the suture is passed from below the annulus and up through the prosthesis. A larger prosthesis is thereby secured above the annulus as the annulus is compressed between the sutures and the device.

Aortic allograft: Kirklin/Barrett-Boyes 120-degree rotation technique

Transplantation of human aortic valves has become possible because of cryopreservation techniques and tissue banking, resulting in the availability of valves of various sizes for aortic surgery. Experience has shown that aortic allograft valves are durable, and their hemodynamic performance is superior to that of any other replacement device currently available. The virtual absence of embolism without the need for anticoagulation makes aortic allografts very attractive, especially in young patients and in those in whom anticoagulants are contraindicated. A clear understanding of the anatomy and geometry of the aortic root is essential because the aortic allograft depends on the host aortic tissues for support. Major deformity of the aortic sinuses should be appreciated and corrected, or the procedure should be abandoned in favor of a conventional valve replacement. The 120-degree rotation technique assumes that there are three symmetrically placed commissures in the host aorta that will support the aortic allograft valve. If there is abnormal commissure formation, asymmetric commissure placement, or sinus abnormality, it is preferable to use another method of allograft implantation that uses more graft aortic wall in the repair to compensate for deficiencies in the host.

Figure 31-5, A A transverse aortotomy is made, with the incision extended into the noncoronary sinus of Valsalva midway between the commissures. Alternatively, the aorta can be divided above the sinotubular junction. B The aortic valve is carefully inspected to determine which reconstructive procedures are possible. When a decision is made to replace the aortic valve, it is excised by the usual techniques. The entire valve must be removed, and the annulus must be completely débrided of calcium deposits. C 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 aortic homograft valve that will be placed inside the aortic root will consume space simply because of the thickness of its wall. Therefore, the aortic homograft valve chosen for replacement must be 1 to 2 mm smaller in internal diameter than the measured aortic annulus. Experience has shown that this amount of downsizing is just about right to account for the anticipated minor shrinkage of the graft cusp tissues and for absorption of the septal myocardium. Greater downsizing risks aortic valve incompetence 3 or 4 months after the operation. D The aortic homograft is removed from the liquid nitrogen freezer used at the valve bank and thawed according to protocol. The septal muscle is excised with a finger placed inside the aorta to stabilize the graft and gauge the thickness of the trimmed graft. E Excess aorta is trimmed away from the valve cusps, leaving a 3- to 4-mm rim of aorta beyond the attachment of the cusps. Most of the aortic sinus (sinus aortae) is removed. The aorta is shortened until it is approximately the same distance above the top of the commissural attachment. The graft is rotated 120 degrees counterclockwise from its anatomic position to place the portion of the valve below the right coronary sinus into the host aorta below the left coronary sinus. The purpose of this maneuver is to place the thick septal muscle contained on the graft opposite the flat portion of the outflow tract above the mitral valve. F Three stitches are used to attach the valve to the outflow tract. The first is a double-needle suture of 3/0 polypropylene using two small, strong needles. This monofilament suture is chosen because of the needle strength and because the suture loops slide easily without a 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. To aid in aligning the allograft with the aortic root, two sutures of 4/0 polypropylene are placed; these stitches will be removed later because 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. G 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 to expose the subvalvular edge of the graft. A knot is placed in the primary suture, and the stay sutures are tightened to align the graft with the aortic outflow tract. H Stitches are placed between the graft and the aortic outflow tract below the level of the annulus. Because the aortic annulus is not actually annular but is, in fact, crescent-shaped (semilunar), the stitches will be below the fibrous “annulus” in the subcommissural region (interleaflet triangle), and they will come through this fibrous tissue at the midpoint 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. I With the opposite needle, the stitches between the graft and the aortic outflow tract are placed below the right coronary sinus and completed below the noncoronary sinus. J The commissures of the aortic homograft are pulled out of the left ventricle so that the valve assumes its normal position and configuration. The commissures of the homograft are attached to the host aorta by continuous sutures of 4/0 polypropylene. Separate stitches are used for each aortic sinus. The first stitch is taken horizontally through the aortic sinus, slightly above the aortic annulus, and then passed through the graft. K The initial stitches should be placed deep in the sinus of the host to preserve function of 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 that the graft commissure is placed flat against the host aortic wall. The final stitches securely fasten the commissure of the graft to the aortic wall. L Suturing proceeds in each aortic sinus until the graft is completely attached. In general, suturing of 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. Suturing of the left sinus follows, and the repair is completed with suturing of the noncoronary sinus.

Aortic allograft: Ross intact noncoronary sinus technique

This technique is probably the most useful and reproducible method for replacing the aortic valve with an aortic allograft valve by the “freehand” technique. It is particularly useful in patients with aortic valve incompetence due to leaflet prolapse because this condition is usually caused by deformity and enlargement of the noncoronary sinus of Valsalva. The noncoronary sinus of the graft is not disturbed, so it serves as a substitute for the deformed sinus of the host. Because the sinotubular junction (sinus rim) of the noncoronary sinus of the graft remains intact, two of the commissures of the graft remain in a fixed position. The need to properly position only one commissure of the graft simplifies valve implantation and makes graft valve competence more likely.

Figure 31-6, A The principles of aortic root anatomic assessment, valve excision, annular sizing, choice of allograft size, and method of trimming are exactly as described for the 120-degree rotation technique (see Figure 31-5 , A-D ), except that the noncoronary sinus of the graft remains intact and is not trimmed. A significant length of graft aorta is left above the sinus rim. This will be trimmed later during closure of the aorta. Transecting the aorta rather than using an oblique incision is probably preferable for the reasons explained earlier. B The graft is attached to the aortic outflow tract exactly as shown in Figure 31-5 , F . Only one alignment suture is shown here. The actual suture used for the repair is placed below the medial commissure. C The graft is lowered into the aortic outflow tract, and the aortic tissue is inverted to expose the lower edge of the graft. The lower suture line proceeds as demonstrated in Figure 31-5 , H and I . Shown here are the final stitches taken in the noncoronary sinus. An effort is made to keep the lower suture line in a level plane. Maintaining a level suture line is not possible in the segment of the right coronary sinus occupied by the conduction system; there, sutures must be placed through the fibrous annulus. Because many patients have deformed noncononary sinuses that are much deeper than the other sinuses, it may be necessary to adjust the position of the lower suture line in this segment. In some cases it is actually more desirable to bring the lower suture line above the annulus into the aortic sinus to compensate for the deformity, rather than distorting the graft by attempting to pull it down to achieve a subannular suture line, as described for the 120-degree rotation technique. D The sinus aorta of the graft is attached to the sinus aorta of the host using continuous stitches of 4/0 polypropylene. The suture line is started deep in the sinus at the midpoint with a horizontal stitch, as described in Figure 31-5 , J . The initial stitches the are placed deep in the sinus aorta to preserve sinus of Valsalva function. Suturing begins in the right coronary sinus and proceeds to the top of each adjacent commissure of the graft. Repair of the left coronary sinus follows. E Noncoronary sinus repair is accomplished by one of two methods. In one method, the aorta is closed over the graft if the noncoronary sinus of the host is enlarged and the graft will not be compressed or distorted by the repair. Continuous 4/0 polypropylene suture is used to close the aorta to a point above the sinus rim. The graft aorta is excised above the sinus rim. The aorta of the graft is closed to the host aorta just above the sinus rim by continuous sutures. F In the second method, if the noncoronary sinus of the host will not accommodate the graft without distortion, the edges of the aortotomy are left open to allow the graft sinus to expand without restriction. The edges of the aortotomy are loosely attached to the adventitia of the graft at an appropriate point. The graft is tapered and worked into the aortotomy closure above the sinus rim.

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