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Aortic Root Enlargement Techniques


Aortic Root Enlargement Techniques
Keywords: Aortic Root Enlargement Techniques, Operations for Valvular Heart Disease

Abstract
This chapter discusses the commonly used aortic root enlargement techniques that increase the diameter of the aorta with small annulus and allow the implantation of larger prosthetic valves with better hemodynamic performance. In addition, some other surgical considerations in patients with small aortic root will also be discussed.


Introduction
·  Aortic valve replacement (AVR) is one of the most commonly performed operations in cardiac surgery. It is not only effective in alleviating symptoms in patients suffering from aortic valve disease, but also improves survival. However, in patients with a small aortic annulus, the benefits of this operation are dependent on the surgeon’s ability to avoid patient-prosthesis mismatch (PPM). PPM was first described by Rahimtoola in 19781 as: “Mismatch can be considered to be present when the effective prosthetic valve area, after insertion into the patient, is less than that of a normal human valve.” Pibarot and Dumesnil2 defined PPM as a prosthetic valve effective orifice area (EOA) indexed to a body surface area of less than 0.85 cm2/m2. PPM has been shown to be associated with a number of adverse outcomes, including worse hemodynamic performance, reduced left ventricular mass regression, and lower survival. If PPM is anticipated with the type of prosthesis that is being planned, the surgeon can either implant another type of prosthesis with a larger EOA, such as a stentless bioprosthesis, a new-generation mechanical prosthesis, or an aortic homograft, or he or she can surgically enlarge the aortic root to accommodate a larger prosthesis of the same type.
·    The well-known and documented repercussions regarding PPM3 have heightened the desire of surgeons to master aortic root enlargement techniques. In this chapter, we will discuss the commonly used aortic root enlargement techniques, including posterior enlarging techniques, such as the Nicks4 and Manougian5 procedures, and anterior enlarging strategies such as the Konno-Rastan aortoventriculoplasty and Ross-Konno AVR procedure.6-8 These techniques increase the diameter of the aorta with a small annulus and allow the implantation of larger prosthetic valves with better hemodynamic performance. In addition, some other surgical considerations9-11 in patients with a small aortic root will also be discussed.

Step 1. Preoperative Considerations
·    It is important to evaluate adult patients for concomitant coronary artery disease with stress testing and left heart catheterization. The coronary angiogram should be carefully studied for anomalous origin of either main coronary artery, and the location of the first septal branch of the left anterior descending artery should be identified if the pulmonary autograft operation is under consideration.
·    The echocardiogram should be reviewed for evidence of left ventricular hypertrophy and to assess left ventricular function. Careful preoperative measurement of the aortic annulus can guide intraoperative valve sizing to avoid PPM and to identify patients in whom aortic root enlargement is likely. Concomitant subaortic stenosis should be identified because this can be addressed with myotomy/myectomy if required.
·    The echocardiogram can also demonstrate concomitant poststenotic dilation of the ascending aorta or a true ascending aortic aneurysm. If the pulmonary autograft operation is under consideration, the pulmonary valve should be interrogated for insufficiency or other abnormalities. It is important to note mitral valve structure and degree of insufficiency on the preoperative echocardiogram because these may be altered with aortic root enlargement.
·    Adult congenital patients, in particular, who may have a history of associated arch anomalies may require a computed tomography (CT) or magnetic resonance imaging (MRI) scan to ensure that these structures and potential anatomic anomalies are well defined.
·  A resting electrocardiogram should be reviewed to identify any preoperative conduction abnormalities. Patients should be evaluated for concomitant atrial fibrillation or other rhythm disturbances that can be addressed during the operation.

Step 2. Surgical Anatomy
·    The aortic root consists of the aortic annulus, aortic cusps, aortic sinuses, and the sinotubular junction. The aortic root represents the outflow tract from the left ventricle. It provides supporting structures for the leaflets of the aortic valve and forms a bridge between the left ventricle and ascending aorta. All aortic root enlargement procedures are described based on an anatomic understanding of the coronary artery ostia, coronary sinuses, and commissures. Special attention should be paid to the relationship of these structures to the conduction system, the mitral valve and its apparatus, and the interventricular septum. In addition, the ability to distinguish the membranous portion of the septum is of critical importance.
·  The left ventricular outflow tract is best appreciated when viewed directly down into the aortic annulus. The aortic valve and pulmonary valve, although closely related, have different planes. The infundibular portion of the right ventricle elevates the plane of the pulmonary valve and trunk above the aortic valve, placing the pulmonary valve higher and more posterior. The aortic valve shares fibrous continuity with the anterior leaflet of the mitral valve (Fig. 11.1).
·  The space between the fibrous attachments of the aortic valve leaflets is termed the interleaflet triangle. These triangles are more flexible than the other segments of the aortic root (Fig. 11.2). The commissure between the right and left coronary cusps is usually located directly across from the pulmonary artery, with a mirror image configuration of the pulmonary valve cusps. The commissure between the right coronary cusp and noncoronary cusp is located anteriorly and is closely related to the interventricular septum and the conduction system. The commissure between the left coronary cusp and noncoronary cusp is located more posterior and to the right. This commissure is located opposite the middle portion of the anterior leaflet of the mitral valve (see Fig. 11.2).
·    Various portions of the aortic valve are above, at, and below the true aortic annulus. The tops of the commissures rest above the aortic annulus, well into the sinus portion of the aorta. The central portions of the leaflets meet below the aortic annulus during diastole, within the left ventricular outflow tract. The true aortoventricular junction is between these two levels (Fig. 11.3).
·   The right coronary artery arises from the right coronary sinus and courses rightward in the atrioventricular groove. The left main coronary artery is short and branches immediately into the left circumflex and left anterior descending arteries. The left circumflex artery courses laterally in the atrioventricular groove, being near the posterior mitral annulus. The left anterior descending artery lies posterior to the pulmonary artery in its proximal portion before coursing down the anterior interventricular groove. The first septal branch of the left anterior descending artery lies directly behind the posterior leaflet of the pulmonary valve (Fig. 11.4).


Step 3. Operative Steps
1. Left Ventricular Outflow Tract Exposure
·  Of paramount importance, regardless of any proposed technique, is exposure of the left ventricular outflow tract. In many cases a complete division of the ascending aorta, approximately 1 cm above the sinotubular junction, provides excellent exposure to the aortic valve and left ventricular outflow tract. Alternatively, a spiraling-type incision down into the noncoronary sinus may be used if extensive enlargement is not anticipated.
·    The aortic valve is excised and the annulus is d├ębrided. A careful determination is made as to the minimum size of prosthesis that would be acceptable for the patient’s body size. If root enlargement is indicated to achieve an adequately sized prosthesis, the appropriate technique is used.
2. Root Enlargement
·  Posterior enlargement of the aortic root is performed by either the Nicks-Nunez or Rittenhouse-Manouguian technique (Fig. 11.5). Both approaches are arguably the most commonly accepted and widely used techniques for aortic root enlargement and will be a large focus of this chapter. The Nicks-Nunez method is a vertical incision through the commissure between the left coronary cusp and noncoronary cusp, extending down into the interleaflet triangle. Limiting the incision to just the interleaflet triangle can enlarge the root sufficiently by 2 to 3 mm. If greater enlargement is required, the incision can be extended further into the anterior leaflet of the mitral valve and the roof of the left atrium. The Rittenhouse-Manouguian method is a vertical incision through the midportion of the noncoronary sinus, through the aortic annulus and into the anterior leaflet of the mitral valve and roof of the left atrium. The incisions in the anterior leaflet of the mitral valve can be extended almost to the free edge of the leaflet, dramatically enlarging the outflow tract.
·    Anterior enlargement of the aortic root, or aortoventriculoplasty, is performed according to the technique described by Konno and Rastan (Fig. 11.6). A vertical aortotomy is performed, and the incision is continued into the right coronary sinus, well leftward of the right coronary artery. The incision is then extended through the aortic annulus, near the commissure, between the right and left coronary leaflets. The incision is carried into the interventricular septum only as far as necessary to achieve the desired enlargement. Deep incisions place the first septal branch of the left anterior descending artery at risk for injury. A second incision is made on the right ventricular free wall to enlarge the right ventricular outflow tract.


3. Root Reconstruction
Nicks-Nunez Technique, Patch Reconstruction
·   After the aortic root has been enlarged sufficiently, a diamond-shaped patch of autologous pericardium, prosthetic material, or composite of both is fashioned. One end of the patch is inserted into the distal end of the enlargement at the level of aortic-mitral continuity if the incision is only into the interleaflet triangle. Interrupted sutures with pledgets are preferred because the interleaflet triangle lacks fibrous strength. The sutures are then passed through the sewing ring of the aortic valve prosthesis. The remainder of the valve sutures are placed through the aortic annulus in standard fashion (Fig. 11.7).
·    The patch is then tailored for closure of the aortotomy if a spiraled incision has been used, or it is transected flat at the level of the transverse aortotomy and incorporated as part of the reanastomosis of the aortic root to the ascending aorta (Fig. 11.8).

·    If the incision has been carried farther into the left ventricular outflow tract by crossing into the anterior leaflet of the mitral valve and left atrium, reconstruction is begun by placing the patch into the deepest portion of the incision. The defect in the anterior leaflet is repaired with the patch. Interrupted sutures without pledgets are used for accuracy and strength (Fig. 11.9).
·   At the level of the aortic annulus, interrupted sutures with pledgets are placed and passed, first through the patch and then through the prosthetic valve. The remainder of the valve sutures are placed through the aortic annulus in standard fashion. If the left atrial wall is flexible, and the defect is small, the left atrial wall can be approximated directly to the patch. Otherwise, a second patch is fashioned to reconstruct the left atrial defect (Fig. 11.10).
·   The patch is then tailored for closure of the aortotomy or incorporated as part of the aortic reanastomosis, as previously described.
Rittenhouse-Manouguian Technique, Patch Reconstruction
·     After enlargement of the root by extending the incision across the noncoronary portion of the aortic annulus into the anterior leaflet of the mitral valve and roof of the left atrium, a diamond-shaped patch of either autologous pericardium or prosthetic material (e.g., polytetrafluoroethylene [PTFE] or Dacron) is fashioned. As with the Nicks-Nunez method, reconstruction is begun by placing the patch into the deepest portion of the incision. The defect in the anterior leaflet is repaired with the patch, using interrupted or continuous sutures without pledgets for accuracy and strength (Fig. 11.11).


·  At the level of the aortic annulus, interrupted sutures with pledgets are placed and passed, first through the patch and then through the prosthetic valve (Fig. 11.12A). The remainder of the valve sutures are placed through the aortic annulus in standard fashion (see Fig. 11.12B). If the left atrial wall is flexible, and the defect is small, it can be approximated directly to the patch. Otherwise, a second patch is fashioned to reconstruct the left atrial defect (see Fig. 11.12C).
·    The patch is then tailored for closure of the aortotomy if a spiraled incision has been used, or it is transected flat at the level of the transverse aortotomy and incorporated as part of the reanastomosis of the aortic root to the ascending aorta.
Konno-Rastan Aortoventriculoplasty
·      The aortic root is mobilized by careful dissection anteriorly between the right coronary sinus and the pulmonary artery. This dissection is performed to the left side of the right coronary artery and is carried down to the level of the aortic annulus. The aortic root is enlarged with an incision through the right coronary portion of the aortic annulus, near the commissure, between the right and left coronary cusps. The incision is deepened into the interventricular septum, and a matching incision is made on the right ventricular free wall to enlarge the right ventricular outflow tract (Fig. 11.13).
·    A diamond-shaped patch of prosthetic material is fashioned and placed deep into the inter- ventricular septal incision. Continuous sutures are used to attach the patch to the ventricular muscle, up to the level of the aortic annulus (Fig. 11.14).


·   A second triangular patch is fashioned. Interrupted sutures with pledgets are used to attach the base of the triangular right ventricular outflow tract patch to the junction of the diamond- shaped left ventricular outflow tract patch at the level of the aortic annulus. The sutures are then passed through the sewing ring of the prosthetic valve (Fig. 11.15). The remainder of the valve sutures are placed through the aortic annulus in standard fashion, and the prosthesis is secured into position.
·   The right ventricular outflow tract patch is then folded over the right ventricular free wall defect, and continuous sutures are used to attach the patch to the ventricular muscle. The left ventricular outflow tract patch is tailored to close the defect in the aorta using the continuous suture technique (Fig. 11.16).
Aortic Allograft—Full Root Technique With Anterior Leaflet of the Mitral Valve
·     The aortic allograft is prepared with the attached, intact, anterior leaflet of the mitral valve. A small rim of donor left atrial tissue is also usually present and should be retained on the allograft. The remnants of the chordae are removed from the allograft anterior leaflet. In this fashion, the allograft can be used to reconstruct very large defects of the aortic root and enlarge the root substantially.
·   The aortic valve and sinus tissue are removed. The coronary arteries are mobilized on generous buttons of sinus tissue. The left ventricular outflow tract is enlarged posteriorly with either a Nicks-Nunez or Rittenhouse-Manouguian incision extending down into the anterior leaflet of the mitral valve (Fig. 11.17).


·    The anterior leaflet of the allograft is inserted into the defect in the patient’s anterior leaflet and attached using interrupted sutures, without pledgets, for accuracy and strength. Care and precision are used for this reconstruction to avoid distorting the mitral valve and causing undue tension (Figs. 11.18 and 11.19).
·  The allograft is attached to the left ventricular outflow tract using interrupted sutures for accuracy. This proximal suture line is then reinforced with biologic glue. If the left atrial wall is flexible, and the defect is small, it can be approximated directly to the rim of the atrial wall of the allograft. Otherwise, a patch of autologous pericardium or allograft aorta is fashioned to reconstruct the left atrial defect (Fig. 11.20).
·  The coronary artery buttons are attached in the appropriate position to the aortic allograft with continuous sutures. The allograft is attached to the ascending aorta with continuous sutures, and all suture lines are reinforced with biologic glue.
Ross-Konno Reconstruction
·     Severe hypoplasia of the left ventricular outflow tract in young patients can be successfully managed with combined aortoventriculoplasty and pulmonary autograft replacement of the aortic valve.
·     Bicaval cannulation and cardiopulmonary bypass are initiated, and a transverse aortotomy is performed after cardioplegic arrest. The aortic valve is excised, and the annulus is d├ębrided. The sinus tissue is removed, and the coronary arteries are mobilized on generous buttons of sinus tissue. The pulmonary artery is carefully dissected off the aorta and top of the right ventricle until the ventricular muscle fibers are identified, running in a perpendicular orientation. This portion of the dissection is begun at the commissure between the left and right coronary cusps and carried underneath the pulmonary artery. The pulmonary artery is transected near the bifurcation, and the pulmonary valve is carefully inspected.
·      A small right-angled clamp is passed well below the pulmonary annulus, along the line with the anterior commissure. The clamp is pushed out through the right ventricular free wall, and the right ventricle is divided well below the pulmonary annulus, with direct visualization of the pulmonary valve leaflets. Scissors are used to divide the right ventricular outflow tract anteriorly, leaving a generous portion of the free wall with the autograft. Sharp dissection of the ventricular septum with a knife is used to separate the pulmonary trunk from the right ventricle to protect the first septal branch of the left anterior descending coronary artery.

·    A vertical incision is made through the aortic annulus, near the commissure between the right and left coronary leaflets. The incision is carried into the interventricular septum to enlarge the left ventricular outflow tract (Fig. 11.21). The right ventricular muscle portion of the autograft is inserted deep into the left ventricular outflow tract (Fig. 11.22A), and interrupted sutures are used to attach it to the defect in the interventricular septum (see Fig. 11.22B). The autograft is then attached to the aortic annulus with interrupted sutures. The sutures are secured, and the suture line is reinforced with biologic glue.
·    The coronary arteries are reimplanted onto the autograft in the appropriate position using a continuous suture technique. The autograft is anastomosed to the ascending aorta with a continuous suture technique, and the suture lines are reinforced with biologic glue.
·  The right ventricular outflow tract is measured, and an appropriately sized pulmonary homograft is selected. The distal end of the pulmonary homograft is attached to the bifurcation of the patient’s pulmonary artery with continuous sutures. The proximal portion of the pulmonary homograft is attached to the right ventricular outflow tract using continuous sutures. Part of the suture line may include the pulmonary autograft. If additional enlargement of the right ventricular outflow tract is necessary, a patch of autologous pericardium is used to augment the right ventricular free wall.


Step 4. Other Considerations
1. Two-Directional Enlargement
·  In patients for whom the conventional posterior root enlargement technique is not wide enough to implant a prosthetic valve of desired size, two-directional enlargement involving a combination of both posterior and anterior enlargement techniques could be used9 (Fig. 11.23). For this technique, the posterior enlargement is performed first, and then an additional aortotomy is made anteriorly and extended to the ventricular septum. The aortic annulus could be enlarged by 68% after this two-directional enlargement technique.
· The aortotomy is made obliquely toward the noncoronary sinus. The aortic annulus is measured with dilators after removal of the aortic valve, and posterior enlargement is performed according to the Nicks or Manouguian procedure. An additional anterior enlargement is then made just to the commissure, between the left and the right coronary cusps. Reconstruction of the annulus and repair of the aortotomy are carried out with a bifurcated Dacron patch.
2. Myectomy or Myotomy
·    In patients for whom the preoperative evaluation has also revealed subaortic narrowing or obstruction, a concomitant myotomy or myectomy may be an option, in addition to AVR. Exposure is obtained by either an aortotomy or a complete transection of the ascending aorta. The coronary artery ostia are then identified to avoid any iatrogenic injury. In addition, the valve leaflets, commissures, and area of the presumed conduction system are also well identified and protected during the process of myectomy or myotomy.
·     Optimal visualization of the ventricular septum is facilitated by posterior displacement of the anterior wall of the left ventricle with a sponge or sponge stick. A small suction cannula may also be placed across the aortic annulus to retract the anterior mitral valve leaflet and papillary muscles posteriorly and rightward away from the ventricular septum. The myotomy or myectomy incision is made using a no. 11 blade scalpel, beginning the incision at the midventricular level and extending upward to within 8 to 10 mm of the nadir of the annulus of the right coronary cusp (Fig. 11.24). Any incision made at the base of the ventricular septum that is more rightward than the nadir of the right cusp will injure the membranous septum and conduction tissue, with concerns for resultant complete heart block. A second longitudinal incision parallel to the first incision is made to be carried up to within 8 to 10 mm of the aortic annulus, at the commissure between the right and left coronary cusps. The area to the left of this incision is the left ventricular free wall. These two incisions are joined superiorly, and a hook may be used to allow for better traction of the proposed resected muscle, which can be easily elevated. A deep wedge of septum is then resected, beginning at the base of the septum and working toward the midventricle.
· By carefully understanding preoperative transthoracic echocardiography (TTE) and/or transesophageal echocardiography (TEE) measurements, care can be taken to avoid the iatrogenic creation of a ventricular septal defect.

3. Bentall-Type Aortic Upsizing Procedures
·      In patients with a small aortic annulus that needs aortic root replacement, Bentall-type aortic upsizing procedures can be considered.


Step 5. Postoperative Care
·  Standard postoperative management in the intensive care unit includes ventilator support, continuous cardiac output monitoring with a pulmonary artery catheter, and other routine care measures for a cardiac surgical patient. Right and left atrial pressure lines are useful for direct continuous measurement of atrial pressures.
·  A judicious balance between fluid resuscitation and inotropic support is required. Many of these patients have left ventricular hypertrophy, and administration of relatively small amounts of intravenous fluids will drastically alter filling pressures. In addition, the thick ventricular myocardium is sensitive to inotropes and may be irritable after intraoperative myocardial ischemia. The preoperative status of left ventricular hypertrophy and function, in addition to the appearance of the left ventricle on TEE during completion of the procedure, will allow for a framework to drive decision making.
·  Efforts should be made to avoid hypertension because this will place undue strain on the suture lines of the left ventricular outflow tract reconstruction. Placement of an intraaortic balloon pump is preferable to high doses of inotropes and aggressive fluid resuscitation.
·  A high index of suspicion for coronary insufficiency should be held for every patient, whether a full root replacement or simple AVR was performed. Full root replacement with coronary reimplantation can result in kinking of a coronary artery. Prosthetic valve replacement can result in coronary ostial obstruction by a valve stent or sewing ring.
· The typical presentation of coronary insufficiency is the inability to wean from cardiopulmonary bypass. Intraoperative TEE is essential to demonstrate impaired ventricular function, with or without electrocardiographic evidence of coronary ischemia. If a simple valve replacement was performed, the prosthesis should be removed and reinserted or a different prosthesis selected. If a full root replacement was performed, the safest approach is to perform coronary artery bypass surgery on the affected coronary artery.

Step 6. Pearls and Pitfalls
·    Careful and thoughtful preoperative and intraoperative planning will avoid PPM. A value of less than 0.85 is indicative of PPM and may result in reduced recovery of the left ventricle early and late after operation. Effort should be made to keep the ratio above 1.0 for all patients.
·  Root enlargement and root replacement operations are extensive operations, with multiple suture lines outside the heart exposed to systemic arterial pressure. The application of biologic glue can help control intraoperative bleeding by sealing the needle holes. Biologic glue does not seal gaps in an anastomosis, and this feature allows identification of areas that require additional suture or pledgets to control hemostasis. A thorough survey of all suture lines, especially those located in the difficult to reach and visualized posterior locations and around the coronary buttons, should be completed prior to the administration of protamine and other blood products.
·   The first septal branch of the left anterior descending artery should be meticulously preserved during pulmonary autograft harvest and pulmonary homograft implantation. Injury to the first septal branch can result in significant left ventricular dysfunction, which may not fully recover over time.
·    The incisions described in this chapter for root enlargement are placed in areas of the aortic root that avoid the conduction system. Particular attention should be paid to the area below the commissure, between the right and noncoronary leaflets, extending leftward under the right coronary artery ostium, to avoid injury to the conduction system. In addition, attempts to insert a rigid valve prosthesis tightly into a small aortic annulus can produce excessive pressure on the conduction system, resulting in dysfunction or heart block.
·    Due to the significant challenges of future reoperation on the aortic root following any form of enlargement procedure, great care should be taken to ensure appropriate decision making regarding prosthesis selection. Surgeons should be well versed in the long-term outcomes of the various valve prostheses that may be used in the operation.
·  Surgeons should be prepared to perform extensive reconstruction of the aortic root and ascending aorta, as indicated during surgery. The best long-term outcomes can be expected by addressing all associated pathologic processes at the initial operation, rather than leaving behind conditions that could result in early reoperation.

References
1.     Rahimtoola SH. The problem of valve prosthesis—patient mismatch. Circulation. 1978;58:20–24.
2.     Pibarot P, Dumesnil JG, Lemieux M, et al. Impact of prosthesis-patient mismatch on hemodynamic and symptomatic status, morbidity and mortality after aortic valve replacement with a bioprosthetic heart valve. J Heart Valve Dis. 1998;7:211–218.
3.     Pibarot P, Dumesnil JG. Prosthesis-patient mismatch: definition, clinical impact, and prevention. Heart. 2006;92(8):1022–1029.
4.     Nicks R, Cartmill T, Bernstein L. Hypoplasia of the aortic root: the problem of aortic valve replacement. Thorax. 1970;25:339–346.
5.     Manougian S, Seybold-Epting W. Patch enlargement of the aortic valve ring by extending the aortic incision into the anterior mitral leaflet. J Thorac Cardiovasc Surg. 1979;78:402–412.
6.     Konno S, Imai Y, Lida Y, et al. A new method for prosthetic valve replacement in congenital aortic stenosis associated with hypoplasia of the aortic valve ring. J Thorac Cardiovasc Surg. 1975;70:909–917.
7.     Rastan H, Koncz J. Aortoventriculoplasty: a new technique for the treatment of left ventricular outflow tract obstruction. J Thorac Cardiovasc Surg. 1976;71:920–927.
8.     Reddy VM, Rajasinghe HA, Teitel DF, et al. Aortoventriculoplasty with the pulmonary autograft: the Ross-Konno procedure. J Thorac Cardiovasc Surg. 1996;111:158–167.
9.     Otaki M, Oku H, Nakamoto S, et al. Two-directional aortic annular enlargement for aortic valve replacement in the small aortic annulus. Ann Thorac Surg. 1997;63:261–263.
10. Usui A, Ueda Y. Biological Bentall procedure with a Valsalva graft for a small aortic root. Eur J Cardiothorac Surg. 2008;34:224–225.
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