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J Thorac Cardiovasc Surg 2009;137:362-370
© 2009 The American Association for Thoracic Surgery
Congenital Heart Disease |
a King Faisal Heart Institute, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
b Labatt Family Heart Center, the Hospital for Sick Children and the University of Toronto, Toronto, Ontario, Canada
Received for publication May 6, 2008; revisions received September 9, 2008; accepted for publication October 9, 2008. * Address for reprints: Bahaaldin Alsoufi, MD, King Faisal Heart Institute (MBC 16), King Faisal Specialist Hospital and Research Center, PO Box 3354, Riyadh, Saudi Arabia 11211. (Email: balsoufi{at}hotmail.com).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionConclusionsFigure E1Figure E2Figure E3Figure E4Figure E5Figure E6Figure E7Figure E8Table E1References |
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Methods: From 1983 to 2004, 346 children underwent aortic valve replacement (215 underwent the Ross procedure and 131 underwent placement of a mechanical prosthesis). Factors associated with procedure choice were used to construct a propensity score for use as a covariate in regression models to adjust for potential confounding by indication.
Results: Patients undergoing the Ross procedure were younger, more likely to have a congenital cause, and less likely to have a rheumatic or connective tissue cause. They had a lower frequency of regurgitation, required more annular enlargement, and had less concomitant cardiac surgery. Competing-risk analysis showed that 16 years after aortic valve replacement, 20% of patients had died without subsequent aortic valve replacement, 25% underwent second aortic valve replacement, and 55% remained alive without further replacement. After propensity adjustment, factors associated with early-phase death included mechanical valves and a nonrheumatic cause. Mechanical valves were also associated with constant-phase mortality. Repeated aortic valve replacement was associated with the Ross procedure and a rheumatic cause. Both factors were also associated with all-cause cardiac reoperation. In children receiving mechanical prostheses, younger age and smaller valve size were significant risk factors for death. Freedom from homograft replacement after the Ross procedure was 82% at 16 years of follow-up.
Conclusion: Results from this study showed good outcomes and an acceptable complication rate with both valve choices. Given the significantly increased risk of early and late death in younger children receiving smaller mechanical valves, the Ross procedure confers survival advantage in this age group at the expense of increased reoperation risk, especially in patients with a rheumatic cause.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsFigure E1Figure E2Figure E3Figure E4Figure E5Figure E6Figure E7Figure E8Table E1References |
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Aortic valve disease is common in children and frequently requires intervention. Congenital aortic valve disease is the most common pathology in North America and is encountered in approximately 5% of children with congenital heart disease.1-3
Although the incidence of rheumatic valve disease has significantly decreased in the Western world, it remains a major cause of aortic valvulopathy in developing countries.4 Several developments in interventional cardiology allow for early treatment of congenital aortic stenosis, and recent experience with aortic valve repair techniques showed encouraging short-term and midterm results in both congenital and rheumatic valve disease.5-8 Nonetheless, in patients with significant valve destruction or after repair or intervention failure, aortic valve replacement (AVR) is required. AVR in children is associated with several challenges. Although many replacement options are available, all alternatives have several limitations.2,3,9-13 AVR with a mechanical prosthesis and the Ross procedure using pulmonary autografts are the most commonly used valve substitutes in children. Mechanical valves in children are associated with increased frequency of complications, including morbidity related to long-term anticoagulation, deterioration of ventricular function caused by the development of patient–prosthesis mismatch as the child outgrows the initial valve, and the need for subsequent prosthetic valve replacement.2,3,11-13 On the other hand, although the Ross procedure has growth potential and does not require long-term anticoagulation, the procedure is technically demanding, and late autograft failure, aortic root dilatation, and homograft reoperations are common.2-4,14-25
Although several case series exist in the literature reporting outcomes after AVR in children, only a few offered comparisons between different valve options. We aimed to review a large single-institution experience with AVR in children and to compare indications and outcomes of children undergoing mechanical valve replacement with those of children undergoing the Ross procedure while adjusting for potential confounding by indication.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsFigure E1Figure E2Figure E3Figure E4Figure E5Figure E6Figure E7Figure E8Table E1References |
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Operative Details
Detailed steps of the surgical intervention will not be discussed in this section; however, some important information will be briefly listed.4 Midline sternotomy was performed, and standard cardiopulmonary bypass and myocardial protection techniques were used in all cases. For AVR with a mechanical prosthesis, the valve was secured to the annulus with multiple mattressed sutures, with the pledgets placed at the ventricular aspect of the annulus. For the Ross procedure, the pulmonary autograft was implanted as a full root, with coronary transfer in all cases. The autograft muscle cuff was trimmed with sutures placed almost directly at the autograft annulus. The proximal suture line was performed with running polypropylene sutures. The neoaortic annulus was not reinforced in these patients, so as not to limit growth. In patients with left ventricular outflow tract (LVOT) obstruction, a modified Ross–Konno technique was used. Part of the septum was cored out to completely open up the LVOT without creating a large ventricular septal defect. In those patients the fibrous annulus of the aortic valve was often divided, and the cut was partially taken down to the septum. In our current practice, in patients with a dilated aortic annulus of greater than 29 to 30 mm or with an aortic annulus 2 to 3 mm larger than the pulmonary valve annulus, the Ross procedure is not considered, and we rarely use any aortic annulus reduction techniques. The distal suture line was occasionally reinforced with Teflon felt in patients with a dilated ascending aorta.
The immediate postoperative results were assessed in all patients in the operating room by means of transesophageal echocardiographic analysis.
Follow-up
Patients were evaluated clinically and by means of detailed echocardiographic analysis on discharge, 6 weeks after the operation, at 6 months, and yearly thereafter. Patients with mechanical valves were started on intravenous heparin, maintaining the partial thromboplastin time ratio at between 1.5 and 2 times that of baseline. In addition, all patients received oral sodium warfarin, aiming to maintain an international normalized ratio within the range of 2.0 to 3.0. Subsequent to hospital discharge, anticoagulation was followed by specialized local anticoagulation clinics with established monitoring protocols.
Late outcomes were determined from recent office visits at King Faisal Specialist Hospital and Research Center or from direct correspondence with patients' families. The median follow-up duration was 6.3 years and was longer for patients who received a mechanical prosthesis (8.3 years; range, up to 22.9 years) versus those who underwent the Ross procedure (5.7 years; range, up to 16.4 years; P = .01).
Statistical Analysis
Data are presented as means with standard deviations, medians with minimums and maximums, and frequencies, as appropriate. Differences in patients' characteristics were calculated by using Student's t tests with the Sattertwaite correction and the Fisher's exact test. Time-dependent outcomes after AVR were parametrically modeled by using up to 3 phases of risk (early, constant, and late) as necessary. Competing-risk analysis was performed to model the probability over time of each of 3 mutually exclusive end points: death, valve reoperation, and alive and free from reoperation. Non–time-dependent outcomes were modeled in logistic regression models.
To correct for confounding by indication in the procedure assignment (mechanical valve placement or the Ross procedure), a propensity score was created, modeling the probability of every patient to be assigned to the mechanical valve procedure over the Ross procedure based on patient demographics and medical characteristics. Variable selection was based on univariate differences between groups (a priori), with backward selection in the logistic multivariable equation to obtain the final model. A total of 8 variables were selected (7 of them statistically significant in the model) for an events-per-variable value of 16.4 (see Table E1). The model was highly statistically significant (P < .0001) and had excellent discriminatory power (c-statistic = 0.883). There was no colinearity between variables, and no interaction criteria were included. There was very limited overlap between propensity scores in both groups, and therefore we used it as a covariate in statistical models. Differences in outcomes between the patients who had a mechanical valve procedure or the Ross procedure are reported in the form of hazard/odds ratios for event if the patient has a mechanical valve procedure instead of the Ross procedure in both propensity-unadjusted models and propensity-adjusted models.
Variables other than aortic valve type, potentially affecting the likelihood of mortality and reoperation, including sex, year of operation, age at operation, cause, pathology, previous operations, preoperative catheter intervention, concomitant cardiac operation, and LVOT enlargement, were included in a multivariable stepwise model (P < .05 to enter) along with aortic valve type. Backward selection was used to obtain final models for all individual phases of risk for both outcomes. Finally, procedure-specific variables (mechanical valve size, homograft size, homograft preservation [fresh or cryopreserved], and homograft type [pulmonary or aortic]) were modeled individually in each phase of risk for both mortality and reoperation. The clinical relevance of covariates found to influence outcomes was established through stratification analysis.
All statistical analyses were performed with SAS statistical software version 9.1 (SAS Institute, Inc, Cary, NC).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsFigure E1Figure E2Figure E3Figure E4Figure E5Figure E6Figure E7Figure E8Table E1References |
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Before AVR, 20 (6%) patients had undergone percutaneous aortic valve interventions, and 97 (28%) patients had undergone surgical intervention to address aortic valve lesions, other cardiac lesions, or both. Patients' demographic and operative characteristics at the time of AVR are listed in Table 1 .
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The most commonly used mechanical prosthesis was Carbomedics (Austin, Tex; n = 123), followed by St Jude (St Paul, Minn; n = 8). Mean mechanical valve size was 22.1 ± 2.5 mm. The mean pulmonary homograft size used for reconstruction of the right ventricular outflow tract (RVOT) in the Ross procedure was 22.7 ± 2.4 mm. Fresh homografts were used in 52% of patients undergoing the Ross procedure, whereas cryopreserved homografts were used in 48%. Pulmonary homografts were used in 83% of patients undergoing the Ross procedure, whereas 17% received aortic homografts. Homografts were not generally matched for the blood group of the patients.
Factors Associated with the Choice of Ross Procedure Versus Mechanical AVR
The Ross procedure was introduced at our institution in 1990, and since then, it has become the most common procedure performed for AVR in children. AVR with a mechanical prosthesis has been used at our institution since the beginning of this study period in 1983. Female patients were found to be more likely to undergo a Ross procedure than to receive a mechanical prosthesis. Children who underwent the Ross procedure were younger, presented in more recent years, and were more likely to have a congenital cause, preoperative stenosis, or mixed aortic disease. Patients who had a mechanical valve placed were older, presented in earlier years, and were more likely to have a rheumatic or connective tissue cause and preoperative aortic regurgitation and to have undergone concomitant cardiac surgery. Arch repair was somewhat more likely in the mechanical valve group, whereas concomitant LVOT enlargement was more likely in the Ross procedure group. In patients undergoing the Ross procedure, concomitant surgical intervention was mainly mitral valve repair (n = 39) in addition to a few cases of ventricular septal defect closure, coronary artery bypass grafting, and pulmonary angioplasty. On the other hand, concomitant surgical intervention in patients receiving a mechanical aortic prosthesis included mitral valve replacement (n = 71), mitral valve repair (n = 7), tricuspid valve repair (n = 16), tricuspid valve replacement (n = 1), aortic root replacement (n = 8), and right ventricle–pulmonary artery conduit change (n = 5). The frequency of previous cardiac operation was similar between groups (Table 1).
Competing Risk Analysis for Death or Subsequent Prosthesis Replacement After Initial AVR
After the 346 initial AVRs, 36 patients had their valves subsequently replaced, and 32 patients died without a further AVR, including 13 (3.7%) operative deaths. The hazard function for time-related transition to a second AVR was characterized by the presence of a late hazard phase that steadily increases as years since surgical intervention progressed (see Figure E1). The hazard function for time-related transition to death without a second AVR was characterized by an early hazard phase with a high level of risk in the immediate postoperative period and a constant hazard phase indicating a continuous attrition rate over time (see Figure E2). The competing risks for the 2 events showed that at 16 years after AVR, approximately 20% of patients have died, 25% have undergone a second aortic valve reoperation, and 55% are alive and free from aortic reoperation (see Figure E3).
Factors Associated with Mortality
There were 13 (3.7%) operative deaths: 5 (2.3%) in patients undergoing the Ross procedure and 8 (6.1%) in patients receiving a mechanical prosthesis. Furthermore, there were 19 additional deaths during the follow-up duration; all were of patients who received a mechanical prosthesis. Factors associated with higher risk of death after initial AVR were sought, and results are shown in Table 2
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An effect of younger age on increased early-phase mortality was seen in children undergoing AVR with a mechanical prosthesis but neutralized in those undergoing the Ross procedure, as seen in the predictive model shown in Figure 1 . Moreover, smaller mechanical valve prosthesis size, strongly linked to age at initial AVR, was associated with constant-phase mortality (hazard ratio, 1.5/mm; 95% confidence interval, 1.2–1.9; P = .0007; see Figure E4).
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Unadjusted risk analysis showed that variables linked to aortic valve reoperation included undergoing the Ross procedure, underlying rheumatic cause, and concomitant cardiac surgery. In addition, placement of a small prosthesis was associated with increased risk for aortic valve reoperation in children who received a mechanical prosthesis (hazard ratio, 1.5/mm; 95% confidence interval, 1.2–3.9; P = .05).
In propensity-adjusted analysis the Ross procedure was strongly linked with late-phase reoperation risk (PE, 2.5 ± 0.5; P < .0001), as shown in Figure 3 . Additionally, underlying rheumatic pathology was an important risk factor for late subsequent aortic valve reoperation (PE, 2.1 ± 0.6; P = .0006; see Figure E5). This effect was more apparent in patients who underwent a Ross operation compared with those who received a mechanical prosthesis (Figure 4 ). We analyzed whether the hemodynamic manifestation before initial AVR was a contributing factor to valve reoperation, especially in patients with a rheumatic cause undergoing the Ross procedure. The presence of pure regurgitation, stenosis, or mixed disease did not significantly influence subsequent reoperation (see Figure E6).
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Functional Status and Additional Late Morbidity
At the most recent follow-up, the majority of survivors (91%) had normal clinical exercise ability and were in New York Heart Association functional class I. There was no significant difference in the number of patients in New York Heart Association class greater than 1 between those undergoing the Ross procedure (8%) and mechanical valve recipients (13%).
For patients who underwent the Ross procedure, 16-year freedom from homograft reoperation was 82% (Figure E8). Homograft reoperation was not influenced by the type of conduit.
Although there was an apparent increase in valve-related morbidity in children who received mechanical prostheses, that difference did not reach statistical significance because of the limited numbers of documented valve-related morbid events. All anticoagulation-related and thromboembolic complications were obviously in patients who received a mechanical prosthesis: bleeding (n = 3), valve thrombosis (n = 2), and embolization (n = 2). There were 3 episodes of endocarditis, all requiring reoperation and aortic valve rereplacement: 2 were after the Ross procedure and 1 was after mechanical valve replacement.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsFigure E1Figure E2Figure E3Figure E4Figure E5Figure E6Figure E7Figure E8Table E1References |
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Factors Associated with the Choice of Ross Procedure Versus Mechanical Valve
The primary objective of this study was to determine the effect of AVR choice on survival and reoperation in children with aortic valve disease. However, examination of the data revealed important differences between these 2 patient groups. Patients undergoing replacement with a mechanical valve were more likely to have associated cardiac diseases requiring concomitant cardiac surgery and more likely to have a rheumatic or connective tissue cause. Children undergoing the Ross procedure, on the other hand, were younger, more likely to have congenital valve disease, or more likely to require enlargement of the LVOT. Many of those variables can influence mortality and reoperation risk. The disparity of characteristics of patients undergoing the Ross procedure versus mechanical valve placement decreases the usefulness of unadjusted comparison. Propensity-adjusted analysis allows fair comparison to determine the effect of procedure type on short- and long-term outcomes.
Mortality Risk
Several variables were found to significantly increase the risk of mortality. Mechanical valves were associated with early- and constant- phase mortality. This is in line with other reports indicating an operative survival advantage for the Ross procedure over mechanical valve placement.2,3 Despite surgical complexity, the Ross procedure is safe in experienced hands. In our series mortality was 2.3%, which is similar to the data from the International Registry for the Ross Procedure (2.5%) compared with 6.1% for mechanical valves.
Despite high association with concomitant cardiac and multivalvular surgery, early mortality after AVR for a rheumatic cause was less than 1% compared with 7% for other causes.
Younger age was found to be significant in unadjusted analysis. The effect of age was neutralized in patients undergoing the Ross procedure but remained important in the mechanical prosthesis group. Operative mortality for patients younger than 5 years in our study was 50% for mechanical valves, whereas it was less than 4% for the Ross procedure. Additionally, the need for LVOT enlargement (Ross–Konno procedure) was not associated with a significant increase in operative mortality (6%). In children less than 2 years of age, our experience with the Ross procedure remains limited to 10 patients with 1 operative death.
More importantly, survival was stable for the Ross procedure, with no late mortality compared with 19 additional cardiac-related deaths in the mechanical prosthesis group. Many of those deaths were sudden in nature, highlighting the delicate problem of compliance with the anticoagulation regimen and its implication on patients' lifestyle that is especially difficult to control in children and young adults. Despite having well-established anticoagulation protocols and follow-up within specialized anticoagulation clinics in Saudi Arabia, educational and social factors might influence compliance with the anticoagulation protocol, and therefore these late outcomes might differ in the Western world compared with those seen in other countries. On the other hand, several other publications from North America and Europe similarly reveal a steady attrition rate in children who have received mechanical prostheses, indicating that this anticoagulation problem in children remains true in developed countries.2,3,11-13
Reoperation Risk
The Ross procedure was a risk factor for aortic valve reoperation and overall cardiac reoperations. There were 28 children thus far who have required AVR at a median of 2.8 years after the Ross procedure. Twenty-seven of those patients who had a rheumatic cause, and 26 had pure aortic regurgitation preoperatively. We have previously reported higher autograft reoperation rates in rheumatic patients compared with those with other causes.4,5 The mode of failure in our series included aortic root dilatation and cusp elongation and prolapse in 46%, recurrent rheumatic disease in 25%, an inflammatory process that is likely recurrent rheumatic disease in 18%, aneurysm formation in 7%, and endocarditis in 4%. We have previously identified risk factors for autograft failure, and those include active rheumatic heart disease, concomitant severe rheumatic mitral regurgitation, pure regurgitation with severe dilatation of the LVOT greater than 29 mm, or discrepancy between the LVOT and RVOT of greater than 2 to 3 mm in favor of the LVOT.5 By adhering to new selection criteria and avoiding patients with the above listed risk factors and by adapting surgical modifications, such as careful trimming of the muscle rim under the autograft and suturing close to the annulus because this muscle rim might dilate and contribute to future failure and occasional reinforcement of the dilated sinotubular junction, we expect that we will be encountering less instances of autograft failures in patients with a rheumatic cause. Since adopting those changes in 1999, only 2 patients with a rheumatic cause required autograft change. Despite a relatively shorter follow-up period, this finding is encouraging considering that most failures were previously evident in the first 2 to 3 years after surgical intervention.
Concerns of pulmonary autograft dilatation have stimulated recent developments in surgical strategies to address late root dilatation. Most recently, inspired by a technique that was previously used in mitral valve replacement with a pulmonary autograft, Slater and colleagues26 described a modified pulmonary autograft implantation procedure in which the pulmonary autograft was encased in a Dacron tube to prevent future dilatation. They suggested that this procedure can be applied to fully grown children and young adults and reported excellent short-term results with respect to autograft valve function and lack of dilatation of the annulus or sinotubular junction.26
Implications on Clinical Practice Internationally
Our patient population is different from that in published reports from the Western world because of the high percentage of rheumatic valve disease. Nonetheless, important information can be obtained from our analysis to help in the difficult decision of AVR strategy in children.
In the Western world the prevalence of rheumatic valve disease is much less, and the majority of patients undergoing AVR have underlying congenital pathology. Children with congenital aortic valve disease might require surgical intervention at an early age and have small annuluses requiring LVOT enlargement. Based on our analysis, the Ross procedure confers survival advantage in this population because mortality risk is low in experienced centers, and some risk factors for mortality are neutralized in this population compared with mechanical valves, in which younger age and smaller prostheses remain important risk factors for early and late death. Similarly, freedom from autograft reoperation in patients without a rheumatic cause after the Ross procedure was high, and therefore the projected autograft longevity in Western series is longer. Into the bargain, mortality risk during valve reoperation in the current era is low, and valve-preserving root replacement techniques in cases associated with root dilatation and autograft regurgitation have been described, which might increase valve longevity despite aortic wall reintervention.27
RVOT reoperation remains a concern in patients after the Ross procedure. Again, mortality risk during RVOT reintervention is low, and recent advances with percutaneous pulmonary valve replacement might allow cardiologists to address this problem without surgical intervention.28 The immediate and short-term results of percutaneous pulmonary valve implantation are very encouraging, and these procedures were recently performed at our institution in patients after the Ross procedure with excellent immediate results.27 The perceived additional advantages of the Ross procedure in children, such as improved survival, the avoidance of anticoagulation-related morbidity, the ability to match somatic growth, and the concern of anticoagulation during pregnancy in female patients, might encourage surgeons to consider the Ross procedure in children as the aortic valve substitute of choice despite RVOT reintervention incidence.
Study Limitations
The present report is a retrospective analysis of patients from a single institution with diverse anatomy who underwent an operation during a 22-year time span. Despite the use of a comprehensive set of variables in all analyses, unmeasured covariates might have contributed to disparate outcomes in the recipient populations. In addition, this study addresses survival and reoperation after AVR in children but does not examine the effect of prosthesis type on cardiac hemodynamics, left ventricular recovery, and ventricular and aortic root dimensions.
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Conclusions |
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Figure E1 |
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Figure E2 |
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Figure E3 |
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Figure E4 |
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Figure E5 |
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Figure E6 |
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Figure E7 |
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Figure E8 |
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Table E1 |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsFigure E1Figure E2Figure E3Figure E4Figure E5Figure E6Figure E7Figure E8Table E1References |
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SE, Standard error.
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