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J Thorac Cardiovasc Surg 2007;133:1336-1343
© 2007 The American Association for Thoracic Surgery
Surgery for Congenital Heart Disease |
Section of Cardiothoracic Surgery, James Whitcomb Riley Hospital for Children and Indiana University School of Medicine, Indianapolis, Ind.
Read at the Thirty-second Annual Meeting of the Western Thoracic Surgical Association, Sun Valley, Idaho, June 21-24, 2006.
Received for publication July 7, 2006; revisions received December 15, 2006; accepted for publication December 18, 2006. * Address for reprints: John W. Brown, MD, Section of Cardiothoracic Surgery, Indiana University School of Medicine, 545 Barnhill Dr., EH 215, Indianapolis, IN, 46202-5123. (Email: jobrown{at}iupui.edu).
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Abstract |
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Methods: From 1994 through 2006, 192 patients (mean age, 3.3 ± 5.0 years) underwent right ventricular outflow tract reconstruction with a polytetrafluoroethylene monocusp valve (192 patients; 202 implants). Intraoperative, early postoperative, and late follow-up echocardiographic data (mean interval, 4.9 ± 3.1 years; range, 6 months to 12 years) were retrospectively obtained to compare clinical outcomes among three preoperative diagnostic groups: patients undergoing initial repair of tetralogy of Fallot or pulmonary atresia/ventricular septal defect (group I), patients undergoing redo right ventricular outflow tract procedures (group II), and patients undergoing complex initial repairs (group III).
Results: There were 4 early and 5 late deaths (9/192; 5%). The difference between the preoperative and postoperative peak right ventricular outflow tract gradients was significant (71.2 vs 23.1; P < .0001). Twenty-five (14%) patients had mild-to-moderate right ventricular outflow tract stenosis at one or more locations proximal and/or distal to the monocusp patch (mean gradient, 44.7 ± 20.3 mm Hg). Freedom from increased pulmonary insufficiency greater than moderate was 86% at 1 year, 68% at 5 years, and 48% at 10 years. Twenty-five patients have undergone 35 reoperations 4.2 ± 3.1 years (range, 3 months to 10 years after initial repair). Kaplan–Meier freedom from reoperation was 96%, 89%, and 82% at 1, 5, and 10 years. Freedom from reoperation in group II (69%) was significantly different from group I (88%; P = .01) and from group III (90%; P = .02), but there was no difference between groups I and III.
Conclusions: Use of a polytetrafluoroethylene monocusp valve prevents early and significantly reduces midterm pulmonary insufficiency. It is relatively inexpensive, easy to construct, and remains free from significant stenosis in the majority of patients. We have not witnessed significant calcification or pulmonary embolization, and the only antithrombic agent used has been low-dose aspirin.
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Introduction |
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The advantage of the valved conduit option is that it yields initially a nearly competent pulmonary valve. Conduit insertion is particularly useful in patients who have peripheral unrepaired pulmonary stenosis or elevated pulmonary vascular resistance. The obvious disadvantages of currently available valved conduits are their lack of durability owing to shrinkage, lack of growth, and/or early valvular dysfunction. These unsolved problems are manifested by the allograft conduit that became popular in the United States during the mid-1980s. Pulmonary homografts have remained popular to the present despite freedom from reoperation of only 50% at 5 years in patients undergoing a non-Ross RVOT conduit repair.2,3
An attractive alternative strategy for many years has been the creation of a monocusp RVOT patch, which has the potential advantages and lacks the disadvantages of both a transannular patch and a homograft valve conduit in certain patient populations. The monocusp RVOT patch can be created with autologous or bovine pericardium,4,5 allograft pulmonary valve cusp,6 or the (off label) use of a polytetrafluoroethylene (PTFE) membrane (0.1-mm PTFE patch; W. L. Gore & Associates, Inc, Flagstaff, Ariz) traditionally used for pericardial closure.7-9 All types of monocusps have shown, particularly in the immediate postoperative period, to significantly reduce or prevent pulmonary insufficiency (PI).10
The elimination of PI is associated with faster recovery of RV function, a lower central venous pressure, and less postoperative chest tube drainage.10 Construction of a pericardial or PTFE monocusp is simple, relatively inexpensive, and reproducible. Allograft pulmonary valve cusps are usually more expensive and more difficult to custom fit into the RVOT. The potential disadvantage of a monocusp patch in comparison with insertion of a pulmonary valve or valved conduit is that, at least in some patients, PI recurs more quickly and completely if the monocusp sticks in the open position, as has been reported with biologic monocusps.6 Recurrent stenosis at the level of the monocusp is rarely seen with any monocusp RVOT patch.6,9
The goal of this retrospective review is to update our previous experience with the PTFE monocusp patch9 and to determine its effects in relieving and preventing RVOT stenosis and regurgitation in three groups of patients: patients undergoing initial repair of TOF or pulmonary atresia/ventricular septal defect (VSD) (group I), patients undergoing redo-RVOT procedures (group II), and patients with complex initial RVOT reconstructions (group III).
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Patients and Methods |
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The initial preoperative diagnoses and diagnostic groups they were assigned are shown in Table 1. Forty-six (24%) patients had had prior cardiac operations, which included repair of the RVOT. Twenty-nine of these 46 patients had had RV-PA conduits before implantation of a PTFE monocusp valve, and they included pulmonary homografts (n = 15), aortic homografts (n = 11), nonvalved Dacron tube graft (n = 2), and Dacron graft with a porcine valve (n = 1). Six patients underwent initial transannular patching without monocusp insertion.
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All PTFE RVOT repairs were performed with a standard PTFE monocusp valve construction technique as previously described.9,11 The monocusp valve is tailored and inserted first to get appropriate width and length. The outflow tract patch is then inserted with a second suture line. Assignment of patients to a particular surgeon was random and without preference. Patients with defects that included an intact pulmonary annulus were evaluated in the operating room. When possible, an aggressive pulmonary valvotomy was performed, the annulus was measured with a Hegar dilator, and the pulmonary valve was spared. In patients with moderate-to-severe hypoplasia of the annulus (generally less than a –2 Z-value), a postrepair RVOT gradient measuring greater than 30 mm Hg, or a postrepair RV pressure greater than 80% of systemic pressure, a transannular repair was performed.5
After obtaining approval from our institutional review board, we performed a retrospective review of medical records with regard to initial cardiac diagnosis, pathophysiologic findings, surgical treatment, and hospital mortality. Data from outpatient visits and from patients who died after hospital discharge were obtained from physicians, hospital records, or death certificates. Medical records and clinical charts were reviewed for all PTFE monocusp valve recipients including operative records as well as preoperative and postoperative catheterization and echocardiography data. Data collected from the operative admission included diagnosis, previous operative procedures, age, sex, and weight at operation. Patient follow-up data were obtained from hospital and clinic visit records. Follow-up information was available within 2 calendar years for 96% of surviving patients. Echocardiography data, derived by continuous-wave Doppler echocardiography, were recorded from serial studies and used to quantitate postoperative PI. Evaluation of the PTFE monocusp valve’s competency and relief of pulmonary outflow tract obstruction included RV systolic pressure, RV-PA gradient, tricuspid regurgitation, and degree of PI. An end-diastolic dimension of the right and the left ventricles (RV and LV) by cardiac magnetic resonance imaging has only recently become available at our institution and was performed on selected patients. Echocardiographic assessment of the PTFE monocusp valve was reported only for patients beyond 6 months after implant, and PI was divided into three grades: trace-to-mild (trace, trace-to-mild, mild), mild-to-moderate (regurgitation flow image confined within the conduit), and moderate-to-severe (moderate, moderate-to-severe, severe; regurgitation flow image extending into the sinus portions of the RV). In the same patient subset, Doppler interrogation was applied to detect the maximal flow velocity across the RVOT reconstruction. The pressure gradient was estimated by the maximal flow velocity according to the Bernoulli equation.
Statistical Analysis
Variables including demographics, diagnosis, previous palliative procedures, types of previous RVOT reconstruction, conduit type and size, type of RVOT disease, need for postoperative extracorporeal membrane oxygenation, ratio between the end-diastolic dimensions of the RV and LV for selected patients, tricuspid insufficiency, RV pressure, and operative procedure-related variables were assessed by univariate analysis with the 
2 test and multivariate logistic regression analysis. In the analysis of risk factors for early death, variables with significant levels of 0.1 in univariate analysis were submitted to a multivariate logistic regression model. Kaplan–Meier analysis was used for the actuarial survival and freedom from reoperation rate. Differences in survival curves were assessed by log–rank test. All analyses were performed with SPSS statistical software (SPSS, Inc, Chicago, Ill). Early mortality was defined as death during initial hospitalization or within 30 days of operation. Any deaths later than that were defined as late mortality. In this series, all early deaths occurred during the initial hospitalization and all late deaths occurred after discharge from the initial hospitalization.
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Results |
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Reoperations
Thirty-five reinterventions were required after PTFE monocusp RVOT reconstruction in 25 of 188 (13%) early survivors. The monocusp was replaced with an RV-PA conduit (n = 13), redo PTFE monocusp valve replacement (n = 10), surgical angioplasty of branch pulmonary stenosis (left or right) (n = 6), stent placement (n = 2), delayed VSD closure (n = 3), and RVOT patch augmentation below an anomalous left anterior descending coronary artery (n = 1). Sixteen, 8, and 1 patient have had 1, 2, or 3 reinterventions, respectively. The average time to reintervention after PTFE monocusp placement was 4.2 ± 3.1 years (range, 3 months to 10 years). Mean age at reintervention was 8.0 ± 6.5 years (range, 18 months to 28 years).
At reoperation, all patients had some degree of PTFE monocusp regurgitation. It was graded as trace-to-mild in 10, mild-to-moderate in 9, and moderate-to-severe in 6 patients. Seventeen of the 25 patients reoperated on after PTFE monocusp insertion had a combination of residual RVOT obstruction and monocusp insufficiency. Residual RVOT stenosis was usually multilevel and was rarely at the level of the monocusp. It usually occurred in younger, smaller infants with a significant degree of RVOT hypoplasia at the time of initial repair. Eight patients had branch PA stenosis and most had some degree of infundibular obstruction. The peak systolic gradient across the RVOT before reintervention in the 25 patients undergoing reinterventions of the PTFE monocusp was 44.7 ± 20.3 mm Hg (range, 10-85 mm Hg), as measured by preoperative echocardiography. At reoperation, 13 patients had their monocusp converted to a biologic valved conduit and 10 had a larger PTFE monocusp outflow patch inserted. Replacement conduit types were as follows: bovine jugular vein conduit (Contegra; Medtronic, Inc, Minneapolis, Minn; n = 8), pulmonary homograft (CryoLife, Inc, Kennesaw, Ga; n = 3), and a stentless porcine aortic root (Medtronic Freestyle; Medtronic, Inc; n = 2). Eight patients underwent surgical angioplasty of the right and/or left PAs with PTFE patches (n = 6) or stent placement (n = 2) owing to branch PA stenosis.
Eight of 26 patients had had a previous RVOT reconstruction (before PTFE monocusp) (18%, 8/44 survivors) and 17 procedures were in patients without any operation before PTFE monocusp insertion (12%, 17/144 survivors; P = .08). Univariate and multivariate analysis showed the diagnosis of TOF plus absent pulmonary valve (P = .005) and higher initial postoperative RV systolic pressure (P = .05) as the strongest predictors for reoperation. Kaplan–Meier freedom from reoperation after PTFE monocusp construction was 96% at 1 year, 89% at 5 years, and 82% at 10 years (Figure 2). Freedom from reoperation in groups I, II, and III at 10 years was 88%, 69%, and 90%, respectively. Freedom from reoperation in group II was significantly higher than in group I (P = .01) and group III (P = .02) but was not different between groups I and III.
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Ventricular dimensions were evaluated in the short axis in 158 patients: the mean ratio between the end-diastolic dimensions of the LV and RV was 0.63 ± 0.18. In patients with mild PI, this ratio was smaller than in those with greater than moderate PI (0.60 ± 0.14 vs 0.66 ± 0.21; P = .07) but was not significant. Patients who underwent PTFE monocusp reoperation had a larger ratio than the ones who did not require reoperation (0.60 ± 0.12 vs 0.76 ± 0.29; P < .001). Excluding the patients who required reoperation, there was no difference (65.3 ± 8.7 vs 63.7 ± 8.6) between patients with trace-to-mild and greater than moderate PI at last follow-up.
The mean RV systolic pressure in all patients was 47.5 ± 16.9 mm Hg. There was no difference between patients with trace-to-mild and greater than moderate PI at last follow-up (47.3 ± 17.0 and 47.7 ± 17.0), but there was a significant difference between patients who underwent redo surgery and all other patients without reoperation (71.3 ± 18.5 vs 42.1 ± 10.9; P < .0001).
The severity of PI was assessed by color Doppler in 180 patients at last follow-up. These results are illustrated in Figure 3. Ninety-four (52%) had trace-to-mild PI, 73 (41%) had mild-to-moderate PI, and 13 (7%) had moderate-to-severe PI. On data obtained 1 year after PTFE monocusp valve insertion, the trace-to-mild degree of PI was detected in 60% of all patients, with moderate-to severe PI in only in 13%. However, progression of PI was observed at 4 to 5 years with mild-to-moderate PI in 46% of all cases, which decreased to 35% at 7 years. The progression of PI to moderate-to-severe PI increased from 15% to 37% at 7 years’ follow-up. Significant tricuspid regurgitation developed in 6 (3%) patients. The echocardiographic analysis at last follow-up showed that freedom from increased PI greater than moderate was 86% at 1 year, 68% at 5 years, and 48% at 10 years. Freedom from increased PI greater than moderate was 53%, 41%, and 49% at 10 years, respectively. There are no differences between all groups I, II, and III.
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Discussion |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionReferences |
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PI, when severe and chronic or associated with distal residual obstruction or elevated pulmonary vascular resistance, results in RV failure. Symptomatic RV failure may be delayed for several years and contribute to deterioration in functional status at late follow-up.14,15
Conventional techniques to reduce PI at the time of initial repair include bioprosthetic valve insertion, valved conduit insertion, or the creation of a monocusp valve. Allograft conduits were the initial valved conduits used for reconstruction of the RVOT by European surgeons; however, early preservation techniques with antibiotics or irradiation sterilization were associated with early allograft conduit valve failure.16 Porcine heterografts mounted in Dacron conduits became available in 1970 in a variety of sizes and were widely used for complex reconstructions in the United States17 before cryopreserved allograft conduits became available in the United States during the mid-1980s. Porcine valved Dacron conduits became obstructed with a thick neointimal peel and the valves calcified within 3 to 5 years, and most of the small-diameter conduits became obstructed. Homann and associates18 reported that after a period of 10 years, 30% of children initially receiving allografts and 70% of patients receiving xenograft conduits had undergone replacement of their initial RV-PA conduits.
The search continues for an ideal RVOT extracardiac conduit. Several centers have advocated using a stented14,17,19,20 or nonstented porcine aortic or xenograft pericardial valve mounted inside a pericardial or PTFE tube for patients older than 10 years. We have used both techniques and have found them satisfactory in teenagers and adults. However, the size and rigidity of the valve ring and frame with the stented porcine or pericardial valve reduces the valve orifice area and increases the risk of transmitting sternal compression through the valved conduit to the left main and or left anterior descending coronary artery. The stentless porcine valve as advocated by Kanter and colleagues20 has a stiff aortic wall support and eliminates the prosthetic frame and the concern of sternal compression. Absence of a stent allows placement of a valve with a significantly larger valve orifice area. We have recently used several stentless porcine roots (Freestyle; Medtronic, Inc) as an RV-PA conduit, and they have worked well in older children and adults. The stentless aortic root in our opinion is too stiff and noncompliant for infants and younger children and the Freestyle frequently requires addition of a proximal hood to complete the RV connection.
In 1993, Yamagishi and Kurosawa7 and Oku and colleagues8 independently introduced 0.1-mm PTFE pericardial membrane as a readily available material with good characteristics for monocusp valve construction and compared it with other monocusp leaflet materials. Our animal studies suggested that 0.1-mm PTFE functioned as well as, or better than, fresh or glutaraldehyde-treated pericardium.21 Initial clinical application of this technique in patients with TOF resulted in improvement of perioperative RV function, and the technique rapidly gained favor.9 It has subsequently been used in more than 200 patients with a wide range of RVOT obstructive and regurgitation defects but is especially valuable in the small infant undergoing primary repair.
The PTFE monocusp with separate RVOT patch has been very useful for our patients with TOF and its variants like VSD with pulmonary atresia who require a transannular patch and in patients requiring a second RVOT procedure after a failed conduit reconstruction (29 patients in this report). The monocusp valve has functioned very well in most patients for the first 2 to 3 years and up to 10 years in some patients, and the monocusp has not produced recurrent RVOT obstruction. Function of the monocusp persists out to 12 years, but some regurgitation develops as the RVOT grows.5,9 We believe that the PTFE monocusp reconstruction of a failed allograft conduit is preferable to using a second allograft conduit which, in several series, failed faster that the first allograft.2,22 Although the monocusp develops some regurgitation over time, it is better than no valve or a valve that will likely become obstructed, as is seen with allograft and xenograft valves in Dacron RV-PA conduits.
Previous reports in the literature suggesting inconclusive perioperative function and clinical benefit of a PTFE monocusp valve may reflect the challenges of freehand construction or the material chosen for monocusp valve construction. In our series, reconstruction of the RVOT with a PTFE monocusp valve has proven to be a simple and reproducible technique demonstrating excellent early postoperative function with minimal PI. In addition, our results suggest a degree of early clinical benefit in patients in whom a PTFE monocusp valve was used when compared with historic transannular repairs without pulmonary valve reconstruction,9 particularly in those with TOF or VSD with pulmonary atresia. The PTFE monocusp valve has also been found to retain a significant degree of competency at midterm follow-up in the TOF group, as well as the group undergoing replacement of the previous RV-PA conduit. As a result, we have favored the PTFE monocusp in both these patient groups. Growth of the RVOT or eventual fibrocollagenous incorporation of the PTFE leaflet may limit long-term function of the monocusp in some patients. The PTFE monocusp valve can be expected to retain adequate function in the early-to-mid postoperative period with the only anticoagulant being low-dose aspirin (80 mg per day).
The decision to insert a biologic valved conduit or upsize the PTFE monocusp patch was left up to the individual surgeon and depended on the availability of a suitable conduit. When a pulmonary homograft conduit was the only conduit available, we were more likely to up-size the RVOT with a second PTFE monocusp patch because we thought it would be more durable than the other available conduits at that time. With the introduction of the bovine jugular venous valved conduit (Contegra) in 2001 for clinical trial, we have selectively used the Contegra in some patients who require conduit revision or replacement to see whether the degree of mid-to-late regurgitation is less with the Contegra as compared with the monocusp valve outflow patch.23
The current study has the limitations of a retrospective review and has no concurrent control group. Furthermore, magnetic resonance imaging and more refined 2-dimensional and even 3-dimensional echocardiographic studies would have provided additional valuable data regarding evaluation of RV function and dimensions as well as the PTFE monocusp valve mechanics. Exercise testing and assessment of volume of oxygen uptake would better evaluate the functional benefits of this and other RVOT reconstruction techniques. Nevertheless, PTFE monocusp valve reconstruction of the RVOT is a safe, effective, and durable technique for the mid term in the majority of patients and may delay or obviate the need to insert a homograft or xenograft valve in late follow-up. Continued use and long-term follow-up including magnetic resonance imaging and exercise testing is necessary to further demonstrate the value of this technique.
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Footnotes |
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References |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionReferences |
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