Volume 13, Issue 4 , Pages 250-259, Winter 2008
Polytetrafluoroethylene Monocusp Valve Reconstruction of the Right Ventricular Outflow Tract
Article Outline
The surgical management of right ventricular outflow tract (RVOT) obstruction in congenital cardiac defects remains controversial. Mild to moderate stenosis and/or insufficiency are reasonably well tolerated. However, the selection of surgical technique can influence both the short-term function and the long-term fate of the right ventricle. Traditional techniques of addressing the RVOT have included either placement of a transannular patch (TAP) or insertion of a valved conduit. Both approaches have their respective short- and long-term disadvantages.1, 2, 3 In patients with continuity between the right ventricle and pulmonary artery, nonvalved, transannular patch repair remains favored by many surgeons. However, this approach results in pulmonary insufficiency with volume-loading of the postischemic right ventricle. Longitudinal data on patients who have undergone placement of a TAP demonstrate that the pressure-loaded, hypertrophied right ventricle undergoes reverse remodeling to a volume-loaded dilated ventricle. There is now a growing trend toward earlier reoperative, pulmonary valve placement in such patients. Residual mechanical pressure-loading due to incomplete relief of pulmonary stenosis (such as with a commissurotomy of a hypoplastic valve and annulus) can also result in the persistence of right ventricular hypertrophy. Both of these resultant effects can contribute to early postoperative right ventricular dysfunction in the postischemic right ventricle.
Limiting early postoperative systolic and diastolic ventricular dysfunction includes frequent dosing of cardioplegia, avoiding injury to large coronary artery branches, limiting the extent of the ventriculotomy, and providing pulmonary valve competence. Both animal and human studies have demonstrated that perioperative pulmonary competence improves right ventricular functional characteristics and positively influences early postrepair morbidity and mortality. Reconstruction of the RVOT with a monocusp patch technique can create a competent and nonstenotic pathway, leading to acute physiologic conditions and right ventricular mechanics that more closely resemble those following of pulmonary valve-sparing techniques. There is additional evidence that this approach may also provide mid-term right ventricular remodeling advantages compared with approaches in which the pulmonary valve is not spared.4 A variety of monocusp materials have been evaluated with variable clinical and functional results.5, 6, 7 In these reports, leaflet construction with 0.1-mm polytetrafluoroethylene (PTFE) pericardial membrane (W. L. Gore & Associates, Inc., Flagstaff, AZ) appeared equal, or superior, to other materials used for construction.7, 8 This approach effectively prevents short-term pulmonary insufficiency and significantly reduces mid-term insufficiency, without evidence of stenosis. Construction of the PTFE valve is an inexpensive and straightforward way to create a competent RVOT in a variety of anomalies. Based on an experience with over 200 implants in humans, this article reviews technical considerations in the construction of the PTFE monocusp.
Operative Technique
Figure 1.
Following a vertical incision in the main pulmonary artery, the pulmonary valve and annulus are inspected. When possible, an aggressive pulmonary valvotomy is performed, and the annulus is then measured with a Hegar dilator. In patients with moderate to severe hypoplasia of the annulus (generally greater than 1 mm smaller than a Z value = −1), or in whom the valve leaflets are significantly dysplastic, the pulmonary artery incision is extended through the annulus. In addition, if the postrepair RVOT gradient measures greater than 25 to 30 mm Hg, a transannular repair is generally performed. The ventriculotomy is oriented to avoid significant right ventricular coronary branches and is carried onto the right ventricle only as far as is necessary to relieve RVOT obstruction and to expose the ventricular septal defect, if present. The pulmonary arteriotomy may also be extended into the right and left branch pulmonary arteries as indicated. Ao = aorta; MPA = main pulmonary artery; RA = right atrium; VSD = ventricular septal defect.
Figure 2.
The length of the ventriculotomy is determined by the extent of the infundibular pathology and by the surgeon's plan to perform either a transatrial or a transventricular repair of the ventricular septal defect. The incision is usually limited to approximately 1 cm but may be carried slightly further in patients with a long, narrow infundibulum. In either case, the ventricular incision does not generally extend beyond the edge of the conal septum. PTFE valve reconstruction can be tailored for any length of ventriculotomy; competence is primarily a function of having adequate conal septum for valve closure surface area. The anterior pulmonary annulus is incised and any functional valve leaflet remnants are left intact. Severely dysplastic leaflet tissue is excised. Horizontal mattress pledgetted stay sutures are placed at the midpoint of the ventriculotomy, and the ventricular septal defect is closed. We generally use a running suture technique. If an interrupted suture technique is utilized, we favor 5-0 Ticron sutures (US Surgical Corp, Norwalk, CT) with thin, soft pledgets, which are low profile and easily endothelialized. Polypropylene stay sutures are then placed at the level of the anticipated hinge point, or cephalad extension of the monocusp valve. This generally corresponds to the sinotubular ridge of the pulmonary valve remnant. Exposure of the “floor” of the RVOT in this manner allows the described technique to maximize the diameter of the outflow tract.
Figure 3.
A bullet-shaped piece of 0.1-mm PTFE is fashioned by placing the material in the ventricular portion of the opening and allowing it to lie flush along the ventricular walls and the majority of conal septum, thereby matching the diameter of the RVOT and maximizing surface area coaptation. This is most easily done with a slightly oversized portion of commercially prepared product (Pericardial Membrane, W. L. Gore & Associates, Inc.). In infants, the monocusp can usually be fashioned within one panel of the tri-fold packaging. The edges of the PTFE are traced with a marking pen according to its points of contact with the epicardial surface. The material is cut to the dimensions outlined by the marks. This complements the contour of the RVOT geometry and helps to ensure the monocusp will lie flush against the conal septum and lateral right ventricular walls. We avoid undersizing the width of the monocusp, as this will result in a reduction of contact surface area with the conal septum in the closed position and lead to early incompetence. After cutting the basic shape, the corners are slightly rounded, placing the hinge point (*) slightly behind the leading edge, and thereby allowing a relatively straight edge at closure.
Figure 4.
The monocusp is sutured with running 6-0 PTFE suture, beginning at the proposed hinge point (*) noted in Fig. 3, and extending onto the epicardial surface of the ventricle with bites including at least one-half the thickness of the myocardium. Care is taken to ensure the superior edge of the monocusp matches any retained posterior leaflet. A proximal stay suture can be placed if desired to maintain orientation of the monocusp.
Figure 5.
The outflow patch, or hood, is constructed using 0.4-mm PTFE cardiovascular patch in an elongated teardrop configuration using continuous running 5-0 or 6-0 PTFE suture. When transitioning onto the monocusp valve, needle bites should not be placed deeper than the existing suture line of the monocusp, so as to avoid reducing the width of the valve with loss of conal septal coaptation.
Figure 6.
Competence of the monocusp valve occurs as a result of its coaptation with the right ventricular outflow septum and any remnants of valve leaflet tissue. The monocusp should reside flush against the outflow patch in the open position (A), leaving little dead space for thrombus formation, and should rest flush against the outflow tract in the closed position (B). The cutaway view in (C) demonstrates the mechanism of competence in RV outflow tracts with and without a remnant posterior pulmonary valve leaflet. LAA = left atrial appendage; LPA = left pulmonary artery; LV = left ventricle; RA = right atrium; RPA = right pulmonary artery; RV = right ventricle; RVOT = right ventricular outflow tract.
Figure 7.
In patients with conduit obstruction and/or insufficiency, a monocusp can be used to provide RVOT competence as an alternative to conduit replacement. Following a standard redo sternotomy and institution of cardiopulmonary bypass with bicaval cannulation, the previous right ventricle—pulmonary artery conduit is opened longitudinally and, when necessary, the incision is extended across the proximal and distal suture lines (A). This is particularly important for degenerative homograft conduits because of the propensity for suture line stenosis in these locations. The redundant edges of the old conduit are trimmed laterally and retracted with stay sutures (B). The monocusp valve is constructed starting in the midportion of the old conduit (C). It is then covered with PTFE (0.4 mm) cardiovascular patch (D). The suture line is started distally and brought proximally as noted in Fig. 5 but shown otherwise here for illustrative purposes. With Dacron conduits, the material can be entirely removed and the remaining posterior fibrous peel becomes the back wall of the RVOT, thus maintaining continuity between the right ventricle and pulmonary artery. The monocusp is sewn to the edges of the outflow tract and, as before, the entire outflow tract is covered with 0.4-mm PTFE cardiovascular patch in a manner similar to that described by Danielson and colleagues for nonvalved conduit replacement.9 Sizing of the monocusp is essentially the same as with other repairs; the material must have adequate length and width to have sufficient surface area contact with the posterior wall. RV = right ventricle.
Figure 8.
Intraoperative transesophageal echocardiography demonstrating PTFE monocusp leaflet (arrow) coaptation with retained posterior pulmonary valve leaflet.
Figure 9.
Echocardiography of PTFE monocusp valve 6 months postoperatively: (A) systolic flow (blue in the online version) demonstrating no flow disturbance or acceleration across the RVOT, indicating no anatomic stenosis or gradient, and (B) diastolic flow-pattern (red in the online version) revealing only trivial pulmonary insufficiency (arrow). (Color version of figure is available online at http://www.optechtcs.com.)
Conclusions
Historically, the literature has been inconclusive regarding the perioperative function and clinical benefit of monocusp RVOT reconstruction. These variable results may reflect the challenges of free-hand construction and certainly are influenced by the material used in valve construction. However, there are now increasing reports of acceptable competence with both monocusp and bicusp procedures, and the trend is away from nonvalved TAP repairs. In our hands, construction of the PTFE monocusp valve has proven to be a simple and reproducible technique demonstrating excellent early postoperative function with minimal pulmonary insufficiency.4 In a nonpublished review of our clinical outcomes with tetrology of Fallot, we found patients with monocusps had a perioperative clinical course similar to those children undergoing pulmonary valve-sparing procedures. There was increased morbidity and use of inotropic support in those with nonvalved TAP repairs. Interestingly, the PTFE monocusp valve has been found to retain a moderate degree of competence at mid-term follow-up. Our recent review of 196 patients demonstrated only mild to moderate insufficiency in 58% of patients at 10 years, and no significant RVOT stenosis.8 Regardless, growth of the RVOT and fibrocollagenous incorporation of the monocusp will result in progressive pulmonary insufficiency and, as such, the PTFE monocusp should not be considered anything but a short- to mid-term functional valve.
We favor the use of the monocusp in a variety of RVOT pathologic conditions. However, it requires certain infundibular anatomic characteristics to be functional. Additionally, it can develop early incompetence in patients with complex lesions characterized by a morphologically distorted RVOT, absence of the conal septum, significant peripheral pulmonary stenosis, or significant pulmonary hypertension. In these patients, as well as those with severe right ventricular dilation and right heart failure, use of a bioprosthetic valve or valved conduit may be preferred over the PTFE valve, due to their more predictable early competence.
References
- Effect of transannular patching on outcome after repair of tetralogy of Fallot. Ann Thorac Surg. 1989;48:783–791
- Surgical significance of acute and chronic pulmonary valvular insufficiency. J Thorac Cardiovasc Surg. 1970;60:549–558
- Morphologic and surgical determinants of outcome events after repair of tetralogy of Fallot and pulmonary stenosis: a two-institution study. J Thorac Cardiovasc Surg. 1992;103:706–723
- PTFE monocusp valve reconstruction of the right ventricular outflow tract. Ann Thorac Surg. 2002;73:871–880
- . Pericardial and synthetic monocusp valves: indication and results. Pediatr Card Surg Ann Semin Thorac Cardiovasc Surg. 1999;2:77–82
- Short-term effect of monocuspid valves on pulmonary insufficiency and clinical outcome after surgical repair of tetralogy of Fallot. J Thorac Cardiovasc Surg. 1996;112:33–37
- Monocusp valve and transannular patch reconstruction of the right ventricular outflow tract: an experimental study. ASAIO J. 1998;44(5):M480–M485
- Right ventricular outflow tract reconstruction with a polytetrafluoroethylene monocusp valve: a twelve-year experience. J Thorac Cardiovasc Surg. 2007;133:1336–1343
- Replacement of obstructed extracardiac conduits with autogenous tissue reconstructions. J Thorac Cardiovasc Surg. 1987;93:555–559
PII: S1522-2942(08)00088-3
doi:10.1053/j.optechstcvs.2008.11.002
© 2008 Elsevier Inc. All rights reserved.
Volume 13, Issue 4 , Pages 250-259, Winter 2008
