Asian Cardiovasc Thorac Ann 2004;12:285-290
© 2004 Asia Publishing EXchange Ltd
Growth of Pulmonary Autograft After Ross Operation in Pediatric Patients
Shahzad G Raja, MRCS,
Marco Pozzi, FECTS
Department of Pediatric Cardiothoracic Surgery, Alder Hey Hospital, Liverpool, UK
For reprint information contact: Shahzad G Raja, MRCS Tel: 44 151 252 5635 Fax: 44 151 252 5643 Email: drrajashahzad{at}hotmail.com Department of Pediatric Cardiothoracic Surgery, Alder Hey Hospital (Royal Liverpool Children’s NHS Trust), Eaton Road, Liverpool L12 2AP, UK.
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ABSTRACT
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The Ross procedure is being used increasingly to treat aortic valve disease in pediatric patients; however, there is an ongoing dispute about the durability of the autograft. From November 1996 to September 2003, 32 pediatric patients (mean age, 11 ± 4.5 years) underwent the Ross procedure for various aortic valve diseases, using the root replacement technique. Clinical and echocardiographic follow-up was performed early (within 30 days), at 3 to 6 months, and yearly after surgery. There were no perioperative deaths. The patients were followed-up for up to 7 years with a median interval of 36 months. Actuarial survival at 7 years was 96% ± 3% and there was 100% freedom from re-operation for autograft valve dysfunction or any other cause. The autograft annulus and sinus increased significantly in size during follow-up and the increase in size paralleled the increase in body surface area, with no evidence of disproportional dilatation. The hemodynamics at the latest follow-up were also similar to those at the time of discharge after surgery. Pulmonary autograft replacement of the aortic valve appears to be the ideal solution in pediatric patients, because of relatively low operative risk, excellent late valve function, and real potential for growth.
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INTRODUCTION
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In the last decade there has been an increasing interest in replacement of the aortic valve with a pulmonary autograft in pediatric patients, according to the operative technique first described by Donald Ross in 1967.1 Clear advantages over mechanical and biological aortic prostheses have been shown. Mechanical valves require long-term anticoagulation and there is always a threat of thromboembolism or bleeding.2 Participation in some sports activity might have to be restricted owing to this threat. Porcine bioprostheses, which do not require anticoagulation, deteriorate rapidly in young patients, and have limited durability.3 Although allografts offer excellent postoperative hemodynamics, do not require anticoagulation, and are associated with a low incidence of thromboembolic phenomena, they also have a high failure rate when implanted in the very young.4 Because of the continued growth of these patients, multiple valve replacements are a major issue. The use of a pulmonary autograft for aortic valve replacement has emerged as an attractive option as it eliminates most of these problems. After the Ross procedure, patients do not require anticoagulation, and the autograft has been shown to be durable and to grow in proportion to somatic growth.5,6 This means that the growing child can have a normal and active lifestyle. The purpose of this study was to review our experience with the Ross procedure in the pediatric age group and to evaluate our results with particular emphasis on pulmonary autograft growth in relation to somatic growth.
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PATIENTS AND METHODS
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All patients less than 18 years of age who underwent the Ross procedure between November 1996 and September 2003 were included in this study. Medical records and charts were reviewed for demographic data, original anatomic diagnoses, prior interventions, and details of the operative procedure, including technical data. The perioperative course and follow-up data were reviewed for conduction abnormalities and arrhythmias, duration of ventilation, neurological sequelae, and other postoperative issues and interventions. All patients underwent a detailed clinical and echocardiographic examination early (within 30 days), at 3 to 6 months, and then yearly after surgery. Thirty-two patients were included in the study. The mean age of the group was 11 ± 4.5 years at the time of surgery (range, 1.4–18 years). The frequency distribution of age at the Ross procedure is shown in Figure 1
. Demographic details, dominant valve pathology, and hemodynamic lesions are shown in Table 1. Twenty-six patients had undergone previous aortic valve interventions. One patient had balloon dilatation on 3 separate occasions, and another had balloon dilatation twice prior to the Ross procedure. Two patients had aortic valve repair prior to replacement with a pulmonary autograft; one of these needed surgery to reattach an aortic cusp which was detached following attempted balloon dilatation. Two of the children had previous surgery: for repair of coarctation of the aorta, and for a ventricular septal defect. The mean follow-up was 33.2 ± 19.1 months (median, 36 months; range, 6–82 months) and was 100% complete.
All operations were performed by the same surgeon. Standard cardiopulmonary bypass with moderate hypothermia (28°C) was used. Myocardial protection was achieved by antegrade cold blood cardioplegia at 4°C infused through the aortic root or directly into the coronary ostia. Cardioplegia infusions were repeated every 20 minutes. The left ventricle was vented through the left atrium in all cases. The aortic valve was exposed through a transverse aortotomy. This allowed excellent exposure of the valve. All patients underwent aortic root replacement with coronary reimplantation using a pulmonary autograft. In all cases, a continuous running suture technique was used. In all except two patients, there were no or only minor discrepancies between the annulus and the autograft, which were addressed during suturing of the autograft and by using a wider muscle cuff on the pulmonary artery. Plication of the annulus had to be carried out in the 2 patients with a significantly dilated annulus which was more than 3 mm larger than the autograft. A cryopreserved pulmonary homograft was used for reconstruction of the right ventricular outflow tract (RVOT) in the first 19 patients, and thereafter a Contegra (Medtronic Heart Valves, Santa Ana, CA, USA) valved conduit was used due to unavailability of the appropriately sized homograft. Reconstruction of the RVOT was undertaken before removing the aortic crossclamp. The conduit for reconstruction of the RVOT was oversized whenever possible. The perfusion data are shown in Table 2.
Early mortality was defined as any death within 30 days or during the initial hospitalization. Postoperative valve-related morbidity and mortality were evaluated and reported according to standard definitions. All patients had a clinical examination, New York Heart Association (NYHA) functional class assessment, chest radiograph, electrocardiogram, and echocardiographic assessment before discharge, at 3 to 6 months, and at yearly intervals thereafter. The echocardiographic assessment included color-flow Doppler to assess the severity of autograft insufficiency, which was graded according to the method described by Perry and colleagues.7 The peak transvalvular flow velocities were measured with continuous-wave Doppler, and peak gradients were calculated. The autograft dimensions were measured as the cross-sectional diameter at the level of the aortic annulus and the maximal diameter of the sinus. The hemodynamics across the pulmonary homograft and the Contegra conduit were also measured.
Data are presented as mean ± standard deviation (unless otherwise stated). Patient survival analysis and time-to-event analysis were performed using Kaplan-Meier methods. The paired Student’s t test was used for analysis of the differences between measurements taken after surgery and at the latest follow-up. A value of p < 0.05 was considered significant. Statistical analysis was performed using Microsoft Excel 2000 and Statistical Package for the Social Sciences version 10.0 for Windows 2000 (SPSS, Chicago, IL, USA). Cross-sectional diameters of the aortic annulus and sinuses of Valsalva were plotted against normal values for body surface area.
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RESULTS
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There were no perioperative deaths. One child died 3 years after surgery. He was brought to the accident and emergency department in a state of shock. Initial resuscitation was unsuccessful. An emergency sternotomy did not reveal any obvious cause of the clinical presentation, and the patient died despite vigorous attempts to resuscitate him. A postmortem examination failed to reveal any pathology of the valves or coronaries. Ventricular arrhythmia was suspected to be the most likely cause of death. The actuarial survival at 7 years was 96% ± 3% (Figure 2).
Conduction abnormalities and arrhythmias were the most common perioperative morbidity. One patient had transient atrial fibrillation and one had nodal rhythm that reverted back to sinus rhythm after 24 hours. Two patients had nonsustained ventricular tachycardia limited to the first 24 hours. Two patients had ventricular ectopics that responded to correction of serum potassium levels, and 3 required inotropic support in the first 12 hours after surgery that was gradually weaned off over the next 24–48 hours. One patient underwent re-operation for bleeding. Three had pneumothorax secondary to removal of the chest drain; this was managed conservatively. Two patients had pericardial effusion; 1 required aspiration under echocardiographic guidance, the other responded to conservative management with diuretics. The durations of mechanical ventilation, cardiac intensive care unit stay, and total hospital stay are shown in Table 2
. There was no early or late re-operation due to autograft valve-related events. Two patients required balloon dilatation due to homograft stenosis.
Preoperatively, 18 patients (56.3%) were in NYHA class I, 11 (34.5%) were in class II, and 3 (9.4%) were in class III. All patients were in NYHA class I at their last follow-up. Echocardiography demonstrated excellent autograft function. The peak aortic gradient which was 7.4 ± 4.0 mm Hg at the time of discharge, did not change much as it was 6.9 ± 3.9 mm Hg ( p = 0.3) at the latest follow-up (Table 3). Ten patients showed trivial and 3 had mild aortic regurgitation at the time of discharge, and the degree of regurgitation remained static on color-flow Doppler at the latest follow-up.
The patients showed significant somatic growth as evidenced by an increase in body surface area from 1.19 ± 3.8 m2 at the time of surgery to 1.37 ± 0.3 m2 ( p = 0.04) at the latest follow-up. The annulus diameter increased significantly from 19.6 ± 3.7 mm at the time of discharge after surgery to 22 ± 2.8 mm ( p < 0.004) at the latest follow-up. The sinus also increased in size from 26.1 ± 5.7 mm at the time of discharge to 29.1 ± 4.4 mm ( p < 0.004) at the last follow-up. This increase in the size of the autograft annulus and the sinus was proportional to the increase in body surface area (Figures 3 and 4). Moreover, the annulus diameter was within normal limits for body surface area after surgery and at the latest follow-up. However, the autograft sinus showed early postsurgical dilatation, with 75% of patients having a sinus size outside the 95th percentile when compared with the aortic sinus of Valsalva diameters of the normal population. Thereafter, the increase in size paralleled the increase in body surface area.
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Figure 3. Relationship of aortic annulus diameter to body surface area in early and late follow-up after the Ross procedure. After surgery, the majority of patients had an annulus size within the 95% confidence limits for the normal population and developed along the expected growth curves of normal population during follow-up.
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Figure 4. Relationship of autograft sinus of Valsalva to body surface area in early and late follow-up after the Ross procedure. There was dilatation early after surgery in more than 75% of the patients, with sinus size outside the 95% confidence limits for the normal population. During follow-up the autograft sinus showed growth parallel to the expected growth curves of the normal population.
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The pulmonary homograft, unlike the autograft, did not show any increase in size. This was reflected by a significant increase in peak gradient from 9.2 ± 3.9 mm Hg after surgery to 15.8 ± 9.5 (range, 7.8 – 49 mm Hg; p = 0.03). Two patients needed balloon dilatation for pulmonary stenosis. Another 2 patients had a pulmonary conduit gradient = 40 mm Hg. Five patients had mild and one had moderate pulmonary homograft valve insufficiency. They remained asymptomatic with normal right ventricular function and minimal dilatation of the right ventricle. None of the patients needed a re-operation because of homograft dysfunction. The Contegra conduit has been used since November 2000 for the reconstruction of RVOT in all patients undergoing Ross procedure at our institution. Early echocardiographic follow-up of this conduit has shown it to be a useful replacement for the pulmonary homograft. Three patients were diagnosed with mild regurgitation after surgery, which remained stable at the latest follow-up. The peak gradient of 11 ± 3.9 mm Hg after surgery was 12.4 ± 6.7 mm Hg at the latest follow-up ( p = 0.35).
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DISCUSSION
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The results of this study show that the Ross operation is an excellent choice for aortic valve replacement in the pediatric age group. The mortality rate of 3.1% is similar to that in prior reports.6,8–10 Moreover, this mortality rate is the same or less than that found in other series using mechanical aortic valves or aortic homografts.11–13 The most common postoperative complication was arrhythmias. This can be explained on the basis that children undergoing the Ross procedure usually have a myocardium that has been exposed to long-standing pressure and/or volume overload. The additional insult of intraoperative ischemia predisposes them to postoperative ventricular dysfunction and nonsustained ventricular or supraventricular tachycardia. The possibility of long crossclamp times contributing to arrhythmias in the immediate postoperative phase cannot be ruled out. The only late death in this series was attributed to arrhythmia, similar to the reports of Elkins and colleagues4 and Matsuki and colleagues.14 The incidence of all other early postoperative complications was the same or less than in other reports.4,8,10,14
An important finding of this study was the increase in growth of the pulmonary autograft. There was a 13% increase in the size of the autograft during follow-up. This increase paralleled the 15% increase in body-surface area during the same period. However, there was distinctly different behavior of the annulus and sinus. The annulus size was within normal limits in the majority of patients after surgery, and increased along the expected growth curves of the normal population during follow-up. In sharp contrast, the sinus showed an initial significant increase in size, which could be attributed to early postsurgical dilatation secondary to exposure to a high-pressure systemic circulation. However, thereafter the increase in size was again parallel to the normal growth curves, with no evidence of undue aneurysmal dilatation, suggesting normal growth of the autograft. This finding is similar to that previously reported by Simon and colleagues6 and Solymar and colleagues.15 Also, in our study, 10 patients had trivial and 3 had mild regurgitation after surgery and this remained stable during follow-up despite the noted dilatation. The failure of regurgitation to deteriorate with time indicates maintained valve function, which may be attributed to growth and remodeling of the valve cusps. This phenomenon of passive dilatation of the pulmonary autograft was demonstrated by Schoof and colleagues16 in their animal study. However, in clinical practice, progressive dilatation leading to significant regurgitation has been reported only in a small number of cases with the pulmonary valve placed in the systemic circulation.17,18 Since in our series we did not have any re-operations for autograft dysfunction, we are unable to prove that there was true growth. However, as the valves have remained competent over a long period we take this as indirect evidence of growth because if it was just passive dilatation there should have been decreased coaptation with the passage of time.
Another important finding of our study was the relatively stable autograft valve function in the 20 patients with a bicuspid aortic valve. The incidence of regurgitation in those with a bicuspid aortic valve (8/20) was similar to that in patients with a tricuspid aortic valve (5/12; p = 0.96). As follow-up for 7 years has not shown any unusual dilatation or valve dysfunction, based on our results at this point, we can assume that a bicuspid aortic valve does not predispose to early autograft failure. However, a longer follow-up is needed to substantiate this claim. There is a 1% to 7% incidence of re-operation for pulmonary autograft dysfunction following the Ross operation in pediatric patients, which is much less than the 36% reported for aortic valve replacement with a mechanical valve and 72% for bioprostheses in the same population.5,9,10,11 In this series, no re-operation was needed for pulmonary homograft dysfunction during follow-up, although two patients needed balloon dilatation for pulmonary stenosis. This may well be attributed to the relatively short follow-up compared with some other studies. Moreover, 10% (2/19) of patients had a gradient > 40 mm Hg across the homograft. This was relatively high compared with some of the other series, although it substantiates the claim that the right ventricular outflow tract is the predominant "weak point" of the Ross procedure.19,20 The degeneration of the homograft is speculated to be a result of the immune response.19 We believe that the pulmonary homograft, unlike the autograft, fails to adapt to increasing heart size and stroke volume, and possibly starts to degenerate early.
An additional important feature of our series was the use of the Contegra conduit for reconstruction of the RVOT. The Contegra is a biological valved conduit consisting of a glutaraldehyde-preserved heterologous bovine internal jugular vein, having a trileaflet venous valve. Since November 2000, the Contegra has been used in 13 patients at our institution. Unavailability of appropriately sized homografts prompted us to use the Contegra. We find it an attractive option for use in the Ross operation. Our choice is guided by the fact that this new conduit has provided consistently good results in the first 3 years of its use. Only 3 patients developed mild regurgitation after surgery, which was stable upon follow-up and the gradient across the valve has not shown a significant increase. In addition, excellent off-the-shelf availability, easy tailoring and suturing, a large variety of available sizes (12 to 22 mm internal diameter), no need for proximal or distal extension, and adequate hemodynamics are some of the other advantages which make the Contegra our first choice for RVOT reconstruction after the Ross operation.
The limitations of this study include the fact that it was a retrospective analysis, the cohort size was small, and the length of follow-up relatively short compared with some of the other published studies. Our 7-year experience with the Ross procedure, using the root replacement technique, has confirmed the suitability and safety of this operation for pediatric patients with aortic valve disease. It avoids anticoagulation and provides excellent hemodynamics, thus allowing an active lifestyle. There is a very low incidence of technical failure with this technique. Moreover, the pulmonary autograft in the aortic position after the Ross procedure shows normal growth along established growth curves, with an initial phase of passive dilatation in the early postoperative period.
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ABSTRACT
INTRODUCTION
