Externally stented polytetrafluoroethylene valved conduits for right heart reconstruction

J THORAC CARDIOVASC SURG 90:833-841, 1985

Externally stented polytetrafluoroethylene valved conduits for right heart reconstruction An experimental comparison with Dacron valved conduits Valve-containing conduits have made possible the repair of many congenital anomalies that involve right ventricular-pulmonary arterial discontinuity. The distressing problem of neointimal peel formation with eventual conduit obstruction in patients with Dacron valved conduits bas led to the need for premature replacement in many patients. Extemally stented polytetrafluoroethylene bas demonstrated superior patency in the venous system experimentally and clinically and was believed to have potential advantages over Dacron for conduit construction. This study compares the t:ranseonduit resistance and the thickness of the neointimal peel in right ventricular-pulmonaryarterial conduits constructed of extemally stented poIytetrafluoroethylene with those of woven Dacron. The 19 mm extemally stented polytetrafluoroethyIene conduits(lmpra, Inc.) containinga Hancock porcinevalve (Extracorporeal Inc.) were implanted in six adult mongrel dogs followed by proximal occlusion of the pulmonary artery. In six additional animals, a Dacronvalved conduit of similar size and length was inserted.Cardiac output, transconduit gradient, and resistance were measured at operation andat 3 mont:m. AU conduitsweresubsequently explanted,opened longitudinally, and the thickness of the neointimal peel (excluding suture lines) measured. No hemodynamic differences were noted during the 3 month foUow-up. However, the thickness of the neointimal peelwas fourfoldgreater in Dacron conduits(609 ± 144p,) than in the conduitsconstructedof externally stented po1ytetrafluoroethylene (156 ± 50 p,) (p < O.OI~ The thick peel in Dacron conduits extended into the outflow portion of the porcine valve cusps and prevented their fuU excision. The neointima in external1y stented polytetrafluoroethylene conduitswas thin and uniform and did not extend onto the leaflets or limit their mobility. This study demonstrated that (I) the early hemodynamic performance of externally stented polytetrafluoroethylene conduits was comparable to that of Dacron conduits; (2) Dacron conduits were subject to an accelerated rate of peel formation that affected leaflet mobility and may be a factor in early valve degeneration; (3)a thin neointimaformed in extemally stented polytetrafluoroethylene conduits and valve leaflet motionwas preserved. This study showedthat extemally stented polytetrafluoroethylene conduits offer advantages over Dacron valved conduits and warrant clinical application.

John W. Brown, M.D., Michael P. Halpin, M.D. (by invitation), Fred J. Rescorla, M.D. (by invitation), Bruce W. VanNatta, M.D. (by invitation), Andrew C. Fiore, M.D. (by invitation), Gary D. Shipley, M.D. (by invitation), Moges Bizuneh, M.S. (by invitation), Randall Bills (by invitation), and Bruce Waller, M.D. (by invitation), Indianapolis, Ind.

From the Department of Surgery, Section of Cardiothoracic Surgery, and the Department of Pathology (Dr. Waller), Indiana University School of Medicine, Indianapolis, Ind. Read at the Sixty-fifth Annual Meeting of The American Association for Thoracic Surgery, New Orleans, La., April 29-May I, 1985. Address for reprints: John W. Brown, M.D., Section ofCardiothoracic Surgery, Emerson Hall, R. 212, 545 Barnhill Dr., Indianapolis, Ind. 46223.

"\lved external conduits continue to be necessary for the repair of several complex cyanotic anomalies.!" The valveless tubes of prosthetic material first used for these repairs in the mid-1960s'·2 were succeeded by aortic homograft conduits in the late 1960s and early 1970s. 3 Woven Dacron conduits containing glutaraldehydepreserved porcine valves were introduced in 1973 by Bowman, Hancock, and Maim7 and became popular in 833

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Thoracic and Cardiovascular Surgery

conduit eliminates the progressive buildup of the thick neointimal peel." The current study compared the transconduit resistance and the thickness of the neointimal peel in RV-PA valved conduits constructed of externally stented polytetrafluoroethylene (PTFE) with the commercially available woven Dacron conduits.

Material and methods

Fig. 1. Anterior diagram of the heart demonstrating technique for conduit-pulmonary artery anastomosis with the aid of a vascular clamp. Note tape around the proximal pulmonary artery. the United States because homografts were difficult to obtain. In Europe and Great Britain. the "fresh" antibiotic-sterilized aortic homograft remained popu-

lar.' Initial results with the Dacron valved conduit seemed satisfactory, but long-term follow-up in clinical series has shown a high incidence of progressive neointimal hyperplasia of the conduit, which produced obstruction and heterograft valve calcification and dysfunction."!' We became interested in the experimental evaluation of valved cardiac conduits in the early 1970s and noted porcine heterograft valve degeneration, but we" did not observe neointimal hyperplasia in Dacron valved conduits placed between the left ventricle and aorta. We subsequently began an extensive laboratory effort to better understand right ventricular-pulmonary arterial (RV-PA) conduit obstruction and made several observations: (1) Acquired obstruction at the right ventricularconduit anastomotic site is uncommon in patients but common in dogs. It can be prevented by adding a semirigid stent at the right ventricular anastomotic site." (2) Calcific degeneration of the porcine valve as well as exuberant neointimal proliferation occurs at an accelerated rate (3 to 6 months) in canine RV-PA valved Dacron conduits; thus, the dog is an excellent model to use in studying this problem. (3) The rteointimal proliferation is greatest immediately proximal and distal to the valve. (4) A neointimal peel forms in mechanical valves as well as tissue valves in experimental RV-PA conduits constructed of woven Dacron. (5) Omission of the valve from the Dacron RV-PA valved

A group of 12 adult mongrel dogs, weighing 18 to 24 kg, were anesthetized with thiopental sodium (25 mg/kg body weight), intubated, and mechanically ventilated with oxygen and halothane. Femoral arterial pressure and electrocardiograms were continuously recorded. A 93A-131-7F Swan-Ganz flow-directed thermodilution catheter was inserted through the femoral vein into the pulmonary artery for right ventricular pressure, pulmonary arterial pressure, and cardiac output determinations. Pressure measurements were obtained with Statham transducers and values were recorded on a Honeywell multichannel recorder. Cardiac output was measured with the American Edwards Model 9520 computer. Through an incision in the left fifth intercostal space, the pericardium was opened longitudinally and the proximal pulmonary artery encircled with a Dacron tape. Animals were then systemically heparinized (1.5 mg/kg). In Group I (N = 6) the distal end of an 18 rom Hancock porcine-valved conduit (Model 100, Extracorporeal Inc., King of Prussia, Pa.) was sewn end to side to the distal main pulmonary artery with the use of a partially occluding vascular clamp and continuous 4-0 polypropylene suture (Fig. 1). The proximal end of the conduit was inserted by first excluding an area on the anterior wall of the right ventricle (6 by 2 em) with a continuous 2-0 polypropylene mattress suture over small strips of Teflon felt (Fig. 2). With the continuous suture drawn taut, a vertical incision was made through the excluded anterior wall of the right ventricle. The proximal end of the conduit was cut obliquely and the graft was sewn end to side to the ventriculotomy with running 4-0 polypropylene suture (Fig. 3). The original 2-0 running mattress suture and Teflon strips were removed to allow flow into the conduit. The grafts were punctured with a small needle to allow any retained air to escape. With the conduit open, the proximal pulmonary artery was occluded with the Dacron tape (Fig. 4). Cardiac outputs were obtained with the Swan-Ganz catheter and pull-back pressure tracings were obtained from the distal pulmonary artery and right ventricle before and after insertion of the conduit. Heparin was reversed and the chest was closed. In the second group (N = 6) a 21 mm Hancock porcine aortic valve was inserted into the

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Fig. 2. Anterior diagram of the heart demonstrating completed pulmonary artery anastomosis (inset) and technique for temporary exclusion of a full-thickness portion of the anterior right ventricle using running mattress suture over Teflon strips.

Fig. 3. Anterior diagram of the heart demonstrating technique for closed proximal conduit anastomosis to the temporarily excluded portion of the right ventricle.

midportionof a 19 mm externally reinforced PTFE graft (Impra, Inc., Tempe, Ariz.) (Fig. 5). The graft was inserted by the technique described earlier. The 21 mm porcine valves used in Group II included the standard sewing ring, which took up 3 to 4 mm of the diameter of the lumen (Fig. 5). As the 18 mm standard Hancock conduits used in Group I did not have a sewing ring on the valve, the actual valve orifice was comparable in the two groups.

Fig. 4. Anterior diagram of the heart demonstrating completed conduit insertion and ligation of proximal pulmonary artery.

Anticoagulants were not administered to either group postoperatively. Prophylactic antibiotics (cefamandole) were given during the procedure and for 5 days postoperatively. Right heart pressures, cardiac output measurements, and angiocardiograms were performed 3

The Journal of Thoracic and Cardiovascular Surgery

8 3 6 Brown et al.

Fig. 5. Photograft of end and side views of externally stented polytetrafluoroethylene (ES-PTFE) conduit containing Hancock-Extracorporeal porcine valve.

15 P<.09 Gradient/Cardiac output

10-.

5]-------r--

mmHg/I/min.

"DACRON 00 ES-PTFE

I

I

I

o

3 Time months

Fig. 6. Comparison of transconduit resistance (gradient/ cardiac output) in Dacron and externally stented polytetrafluoroethylene (ES-PTFE) valved conduits.

months postoperatively and the animals were put to death. The conduits were removed and postmortem gross and microscopic examinations performed as previously described." The conduits were opened longitudinally and the anastomotic suture lines were excised. Tissue sections were taken from identical sites in the Dacron and externally stented PTFE conduits as well as the valve leaflets themselves. The thickness of the neointimal peel was measured proximal and distal (within 1 em of the stent or sewing ring) to the porcine valve. Four histologic measurements were obtained with the micrometer eyepiece and averaged. The valve leaf-

lets were sectioned in each group and evaluated for fibrous thickening. Hemodynamic parameters and conduit neointimal thickness were measured for both groups with statistically significant differences assessed by two-way analysis of variance with unequal replication. All animals involved in this study were housed in a licensed kennel and were under the daily care of a board-eertified veterinarian. Each animal received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health (NIH publication #80-32, revised 1978). Results All 12 animals survived the 3 month follow-up period. No animal required reoperation and no graft or wound infections were observed. The neointimal thickness and transconduit resistance (calculated by dividing the transconduit gradient by the cardiac output) are shown in Table I. Fig. 6 compares the transconduit resistances and demonstrates no significant difference between groups (p < 0.09). The measured thickness of the neointimal lining of the conduits is compared in Fig. 7 and shows a fourfold thicker peel in the Dacron valved conduits than in the

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December, 1985

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Table I. Conduit resistance (GjCO) and neoiniimal thickening in Dacron and ES-PTFE conduits Operation

G/CO NP

I

At 3 rna

ES-PTFE conduit (N = 6) 9.93 ± 1.83 6.5 ± 5.55 156 ± 50

Dacron valved conduit (N

G/CO NP P Value

7.75 ± 1.71 <0.09

= 6)

4.41 ± 1.3 609 ± 144 <0.09 resistance <0.01 NP thickness

Legend: ES-PTFE, Externally stented polytetrafluoroethylene. CO, Cardiac output (L'rnin). G, Transconduit gradient (mm Hg). NP, Neointimal peel thickness (,,). Each value is expressed as mean ± standard error of the mean.

externally stented PTFE conduits (p
Discussion Nonvalved conduits to establish continuity between the right ventricle and pulmonary artery in children with complex heart disease were first used by Klinner and Zenker' (1963) and by Rastelli and associates' (1964) for pulmonary atresia. Since that time, repair of other complex lesions, including transposition of the great arteries, truncus arteriosus, double-outlet right ventricle, tetralogy of Fallot, and others, has been made possible with conduits." An aortic homograft with an integral valve was first used to establish RV-PA continuity by Ross and Somerville' in 1966. Bowman, Hancock, and Malm,? in 1973, first introduced the use of a porcine heterograft valve in a woven Dacron tube to bypass complex right heart obstruction. Concomitant with right heart conduit applications, we" and others":" introduced valved conduits for complex left ventricular outflow obstruction. The porcine valve--containing Dacron conduits soon dominated aortic homograft usage in this country because homograft conduits were not commercially available and were frequently difficult to obtain. The Mayo Clinic reported early calcification

600

Ci)

z 0 a:

500

0

!

(J) (J)

w

400

Z

ll::

0

...J: oJ

300

0w z

200

< ~ i= z

100

DACRON

ES-PTFE

Fig. 7. Comparison of neointimal thickness (microns) in Dacron and ES-PTFE valved conduits.

and proximal anastomotic angulation of homograft aortic conduits necessitating replacement in 28% of patients at 5 years and 59% at 10 years." The early results with Dacron valved conduits seemed quite good with the probability of reoperation for obstruction being 6% at 5 years." Soon after these early encouraging results, however, failures with the Dacron valved conduits began appearing. Neointimal proliferative obstruction and heterograft valve degeneration were leading causes of obstruction. Several centers reported this disturbing obstructive neointimal peel, which was maximal in thickness proximal and distal to the heterograft valve.9-14.21.22 In 1981, Agarwal and associates" outlined potential sites and mechanisms of conduit stenosis, including (1) extrinsic compression by the sternum, (2) obstructive proximal anastomosis, (3) valvular stenosis, (4) fibrous neointimal peel, and (5) conduits that were not of adequate size. In 1982, Agarwal and colleagues reported a carefully analyzed operative and autopsy series and showed a 62% incidence of obstructive neointimal formation in their large series of explanted conduits. They postulated that conduit neointimallining separated from the woven graft and that hematoma formed between the neointima and the graft and caused luminal narrowing. They also observed heterograft valve

8 3 8 Brown et ai.

Fig. 8. Photomicrographs comparing intimal thickness (intimal peel, IP ) in externally stented polytetrafluoroethylene (ES-PTFE) conduit (A and B) and Dacron valved conduit (C and D). A, Low-magnification (XIO) view of ES-PTFE conduit showing minimal intimal peel. B. Close-up of boxed area in A (xlOO) showing a thin fibrous intima. C, Low-power (X 10) view of Dacron valved conduit showing very thick intimal peel. D, Close-up of boxed area in C (XlOO) showing thick fibrous intima. (Hematoxylin and eosin stains, reduced 28%).

degeneration in about a third of their explanted clinical conduits. Schaff and co-workers" from the Mayo Clinic recently reported the world's largest clinical experience with RV-PA conduits. In their early experience, reported by McGoon and colleagues," they used aortic homografts that were freeze stored and antibiotic sterilized and observed a 28% 5 year and 59% 10 year reoperation rate because of homograft obstruction. They then switched to the porcine-valved Dacron conduits, which initially seemed better than homografts with only a 6% 5 year incidence of reoperation for obstruction. Schaff and

associates" reported the first 100 reoperations for obstructed Dacron conduits and stated that calcification of the homograft or heterograft valve was noted in 85 of 100 patients and contributed to the conduit obstruction in 71. Most patients had multiple areas of obstruction. The porcine valve was the major cause for obstruction in approximately one third of their patients. They further reported that an exuberant fibrous peel contributed to proximal and distal conduit obstruction in most patients with Dacron conduits. Several other clinical series have corroborated these findings.":" We have had a long interest in the left ventricular-

Volume 90 Number 6 December, 1985

aortic application of valved external conduits and observed that neointimal hyperplasia did not develop in either experimental animals or patients when the same Dacron valved conduits were used for left heart obstruction. 15• 24-28 We 16• 29 subsequently set out to study acquired right heart conduit obstruction in an animal model and concluded and published the following: (1) Neointimal hyperplasia in an RV-PA valved Dacron conduit develops relatively more quickly (3 to 6 months) in the dog than in man. (2) Neointimal distribution and gross and histologic appearance are identical to that of published reports of clinical Dacron valved conduits. (3) Neointimal hyperplasia develops in a similar location and to the same degree irrespective of the type of valve (tissue versus mechanical) in the right heart conduit. (4) A thick neointimal peel doesnot form in the woven Dacron graft if the valve is omitted. (5) No hemodynamic differences were noted between valved and nonvalved Dacron conduits in animals with normal pulmonary vascular resistance. We postulated that the thick neointima seen in Dacron valved conduits was a result of continuous accumulation of thrombus because of the relatively low-pressure phasic flow through the right heart. The omission of the valve allowed a to-and-fro washing motion that retarded the neointimal buildup on valveless conduits. Dacron has a long history of satisfactory performance in the arterial system, but it has not performed well as a venous replacement.v" In a previous series of experiments, we used various graft materials to replace the thoracic and abdominal vena cava of dogs. We compared knitted and woven Dacron with externally stented and nonstented PTFE and compared these prostheses with autogenous vein. We determined that externally stented PTFE had a patency rate better than that of any prosthesis yet reported and similar to that of autogenous vein. It was also significantly superior to PTFE that was not externally reinforced. We surmised that the external stenting prevented compression of the grafts by the positivepressure environment of the abdomen and the variable pressure in the thorax. We also believed that the stenting maintained the circular lumen throughout the graft and this kept the resistance to flow through the graft at a minimum. 30. 31 On the basis of these venous replacement studies, we postulated that externally stented PTFE might offer promise for right heart conduits. In the current study, wehave compared Dacron and externally stented PTFE right heart conduits of equal length and of similar caliber containing the same porcine valve. All conduits wereimplanted by the same investigators using the same technique. This study demonstrated two important dif-

Externally stented PTFE valved conduits

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ferences betweengroups: (1) The neointimal peel formation on externally stented PTFE was only one fourth of that on woven Dacron during the study period and (2) the porcine heterograft valves showed less evidence of dysfunction and degeneration in externally stented PTFE conduits. It appeared grossly that the neointimal peel that forms on Dacron migrates retrogradely into the sinuses of the porcine valve, limiting their mobility. The organized thrombosis that develops in the cusps of the valve may initiate an inflammatory reaction that may eventually lead to calcification. In the externally stented PTFE conduit the neointima remained thin and there was no tendency for the motion of the cusps to be inhibited. Longer follow-up of externally stented PTFE conduits is being conducted to see if these favorable characteristics continue. As we" have previously reported, right-sided Dacron conduits without valves are compatible with long-term good results when the pulmonary vascular resistance is low. When pulmonary vascular resistance is elevated, a valve is essential to prevent postoperative right-heart failure. This study demonstrated that externally stented PTFE valved conduits did not develop the disturbingly thick neointimal peel that OCCurs in woven Dacron valved conduits. Although no hemodynamic differences could be demonstrated in this short period of follow-up, the porcine heterograft valve grossly appeared better preserved in the externally stented PTFE conduits, largely becauseof the lack of intimal peel migration into the cusps of the valve. The external support on the PTFE graft allowed it to negotiate the angles of implantation without kinking and would have lessened the chances for compression by the chest wall. The heterograft valve will undoubtedly degenerate with time, although its durability in the right heart is far superior to its durability in the left heart." Prevention of neointimal peel migration into the valve cusps by using externally stented PTFE may further improve heterograft valve durability. Recently introduced mechanical valves with potentially better hemodynamics and lower thromboembolic rates are being evaluated in externally stented PTFE conduits in our laboratory and may offer an attractive alternative to heterograft-valved conduits. This experimental study demonstrates that right heart conduits constructed of externally stented PTFE offer distinct advantages over Dacron valved conduits and warrant careful clinical trial. The Dacron valved conduits and porcine aortic valves were provided by Extracorporeal Laboratories (Hancock), King of Prussia, Pennsylvania. The externally stented polytetrafluoroethylene grafts were provided by Irnpra, Inc., Tempe, Arizona.

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8 40 Brown et al.

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The skilled secretarial assistance of Ms. Geri French and Mrs. Norma Hazelwood is gratefully acknowledged. 15

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REFERENCES Klinner W, Zenker R: Experience with correction of Fallot's tetralogy in 178 cases. Surgery 57:353-357, 1965 Rastelli GC, Ongley PA, David GD, Kirklin JW: Surgical repair for pulmonary valve atresia with coronary-pulmonary artery failure. Report of case. Mayo Clin Proc 40:521-527, 1965 Ross DN, Somerville J: Correction of pulmonary atresia with a homograft aortic valve. Lancet 2:1446-1447, 1966 McGoon DC, Rastelli GC, Ongley PA: An operation for the correction of truncus arteriosus. JAMA 205:69-73, 1968 Rastelli GC: A new approach to "anatomic" repair of transposition of the great arteries. Mayo Clin Proc 44:112, 1969 Rastelli GC, McGoon DC, Wallace RB: Anatomic correction of transposition of the great arteries with ventricular septal defect and subpulmonary stenosis. J THORAC CARD10VASC SURG 58:545-551, 1969 Bowman FO, Hancock WD, Maim JR: A valve-containing Dacron prosthesis. Its use in restoring pulmonary artery-right ventricular continuity. Arch Surg 107:724728, 1973 Di Carlo D, de Leval MR, Stark J: "Fresh," antibiotic sterilized aortic homografts in extracardiac valved conduits. Long-term results. Thorac Cardiovasc Surg 32: 1014, 1984 McGoon DC, Danielson GK, Puga FJ, Ritter DG, Mair DD, Ilstrup DM: Late results after extracardiac conduit repair for congenital cardiac defects. Am J Cardiol 49:1741-1749,1982 Agarwal KC, Edwards WD, Feldt RH, Danielson GK, Puga FJ, McGoon DC: Clinicopathological correlates of obstructed right-sided porcine-valved extracardiac conduits. J THORAC CARDIOVASC SURG 81:591-601, 1981 Agarwal KC, Edwards WD, Feldt RH, Danielson GK, Puga FJ, McGoon DC: Pathogenesis of nonobstructive fibrous peels in right-sided porcine-valved extracardiac conduits. J THORAC CARDIOVASC SURG 83:584-589, 1982 Miller DC, Stinson EB, Oyer PE, Billingham ME, Pitlock PT, Reitz BA, Jamieson SW, Baumgartner WA, Shumway NE: The durability of porcine xenograft valves and conduits in children. Circulation 66:Suppl 1:172-185, 1982 Yergesslich KA, Gersony WM, Steeg CN, Hordof AJ, Bowman FO Jr, Maim JR, Krongrad E: Postoperative assessment of porcine-valved right ventricular-pulmonary artery conduits. Am J Cardiol 53:202-205, 1984 Stewart S, Manning J, Alexson C, Harris P: The Hancock external valved conduit. A dichotomy between late clinical

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results and late cardiac catheterization findings. J THORAe CARDIOVASC SURG 86:562-569, 1983 Brown JW, Myerowitz PD, Cann MS, McIntosh CL, Morrow AG: Apical-aortic anastomosis. A method for relief of diffuse left ventricular outflow obstruction. Surg Forum 25:147-149,1974 Fiore AC, Peigh PS, Robison RJ, Giant MD, King H, Brown JW: Valved and nonvalved right ventricularpulmonary arterial extracardiac conduits. J THORAC CAR. D10VASC SURG 86:490-497, 1983 Bernhard WF, Poirier Y, La Farge CG: Relief of congenital obstruction to left ventricular outflow with a ventricular-aortic prosthesis. J THORAC CARDIOVASC SURG 69:223229, 1975 Cooley DA, Norman JC, Mullins CE, Groce RR: Left ventricle to abdominal aorta conduits for relief of aortic stenosis. Cardiovasc Dis Bull Texas Heart Inst 2:376-383, 1975 Dembitsky WP, Weldon CS: Clinical experience with the use of a valve-bearing conduit to construct a second left ventricular outflow tract in cases of unresectable intraventricular obstruction. Ann Surg 184:317-323, 1976 Moodie DS, Mair DD, Fulton RE, Wallace RB, Danielson GK, McGoon DC: Aortic homograft obstruction. J THORAC CARDIOVASC SURG 72:553-561, 1976 Bailey WW, Kirklin JW, Bargeron LM Jr, Pacifico AD, Kouchoukos NT: Late results with synthetic valved external conduits from venous ventricle to pulmonary arteries. Circulation 56:Suppl 2:73, 1977 Ciaravella JM Jr, McGoon DC, Danielson GK, Wallace RB, Mair DD, Illstrup DM: Experience with the extracardiac conduit. J THORAC CARDIOVASC SURG 78:920-930, 1979 Schaff HY, Di Donato RM, Danielson GK, Puga FJ, Ritter DG, Edwards WD, McGoon DC: Reoperation for obstructed pulmonary ventricle-pulmonary artery conduits. J THORAC CARDIOVASC SURG 88:334-343, 1984 Brown JW, Salles CA, Kirsh MM: Extraanatomical bypass of the aortic root. An experimental technique. Ann Thorac Surg 24:433-438, 1977 Brown JW, Kirsh MM: Technique for insertion of apicoaortic conduit. J THORAC CARDIOVASC SURG 76:90-92, 1978 Brown JW, Dunn JM, Brymer JF, Kirsh MM: Simultaneous treatment of aortic stenosis and coarctation by left thoracotomy with apical aortic conduit. Ann Thorac Surg 25:364-367, 1978 Rocchini A, Brown JW, Crowley DC, Girod E, Behrendt D, Rosenthal A: Clinical and hemodynamic follow-up of left ventricular to aortic conduits in patients with aortic stenosis. J Am Coli Cardioll:1l35-1143, 1983 Brown JW, Girod DA, Hurwitz RA, Caldwell RL, Rocchini AP, Behrendt DM, Kirsh MM: Apicoaortic valved conduits for complex left ventricular outflow obstruction. Technical considerations and current status. Ann Thorac Surg 38:162-168, 1984 Fiore AC, Peigh PS, Sears NG, Deschner WP, Brown

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JW: The prevention of extracardiac conduit obstruction. An experimental study. J Surg Res 34:463-472, 1983 30 Robison RJ, Peigh PS, Fiore AC, Deschner WP, Sears NJ, Whitaker JS, King H, Brown JW: Venous prostheses. Improved patency with external stents. J Surg Res 36:306-

311, 1984 31 Fiore AC, Brown JW, Cromartie RS, Ofstein LC, Peigh PS, Sears NJ, Deschner WP, King H: Prosthetic replacement for the thoracic vena cava. J THoRAc CARDIOVASC SURG 84:560-568, 1982 32 Dunn JM: Porcine valve durability in children. Ann Thorac Surg 32:357-368, 1981

Discussion DR. GUILLERMO KREUTZER Buenos Aires, Argentina

None of the available valved conduits has any growth potential and all tend to deteriorate. Although autologous pericardium has been shown to shrink when used in relation to atrial pressures, it has been widely used in the right ventricular outflow tract and even in the aorta, without evidence of shrinkage. My colleague Dr. Schlichter' has developed the idea of an autologous pericardial valved conduit. From June, 1983, to December, 1984, seven patients have been subjected to total repair of their malformations with a valved extracardiac conduit constructed solely with autologous pericardium. [Slide) This is a diagram with sizes for the construction of a 14 mm conduit. The pericardial trapezoid is superimposed on the rectangle, 3 mm from the distal end. Sutures are then placed from A and A' to D and D' and from C to D and D'. The three dotted areas are resected. The conduit is closed over a Hegar dilator. Tailoring of the conduit requires a mean time of 35 minutes, and it is prepared by one surgical team while another one continues with the surgical procedure. Four infants aged 3 to 5 months with truncus arteriosus and three children aged 6 to 8 years with complete or corrected transposition, ventricular septal defect, and subpulmonary stenosis were treated with these pericardial grafts. The diameters of the conduits were 12 mm in one, 14 mm in three, and 20 mm in the older patients. The six survivors were followed up for from 4 months to 2 years postoperatively. No pulmonary valve incompetence was noted. In the two hemodynamic restudies no gradients were demonstrated across the valve. Certainly these valves could become incompetent in the long term, but the patients will have had the benefit of valve competence during the early postoperative period. Although these conduits have to be followed up for a longer period of time, they compare favorably to the available grafts, as they may have growth potential and would not have to be changed" even when used in small infants. REFERENCE Schlichter AJ, Kreutzer GO: Autologous pericardial valved conduit. Rev Latina Card Inf 1:43-48, 1985

Externally stented PTFE valved conduits 8 4 1

DR. ROBERT M. SADE Charleston. S. C.

In 1978 I operated on a l-day-old infant and did a PTFE (Gore-Tex) graft shunt on the left side for pulmonary atresia with absent main pulmonary artery and ventricular septal defect. The shunt failed 3 years later and 1 did another one on the other side. Three months ago, 1 repaired his severe pectus excavatum, and 2 weeks ago I reopened his chest to do a complete repair of pulmonary atresia. At the time of the original operation for pectus, I could not see the ventricles because they were all the way to the left side of the chest and they were tightly covered by the left chest wall, where the cartilages were deformed. After the pectus was repaired, however, exposure of the right ventricle was good. Following repair of the ventricular septal defect, I inserted a graft, which was specially manufactured for us by W. L. Gore & Associates, Inc., between the right ventricle and pulmonary artery. This graft is a 20 mm externally stented graft of a type that is manufactured in smaller sizes, up to 16 mm. However, we thought 16 mm would be too small for this boy for a permanent repair, so we asked W. L. Gore to manufacture a 20 mm graft. I removed two rings at the pulmonary end of the graft and found the suture line was easy to construct. At the ventricular end of the graft, I cut a large bevel, 50% of which was into the ringed segment of the graft, and then removed 1 em from each ring at the edge of the bevel. This left a very nice suturing edge available to sew.to the right ventriculotomy. The purpose of using an externally stented graft for this child was that the anteroposterior diameter of the chest was still extremely narrow despite the pectus repair, and we were afraid that an ordinary graft would be obstructed. The chest wall closed over the graft with no difficulty, however, and there was no hemodynamic change. The graft remained fully open and was circular in its cross section. The child's right ventricular pressure following this repair was 40 mm Hg and he has done very well hemodynamically. I would like to congratulate Dr. Brown and his colleagues on their excellent continuing series of investigations of cardiac conduits. Besides the thinner neointimal peal that they found, another advantage of the external stent may be prevention of conduit compression by chest wall in some cases in which this complication could be very difficult to prevent otherwise. DR. BROWN (Closing) I would like to thank Dr. Kreutzer and Dr. Sade for their interesting comments. I found Dr. Kreutzer's conduit a very interesting one and one that I would like to compare with the other RV-PA conduits we have tested with our laboratory model. I would worry about the lack of external support, as Dr. Sade mentioned, and the significant risk of sternal compression that was seen in the early heterograft experience for right ventricular outflow reconstruction. Dr. Sade's interesting case report brings to light a very important aspect of external stenting. His technique prevents conduit compression and maintains the circular lumen. The resistance through a circular lumen is much less than that of any other shape.