Ann Thorac Surg 1997;64:154-158
© 1997 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Fate of Trileaflet Equine Pericardial Extracardiac Conduit Used for the Correction of Anomalies Having Pulmonic Ventricle–Pulmonary Arterial Discontinuity
Makoto Ando, MD,
Yasuharu Imai, MD,
Yoshinori Takanashi, MD,
Shuichi Hoshino, MD,
Kazuhiro Seo, MD,
Masatsugu Terada, MD
The Heart Institute of Japan, Tokyo Women's Medical College, Tokyo, Japan
Accepted for publication January 27, 1997.
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Abstract
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Background. External conduits used for the repair of congenital heart diseases having discontinuity between the pulmonic ventricle and the pulmonary artery still carries a high risk of reoperation. Between June 1983 and June 1992, handmade equine pericardial conduit with fabricated trileaflet valve had been the conduit of choice in our institute. The aim of this study is to clarify the temporal sequence of conduit obstruction in this material and to formulate the optimal surgical strategies for this disease entity.
Methods. One hundred forty-three patients have undergone extracardiac conduit repair using this conduit. Postoperative catheterization performed within 2 months showed pulmonary to systemic ventricular systolic pressure ratio of 0.57 ± 0.17 with the pressure gradient between pulmonic ventricle and pulmonary artery of 21.1 ± 17.2 mm Hg. In 63 patients among the survivors, a series of Doppler two-dimensional echocardiographic images could be clearly obtained.
Results. Moderate-to-severe degree of pulmonary insufficiency represented only 3.2% of all cases within 3 months, which rapidly increased to 14.3% at 1 to 3 years and 32.8% at 3 to 5 years. However, the rate of increase of pulmonary insufficiency diminished beyond 5 years with 34.9% at 5 to 7 years and 40.0% at 7 to 9 years. Estimated pressure gradient calculated by Bernoulli's equation applied in the same patient subset was 4.1 ± 7.9 mm Hg within 3 months, which progressively increased to 7.1 ± 11.8 mm Hg at 1 to 3 years, 21.0 ± 24.0 mm Hg at 3 to 5 years, 40.2 ± 25.9 mm Hg at 5 to 7 years, and 71.3 ± 34.0 mm Hg at 7 to 9 years. Among patients with a pressure gradient across the conduit of more than 40 mm Hg at follow-up catheterization, the primary cause of the obstruction was attributed to degeneration of the valve in 7 patients, whereas sternal compression was strongly suspected as the primary cause in the other 8 patients. Intimal peel was not obvious in the excised specimens.
Conclusions. Degeneration of the valve in the equine pericardial conduit became prominent at 3 to 5 years after the operation, whereas the pressure gradient across the conduit continued to progress thereafter. A thick and hardened valve from degeneration and varying degrees of external compression by the sternum were delineated at the site of stenosis.
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Introduction
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See also page 158.
External conduit repair (ECR) for the repair of congenital heart diseases having discontinuity between the pulmonic ventricle and the pulmonary artery still carries a high risk of developing late obstruction of the conduit requiring reoperation. Reasons for this phenomenon include degeneration or calcification of the integrated valve, intimal peel formation on the graft lumen, compression by the bony thorax, and other factors. Various types of conduit materials used for the ECR have failed to overcome these problems and the ideal one has not yet been developed.
From the late 1970s to the early 1980s, porcine valved Dacron conduits had been used in many institutes, including our own from 1978 to 1982, and provided for ready-made prosthesis that might have been favorable for this type of repair. However, disappointing results with this conduit led to the conclusion that alternative conduit material should be sought [1–6]. After the era of the porcine valved Dacron conduit, the mainstream for this repair has employed a cryopreserved aortic or pulmonary allograft.
The conduit of choice in our institute from 1983 to 1992, however, was the handmade trileaflet valved equine pericardial conduit. The initial experience with this material revealed satisfactory performance but subsequently failed to show a significant difference in late outcome among short-term survivors from the Hancock conduit. Event (late death, reoperation, and infective endocarditis) free curve in this material showed rapid decrease from 84% to 54% from 8 through 12 years [7].
The aim of this report is to clarify the functional significance of the trileaflet valve and the temporal sequence of conduit obstruction in the equine pericardial conduit, and thereby attempt to formulate the optimal surgical strategy for this patient subset.
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Materials and Methods
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Between June 1983 and June 1992, 143 patients underwent ECR using an equine pericardial conduit bearing a trileaflet valve. The conduit was handmade using equine pericardium preserved in glutaraldehyde (Xenomedica; Baxter, Chicago, IL). Three pieces of the same material, in the shape of semilunar cusps, were sutured to the internal lumen of the conduit to create a trileaflet valve. The maximum diameter of the conduit was determined according to the patient size and the configuration of the pulmonary artery, ranging from 12 to 35 mm (median, 22 mm). Mean age at operation was 7.6 ± 5.8 years. Cardiac anomalies included pulmonary atresia with ventricular septal defect in 32, pulmonary atresia with ventricular septal defect with major aortopulmonary collateral arteries in 31, complete transposition of the great arteries with pulmonary stenosis in 29, truncus arteriosus in 19, atrioventricular discordance in 17, double-outlet right ventricle in 11, tetralogy of Fallot with associated coronary anomalies in 1, and miscellaneous anomalies in 3. In patients with atrioventricular discordance, double-switch operation was introduced in 1990 consisting of atrial switch combined with reconstruction of right ventricle to pulmonary artery either by inserting an equine pericardial conduit or approximating the pulmonary artery directly to the right ventricular incision. In the earlier series of atrioventricular discordance, conventional repair using a porcine valved Dacron external conduit connecting the apex of the morphological left ventricle to the pulmonary artery was used. Mean follow-up period was 5.95 ± 2.62 years.
The survivors were followed up periodically with echocardiography. Among them, a series of Doppler two-dimensional echocardiographic images could be clearly obtained in 63 patients. The initial study was done within 3 months with subsequent repeat echocardiography. The rest of patients were eliminated from this study because of poor records of the echocardiogram. Pulmonary insufficiency found at Doppler echocardiographic investigation was divided into three grades: trace-to-mild, mild-to-moderate (regurgitation flow image confined within the conduit), and moderate-to-severe (regurgitation flow image extending into the sinus portion of the pulmonary ventricle). In the same patient subset, Doppler interrogation was applied to detect the maximal flow velocity (v) across the conduit. The pressure gradient (PG) at the point was estimated by the maximal flow velocity according to Bernoulli's equation (PG = 4 v2).
Descriptive expression of the data include mean ± standard deviation for continuous variables and median value for discontinuous variables. Statistical analysis was made by paired Student's t test where appropriate for continuous and Wilcoxon's signed rank test for categoric variables.
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Results
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Early deaths within 30 days were seen in 9 patients (6.3%) and late deaths in 17 (12.7%). On catheterization performed within 2 months after ECR, systolic pressure ratio of pulmonary to systemic ventricle was 0.57 ± 0.17 with the pressure gradient between pulmonic ventricle and pulmonary artery of 21.1 ± 17.2 mm Hg. Replacement of the conduit was indicated in 6 patients with the interval from ECR ranging from 47 to 95 months (mean, 66.8 ± 18.7 months), yielding an incidence of 0.8 times per 100 patient-years.
The grades of pulmonary insufficiency observed in 63 patients are illustrated in Fig 1
. On control data obtained within 3 months after ECR, the trace-to-mild degree of regurgitation was detected in 60.3% of all patients with the moderate-to-severe regurgitation in only 3.2%. However, significant deterioration of the valve was observed at 1 to 3 years with moderate-to-severe regurgitation in 14.3% of all cases, which increased to 32.8% at 3 to 5 years, 34.9% at 5 to 7 years, and 40.0% at 7 to 9 years. Estimated pressure gradient calculated by Bernoulli's equation applied in the same patient subset is illustrated in Fig 2A. Pressure gradient observed within 3 months was 4.1 ± 7.9 mm Hg, which progressively increased to 7.1 ± 11.8 mm Hg at 1 to 3 years, 21.0 ± 24.0 mm Hg at 3 to 5 years, 40.2 ± 25.9 mm Hg at 5 to 7 years, and 71.3 ± 34.0 mm Hg at 7 to 9 years.
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Fig 2. . (A) Time-related changes of maximum pressure gradient at conduit portion in 63 patients on echocardiographic investigation. The mean value in each period is listed below. Comparative analysis with the data obtained within 3 months in each individual yields the p value. (B) Time-related changes of pressure gradient across the conduit on cardiac catheterization in 31 patients (representing 21.7% of all cases).
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Late follow-up catheterizations were done in 31 patients, and is summarized in Table 1 together with initial catheterization data. The time-related changes in pressure gradient across the conduit in serially studied patients is illustrated in Fig 2B
. In this patient group, a pressure gradient across the conduit of more than 40 mm Hg was defined as severe conduit stenosis. In 8 patients, angiography suggested that the principle cause of obstruction was the sternal compression of the conduit (Fig 3).
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Fig 3. . Right ventriculograms in 15 patients who had pressure gradient across the conduit of more than 40 mm Hg. (A) Stenosis occurred predominantly at the valve attachment site (arrow) with minor contribution of sternal compression (n = 7). Although the portion adherent to the sternum seemed widely patent, turbulent flow occurring at this site may induce the injury at the subvalvular portion and thus contribute to the degeneration of the valve structure. (B) The compressive effect of the sternum superimposes on the adjacent sclerotic valve (arrows), thus multiplying the obstruction of the lumen (n = 6). (C) Bony thorax tightly compresses the conduit structure (arrows) although the valve maintained apparent pliability (n = 2).
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Comment
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There have been several reports dealing with late outcome of ECR for the establishment of pulmonic ventricle to pulmonary arterial continuity, and a disturbing incidence of need for reoperation has been reported regardless of the conduit material. From the late 1970s to early 1980s, the commercially available Dacron conduit with integrated porcine valve (mainly Hancock conduit) was used in many institutes and various reports dealing with its late outcome have been published in later years [1–6]. Within these reports, the emphasis has been on the conduit's shortcomings, including excessive intimal hypertrophy (intimal peel formation) caused by the incomplete anchoring of the neointima to the graft [9], degenerative tendency of the porcine valve associated with augmented thickness of the intimal peel [10], and other problems. Eventually, in the mid 1980s, the porcine-valved Dacron graft was considered unsuitable for ECR and gave way to alternative materials, namely, the cryopreserved allograft. However, long-term outcome of the allograft conduit has been recently clarified and proved to be somewhat disappointing [11, 12]. From 1976, we used the Hancock Dacron graft and have observed almost the same late outcome events as those described in other reports.
Since 1983, equine pericardial conduit bearing a trileaflet valve has been introduced in our institute as an alternative for the Hancock conduit. Pliability and ease of handling of this material allowed the construction of a conduit with a morphologically preferable configuration. Restricted availability of the allograft in our country also prompted us to use this pericardial tube. Early results of this conduit material were satisfactory regarding valve function, freedom from obstruction, and preservation of ventricular function. However, actuarial survival rates among short-term survivors in valved Dacron conduit and valved equine pericardial conduit were 87.5% and 88.7% at 10 years, respectively, yielding no significant difference in durability of these two conduits [7].
Agarwal and coworkers [13] mentioned that major stenosis affecting the porcine-valved Dacron conduit occurred in the valve alone in 38%, graft alone (predominantly caused by intimal thickening) in 31%, and both graft and valve in 31% of patients. Intimal peel formation was not prominent in the excised specimens of the valved equine pericardial conduit at explantation. This may be attributed to the difference of the anchoring of the neointima onto the equine pericardium compared to the Dacron graft.
We focused on the time-related changes of the valve that progressively became fixed in the semiclosed position because of degeneration or calcification showing the general pattern seen in the glutaraldehyde fixed material, eventually causing stenosis together with pulmonary insufficiency. According to our echocardiographic data, the moderate-to-severe degree of pulmonary insufficiency occurs in only 3.2% of patients within 3 months, which increased rapidly to 14.3% at 1 to 3 years and 32.8% at 3 to 5 years. However, the rate of increase in pulmonary insufficiency diminished beyond 5 years with 34.9% at 5 to 7 years and 40.0% at 7 to 9 years. In contrast, obstruction continued to increase with time, both on echocardiography and cardiac catheterization. It is suggested that the patients' growth is related to the increasing obstruction. Our particular interest is in the patient subset with atrioventricular discordance who underwent ECR with a Hancock Dacron conduit from left ventricular apex to central pulmonary artery coursing through the right pleural cavity, thus avoiding sternal compression; only 1 of 23 patients required conduit replacement for the stenosis at the bifurcated graft for the nonconfluent pulmonary artery [7]. According to the angiographic findings in patients who had developed severe conduit stenosis, some had apparently well functioning valves and a low incidence of valvular stenosis. In these patients, the common finding was that the space between the outflow tract of pulmonic ventricle and the sternum was narrowed and the conduit was compressed. This finding was prominent at the point just distal to the site where the conduit arises perpendicularly from the ventricular incision, which shows the inherent property of the ECR regardless of the conduit material.
Vouhe and colleagues [14] reported the comparative study of Rastelli and LeCompte procedures, which share a common concept with our current preference of the establishment of direct continuity between right ventricle and pulmonary artery for the same patient subset [15]. The combination of residual outflow tract and acquired obstruction was significantly higher in the Rastelli group, but was attributed to the growth potential of the LeCompte procedure [14]. However, we postulate that redirection of the pulmonary outflow tract by the effect of straightening the posterior floor owing to tension created by the approximated pulmonary artery (Fig 4), which eliminates the compression by the sternum, has great impact on the late outcome besides growth potential.
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Fig 4. . Representative right ventriculogram in patients with pulmonary atresia with ventricular septal defect undergoing direct approximation of the pulmonary trunk to the right ventriculotomy at reoperation for obstructed extracardiac conduit. (A) Before reoperation. (B) After reoperation. The floor of the outflow is directed toward the posterosuperior direction by the effect of retraction by the approximated pulmonary artery (arrows), allowing a generous-sized outflow tract to be reconstructed.
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In summary, hardening of the valve mounted in the equine pericardial conduit became prominent at 3 to 5 years after the operation, whereas the pressure gradient across the conduit continued to progress thereafter. Intimal peel formation was not obvious at reoperation and seemed to have less contribution to the conduit stenosis. A thick and hardened valve from degeneration and varying degrees of external compression by the sternum were delineated at the site of stenosis.
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Footnotes
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Address reprint requests to Dr Ando, Department of Pediatric Cardiovascular Surgery, The Heart Institute of Japan, Tokyo Women's Medical College, 8-1 Kawaka-Cho, Shinjuku-Ku, Tokyo, 162 Japan.
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References
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Abstract
Introduction
