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Ann Thorac Surg 1999;68:521-525
© 1999 The Society of Thoracic Surgeons

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Original Articles

Intermediate-term results in pediatric aortic valve replacement

^a Division of Cardiothoracic Surgery, Department of Surgery, Seattle, Washington USA
^b Division of Pediatric Cardiology, Department of Pediatrics, Children’s Hospital and Regional Medical Center and the University of Washington, Seattle, Washington, USA

Address reprint requests to Dr Lupinetti, Children’s Hospital and Regional Medical Center, 4800 Sand Point Way NE, Seattle, WA 98105
e-mail: mlupin{at}chmc.org

Presented at the Thirty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan. 25–27, 1999.

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. Aortic valve replacement (AVR) in children is now more commonly performed with human tissue valves.

Methods. The results of 100 consecutive pediatric AVRs (50 mechanical, 50 human) were reviewed.

Results. There were five perioperative deaths in the mechanical group and one in the human group (p = 0.2). Late complications in the mechanical group included 4 late deaths, 2 cases of endocarditis, 3 thromboembolic complications, and 10 reoperations on the aortic valve. In the human group, there were no late deaths, 2 reoperations for allograft aortic valve deterioration (both in Marfan’s patients), and 1 reoperation for allograft pulmonary valve stenosis. Four-year actuarial survival was 83% in the mechanical group and 98% in the human group (p = 0.02). Four-year actuarial survival free of all valve-related complications was 61% in the mechanical group and 88% in the human group (p = 0.008).

Conclusions. Human valves in children requiring AVR provide superior intermediate-term survival and freedom from valve-related complications compared to mechanical valves. Marfan’s syndrome may represent a rare remaining contraindication for human AVR in children.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
Aortic valve replacement (AVR) in children has undergone substantial evolution with the widespread application of human tissue substitutes. Allograft aortic valves and pulmonary valve autografts (the Ross procedure) are thought to be superior to the mechanical valves most commonly used in an earlier era. Both allografts and autografts provide better hemodynamics, freedom from anticoagulation, and resistance to thrombosis and infection [1–7]. Autografts offer the additional benefit of growth [8]. Although a technically more demanding procedure than implantation of a prosthetic valve, AVR with human tissues has been accomplished in many centers with little or no operative mortality.

The long-term results of AVR with human valves are less certain. One important difficulty in proving the superiority of human tissues is the heterogeneity of patients undergoing the operation. Particularly in high-risk situations, the patient, rather than the device, may be the primary determinant of the outcome [9]. Selective use of autografts and allografts for better risk patients can create a bias that makes the results of prosthetic valve replacements appear to be even more unsatisfactory. Short of a large, randomized trial, with the attendant ethical problems, it may be challenging to achieve a fair comparison of human and prosthetic AVR.

The recent experience of this institution with pediatric AVR was analyzed. Because of a change in surgical approach, there was a unique opportunity to compare mechanical to human AVR in a comprehensive, unselected fashion. The immediate and intermediate-term results of 100 consecutive AVRs during 11 years were reviewed, and all perioperative and late postoperative events were investigated.

	Material and methods

Top Abstract Introduction Material and methods Results Comment References

 
The results of 100 consecutive AVRs performed at Children’s Hospital and Regional Medical Center from January 1, 1987, through April 30, 1998, were reviewed. Demographic information, operative details, and late postoperative data were obtained from the medical record. Late follow-up was established from clinic records, including echocardiographic data and catheterization findings when available and from personal communication with the patients, families, and referring physicians.

Fifty of the 100 operations were performed with mechanical valves manufactured by St. Jude Medical (St. Paul, MN) or Carbomedics (Austin, TX), and 50 were performed with human valves, either autografts (37) or aortic or pulmonary valve allografts (13). Until 1994, all AVRs were performed with mechanical valves. Beginning in 1994, with a change in surgical staff and approach, human valves were used. In 1996, there was a single patient who required a mechanical AVR. Otherwise, these groups consist of 50 consecutive mechanical and 50 consecutive human AVR. Within the human AVR group, the autograft, or Ross procedure, was performed whenever technically possible. Technical limitations that precluded use of the pulmonary autograft are shown in Table 1.

All human AVRs were performed as root replacements with implantation of coronary arteries onto the autograft or allograft. Four human valve recipients required Konno-Rastan root enlargements, and 1 required aortic root reduction. Concomitant operations were performed in 9 patients, consisting of allograft pulmonary valve replacements (other than as part of the Ross procedure) in 5, mitral valve repair in 2, repeat mitral valve replacement with a St. Jude valve in 1, and aortic arch replacement (for Marfan’s syndrome) in 1. Reconstruction of the right ventricular outflow tract in autograft recipients was performed using pulmonary valve allografts in 35 patients and aortic valve allografts in 2. All right ventricular outflow tract reconstructions were performed after myocardial perfusion was resumed to reduce the duration of myocardial ischemia.

Group mean values, standard deviations, and 70% confidence limits were calculated. Standard definitions were used for reporting postoperative valve-related complications [10]. Results were recorded and analyzed with StatView statistical software (Abacus Concepts, Berkeley, CA). Fisher’s exact test was used for contingency table analyses. Survival curves were constructed and analyses of statistical significance were performed using the Mantel-Cox log rank test. Logistic regression was used to evaluate risk factors for the late development of left ventricular outflow tract obstruction. A p value less than 0.05 was considered significant.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
The age of the patients undergoing mechanical AVR ranged from 1 to 20 years, with a mean age of 12.1 ± 4.6 years. The age of the patients undergoing human AVR ranged from 1 to 22 years with a mean age of 10.4 ± 6.0 years (p = 0.1). The weight of the patients undergoing mechanical AVR ranged from 6.2 to 110 kg (mean, 46.8 ± 24.6 kg), compared to a range of 8.9 to 82.9 kg in the human group (mean, 38.9 ± 22.9 kg; p = 0.1).

Previous operations that were performed on these patients before their immediate AVR are shown in Table 2. There were 31 recipients of mechanical AVR who had at least one previous operation (6 patients had two operations), and there were 37 operations altogether. Seven of these previous operations were AVRs. In the human AVR group, 38 patients had at least one operation (8 patients underwent two operations and 5 patients had three operations), and there were 56 operations in all. Ten human AVR recipients had previously undergone a mechanical AVR, and 6 of these AVRs were performed with a Konno-Rastan ventriculoplasty. In addition, there were 8 patients in the human group who had undergone a percutaneous balloon aortic valvotomy, but no surgical procedure.

There were five perioperative deaths in the mechanical AVR group (10%; 70% confidence limit, 6% to 36%) and one death in the human group (2%; 70% confidence limit, 0.3% to 26%). This difference in operative mortality was not statistically significant (p = 0.2 by Fisher’s exact test). Perioperative complications included three strokes, one in the mechanical group and two in the human group. The two strokes in the human valve group occurred in patients with previously implanted mechanical valves. Each of these patients had a history of a previous stroke. In both patients, the strokes were mild and have responded to rehabilitation. There were 5 patients who developed complete heart block after valve replacement and required insertion of permanent pacemakers; 3 of these patients had received a mechanical valve and 2 had received an autograft.

Follow-up in the mechanical group was from 1 to 142 months, with a mean follow-up of 65 months. Follow-up was 82% complete, and 11 patients have been lost to follow-up. Follow-up in the human valve group was 5 to 55 months, with a mean follow-up of 30 months. Follow-up was 100% complete.

Late complications in the mechanical group included 4 late deaths, 2 cases of endocarditis, 3 thromboembolic complications (2 strokes and 1 valve thrombosis), and 12 cases of nonstructural degeneration (1 paravalvular leak causing hemolysis and 11 cases of left ventricular outflow obstruction). There were 10 reoperations on the aortic valve. There were no cases of anticoagulant-related hemorrhage.

In the human group, there were no late deaths and no cases of endocarditis, thromboembolic complications, or hemolysis. Three human AVR recipients required reoperations: 2 of these were for Marfan’s syndrome patients with annuloaortic ectasia who had undergone root replacement with aortic valve allografts. One developed severe aortic and left ventricular dilatation and underwent mechanical AVR (the only mechanical AVR performed out of sequence in this series). The other Marfan’s patient developed allograft stenosis and underwent repeat allograft AVR with excellent results. The third reoperation in the human AVR group occurred in an autograft recipient who developed late stenosis of his pulmonary valve allograft and underwent replacement with a new allograft.

The late development of left ventricular outflow obstruction, defined as peak transvalvar gradients exceeding 50 mm Hg, as demonstrated by cardiac catheterization or echocardiography, was encountered in 11 patients in the mechanical group. This resulted in reoperations in 7 patients. In the remaining 4 patients, reoperation is anticipated, but has not yet been performed. Logistic regression analysis (Table 3 ) demonstrated that the risk of late development of left ventricular outflow obstruction was significantly related to younger patient age (p = 0.01), lower patient body weight (p = 0.01), and smaller valve diameter (p = 0.04).

View larger version (11K): [in this window] [in a new window]   Fig 1. Actuarial patient survival, including operative mortality.

View larger version (11K): [in this window] [in a new window]   Fig 2. Actuarial patient survival free of any cardiac reoperation, including operative mortality.

View larger version (11K): [in this window] [in a new window]   Fig 3. Actuarial patient survival free of all valve-related complications, including operative mortality.

	Comment

Top Abstract Introduction Material and methods Results Comment References

A major obstacle to the demonstration of survival benefits of a particular valve replacement device is the difficulty in assuring comparability among patient groups. It is generally recognized that selection of good-risk patients can create an erroneously favorable impression of a valve substitute, and that higher risk patients may have poorer outcomes regardless of the quality of the tissue or prosthesis that they receive [9]. It is unlikely that human and mechanical valves will ever be evaluated in a randomized trial, the gold standard of clinical comparison. The ethical problems in allowing randomization of patients to receive a valve substitute most surgeons consider inferior would make such a trial problematic. Furthermore, there would probably be great difficulties encountered with obtaining informed consent and accruing adequate numbers of patients. Therefore, claims of benefits resulting from a particular valve must be scrutinized carefully to assure proper statistical analyses, adequate duration of follow-up, and absence (or at least appropriate recognition) of confounding variables.

This series of children undergoing AVR offers a rare opportunity for comparison of valve replacement strategies. Because the transition within this institution from mechanical to human valves was instantaneous and nearly complete, patient selection was not a factor. Throughout the period of study, the cardiologists referring patients for AVR and their indications for operation remained relatively constant. Anesthesiology, operating room, and intensive care unit procedures and personnel were also not substantially altered. Furthermore, close analysis of the patients, their original cardiac anatomy, and previous surgical history shows that the human AVR recipients were at least as complicated and of as high or higher risk than the mechanical group. It must be acknowledged that there is potential for disparity whenever noncontemporaneous groups are compared. The latter group must be regarded as potentially benefiting from some change, however subtle, in patient management. Duration of follow-up alone may bias results against an earlier group, although it is hoped that actuarial analyses reduce the likelihood of this error. Despite these caveats, the survival advantage of human AVR appears quite compelling. In addition to showing a survival advantage, the human valve recipients in this series were significantly less likely to have valve-related complications. Previous reports of children undergoing the Ross procedure have described freedom from reoperation on the autograft of 90% at 8 years [2] and 68% at 15 years [1].

The most common nonfatal late problem in the mechanical valve group was important left ventricular outflow obstruction. This problem affected 11 patients in this series and led to reoperation in 7. "Important" obstruction was defined in this series as a gradient exceeding 50 mm Hg, a number selected as a common indication for operation or reoperation in left ventricular outflow obstructive disease. The nature of this obstruction was quite consistent. All of the mechanical AVR patients who underwent reoperation for recurrent obstruction had pannus formation on the ventricular side of the prosthetic valve. This pannus did not impair motion of the prosthetic valve leaflets. It did, however, create a cylindrical impediment to left ventricular ejection. Such obstruction has never been encountered in the human valve recipients in the current series, and has rarely been described elsewhere. Other series have found that freedom from left ventricular outflow obstruction after the Ross procedure in children is as high as 89% after 8 years [2].

The experience in this and other institutions supports the use of the Ross procedure as the preferred approach for AVR in children. Previous experience at this institution has shown that autografts provide better results than allografts, as evidenced by more significant improvement in left ventricular wall thickness and lower outflow tract velocity [15]. Although these advantages are known to persist for only a short time, it is likely that the long-term advantages of the autograft over the allograft will eventually be demonstrable as well. There are situations, however, when the Ross procedure is not possible, usually due to congenital absence or deformity or due to previous surgical interventions that make autograft retrieval impossible. In these patients, aortic valve allografts would appear to be the preferred substitute, as they may provide results nearly as good as those obtained with autografts [1]. A recent randomized trial including both children and adults found equally good short-term results with autografts and allografts [7]. Thus, it would seem that mechanical valves in the aortic position should almost never be used in children.

A possible exception is the patient with Marfan’s syndrome and annuloaortic ectasia. The literature does not describe the use of the pulmonary valve autograft in such patients, presumably because the pulmonary valve is assumed to have the same pathology as the aortic valve. It should be noted, however, that pulmonary valves and arteries in Marfan’s patients have not been characterized as thoroughly as have aortic tissues [16]. The children with Marfan’s syndrome undergoing AVR in this series both initially received aortic allograft valves. Because both patients required reoperations, it is difficult to include such patients in a more sweeping recommendation that children receive human valves in all cases. The use of allografts for AVR in Marfan’s patients has not been widely described, and the few reports of allograft AVR in Marfan’s patients show less than ideal results [17, 18]. The aortic valve-sparing techniques as described by David and Feindel [19] may offer the best hope for a long-term solution for Marfan’s patients who have little or no attenuation of the aortic valve leaflets. We have applied those methods to our more recent Marfan’s patients instead of replacing the valve and have obtained excellent short-term results.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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