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Aortic Valve Repair


Aortic Valve Repair
Keywords: Aortic Valve Repair, Operations for Valvular Heart Disease, aortic valve Repair, aortic valve surgery, cardiac surgery



Abstract
Aortic valve repair has been shown to yield good outcomes for select patients when performed by trained surgeons. In this chapter, we will discuss the surgical anatomy of the aortic valve, the surgical steps to aortic valve repair, as well as the pre-, intra-, and postoperative considerations that need to be addressed for a successful repair.

 
Figure 12.1 (A) Aortic valve anatomy. (B) Ventriculoatrial junction.


Step 1. Introductory Considerations
·    Aortic valve repair (AVr) has been shown to have a lower rate of valve-related complications compared to aortic valve replacement (AVR).1-3
· It is especially beneficial for those in the younger age group due to a higher rate of bioprosthetic degeneration in the case of AVR and the cumulative risk of thromboembolism and bleeding in mechanical aortic valves.3

Step 2. Surgical Anatomy
·    The aortic valve (AV) is comprised of the functional aortic annulus and cusps.
· The functional aortic annulus is comprised of the sinotubular junction (STJ) and ventriculoaortic junction (VAJ4,5; Fig. 12.1).
·    The basal ring is the plane that passes through the nadir of the aortic cusps.
·    At the right noncoronary commissure, the membranous septum is the border of dissection for the VAJ. At the left-right coronary commissure, the ventricular muscle is the border for VAJ dissection. These anatomic borders illustrate why the VAJ does not reach the basal ring.
·  The VAJ level approximates the basal ring level at the noncoronary sinus (NCS), noncoronary left commissure, and left coronary sinus (LCS).
·  The aortic cusp geometric height is the maximum tissue height. The effective height measures from the basal ring plane to the level of the central coaptation of the cusps (Fig. 12.2). The noncoronary cusp (NCC) is higher than the right coronary cusp (RCC) and left coronary cusp (LCC).4,6
·  The AV cusp coaptation normally occurs at the midlevel, between the STJ and VAJ.4,7,8 Effective cusp coaptation length is 2 to 6 mm.4,7
·   Cusp mobility is a function of the free margin length in relation to the length of annular cusp insertion.4 These lengths are adjusted appropriately during a repair to reestablish valve competency while ensuring good mobility.
·  Alteration in one component of the AV leads to alteration in the others. Each component should be seen in relation to the others.
·  A repair-oriented classification of aortic insufficiency (AI) has been developed to guide patient selection and treatment3 (Fig. 12.3).
·  Various forms of cusp division and fusion can occur, resulting in unicuspid, bicuspid, and quadricuspid anomalies, which may be associated with aortopathy and congenital cardiac diseases.

Step 3. Preoperative Considerations
·   The most common cause of AI is dilation of the functional aortic annulus. Thus, a focused history on the presence of hypertension, family aortic and connective tissue disorders, and the acuity of signs and symptoms will help with management. A history of infective endocarditis, or rheumatic heart disease or the presence of myxomatous mitral disease may infrequently be associated.
·    Preoperative echocardiography (echo) is essential for identifying the cause of the AI and will help guide the intraoperative evaluation. It should be able to demonstrate the aortic root and ascending aorta dimensions. The echocardiogram will also be able to show the anatomy of the cusps and the presence of prolapse, fenestrations, bands, calcifications, and vegetations. The quality and direction of the AI jet should also be examined.
 
Figure 12.2 The coaptation height and length and geometric height of the AV leaflets.

Figure 12.3 Functional classification of aortic valve insufficiency.

·    Cusp prolapse occurs when one or more cusps coapt below the normal height of coaptation, at the midheight of the sinus of Valsalva. The presence of an eccentric jet is a sensitive indicator of prolapse. The presence of a fibrous band is a very specific sign of cusp prolapse and identifies the prolapsing cusp8 (Fig. 12.4).
·  In patients in whom the aortic dimensions are borderline, a preoperative chest computed tomography (CT) scan will aid in a more definitive measurement of the dimensions.

Step 4. Operative Steps
1. Surgery
Isolated Aortic Insufficiency8
·     A transverse aortotomy is performed, 1 cm from the STJ, leaving 2 to 3 cm of posterior aorta intact. The distal aorta is retracted cephalad for a better exposure of the AV; 4-0 polypropylene sutures are placed at the level of each commissure (Fig. 12.5).
·    Axial traction (perpendicular to the annular plane) is placed on the commissural retraction sutures to assess the AV. The AV anatomy is thoroughly examined, including the cusp coaptation, amount of excess tissue, leaflet mobility, presence of restrictions and calcifications, and bands. The characteristic of the aortic sinuses are likewise examined for suggestions of aneurysmal degeneration such as wall thinning and coronary ostia displacement (Video 12.1).
·  A prolapsing cusp can be identified by the presence of excess free margin length and, occasionally, a transverse fibrous band.
·     Radial traction (parallel to the annular plane) is then applied to the commissural stitches, and the center of the cusp free margin is pushed gently to the left ventricle. A nonprolapsing cusp will remain at the physiologic level, which is halfway between the cusp base and its maximal height at the commissure. A prolapsing cusp will be able to be pushed lower into the left ventricle due to excessive amounts of tissue.
·    Cusp repair is then performed using free margin plication or resuspension or both. Annular stabilization can be performed with a subcommissural annuloplasty (SCA) or external or internal ring.
 
Figure 12.4 Transeosphageal echocardiographic images. (A) Eccentric aortic insufficiency jet. (B) Cusp prolapse and fibrous band (white arrow). (C) Fibrous band (white arrow). (D) Fibrous band (black arrow).

Figure 12.5 Aortic valve exposure using axial traction.

Cusp Prolapse Repair9-11
·  A 7-0 polypropylene suture is passed through the center of the two nonprolapsing cusps which will serve as reference. Gentle axial traction is applied to the reference cusps, and the prolapsing cusp is pulled parallel to the reference cusp. A 6-0 polypropylene suture is passed through the prolapsing cusp from the aortic to the ventricular side, where it meets the center of the reference cusp. The direction of traction is then reversed, and the same suture is passed from the ventricular to the aortic side at the point where it meets the middle of the reference cusp. This excess free margin is then plicated by tying the suture with the excess tissue on the aortic side. Further plication is done until it is 5 to 10 mm onto the body of the aortic cusp, using interrupted or running locked 6-0 polypropylene sutures. Significant excessive tissue may be resected before the plication (Fig. 12.6; Video 12.2).
·  In the case of two prolapsing cusps, a 6-0 suture is passed through the center of the free margin of the reference nonprolapsing cusp. One prolapsed cusp is then pulled parallel to the reference cusp, and a 6-0 suture is passed through the free margin at the point where it meets the center of the reference cusp. Then the suture is passed back through the cusp at an equivalent distance from that cusp’s center, toward the other side. Plication then proceeds as above and is repeated for the second prolapsing cusp.
·    In the case of all three cusps prolapsing, careful surgical art and judgment are applied, with the goal of plicating the free margins enough so that the cusps coapt at the midpoint level of the aortic sinuses.
Figure 12.6 Cusp repair: central margin plication. (A) A polypropylene 7-0 suture is passed through the center of the two nonprolapsing reference cusps and gental axial traction is applied. The prolapsing cusp is then pulled parallel to the reference cusp and a polypropylene 6-0 suture is passed through the prolapsing cusp, from the aortic to the ventricular side, at the point where it meets the center of the reference cusp. (B) The direction of the traction is reversed, and the same suture is passed from the ventricular to the aortic side of the cups where it meets the middle of the reference cusp. (C) The excess free margin which is now delineated is plicated by tying the suture, leaving the excess tissue on the aortic side. (D) The plication is extended 5-10 mm onto the body of the cusp by additional interrupted or running locked polypropylene 6-0 sutures.

·    Resuspension of the free margin allows symmetric shortening and reinforcement, which is particularly useful if there are cusp stress fenestrations. A 7-0 polytetrafluoroethylene suture is passed through the free margin, 0.5 to 1 mm from the edge. A second suture is passed 1 to 1.5 mm below the first, going beyond the fenestration if there is one.12 When appropriate correction has been reached, the two sutures are tied at the opposite ends (Fig. 12.7).
·    Decalcification is done to optimize leaflet mobility. A no. 11 blade is used to shave off the calcium through a plane in the leaflet, taking care to avoid perforation. Excessive calcification, restriction, and fibrosis do not result in a good valve repair and is an indication to proceed with valve replacement.
·    Type III lesions with limited calcification and fibrosis may be amenable for repair through decalcification, resection, and patching. Cusp perforations may also be repaired with a patch. A pericardial patch is trimmed to resemble the defect in shape, with an additional 2-mm margin around it. This is secured to the aortic surface of the cusp using a continuous Prolene 5-0 or 6-0 suture. As yet, there is no proven benefit for the use of one type of patch material or another. Nontreated autologous pericardium is preferred for simple repair and bovine pericardium for complex repair.13 AV repairs necessitating a patch are at higher risk of failure, possibly due to the progression of the inherent disease of the leaflet, as well as deterioration of the patch material (Fig. 12.8).
 
Figure 12.7 Cusp repair: resuspension of the free margin. (A) A polypropylene 7-0 suture is passed through the center of the two nonprolapsing reference cusps and gentle axial traction is applied. (B) A Gore-Tex 7-0 suture is passed twice on the top of the commissures of the prolapsing cusp. (C) One arm of each of the sutures are then passed using a running technique over and through the length of the free margin. (D) Using gentle traction on the sutures and an opposite traction on the middle of the free margin, the first half of the free margin is shortened by wrinkling the tissue until it reaches the same length as the adjacent reference cusp. (E) Wrinkling is then done on the second half using the same technique, allowing symmetric shortening. (F) The suture ends are passed through the aortic wall and tied.
Figure 12.8 Pericardial patching using autologous or bovine pericardial patch.
Annular Stabilization8,14
·   Annular stabilization improves the durability of AV repair by stabilizing and reducing the diameter of the VAJ and STJ, thereby increasing cusp coaptation. The most durable is the prosthesis-based annuloplasty that is part of a valve-sparing root replacement (see the following).
·    SCA is simple and reproducible. It is done using pledgeted braided sutures, with the first arm passed from the aortic to the ventricular side, into the interleaflet triangle, and coming out on the other side of the commissure on the same level as the entry point. The second arm of the suture is passed in a similar fashion, just below the first. The opposite pledget is placed, and the suture is tied. This is done for all the interleaflet triangles. The annuloplasty effect is greater if the SCA sutures are placed closer to the VAJ. Typically, SCA sutures are placed between the upper and middle thirds of the height of the interleaflet triangle (Fig. 12.9; Video 12.3).
·  The use of basal rings, both external and internal, is still under study. External rings are flexible circumferential bands implanted around the lowest outer portion of the aortic root, with the interrupted sutures passed from inside the root, 1 to 2 mm below the cusp. Internal rings are implanted 1 to 2 mm below the cusps, with the sutures tied externally at the base of the aortic root.
·    Although annular stabilization provides durability to the AV repair, care should be taken to avoid overreduction, which could lead to aortic stenosis but may also cause cusp prolapse and AI. Internal rings also have a theoretical increased risk for thromboembolic events.
 
Figure 12.9 Subcommisural annuloplasty. (A) Passing the sutures from one sinus to the other. (B) Illustration of the placement of the pledgeted sutures in relation to the interleaflet triangle.
Aortic Insufficiency Associated With Aortic Root Aneurysm
·    The aorta is transected 1 cm from the STJ. An initial assessment of the aortic root and valve cusps are done (as described previously) to assess for the viability of repairing the valve and of preserving or replacing the root. In the case of borderline clinical indications for aortic root aneurysm, the presence of thinned-out aortic sinuses and displacement of one or both coronary ostium guides us to performing a root replacement. If the AV is deemed reparable, the aortic root replacement is first performed through a reimplantation or remodeling technique.
·   Graft sizing is critical to achieve correct alignment of the AV structures. One method is to apply adequate radial and axial traction on the commissural sutures to re-create the most competent valve configuration and then measuring the STJ in this position using a Hegar dilator or Freestyle valve sizer (Medtronic, Minneapolis; Fig. 12.10). Another simple but effective method is by measuring the height of the interleaflet triangle at the NCC-LCC commissure. This height would approximate the VAJ diameter, STJ diameter, and graft size of a Valsalva graft (Vascutek Ltd, Renfrewshire, Scotland, UK). In case of noncorrespondence of graft size, one size above is chosen15 (Fig. 12.11A–D). The Valsalva graft is then patterned according to the height of the two other commissures (see Fig. 12.11E).
Figure 12.10 Graft sizing using a Freestyle valve sizer.

· After the proximal aortic root anastomosis and implantation of the coronary buttons, cardioplegia is applied through the graft for myocardial protection as well as to check for hemostasis. During this time, a limited transesophageal echocardiography (TEE) may be performed to check the AV function after the root replacement. The cardioplegia fluid is then carefully suctioned, taking care not to disturb the cusp positions. This postcardioplegia position is the most physiologic evaluation available for the AV on an arrested heart. The cusps are then examined for symmetry and coaptation, and repair is done as described previously.
·    A notable percentage of cusp prolapses are not obvious preoperatively but become evident after aortic root repair and thus always merit reevaluation.
·    Root replacement using the remodeling technique often necessitates an annular stabilization technique.
· The distal graft anastomosis is then performed, taking care to avoid distortion of the commissures.

2. Postrepair Evaluation
·    The target effective height is 9 mm, which can be measured with a ruler while the aorta is still open.16
·   TEE is critical for intraoperative postrepair evaluation. This is done during the weaning off of cardiopulmonary bypass and confirmed once off-pump on full heart ejection. Factors that necessitate re-repair are the presence of more than grade I AI, any eccentric AI jet, coaptation length less than 5 mm, and coaptation level below the aortic annulus.3 Three-dimensional TEE may aid in the assessment of coaptation surface area, which is a better surrogate for coaptation reserve.
·   An algorithm proposed by le Polain de Waroux et al.17 may be followed. Re-repair is warranted if the coaptation tips are below the annulus. Any residual AI with a leaflet coaptation length of less than 4 mm also warrants re-repair.
·   Other notable factors are the AV gradients for induced aortic stenosis and wall motion abnormalities in cases in which coronary buttons were involved.
 
Figure 12.11 Graft sizing using the NCC-LCC commissure height as reference. (A) Meauring the NCC-LCC commissure height. (B) This height corresponds to the height of the sinus portion of the Valsalva graft. (C) This also corresponds to the graft diameter. (D) The implanted graft, showing the lie of the NCC-LCC commissure. (E) The graft is patterned according to the height of the LCC-RCC and NCC-RCC commissures for subsequent implantation.
Bicuspid Aortic Valve
·    Repair of bicuspid aortic valve (BAV) AI has been gaining acceptance during the last decade, showing a high rate of reparability and a comparable rate of survival of patients to age-and gender-matched groups.18
· BAV is often associated with aortopathy and is thus commonly managed with a root replacement procedure, especially in younger individuals.19
·    Type 0 BAVs have two symmetric cusps and two commissures. The mechanism of AI is cusp prolapse due to excess tissue. The degree of prolapse is assessed based on the nonprolapsed reference cusp. In case both cusps are prolapsed, the goal is to restore the coaptation level to the midpoint of the sinuses of Valsalva. Shaving and decalcification can be done as needed20 (Fig. 12.12A).
·    A type 1 BAV is comprised of one large nonconjoint cusp and two smaller fused cusps, with a median raphe or pseudocommissure (see Fig. 12.12B and C). The conjoint cusp has a large base of leaflet implantation. The mechanism of AI may be from a restrictive raphe or prolapse of the conjoint cusp. If the raphe is only mildly fibrosed, it is shaved off to improve the mobility of the cusp (Fig. 12.13). If the raphe is restrictive, a conservative resection is done. If there is an adequate amount of cusp tissue preserved, this may be closed primarily using locked or interrupted 6-0 polypropylene sutures (Fig. 12.14). If there is no adequate tissue, pericardial patching is performed as described previously. Refinement of the repair may be done using plication or resuspension20 (see Fig. 12.8).
·   In case of an associated root replacement, the leaflet base implantation of the two cusps is maintained in a symmetric fashion—that is, adjusted to an equal distribution, as in the case of a type 1 BAV. The pseudocommissure is reimplanted in the graft at its natural height.
 
Figure 12.12 Biscupid aortic valve. (A) Type O valve. (B) Type 1 valve with prolapsing conjoint cusp. (C) Type 1 valve with restrictive raphe.
Figure 12.13 Type 1 bicuspid aortic valve with noncalcified median raphe. (A) Mildly thickened and fibrosed raphe. (B) Shaving of the raphe with intent of preservation.
Unicuspid Aortic Valve21
·     A unicuspid aortic valve (UAV) frequently presents as aortic stenosis, but may also present as AI. It may also be associated with aortopathy, and those patients present even younger than BAV patients.
·    The aortic pathology is first addressed. The posterior commissure is usually normal and is preserved. A tongue of aortic root on the opposing side is also preserved; this will be part of the neocommissure for a bicuspidization technique. The dysplastic cusp (usually the RCC) and adjacent raphe are resected. Two patches are tailored to reconstruct the rest of the remaining two cusps and are joined to form the neocommissure. Plication sutures are placed with the aim of achieving a target height of 10 mm (Fig. 12.15).
Quadricuspid Aortic Valve22
·      Most cases of a quadricuspid aortic valve (QAV) are incidentally diagnosed, suggesting that is it very much compatible with life. It may present as aortic stenosis, AI, or a mix of both. It may also be associated with aortopathy.
·  If the cusps are well-preserved and judged reparable, the procedure may be done with resection, reconstruction, and tricuspidization or bicuspidization. Annular stabilization is warranted if the root is preserved.
·      Other congenital defects should be sought, such as an anomalous origin of the coronaries.
·      Most QAVs are not reparable and are treated with an AVR.
 
Figure 12.14 Type 1 bicuspid aortic valve repair with calcified median raphe. (A) Resection of restrictive raphe. (B) Assessment of adequacy of remaining tissue by placing two arms of a polypropylene suture on the margin of the conjoint cusps on either sides of the resected raphe. (C) If adequate tissue is available, primary reapproximation is done using interrupted or running locked polypropylene 6-0 sutures.
Figure 12.15 Unicuspid aortic valve repair. (A) Dissection of the aortic root, preserving a tongue of aortic tissue opposite that of the commissure. (B) Using pericardial patches, the cusps are reconstructed to function like a symmetric bicuspid valve.
Step 5. Postoperative Considerations
1. Medical Management
· Aspirin is administered routinely. Blood pressure control is ensured to reduce the hemodynamic stress, help arrest the disease process of aortic dilation, and reduce stress on repaired cusps.
·    Close follow-up is necessary to optimize the monitoring of the durability of the AV repair. This is essential, especially for those patients whose aortic roots were preserved and are expected to dilate potentially over time. We recommend follow-up with postrepair echocardiography at 3, 6, and 12 months and annually thereafter.
2. Outcomes
·     Early mortality rate is low at 0% to 2.0%.1-3,10,11,13,16 Overall survival is 80% to 87% at 9 to 10 years, which is comparable to patients who underwent AVR. Rates of major adverse cardiac and cerebrovascular events and valve-related complications such as thromboembolic events, bleeding, and endocarditis are low.1,3,4,8,11,13
·     Freedom from AV reintervention is 89% to 92% at 10 years.1,2,16 The most common cause of AV reintervention is recurrent AI. Risk factors for this include the presence of residual AI postoperatively, short coaptation length, low level of coaptation, and large aortic annulus.16,17
·     The outcomes for AVr for isolated AI is similar to that of AI associated with aortic dilation, independent of the surgical technique used.3,8 There is a higher rate of AI recurrence for AVr performed on type III (restrictive) leaflets, especially if rheumatic.3,17
·      Re-repair is still a good option in case of initial failure, and freedom from AVR is 92% at 10 years.2
·      Results are comparable for AVr in BAV and tricuspid aortic valve (TAV).2,13,18 Quantitative outcomes results for UAV and QAV are still being developed, but recent reports have shown that AVr in these valves may be considered as a feasible alternative to outright replacement.21,22
Step 6. Pearls
·     The most commonly involved cusp in a prolapse is the RCC. However, the TEE is not able to evaluate the NCC and LCC fully. The presence of an eccentric jet and/or a fibrous band is highly suspicious for prolapse.
·     There are excellent outcomes for AVr in types I and II AI, especially for patients who have not yet manifested with heart failure. This could promote consideration for an earlier surgical intervention.
·     Type III AI (restrictive) has a less durable result for AVr and should have a lower threshold for AVR.
·    AVr should be treated as a specialized field of cardiac surgery, and triage to particular centers and surgeons is advised.

References
1.      De Meester C, Pasquet A, Gerber B, et al. Valve repair improves the outcome of surgery for chronic severe aortic regurgitation: a propensity score analysis. J Thorac Cardiovasc Surg. 2014;148:1913–1920.
2.      Aicher D, Fries R, Rodionycheva S, et al. Aortic valve repair leads to a low incidence of valve-related complications. Eur J Cardiothorac Surg. 2010;37:127–132.
3.      Boodhwani M, de Kerchove L, Glineur D, et al. Repair-oriented classification of aortic insufficiency: impact on surgical techniques and clinical outcomes. J Thorac Cardiovasc Surg. 2009;137:286–294.
4.      El Khoury G, De Kerchove L. Principles of aortic valve repair. J Thorac Cardiovasc Surg. 2013;145:S26–S29.
5.      De Kerchove L, Jashari R, Boodhwani M, et al. Surgical anatomy of the aortic root: implication for valve-sparing reimplantation and aortic valve annuloplasty. J Thorac Cardiovasc Surg. 2015;149:425–433.
6.      Schafers HJ, Schmied W, Psych D, et al. Cusp height in aortic valves. J Thorac Cardiovasc Surg. 2013;146:269–274.
7.      Venoverschelde JL, Van Dyck M, Gerber B, et al. The role of echocardiography in aortic valve repair. Ann Cardiothorac Surg. 2013;2:65–72.
8.      Boodhwani M, De Kerchove L, Watremez C, et al. Assessment and repair of aortic valve cusp prolapse: implications for valve-sparing procedures. J Thorac Cardiovasc Surg. 2011;141:917–925.
9.      Boodhwani M, De Kerchove L, Glineur D, El Khoury G. A simple method for the quantification and correction of aortic cusp prolapse by means of free margin plication. J Thorac Cardiovasc Surg. 2010;139:1075–1077.
10.    De Kerchove L, Glineur D, Poncelet A, et al. Repair of aortic leaflet prolapse: a ten-year experience. Eur J Cardiothorac Surg. 2008;34:785–791.
11.    De Kerchove L, Boodhwani M, Glineur D, et al. Cusp prolapse repair in trileaflet aortic valves: free margin plication and free margin resuspension techniques. Ann Thorac Surg. 2009;88:455–461.
12.    David T, Armstrong S. Aortic cusp repair with Gore-Tex sutures during aortic valve-sparing operations. J Thorac Cardiovasc Surg. 2010;139:140–142.
13.    Nezhad ZM, De Kerchove L, Hechadi J, et al. Aortic valve repair with patch in non-rheumatic disease: indication, techniques and durability. Eur J Cardiothorac Surg. 2014;46:997–1005.
14.    De Kerchove L, Vismarra R, Mangini A, et al. In vitro comparison of three techniques for ventriculo-aortic junction annuloplasty. Eur J Cardiothorac Surg. 2012;41:1117–1124.
15.    Boodhwani M, El Khoury G, De Kerchove L. Graft sizing for aortic valve sparing surgery. Ann Cardiothorac Surg. 2013;2:140–143.
16.    Kunihara T, Aicher D, Rodionycheva S, et al. Preoperative aortic root geometry and postoperative cusp configuration primarily determine long-term outcome after valve-preserving aortic root repair. J Thorac Cardiovasc Surg. 2012;143:1389–1395.
17.    Le Polain de Waroux JB, Pouleur AC, Robert A, et al. Mechanisms of recurrent aortic regurgitation after aortic valve repair. JACC Cardiovasc Imaging. 2009;2:931–939.
18.    Svensson L, Al Kindi A, Vivacqua A, et al. Long-term durability of bicuspid aortic valve repair. Ann Thorac Surg. 2014;97:1539–1548.
19.    Navarra E, El Khoury G, Glineur D, et al. Effect of annulus dimension and annuloplasty on bicuspid aortic valve repair. Eur J Cardiothorac Surg. 2013;44:316–323.
20.    Boodhwani M, De Kerchove L, Glineur D, et al. Repair of regurgitant bicuspid aortic valves: a systematic approach. J Thorac Cardiovasc Surg. 2010;140:276–284.
21.    Franciulli M, Aicher D, Radle-Hurst T, et al. Root remodeling and aortic valve repair for unicuspid aortic valve. Ann Thorac Surg. 2014;98:823–829.
22.    Idrees JJ, Roselli E, Arafat A, et al. Outcomes after repair or replacement of dysfunctional quadricuspid aortic valve. J Thorac Cardiovasc Surg. 2015;150:79–82.