Aortic Valve-Sparing Operations
Keywords: Aortic Valve-Sparing Operations, Operations for Valvular Heart Disease, aortic root aneurysm, aortic insufficiency
Aortic valve-sparing operations have become part of the surgical armamentarium to treat aortic root aneurysm and ascending aorta aneurysm with aortic insufficiency. Both types of procedures, remodeling of the aortic root and reimplantation of the aortic valve have provided excellent long term results when the procedure is correctly matched to the aortic root pathology.
· The aortic root is the anatomic segment between the left ventricle and ascending aorta. From the surgical viewpoint, it consists of the aortic annulus (AA), aortic cusps, aortic sinuses, and sinotubular junction (STJ). Although the term aortic annulus may be anatomically incorrect, it is often used in surgical anatomy and pathology to describe the aortoventricular junction. Approximately 45% of the circumference of the AA is attached to muscular interventricular septum, and 55% is attached to fibrous tissue, as shown in Fig. 13.1. This fibrous tissue is the membranous interventricular septum and the fibrous body that connects the anterior leaflet of the mitral valve to the aortic root.
· The AA is scalloped and attaches the aortic cusps to the aortic root and left ventricle. The portion of the AA corresponding to the noncoronary cusp is attached entirely to fibrous tissue, whereas the portions corresponding to the left and right coronary cusps are partially attached to fibrous tissue and partially to cardiac muscle. The highest point of the AA, where two cusps meet, is the commissure. The anatomic arrangement of the AA creates a triangular space beneath the cusps, termed the subcommissural triangle. There are three commissures and three subcommissural triangles. The STJ lies immediately above the commissures and separates the aortic root from the ascending aorta. The arterial wall contained between the AA and STJ creates the aortic sinuses, or sinuses of Valsalva. The three aortic cusps have a crescent shape and often are of different sizes, but the length of the base of a cusp is always 1.5 times longer than the length of its free margin (FM), as illustrated in Fig. 13.2. Thus, a large cusp will have a proportionally longer base (AA), longer FM, longer intercommissural distance along the STJ, and larger aortic sinus. The noncoronary and right cusps and sinuses are often larger than the left cusp and left aortic sinus.
· The AA is a three-dimensional structure that evolves along three separate planes, as illustrated in Fig. 13.3A–C. Each aortic cusp is inserted in the annulus along a horizontal plane (see Fig. 13.3D). For practical purposes, we usually refer to its diameter as the maximal distance at the level of its nadir.
· The relationship of the diameters of the AA at this level and at higher levels until reaching the commissures (STJ) varies with age. In children and young adults, the diameter of the AA is 15% to 20% larger than its diameter at the level of the commissures (STJ). As the elastic fibers of the arterial wall decrease with age, the STJ dilates and tends to become equal to the diameter of the lower AA in adults. However, the AA of each cusp evolves along a single horizontal plane (see Fig. 13.3).
· Ascending aortic aneurysms can cause aortic dissection or rupture when their transverse diameter exceeds 55 mm. Aneurysms of the ascending aorta can also cause dilation of the STJ, with consequent aortic insufficiency due to lack of coaptation of the cusps, as illustrated in Fig. 13.4. One or more aortic sinuses may also become secondarily dilated, but the AA often remains normal. Patients with ascending aortic aneurysms and aortic insufficiency are usually in their sixth or seventh decade of life. If the aortic cusps are normal or minimally elongated along their FMs, it is possible to replace the ascending aorta with correction of the diameter of the STJ, replace one or more sinuses if necessary, repair the cusps if there is prolapse, and reestablish aortic valve competence.
· Aortic root aneurysms usually start with dilation of the aortic sinuses and, with time, the dilation extends proximally into the AA and distally into the STJ. Patients with an aortic root aneurysm are usually in the second to fourth decade of life when they need surgery, and the aneurysm is often associated with genetic syndromes, such as Marfan syndrome, Loeys-Dietz syndrome, and others. The two subcommissural triangles of the noncoronary cusp flatten as the AA dilates, which decreases the coaptation area of the cusps and may cause aortic insufficiency (Fig. 13.5). The indication for surgery is usually based on the diameter of the aortic sinuses and family history of aortic dissection. In most cases, surgery is recommended when the diameter reaches 50 mm and less if there is a family history of aortic dissection.
· This chapter reviews the operative techniques used to preserve the aortic valve in patients with ascending aortic aneurysm and aortic insufficiency, as well as patients with aortic root aneurysm, with or without aortic insufficiency. The term aortic valve-sparing operation was introduced to describe these procedures.
Figure 13.1 Photograph of an aortic root.
Figure 13.3 Geometric relationship among various components of the aortic root.
Figure 13.2 The aortic annulu evolves along a cylinder.
Step 2. Preoperative Considerations
· Patients with an ascending aortic aneurysm are usually asymptomatic, even if they have aortic insufficiency. Although echocardiography often establishes the diagnosis of an ascending aortic aneurysm and provides information regarding aortic valve function, computed tomography (CT) or magnetic resonance imaging (MRI) of the aorta is necessary to determine the extent of the aneurysm. The transverse arch is often involved in older patients with aneurysm of the ascending aorta and aortic insufficiency.
· Most patients with aortic root aneurysm are asymptomatic and have only mild or no aortic insufficiency. Some patients complain of vague chest pain. Severe chest pain is suggestive of rapid expansion or an intimal tear with dissection. Echocardiography establishes the diagnosis and gives information regarding aortic valve function. CT or MRI of the aorta is also diagnostic and provides useful information on the remaining thoracic aorta, although the transverse arch is seldom involved.
· Transesophageal echocardiography (TEE) is the best diagnostic tool to study the aortic valve and the mechanism of aortic insufficiency in patients with ascending aortic or aortic root aneurysm, as well as to measure the diameters of the AA, STJ, and cusp height. Each component of the aortic root must be carefully interrogated, particularly the aortic cusps. The number of cusps, their thickness, appearance of their FMs, and excursion of each cusp during the cardiac cycle must be examined in multiple views. The coaptation lines of the aortic cusps should be interrogated by color Doppler imaging. The direction and size of the regurgitant jets should be recorded in many views. Information regarding the morphologic features of the AA, aortic sinuses, STJ, and ascending aorta should be obtained. Obviously, the aortic cusps are the most important determinant of aortic valve repair. If the cusps are thin and mobile and have smooth FMs, the feasibility of aortic valve repair is very high, including patients with bicuspid aortic valves.
Figure 13.5 Dilation of the sinotubular junction prevents the cusps from coapting and causes aortic insufficiency.
Figure 13.4 Dilation of the aortic annulus flattens the subcommissural triangles of the noncoronary cusp and pulls the belly of the cusps apart.
Step 3. Operative Steps
· Aortic valve-sparing operations are usually performed through a median sternotomy, but the procedure can also be done through a limited skin incision (8–10 cm) and a partial or full median sternotomy.
· Cardiopulmonary bypass is established by inserting an arterial cannula into the proximal aortic arch if only the aortic root and proximal ascending aorta are involved or into the right axillary or innominate artery if the aortic arch needs replacement. Venous drainage for car- diopulmonary bypass is usually done with a single double-stage cannula placed in the right atrium or with bicaval cannulation when the mitral valve also needs repair. The heart is protected during aortic clamping by giving cold blood cardioplegia directly into the coronary arteries intermittently. I maintain the systemic temperature at around 34°C (93°F). If the aortic arch needs replacement, it is done first under moderate systemic hypothermia (22°–25°C; 72°–77°F) and continuous antegrade cerebral perfusion through the right axillary or innominate artery. A cannula is also inserted into the left carotid artery if the pressure in this artery is less than 50% of that in the innominate artery. If the mitral valve needs repair, it is done before the aortic root pathology is addressed.
· Intraoperative TEE is indispensable in aortic valve-sparing operations for assessment of aortic valve function before and after repair of the valve.
· The ascending aorta is transected 5 to 6 mm above the STJ and the aortic cusps are inspected. Although this inspection is largely to confirm what a preoperative transesophageal echocardiogram has already shown, stress fenestration close to the commissural areas and minor degrees of elongation of the FMs are not easily detected preoperatively.
· The aortic insufficiency is usually due to dilation of the STJ. Correction of the valve dysfunction is accomplished by reducing the diameter of the STJ by suturing a graft of appropriate diameter to it. The simplest method to determine the diameter of the graft is to approximate the three commissures until the cusps coapt centrally. Valve sizers such as the Medtronic Freestyle (Medtronic, Minneapolis) are metric and handy for this purpose. When in doubt between two sizes, it is safer to take the larger one because the STJ can be further reduced under echocardiographic guidance after completion of the operation by plication of the spaces between two commissures. In adult patients, small-caliber grafts may increase left ventricular afterload. Thus, if the estimated diameter of the STJ is 22 mm in a patient with a body surface area of 2 m2, a larger graft (26 or 28 mm) should be used and reduced to 22 mm at the end where the graft is going to be used to correct the diameter of the STJ. Fig. 13.6 illustrates this operative procedure. Before the graft is sutured to the STJ, the graft should be divided into thirds to correspond to each commissure. If one cusp is larger than the others, the intercommissural distance should be proportionally larger.
Figure 13.6 Replacement of the ascending aorta with an appropriately sized graft restores valve competency by reducing the sinotubular junction.
· If the noncoronary aortic sinus is excessively dilated or dissected (in cases of aortic dissection), it should be replaced. The graft is divided into thirds according to the spaces between commissures, and a neoaortic sinus is fashioned, as illustrated in Fig. 13.7. The height of the tailored neoaortic sinus should be approximately the same as the diameter of the graft. Next, the commissures of the noncoronary cusp are secured to the graft, and the neoaortic sinus is sutured to the remnant of the arterial wall and AA with continuous 4-0 polypropylene sutures. The remaining part of the graft is sutured to the STJ along the left and right aortic sinuses. If the noncoronary and right aortic sinuses are dilated or dissected, they should be replaced as described previously and illustrated in Fig. 13.8. In this case, the right coronary artery should be reimplanted into its neoaortic sinus.
· Finally, if all three aortic sinuses are dilated, the sinuses are excised, leaving 5 mm of arterial wall attached to the AA. The coronary arteries are detached from their sinuses along with 5 mm of arterial wall around their orifices (Fig. 13.9A). The three commissures are suspended at the same level and positioned in such way as to allow the three cusps to coapt centrally (see Fig. 13.9B). The diameter of the circle that includes all three commissures can be estimated with metric aortic valve sizers. As before, when in doubt between two sizes, it is safer to choose the larger one. Three neoaortic sinuses are tailored in one of the ends of the graft (see Fig. 13.9C). The width of the neoaortic sinuses is proportional to the size of the cusps and intercommissural distances. The arterial wall immediately above the commissures is secured to the graft, and the neoaortic sinuses are sutured to the remnants of the native aortic sinuses and AA with continuous 4-0 polypropylene sutures (see Fig. 13.9D). The coronary arteries are reimplanted into their respective sinuses (see Fig. 13.9E). To avoid late aneurysm formation in the arterial buttons, the diameter of the openings in the neoaortic sinuses should not exceed twice the diameter of the coronary arteries.
· The foregoing operative techniques are known as remodeling of the aortic root. After correction of the dilated STJ and replacement of one or more aortic sinuses, as described previously, the cusps should coapt well above the level of the nadir of the AA. If one or more cusps coapt at a lower level than the others, the FM is elongated and should be shortened by plication along the nodule of Arantius, as illustrated in Fig. 13.10. This is done with 6-0 or 5-0 polypropylene sutures, depending on the thickness of the cusp.
· A cusp with stress fenestration along its commissural edge can be reinforced by weaving a double layer of fine (6-0 or 7-0) polytetrafluoroethylene sutures along its FM, as illustrated in Fig. 13.11. After completion of the aortic root remodeling, valve competence is assessed by injecting cardioplegia into the graft under pressure. If the ventricle does not distend, there is no aortic insufficiency or only a trace because mild aortic insufficiency causes distention of the ventricle.
Figure 13.9 All three aortic sinuses can be replaced with a tailored tubular Dacron graft.
· Although the previously described aortic root remodeling procedure, with replacement of all three aortic sinuses, has been used to treat patients with aortic root aneurysm, I believe that the AA dilates in some patients late after surgery, particularly in those with an associated genetic syndrome, limiting the durability of the valve repair. Thus, in young adults with an aortic root aneurysm, the technique of reimplantation of the aortic valve has been shown to provide more durable results. This operation is more complicated than remodeling the aortic root because greater knowledge of the functional anatomy of the aortic valve is needed to reconstruct the AA, STJ, aortic sinuses, and sometimes the aortic cusps as well.
· Reimplantation of the aortic valve starts by freeing the aortic root from surrounding structures and excising the three aortic sinuses, as described earlier for the remodeling procedure (see Fig. 13.9A and B). Five to 6 mm of aortic sinus wall is left attached to the AA all around. Stay sutures are placed immediately above each commissure for traction.
Figure 13.10 Cusp prolapse can be corrected by plication along the nodule of Arantius.
Figure 13.11 Cusps with large fenestration can be reinforced with a double layer of fine expanded polytetrafluorethylene suture above and below the defect.
· The aortic root is then dissected free from the pulmonary artery and right ventricle, down to a level immediately below the AA. On the right side of the aortic root, it may be difficult, if not impossible, to separate the subcommissural triangles of the noncoronary cusp from the right and left atria because their insertion in the root may be at a higher level than the base of those triangles. The dissection is extended down to the level of the insertion of the atria in the aortic root. Next, multiple horizontal mattress sutures of 2-0 or 3-0 polyester are passed from the inside to the outside of the left ventricular outflow tract, immediately below the nadir of the AA, through a single horizontal plane along the fibrous portion of the outflow tract, and along its scalloped shape in the interventricular septum, as illustrated in Fig. 13.12A. These sutures are passed through the base of the subcommissural triangles of the noncoronary cusp, along a horizontal plane that corresponds to a level immediately below the nadir of the AA. Depending on the height of the membranous septum, the sutures may have to be a bit higher than the nadir of the AA to avoid the bundle of His. These sutures may incorporate part of the right and left atria if their insertion is higher than that horizontal plane. If the membranous septum and anterior leaflet of the mitral valve is often thin and soft, Teflon pledgets should be used in these sutures.
· The heights of the cusps are averaged, and a tubular Dacron graft with a diameter equal to double of that average is selected for reconstruction of the root. Conversely, the diameter of the graft can be estimated as described for the remodeling technique or by using the height of the commissure between the left and noncoronary cusps.
· Three equidistant marks are placed in one end of the graft to correspond to each commissure. A triangular segment of 5 mm is cut off along the mark that corresponds to the subcommissural triangle of the left and right cusps (see Fig. 13.12A). The sutures previously placed in the left ventricular outflow tract are now passed through the graft. The sutures should be spaced symmetrically if the AA is not dilated (see Fig. 13.12B). If there is obvious dilation of the AA, the sutures should be spaced symmetrically along the muscular component of the outflow tract and closer together beneath the subcommissural triangles of the noncoronary cusp because that is where dilation occurs in patients with connective tissue disorders. The level at which these sutures are passed through the graft is also important and should reproduce what was done when they were passed through the left ventricular outflow tract.
· The sutures are tied on the outside of the graft. Care must be exercised not to purse-string this suture line. The graft is then cut in a length of approximately 5 cm and pulled up gently, and the three commissures are also pulled vertically and temporarily secured to the graft with transfixing 4-0 polypropylene sutures, but they are not tied (see Fig. 13.12C). Once the three commissures are suspended inside the graft, the commissures and cusps are inspected to make sure that they are all correctly aligned. Next, the sutures are tied on the outside of the graft and used to secure the AA into the graft. This is accomplished by passing the suture sequentially from the inside to the outside right at the level of the annulus and from the outside to the inside at the level of the remnants of the arterial wall. I start at the level of the commissure and stop at the nadir of the AA, where the sutures are tied together on the outside of the graft. The coronary arteries are reimplanted into their respective sinuses.
· The coaptation level of the aortic cusps is inspected; it should be well above the level of the nadir of the annulus. If one or two cusps coapt at a lower level, the FM can be shortened, as illustrated in Figs. 13.10 and 13.12D. If fenestrations are present, the FM can be reinforced with a double layer of 6-0 or 7-0 polytetrafluoroethylene sutures (see Fig. 13.11). The graft can be clamped distally, and cardioplegia given into the aortic root to test for valve competence, as described for remodeling of the aortic root.
· Finally, the graft is sutured to the distal ascending aorta, as illustrated in Fig. 13.12E. I believe that the most durable reimplantation procedure is when a straight tubular Dacron graft is used. If neoaortic sinuses are desirable, a graft 2 or 4 mm larger than what is needed is selected and plicated to reduce its diameter in the area corresponding to the nadir of the AA and in between commissures (see Fig. 13.12E). The average graft size used in reimplantation of the aortic valve is 28 to 30 mm when a straight graft is used and 30 to 32 mm when neoaortic sinuses are created.
· Reimplantation of the aortic valve is also extremely valuable for patients with an incompetent bicuspid aortic valve, when the AA is frequently dilated. Patients with acute type A aortic dissection who have a dilated aortic root are also good candidates for this type of aortic valve-sparing procedure.
Figure 13.12 Reimplantation of the aortic valve.
Step 4. Postoperative Care
· The operative mortality rate for aortic valve-sparing operations is low in elective cases (< 2%), even in patients who require more extensive operations, including mitral valve repair, replacement of the aortic arch, and myocardial revascularization. These patients do not require any procedure-specific care in the intensive care unit or ward. In my experience, patients with an ascending aortic aneurysm and aortic insufficiency often have a transverse arch aneurysm and sometimes mega aorta syndrome. These patients require more extensive vascular surgery than those with aortic root aneurysm, with consequently higher rates of postoperative complications such as stroke, myocardial infarction, renal failure, and respiratory failure. However, more than 90% of all patients experience no serious postoperative complications.
· Postoperative bleeding is relatively common and, in my experience, approximately 50% require blood products. New heart block is rare (< 1%). Atrial fibrillation occurs in approximately 20% of these patients and is managed pharmacologically. Patients with an aortic root aneurysm associated with a genetic syndrome and those with an aortic dissection should receive a beta blocker, if tolerated. No oral anticoagulation is given unless atrial fibrillation persists for more than 24 hours or they have had a mitral annuloplasty ring or band, in which case they receive heparin initially and warfarin for 3 months.
· Echocardiographic studies to assess aortic valve function should be performed annually in all patients. In those with more extensive vascular disease or aortic dissection, periodic CT scanning or MRI of the aorta is also important during follow-up.
Step 5. Pearls and Pitfalls
· Aortic valve-sparing operations are complex procedures. A sound knowledge of the functional anatomy and pathology of the aortic root and technical expertise are needed for their performance. As with any other type of heart valve repair, it should not be performed if the aortic cusps are grossly abnormal. From the preoperative selection of patients by TEE to the intraoperative analysis of the aortic cusps and root and what is needed to restore the functional anatomy of the aortic valve, every step is crucial.
· Sizing of the graft is difficult for the surgeon who is learning to perform these operations. Sizing of the graft is easier for remodeling of the aortic root than for reimplantation of the aortic valve. The guidelines for sizing the graft for reimplantation of the aortic valve given in this chapter are based more on clinical experience than on scientific investigation of functional anatomy. The length of the FMs of the cusps, degree of scalloping of the AA, and diameter of the STJ can all be altered during reconstruction of the root, but the height of the cusps cannot. For this reason, I use the average height of the cusps to estimate the appropriate diameter of the AA at the level of its nadir. By using grafts with a diameter equal to twice the average height of the cusps, the radius of the reconstructed AA becomes equal to the height minus the thickness of the aortoventricular junction because it is sutured inside the graft. This reduction in diameter of the annulus has proven effective in allowing the cusps to coapt well above the nadir of the annulus, and it provides a good seal of the aortic orifice during diastole.
· The level of coaptation of the aortic cusps has been shown to be important for the durability of these procedures. If the cusps coapt at the same level as the annulus, the probability of prolapse of a cusp with consequent aortic insufficiency is greatly increased, compared with cusps that coapt at least 8 mm above the nadir of the AA. Thus, sizing of the graft and shortening the length of the cusps’ FMs are extremely important determinants of late valve function.
· As illustrated in Fig. 13.3, the AA evolves along single horizontal planes. The only geometric shape suitable to stabilize a dilated AA is a cylinder. Thus, a straight tubular Dacron graft is probably the best shape for reimplantation of the aortic valve. Newer grafts with neoaortic sinuses are spherical and probably deform the AA once the valve is secured inside them. Thus, I do not recommend these grafts for reimplantation.
· Aortic valve-sparing operations are extensive, and hemostatic anastomoses between the various components are of utmost importance. Coagulopathy at the end of a long cardiopulmonary bypass is common, and every measure must be taken to avoid mechanical bleeding.
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