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Right Ventricular Outflow Tract Reconstruction With Bicuspid Valved Polytetrafluoroethylene Conduit
Right Ventricular Outflow Tract Reconstruction With Bicuspid Valved Polytetrafluoroethylene Conduit Masahiro Yoshida, MD, Peter D. Wearden, MD, PhD, Onur Dur, MS, Kerem Pekkan, PhD, and Victor O. Morell, MD
Background. In general, all conduits available for right ventricular outflow tract (RVOT) reconstruction eventually become stenotic or insufficient. Owing to the lack of an ideal conduit and with the hope of reducing the incidence of reoperations, we have developed and utilized a bicuspid valved polytetrafluoroethylene (PTFE) conduit for the reconstruction of the RVOT. The purpose of this study was to review our early experience with this conduit. Methods. From October 2008 to September 2009, we have implanted bicuspid valved PTFE conduits in 18 patients with a median age of 1.7 years (range 6 days to 16 years). Their diagnoses include tetralogy of Fallot with pulmonary atresia in 8, truncus arteriosus in 6, congenital aortic stenosis in 2, transposition of great arteries in 1, and interrupted aortic arch with a ventricular septal defect in 1. In 16 patients, a complete biventricular repair was performed. In another 2 cases, the conduit was used for palliative RVOT reconstruction. The conduit sizes
varied from 10 mm to 24 mm in diameter. Three-dimensional flow fields obtained from computational fluid dynamics studies were utilized in the conduit design process. Results. There was no surgical mortality or reinterventions associated with the PTFE conduit placement in our series. At the time of discharge, none of the patients had any echocardiographic findings consistent with significant conduit stenosis or insufficiency. During the follow-up period of 6.2 ⴞ 3.9 months, all patients were alive and only 3 had more than mild pulmonary insufficiency. Conclusions. Our bicuspid valved PTFE conduit has an acceptable early performance, with a low incidence of valve insufficiency and no conduit stenosis. Certainly, longer follow-up is necessary to fully assess its long-term benefits.
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conduit in the RVOT at Children’s Hospital of Pittsburgh. The median age at the time of implantation was 1.7 years (range, 6 days to 16 years). Their diagnoses included tetralogy of Fallot with pulmonary atresia in 8, truncus arteriosus in 6, congenital aortic stenosis in 2, transposition of great arteries in 1, and interrupted aortic arch with a ventricular septal defect in 1 (Table 1). Thirteen patients had a previous procedure that included a palliative RVOT reconstruction in 3, repair for truncus arteriosus in 3, repair for tetralogy of Fallot in 3, bilateral unifocalization in 1, Ross procedure in 1, arch reconstruction in 1, and arterial switch in 1. Concomitant procedure at the time of conduit implantation included VSD closure in 4, repair for truncus arteriosus in 3, Ross procedure in 1, reconstruction of the central pulmonary arteries in 1, aortic valve replacement in 1, and one-stage repair of tetralogy of Fallot with pulmonary atresia with unifocalization in 1. The diameter of the conduit ranged from 10 to 24 mm. The size of the conduit was determined according to the patient’s body weight and body surface area (Fig 1). This research study was approved by our Institutional Review Board.
ased on general experience, all conduits available for right ventricular outflow tract (RVOT) reconstruction eventually become stenotic and/or insufficient, especially in very young patients [1–3]. Owing to the lack of an ideal conduit and with the hope of reducing the incidence of reoperations, we have developed and utilized a bicuspid valved polytetrafluoroethylene (PTFE) conduit using standard stretch PTFE graft and 0.1 mm thick PTFE membrane (W.L. Gore & Associates, Flagstaff, AZ) for the reconstruction of the RVOT. The purpose of this study was to review our early experience with this conduit.
Patients and Methods From October 2008 to September 2009, 18 patients underwent implantation of a bicuspid valved PTFE Accepted for publication Nov 8, 2010. Presented at the Fifty-sixth Annual Meeting of the Southern Thoracic Surgical Association, Marco Island, FL, Nov 4 –7, 2009. Address correspondence to Dr Yoshida, Department of Cardiothoracic Surgery, Children’s Hospital of Pittsburgh, 4401 Penn Ave, Faculty Pavilion, 5th Flr, Pittsburgh, PA 15224; e-mail: masahiro.yoshida@ chp.edu.
© 2011 by The Society of Thoracic Surgeons Published by Elsevier Inc
(Ann Thorac Surg 2011;91:1235–9) © 2011 by The Society of Thoracic Surgeons
0003-4975/$36.00 doi:10.1016/j.athoracsur.2010.11.010
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Department of Cardiothoracic Surgery, Children’s Hospital of Pittsburgh, and Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania
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Table 1. Patient Profile Demographic Age, years (range)
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Body weight, kg (range) Diagnosis Tetralogy of Fallot Truncus arteriosus Congenital aortic stenosis (Ross) TGA IAA with VSD
Value 1.7 ⫾ 1.5 (6 days to 16 years) 20 ⫾ 19 (3.4 to 67) 8 6 2 1 1
IAA ⫽ interrupted aortic arch; TGA ⫽ transposition of great arteries; VSD ⫽ ventricular septal defect.
Operative Technique The valved conduit was constructed in the operating theater at the time of surgery. First, the PTFE conduit is turned inside out, and then the two cusps created from 0.1 mm PTFE membrane are sutured to the inside wall of the conduit using a running 7-0 polypropylene running suture for conduits 14 mm or less in diameter and 6-0 polypropylene for larger ones. Finally, the conduit is turned outside in (Fig 2). The shape and dimensions of the valve leaflets for each specific conduit diameter are shown in Figure 3. Note that the conduit has a small nonvalved portion at the bottom, representing 15% of circumference of conduit. This allows for a minimal amount of regurgitation, which should prevent thrombus formation at the base of the valve sinuses. It has been our practice to place the “valved” portion of the conduit distally, leaving just a few millimeters of conduit wall beyond the top margin of PTFE cusps. The proximal end is then trimmed appropriately to match the opening in the RVOT.
Postoperative Anticoagulation Therapy Low-dose aspirin (1 to 5 mg/kg daily) was started in the hospital and continued for 6 months.
Echocardiographic Evaluation
days of operation. Analysis was performed with JMP 8.01 for Macintosh (JMP, Cary, NC).
Results There was no surgical and late mortality nor events associated with the conduit placement at the mean follow-up of 6.2 ⫾ 3.9 months. All patients were doing well without any need for conduit reinterventions. Echocardiographic evaluation of the conduit was done intraoperatively (T1; n ⫽ 18), at the time of discharge (T2; n ⫽ 18), and during follow-up (n ⫽ 11). Echocardiography showed the presence of trivial or mild insufficiency in 17 (94%) at T1, 17 (94%) at T2, and 8 (73%) at T3. There was only 1 patient who had moderate insufficiency in the operating theater and at discharge. It was a neonate who underwent repair of truncus arteriosus with a 12-mm conduit. We believe that the insufficiency was related to his relatively high heart rate, which prevented adequate valve function. On his latest echocardiogram, there is only mild insufficiency at a lower heart rate. During follow-up examination in 11 patients, there was moderate insufficiency in 3. Two of them developed moderate insufficiency after undergoing catheter balloon angioplasty for peripheral pulmonary stenosis, which could have damaged the PTFE valve. In the remaining case, the echocardiogram showed that one of the valve leaflets was stuck in the open position. Pressure gradient across the conduit was 9 ⫾ 8 mm Hg at T1, 13 ⫾ 8 mm Hg at T2, and 19 ⫾ 15 mm Hg at T3 (Fig 4). During follow-up, only 1 patient, a neonatal repair, had a pressure gradient greater than 30 mm Hg 12 months after surgery, which we believe is related to rapid somatic growth.
Comment Right ventricular outflow tract reconstruction has been performed utilizing different types of conduits, most commonly aortic or pulmonary homografts, which have been associated with a high incidence of stenosis or insufficiency requiring reoperations especially in very
All patients had an intraoperative transesophageal echocardiogram before discharge and during follow-up. These studies were systematically reviewed to assess the presence of pulmonary regurgitation and to determine the mean valve gradient. The pulmonary regurgitation was classified as trivial (grade 1), mild (grade 2), moderate (grade 3), and severe (grade 4) according to features of the jet, assessed with pulsed flow Doppler and color Doppler. Conduit stenosis was assessed by measuring the peak velocity through the valve with continuouswave Doppler technique.
Statistical Analysis Preoperative and postoperative data were retrospectively collected. Descriptive data for continuous variables are presented as means ⫾ SD or as medians with ranges; categorical variables are presented as relative frequencies. Surgical mortality was defined as death within 30
Fig 1. The authors use various sizes of conduit from 10 to 24 mm in diameter. This graft shows the correlation between conduit size and body surface area (BSA). The curved line shows normal pulmonary valve size by Rawlatt.
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Fig 2. Drawings of the steps to make a bicuspid valved conduit. At first, a polytetrafluoroethylene (PTFE) conduit with standard stretch wall is turned inside out. After holding the graft at both ends using Kelly’s clamps, two cusps trimmed from the PTFE sheet of 0.1-mm thickness are sutured using 6-0 or 7-0 polypropylene sutures. Actually, the author put the top of the triangle first and put marking stitches at the middle of both sides. Then, continuous suture is put using the stitch of the top. After completion of suturing two cusps, the conduit is turned back outside in (upper drawings). A special feature of this conduit is having a nonvalved portion at the bottom (lower drawings).
young patients [1–3]. Also, exposure to homograft material has been proven to result in significant allosensitization, which could negatively affects the results of future cardiac transplantation. Over the last couple of years, we have opted to preferentially utilize a PTFE bicuspid valved conduit for RVOT reconstruction with the expectation that they will have a better overall performance than other conduits. Brown and colleagues [4] reported excellent long-term results using a PTFE monocuspid valve in the RVOT. Also, Ando and Takahashi [5] described good long-term results of RVOT reconstruction using PTFE trileaflet valved conduits. Our conduit was designed with a bicuspid valve instead of a trileaflet valve because of one of the author’s prior experience with a trileaflet conduit in which the “posterior” leaflet did not open (Fig 5) during systole in 2 consecutive patients. It was theorized that the flow along
the lesser curvature of the conduit was not sufficient to open the posterior leaflet, and that is why we modified the valve component of the conduit to be bileaflet with a small posterior “nonvalve” segment. The nonvalve segment only represents 15% of the valve circumference, resulting in very little regurgitation. To further investigate the general three-dimensional flow patterns inside curved conduits and to quantify fluid-induced forces important for valve kinematics, computational fluid dynamics studies were performed. Pulsatile blood flow was simulated inside the curved RVOT conduit using the second-order accurate computational fluid dynamics solver (Fluent 6.3.26; ANSYS, Canonsburg, PA), which was originally developed for investigating the reconstructive surgeries for single ventricle palliation [6, 7]. Two conduits of 14-mm and 22-mm diameter were evaluated based on the body surface area, 0.5 m2 Fig 3. The design of each valve. The figures are as follow: circumference (C) ⫽ conduit size ⫻ 3.14; nonvalved portion (nV) ⫽ C ⫻ 0.15; width of sinus (WS) ⫽ (C ⫺ nV ) / 2; height of sinus (HS) ⫽ WS ⫻ 0.7; width of cusp (WC) ⫽ WS ⫻ 1.2; height of cusp (HC) ⫽ HS ⫻ 0.9; and fan of cusp (FC) ⫽ HC ⫻ 0.2.
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Fig 4. Pressure gradients of conduit in the operating room (OR), at discharge, and at clinic by echocardiography.
and 1.35 m2, and the corresponding cardiac outputs, 1.2 L/min and 2.4 L/min, respectively. Blood was chosen as Newtonian fluid with a viscosity of 3.7 l e-3 N-s/m2 and a density of 1,060 kg/m3. Physiologic RVOT flow waveform and blunt flow profile (typical for ventricle) was assigned at the inlet of the conduit in agreement with the clinical measurements. Computational domain of each conduit were discretized using 50,000 tetrahedral elements. According to our simulations, about one diameter distal from the inlet, blood flow skewed toward the major curvature of the conduit. Hence, the flow velocity at the lesser curvature of conduit was slower than that at the major curvature. Furthermore, flow profile was almost symmetrical along the curvature axis, indicating balanced opening forces exerted on each leaflet during the systole (Fig 6). These results perfectly agree with the author’s clinical experience in the operating room. Similar bioengineering studies toward improved designs are ongoing. Yamagishi and associates [8] reported a unique PTFE valved conduit design in 2007. It incorporated bulging sinuses that can generate diastolic vortex flow between
Fig 5. Echocardiography the author experienced in Kobe, Japan. The stuck valve at the bottom of tricuspid valved conduit is shown (arrowhead). It was considered that flow velocity at the lesser curvature of the curved conduit was slower than at the major curvature.
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Fig 6. Newtonian pulsatile blood flow simulated inside the 14-mm conduit for a cardiac output of 1.2 LPM using second-order computational fluid dynamics solver (Fluent 6.3.26). Time-averaged velocity contours shown during systole indicated lower velocity at the lesser curvature of the conduit.
the conduit wall and the leaflets, and hence potentially provide better long-term results than a conduit without sinuses. Future modification to our bicuspid valved conduit may include the creation of sinuses. Our ongoing computational fluid dynamics investigation will identify the benefit of sinus geometry on the RVOT conduit hemodynamics and guide its clinical implementation. Our bicuspid valved PTFE conduit has an acceptable early performance, with a low incidence of valve insufficiency and no conduit stenosis. The lack of allosensitization is another benefit of this conduit, as well as possibly providing a reliable target to deliver percutaneously implantable valves. Certainly, longer follow-up is necessary to fully assess its long-term benefits.
References 1. Kaza AK, Lim HG, Dibardino DJ, Del Nido PJ, Mayer JE, Pigula FA. Long-term results of right ventricular outflow tract reconstruction in neonatal cardiac surgery: options and outcomes. J Thorac Cardiovasc Surg 2009;138:911– 6. 2. Schreiber C, Sassen S, Kostolny M, et al. Early graft failure of small-sized porcine-valved conduits in reconstruction of the right ventricular outflow tract. Ann Thorac Surg 2006;82:179 – 86. 3. Shebani SO, McGuirk S, Brawn WJ, et al. Right ventricular outflow tract reconstruction using Contegra® valved conduit: natural history and conduit performance under pressure. Eur J Cardiothorac Surg 2006;29:397– 405. 4. Brown JW, Ruzmetov M, Vijay P, Rodefeld MD, Turrentine MW. Right ventricular outflow tract reconstruction with a polytetrafluoroethylene monocusp valve: a twelve-year experience. J Thorac Cardiovasc Surg 2007;133:1336 – 43. 5. Ando M, Takahashi Y. Ten-year experience with handmade trileaflet polytetrafluoroethylene valved conduit used for pulmonary reconstruction. J Thorac Cardiovasc Surg 2009;137: 124 –31. 6. Pekkan K, Kitajima HD, Yoganathan AP, et al. Total cavopulmonary connection flow with functional left pulmonary artery stenosis: angioplasty and fenestration in vitro. Circulation 2005;112:3264 –71. 7. Wang C, Pekkan K, Yoganathan AP, et al. Progress in the CFD modeling of flow instabilities in anatomical total cavopulmonary connections. Ann Biomed Eng 2007;35:1840 –56. 8. Miyazaki T, Yamagishi M, Kado H, et al. Expanded polytetrafluoroethylene valved conduit and patch with bulging sinuses in right ventricular outflow tract reconstruction. J Thorac Cardiovasc Surg 2007;134:327–32.
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DISCUSSION
DR YOSHIDA: How? DR BROWN: You have a chart in the manuscript, but how did you come up with the dimensions? DR YOSHIDA: Basically I considered the bottom side of the conduit is slower than the major curvature. So even if we put the commissure vertically, the bottom one must be slower, the velocity slower. That might cause thrombus and also some stagnant flow. So that is why I designed this conduit, which has the nonvalved portion at the bottom. It causes some regurgitation but I think for right ventricular outflow, some regurgitation is acceptable. DR BROWN: I totally agree, but how did you come up with the width of the leaflets and the height of the leaflets? DR YOSHIDA: The basic design of the leaflet was developed through trial and error over the years at Kobe Children’s Hospital in Japan. DR BROWN: Of the 0.1 PTFE leaflets inside the conduit, how did you come up with the dimensions, because they are interesting. I just want to understand. Did you pull this out of the air or did someone teach you? How did you come up with the dimensions of the leaflets themselves? I would like to try this, but I don’t understand how long and wide to construct the leaflets. DR YOSHIDA: Actually, in Japan from my experience of trial and error, we determined this figure, and we have some fear how wide the gap should be. I can show you also in my slide. Actually, I don’t remember, maybe 12% of the circumference. I think 12%. DR BROWN: I don’t understand whether there was an easy way to determine leaflet dimensions when you turn the conduit
inside out. You obviously put the leaflets on the outside of the conduit and then turn it right side out. There must have been some trial and error that came into the construction. My last questions are, why was there progressive regurgitation in the latest follow-up in 25% of the patients? What was the cause of the worsening regurgitation at last follow-up? Are the leaflets not opening all the way or closing all the way? Why do you think the regurgitation increases with time? DR YOSHIDA: Thank you for that question. There were 3 cases that had moderate insufficiency. Two of them developed after a catheter intervention for peripheral pulmonary stenosis. Maybe catheter intervention touched one of the leaflets, causing insufficiency. But the other case, that case had no history of catheter intervention. The conduit has no bulging sinus, it’s just a straight graft. And this may be a disadvantage, since a cusp can touch the wall of the conduit and maybe become immobile. We routinely give aspirin for anticoagulation to avoid stuck leaflet. And we are thinking about putting bulging sinus to avoid leaflets touching a conduit wall. DR BROWN: I think a sinus would facilitate leaflet closure. The next question I have is, what is the smallest conduit that you can do this? DR YOSHIDA: Ten millimeters. DR BROWN: In your manuscript it was 10 mm, but wouldn’t it be nice to have a valved Sano conduit? Can you make a conduit smaller than 10 mm? DR MORELL: My comment is that Dr Yoshida developed this conduit using trial and error. We are working with CarnegieMellon trying to get some engineers working on this valved conduit to see if we can make it work more optimally to prevent late insufficiency. DR BROWN: Well, I really like the idea, and I actually think you could probably take a smaller one, split the conduit, put your two leaflets in, and sew it back together, and maybe you could have a valved Sano conduit for hypoplastic left heart syndrome. DR YOSHIDA: Actually, once we tried to make a 6-mm conduit with a monocusp, but that was also cusp touching the conduit wall in the early phase. So I would not recommend so far. DR BROWN: I very much enjoyed your presentation, and this is an innovative technique. Obviously, your follow-up is only months long, and we need longer follow-up. I look forward to seeing your follow-up at future meetings. Thank you. DR YOSHIDA: Thank you, Dr Brown.
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DR JOHN W. BROWN (Indianapolis, IN): I would like to compliment Dr Yoshida and the group at Pittsburgh for this ingenious RV-PA conduit construction. I have seen several other conduit constructions, and they were difficult for me to figure out how they proportioned the leaflet size. The Yoshida conduit should be inexpensive to construct and could more easily be afforded in the developing world. I like your idea of vertical commissures. This reminds me a little bit of the folding monocusp that Graham Nunn reported at the AATS 2 or 3 years ago. And I have noticed with our experimental bovine bicuspid venous valved conduits that when you orient the leaflets in a vertical fashion, you see the absence of the lesser curve stasis that you described. My first question is how you came up with the width and height of the leaflets and the width of the gap at the bottom? How did you come up with the leaflet size and dimensions?
Background. In general, all conduits available for right ventricular outflow tract (RVOT) reconstruction eventually become stenotic or insufficient. Owing to the lack of an ideal conduit and with the hope of reducing the incidence of reoperations, we have developed and utilized a bicuspid valved polytetrafluoroethylene (PTFE) conduit for the reconstruction of the RVOT. The purpose of this study was to review our early experience with this conduit. Methods. From October 2008 to September 2009, we have implanted bicuspid valved PTFE conduits in 18 patients with a median age of 1.7 years (range 6 days to 16 years). Their diagnoses include tetralogy of Fallot with pulmonary atresia in 8, truncus arteriosus in 6, congenital aortic stenosis in 2, transposition of great arteries in 1, and interrupted aortic arch with a ventricular septal defect in 1. In 16 patients, a complete biventricular repair was performed. In another 2 cases, the conduit was used for palliative RVOT reconstruction. The conduit sizes
varied from 10 mm to 24 mm in diameter. Three-dimensional flow fields obtained from computational fluid dynamics studies were utilized in the conduit design process. Results. There was no surgical mortality or reinterventions associated with the PTFE conduit placement in our series. At the time of discharge, none of the patients had any echocardiographic findings consistent with significant conduit stenosis or insufficiency. During the follow-up period of 6.2 ⴞ 3.9 months, all patients were alive and only 3 had more than mild pulmonary insufficiency. Conclusions. Our bicuspid valved PTFE conduit has an acceptable early performance, with a low incidence of valve insufficiency and no conduit stenosis. Certainly, longer follow-up is necessary to fully assess its long-term benefits.
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conduit in the RVOT at Children’s Hospital of Pittsburgh. The median age at the time of implantation was 1.7 years (range, 6 days to 16 years). Their diagnoses included tetralogy of Fallot with pulmonary atresia in 8, truncus arteriosus in 6, congenital aortic stenosis in 2, transposition of great arteries in 1, and interrupted aortic arch with a ventricular septal defect in 1 (Table 1). Thirteen patients had a previous procedure that included a palliative RVOT reconstruction in 3, repair for truncus arteriosus in 3, repair for tetralogy of Fallot in 3, bilateral unifocalization in 1, Ross procedure in 1, arch reconstruction in 1, and arterial switch in 1. Concomitant procedure at the time of conduit implantation included VSD closure in 4, repair for truncus arteriosus in 3, Ross procedure in 1, reconstruction of the central pulmonary arteries in 1, aortic valve replacement in 1, and one-stage repair of tetralogy of Fallot with pulmonary atresia with unifocalization in 1. The diameter of the conduit ranged from 10 to 24 mm. The size of the conduit was determined according to the patient’s body weight and body surface area (Fig 1). This research study was approved by our Institutional Review Board.
ased on general experience, all conduits available for right ventricular outflow tract (RVOT) reconstruction eventually become stenotic and/or insufficient, especially in very young patients [1–3]. Owing to the lack of an ideal conduit and with the hope of reducing the incidence of reoperations, we have developed and utilized a bicuspid valved polytetrafluoroethylene (PTFE) conduit using standard stretch PTFE graft and 0.1 mm thick PTFE membrane (W.L. Gore & Associates, Flagstaff, AZ) for the reconstruction of the RVOT. The purpose of this study was to review our early experience with this conduit.
Patients and Methods From October 2008 to September 2009, 18 patients underwent implantation of a bicuspid valved PTFE Accepted for publication Nov 8, 2010. Presented at the Fifty-sixth Annual Meeting of the Southern Thoracic Surgical Association, Marco Island, FL, Nov 4 –7, 2009. Address correspondence to Dr Yoshida, Department of Cardiothoracic Surgery, Children’s Hospital of Pittsburgh, 4401 Penn Ave, Faculty Pavilion, 5th Flr, Pittsburgh, PA 15224; e-mail: masahiro.yoshida@ chp.edu.
© 2011 by The Society of Thoracic Surgeons Published by Elsevier Inc
(Ann Thorac Surg 2011;91:1235–9) © 2011 by The Society of Thoracic Surgeons
0003-4975/$36.00 doi:10.1016/j.athoracsur.2010.11.010
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Department of Cardiothoracic Surgery, Children’s Hospital of Pittsburgh, and Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania
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Table 1. Patient Profile Demographic Age, years (range)
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Body weight, kg (range) Diagnosis Tetralogy of Fallot Truncus arteriosus Congenital aortic stenosis (Ross) TGA IAA with VSD
Value 1.7 ⫾ 1.5 (6 days to 16 years) 20 ⫾ 19 (3.4 to 67) 8 6 2 1 1
IAA ⫽ interrupted aortic arch; TGA ⫽ transposition of great arteries; VSD ⫽ ventricular septal defect.
Operative Technique The valved conduit was constructed in the operating theater at the time of surgery. First, the PTFE conduit is turned inside out, and then the two cusps created from 0.1 mm PTFE membrane are sutured to the inside wall of the conduit using a running 7-0 polypropylene running suture for conduits 14 mm or less in diameter and 6-0 polypropylene for larger ones. Finally, the conduit is turned outside in (Fig 2). The shape and dimensions of the valve leaflets for each specific conduit diameter are shown in Figure 3. Note that the conduit has a small nonvalved portion at the bottom, representing 15% of circumference of conduit. This allows for a minimal amount of regurgitation, which should prevent thrombus formation at the base of the valve sinuses. It has been our practice to place the “valved” portion of the conduit distally, leaving just a few millimeters of conduit wall beyond the top margin of PTFE cusps. The proximal end is then trimmed appropriately to match the opening in the RVOT.
Postoperative Anticoagulation Therapy Low-dose aspirin (1 to 5 mg/kg daily) was started in the hospital and continued for 6 months.
Echocardiographic Evaluation
days of operation. Analysis was performed with JMP 8.01 for Macintosh (JMP, Cary, NC).
Results There was no surgical and late mortality nor events associated with the conduit placement at the mean follow-up of 6.2 ⫾ 3.9 months. All patients were doing well without any need for conduit reinterventions. Echocardiographic evaluation of the conduit was done intraoperatively (T1; n ⫽ 18), at the time of discharge (T2; n ⫽ 18), and during follow-up (n ⫽ 11). Echocardiography showed the presence of trivial or mild insufficiency in 17 (94%) at T1, 17 (94%) at T2, and 8 (73%) at T3. There was only 1 patient who had moderate insufficiency in the operating theater and at discharge. It was a neonate who underwent repair of truncus arteriosus with a 12-mm conduit. We believe that the insufficiency was related to his relatively high heart rate, which prevented adequate valve function. On his latest echocardiogram, there is only mild insufficiency at a lower heart rate. During follow-up examination in 11 patients, there was moderate insufficiency in 3. Two of them developed moderate insufficiency after undergoing catheter balloon angioplasty for peripheral pulmonary stenosis, which could have damaged the PTFE valve. In the remaining case, the echocardiogram showed that one of the valve leaflets was stuck in the open position. Pressure gradient across the conduit was 9 ⫾ 8 mm Hg at T1, 13 ⫾ 8 mm Hg at T2, and 19 ⫾ 15 mm Hg at T3 (Fig 4). During follow-up, only 1 patient, a neonatal repair, had a pressure gradient greater than 30 mm Hg 12 months after surgery, which we believe is related to rapid somatic growth.
Comment Right ventricular outflow tract reconstruction has been performed utilizing different types of conduits, most commonly aortic or pulmonary homografts, which have been associated with a high incidence of stenosis or insufficiency requiring reoperations especially in very
All patients had an intraoperative transesophageal echocardiogram before discharge and during follow-up. These studies were systematically reviewed to assess the presence of pulmonary regurgitation and to determine the mean valve gradient. The pulmonary regurgitation was classified as trivial (grade 1), mild (grade 2), moderate (grade 3), and severe (grade 4) according to features of the jet, assessed with pulsed flow Doppler and color Doppler. Conduit stenosis was assessed by measuring the peak velocity through the valve with continuouswave Doppler technique.
Statistical Analysis Preoperative and postoperative data were retrospectively collected. Descriptive data for continuous variables are presented as means ⫾ SD or as medians with ranges; categorical variables are presented as relative frequencies. Surgical mortality was defined as death within 30
Fig 1. The authors use various sizes of conduit from 10 to 24 mm in diameter. This graft shows the correlation between conduit size and body surface area (BSA). The curved line shows normal pulmonary valve size by Rawlatt.
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Fig 2. Drawings of the steps to make a bicuspid valved conduit. At first, a polytetrafluoroethylene (PTFE) conduit with standard stretch wall is turned inside out. After holding the graft at both ends using Kelly’s clamps, two cusps trimmed from the PTFE sheet of 0.1-mm thickness are sutured using 6-0 or 7-0 polypropylene sutures. Actually, the author put the top of the triangle first and put marking stitches at the middle of both sides. Then, continuous suture is put using the stitch of the top. After completion of suturing two cusps, the conduit is turned back outside in (upper drawings). A special feature of this conduit is having a nonvalved portion at the bottom (lower drawings).
young patients [1–3]. Also, exposure to homograft material has been proven to result in significant allosensitization, which could negatively affects the results of future cardiac transplantation. Over the last couple of years, we have opted to preferentially utilize a PTFE bicuspid valved conduit for RVOT reconstruction with the expectation that they will have a better overall performance than other conduits. Brown and colleagues [4] reported excellent long-term results using a PTFE monocuspid valve in the RVOT. Also, Ando and Takahashi [5] described good long-term results of RVOT reconstruction using PTFE trileaflet valved conduits. Our conduit was designed with a bicuspid valve instead of a trileaflet valve because of one of the author’s prior experience with a trileaflet conduit in which the “posterior” leaflet did not open (Fig 5) during systole in 2 consecutive patients. It was theorized that the flow along
the lesser curvature of the conduit was not sufficient to open the posterior leaflet, and that is why we modified the valve component of the conduit to be bileaflet with a small posterior “nonvalve” segment. The nonvalve segment only represents 15% of the valve circumference, resulting in very little regurgitation. To further investigate the general three-dimensional flow patterns inside curved conduits and to quantify fluid-induced forces important for valve kinematics, computational fluid dynamics studies were performed. Pulsatile blood flow was simulated inside the curved RVOT conduit using the second-order accurate computational fluid dynamics solver (Fluent 6.3.26; ANSYS, Canonsburg, PA), which was originally developed for investigating the reconstructive surgeries for single ventricle palliation [6, 7]. Two conduits of 14-mm and 22-mm diameter were evaluated based on the body surface area, 0.5 m2 Fig 3. The design of each valve. The figures are as follow: circumference (C) ⫽ conduit size ⫻ 3.14; nonvalved portion (nV) ⫽ C ⫻ 0.15; width of sinus (WS) ⫽ (C ⫺ nV ) / 2; height of sinus (HS) ⫽ WS ⫻ 0.7; width of cusp (WC) ⫽ WS ⫻ 1.2; height of cusp (HC) ⫽ HS ⫻ 0.9; and fan of cusp (FC) ⫽ HC ⫻ 0.2.
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Fig 4. Pressure gradients of conduit in the operating room (OR), at discharge, and at clinic by echocardiography.
and 1.35 m2, and the corresponding cardiac outputs, 1.2 L/min and 2.4 L/min, respectively. Blood was chosen as Newtonian fluid with a viscosity of 3.7 l e-3 N-s/m2 and a density of 1,060 kg/m3. Physiologic RVOT flow waveform and blunt flow profile (typical for ventricle) was assigned at the inlet of the conduit in agreement with the clinical measurements. Computational domain of each conduit were discretized using 50,000 tetrahedral elements. According to our simulations, about one diameter distal from the inlet, blood flow skewed toward the major curvature of the conduit. Hence, the flow velocity at the lesser curvature of conduit was slower than that at the major curvature. Furthermore, flow profile was almost symmetrical along the curvature axis, indicating balanced opening forces exerted on each leaflet during the systole (Fig 6). These results perfectly agree with the author’s clinical experience in the operating room. Similar bioengineering studies toward improved designs are ongoing. Yamagishi and associates [8] reported a unique PTFE valved conduit design in 2007. It incorporated bulging sinuses that can generate diastolic vortex flow between
Fig 5. Echocardiography the author experienced in Kobe, Japan. The stuck valve at the bottom of tricuspid valved conduit is shown (arrowhead). It was considered that flow velocity at the lesser curvature of the curved conduit was slower than at the major curvature.
Ann Thorac Surg 2011;91:1235–9
Fig 6. Newtonian pulsatile blood flow simulated inside the 14-mm conduit for a cardiac output of 1.2 LPM using second-order computational fluid dynamics solver (Fluent 6.3.26). Time-averaged velocity contours shown during systole indicated lower velocity at the lesser curvature of the conduit.
the conduit wall and the leaflets, and hence potentially provide better long-term results than a conduit without sinuses. Future modification to our bicuspid valved conduit may include the creation of sinuses. Our ongoing computational fluid dynamics investigation will identify the benefit of sinus geometry on the RVOT conduit hemodynamics and guide its clinical implementation. Our bicuspid valved PTFE conduit has an acceptable early performance, with a low incidence of valve insufficiency and no conduit stenosis. The lack of allosensitization is another benefit of this conduit, as well as possibly providing a reliable target to deliver percutaneously implantable valves. Certainly, longer follow-up is necessary to fully assess its long-term benefits.
References 1. Kaza AK, Lim HG, Dibardino DJ, Del Nido PJ, Mayer JE, Pigula FA. Long-term results of right ventricular outflow tract reconstruction in neonatal cardiac surgery: options and outcomes. J Thorac Cardiovasc Surg 2009;138:911– 6. 2. Schreiber C, Sassen S, Kostolny M, et al. Early graft failure of small-sized porcine-valved conduits in reconstruction of the right ventricular outflow tract. Ann Thorac Surg 2006;82:179 – 86. 3. Shebani SO, McGuirk S, Brawn WJ, et al. Right ventricular outflow tract reconstruction using Contegra® valved conduit: natural history and conduit performance under pressure. Eur J Cardiothorac Surg 2006;29:397– 405. 4. Brown JW, Ruzmetov M, Vijay P, Rodefeld MD, Turrentine MW. Right ventricular outflow tract reconstruction with a polytetrafluoroethylene monocusp valve: a twelve-year experience. J Thorac Cardiovasc Surg 2007;133:1336 – 43. 5. Ando M, Takahashi Y. Ten-year experience with handmade trileaflet polytetrafluoroethylene valved conduit used for pulmonary reconstruction. J Thorac Cardiovasc Surg 2009;137: 124 –31. 6. Pekkan K, Kitajima HD, Yoganathan AP, et al. Total cavopulmonary connection flow with functional left pulmonary artery stenosis: angioplasty and fenestration in vitro. Circulation 2005;112:3264 –71. 7. Wang C, Pekkan K, Yoganathan AP, et al. Progress in the CFD modeling of flow instabilities in anatomical total cavopulmonary connections. Ann Biomed Eng 2007;35:1840 –56. 8. Miyazaki T, Yamagishi M, Kado H, et al. Expanded polytetrafluoroethylene valved conduit and patch with bulging sinuses in right ventricular outflow tract reconstruction. J Thorac Cardiovasc Surg 2007;134:327–32.
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YOSHIDA ET AL BICUSPID VALVED PTFE CONDUIT
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DISCUSSION
DR YOSHIDA: How? DR BROWN: You have a chart in the manuscript, but how did you come up with the dimensions? DR YOSHIDA: Basically I considered the bottom side of the conduit is slower than the major curvature. So even if we put the commissure vertically, the bottom one must be slower, the velocity slower. That might cause thrombus and also some stagnant flow. So that is why I designed this conduit, which has the nonvalved portion at the bottom. It causes some regurgitation but I think for right ventricular outflow, some regurgitation is acceptable. DR BROWN: I totally agree, but how did you come up with the width of the leaflets and the height of the leaflets? DR YOSHIDA: The basic design of the leaflet was developed through trial and error over the years at Kobe Children’s Hospital in Japan. DR BROWN: Of the 0.1 PTFE leaflets inside the conduit, how did you come up with the dimensions, because they are interesting. I just want to understand. Did you pull this out of the air or did someone teach you? How did you come up with the dimensions of the leaflets themselves? I would like to try this, but I don’t understand how long and wide to construct the leaflets. DR YOSHIDA: Actually, in Japan from my experience of trial and error, we determined this figure, and we have some fear how wide the gap should be. I can show you also in my slide. Actually, I don’t remember, maybe 12% of the circumference. I think 12%. DR BROWN: I don’t understand whether there was an easy way to determine leaflet dimensions when you turn the conduit
inside out. You obviously put the leaflets on the outside of the conduit and then turn it right side out. There must have been some trial and error that came into the construction. My last questions are, why was there progressive regurgitation in the latest follow-up in 25% of the patients? What was the cause of the worsening regurgitation at last follow-up? Are the leaflets not opening all the way or closing all the way? Why do you think the regurgitation increases with time? DR YOSHIDA: Thank you for that question. There were 3 cases that had moderate insufficiency. Two of them developed after a catheter intervention for peripheral pulmonary stenosis. Maybe catheter intervention touched one of the leaflets, causing insufficiency. But the other case, that case had no history of catheter intervention. The conduit has no bulging sinus, it’s just a straight graft. And this may be a disadvantage, since a cusp can touch the wall of the conduit and maybe become immobile. We routinely give aspirin for anticoagulation to avoid stuck leaflet. And we are thinking about putting bulging sinus to avoid leaflets touching a conduit wall. DR BROWN: I think a sinus would facilitate leaflet closure. The next question I have is, what is the smallest conduit that you can do this? DR YOSHIDA: Ten millimeters. DR BROWN: In your manuscript it was 10 mm, but wouldn’t it be nice to have a valved Sano conduit? Can you make a conduit smaller than 10 mm? DR MORELL: My comment is that Dr Yoshida developed this conduit using trial and error. We are working with CarnegieMellon trying to get some engineers working on this valved conduit to see if we can make it work more optimally to prevent late insufficiency. DR BROWN: Well, I really like the idea, and I actually think you could probably take a smaller one, split the conduit, put your two leaflets in, and sew it back together, and maybe you could have a valved Sano conduit for hypoplastic left heart syndrome. DR YOSHIDA: Actually, once we tried to make a 6-mm conduit with a monocusp, but that was also cusp touching the conduit wall in the early phase. So I would not recommend so far. DR BROWN: I very much enjoyed your presentation, and this is an innovative technique. Obviously, your follow-up is only months long, and we need longer follow-up. I look forward to seeing your follow-up at future meetings. Thank you. DR YOSHIDA: Thank you, Dr Brown.
PEDIATRIC CARDIAC
DR JOHN W. BROWN (Indianapolis, IN): I would like to compliment Dr Yoshida and the group at Pittsburgh for this ingenious RV-PA conduit construction. I have seen several other conduit constructions, and they were difficult for me to figure out how they proportioned the leaflet size. The Yoshida conduit should be inexpensive to construct and could more easily be afforded in the developing world. I like your idea of vertical commissures. This reminds me a little bit of the folding monocusp that Graham Nunn reported at the AATS 2 or 3 years ago. And I have noticed with our experimental bovine bicuspid venous valved conduits that when you orient the leaflets in a vertical fashion, you see the absence of the lesser curve stasis that you described. My first question is how you came up with the width and height of the leaflets and the width of the gap at the bottom? How did you come up with the leaflet size and dimensions?