Ann Thorac Surg 2000;69:176-179
© 2000 The Society of Thoracic Surgeons
Original Articles
Preservation of the pulmonary valve complex in tetralogy of Fallot: how small is too small?
Vivek Rao, MD, PhDb,
Margit Kadletz, MDb,
Lisa K. Hornberger, MDa,
Robert M. Freedom, MDa,
Michael D. Black, MDb
a Division of Cardiology, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
b Division of Cardiovascular Surgery, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
Address reprint requests to Dr Black, Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA 94305-5407
e-mail: michael.black{at}leland.stanford.edu
Presented at the Poster Session of the Thirty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan 25–27, 1999.
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Abstract
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Background. Surgical repair of congenital lesions associated with right ventricular outflow tract obstruction frequently requires the destruction of pulmonary valve (PV) components including the valve annulus. The resultant pulmonary insufficiency may lead to late functional deterioration of right ventricular performance. Acute right ventricular dysfunction has been associated with poor pulmonary runoff, tricuspid valve regurgitation, and pulmonary hypertension. Preservation of PV competence may prevent both early and late right ventricular failure. However, the recent trend towards earlier repair of tetralogy of Fallot (TOF) may preclude preservation of the PV in favor of a transannular patch. We reviewed our experience with surgical repair of TOF to determine if age and/or body size affected the ability to repair the PV.
Methods. We reviewed the clinical records of 50 consecutive children who underwent surgical repair of TOF by one surgeon. The latter 27 patients underwent repair with an intention to preserve their pulmonary valve. In total, 28 patients underwent repair with preservation of their pulmonary valve, and form the basis of this study. Serial echocardiographic assessments were performed early (3 to 6 months) and late (12 months) after surgery.
Results. Pulmonary valve preservation was possible in the majority of children (89%) in whom it was intended. Pulmonary valve competence was observed in 68% of children, with only 5 (16%) children demonstrating severe insufficiency at follow-up. Residual right ventricular outflow tract obstruction was present in only 1 child who underwent repair with pulmonary valve preservation at greater than 2 years of age.
Conclusions. Our data suggest that earlier repair of TOF does not preclude preservation of the pulmonary valve and may indeed facilitate repair. The pulmonary valve remains competent at 12 months, with acceptable gradients, and should participate in somatic growth. Pulmonary valve preservation during repair of TOF may prevent free pulmonary insufficiency, progressive right ventricular dilation, and the need for future prosthetic pulmonary valve replacement.
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Introduction
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The increasing experience with surgery in the neonate has changed the management of several congenital heart defects [1]. Morbidity and mortality rates are extremely low, thus, medical attention is now focused on "long-term outcomes." Complete repair of tetralogy of Fallot (TOF) in the neonate is thought to require destruction of the native pulmonary valve in order to augment the size of the right ventricular outflow tract (RVOT) with a transannular patch [2]. This approach leaves the patient with free pulmonary insufficiency, which may eventually lead to right ventricular (RV) volume overload [3, 4]. Frequently, patients require prosthetic valve replacement in the pulmonary position due to symptoms of right heart failure [5]. Unfortunately, bioprosthetic valve replacement in young patients is prone to early structural valve failure, and mechanical valve replacement is avoided because of the need for permanent anticoagulation [6].
Alternatives to a transannular patch have been proposed, including a fabricated pericardial or homograft monocusp valve [7, 8]. Unfortunately, these valves have not demonstrated reliable long-term durability and have not been shown to improve early or late postoperative outcomes [7–9]. We believe that preservation of the native pulmonary valve with resection of the subvalvular pulmonic stenosis may provide the ideal repair; however, a hypoplastic annulus may result in prohibitive gradients necessitating a transannular patch. We reviewed our recent experience with primary repair of TOF to assess our ability to preserve the native pulmonary valve, especially in small infants.
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Patients and methods
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Between March 1996 and September 1998, 50 children underwent repair of tetralogy of Fallot by a single surgeon (M.D.B.) at the Hospital for Sick Children, Toronto. Among the first 18 children, 5 received a transannular patch and 7 received an autologous pericardial monocusp valve. There were 4 children who had preservation of their native pulmonary valve. Two children were treated with TOF and absent pulmonary valve. A change in surgical philosophy occurred after these first 18 children, and the latter 32 underwent repair with intention to preserve the native pulmonary valve if possible. Of these 32 children, we excluded 5 patients due to: absent pulmonary valve (n = 2), pulmonary valve endocarditis after percutaneous balloon valvotomy (n = 1), and a prior palliative Blalock shunt (n = 2). These latter 2 children presented with a hypoplastic pulmonary annulus, and extremely dysmorphic valves, likely morphological sequelae directly, related to shunt placement. Therefore, our study comprises the first 4 children in whom the pulmonary valve was preserved, in addition to the remaining 27 children who were repaired with an intention to preserve their pulmonary valve. Table 1 summarizes the preoperative demographic data for these 31 children analyzed in this report.
After initiation of cardiopulmonary bypass via ascending aortic and bicaval cannulation, the pulmonary artery was incised longitudinally from just above the annulus to approximately the branch arterial bifurcation. A "mini" infundibular incision was created on the anterior aspect of the RVOT. Inspection of the pulmonary valve and release of the frequent and diffuse subvalvular fibrosis, in combination with a pulmonary valvuloplasty via the main pulmonary arteriotomy, enabled optimal enlargement of the pulmonary valve complex. The ventricular septal defect was repaired via the right atrium. Closure of the pulmonary arteriotomy and infundibulotomy was achieved with autologous or donor human pericardium.
Two-dimensional transthoracic or transesophageal echocardiography was performed preoperatively, intraoperatively at the end of the surgical repair, 3 to 6 months after surgery, and late (12 to 15 months) after repair. Standard views were obtained at each study including an estimate of right ventricular (RV) dimensions, RV-pulmonary artery peak and mean gradients, and an assessment of valvular competence. Valvular competence was evaluated from at least two echocardiographic views and graded by a single observer (L.H.). Valvular competence was scored as 0 = no insufficiency, 1 = trivial, 2 = mild, 3 = moderate, and 4 = severe. Follow-up was obtained in September 1998 (9 ± 7 months, range 1 to 25 months) and is 100% complete.
Statistical analysis
Statistical analysis was performed using the SAS software program (SAS Institute, Cary, NC). Continuous variables are expressed as the mean ± SD. Repeated measures analysis of variance (rm-ANOVA) was employed to simultaneously evaluate the main effects of age, body surface area (BSA), weight, and time on postoperative pulmonary valve function. The correlation between age and the weight-annulus ratio was determined using the Pearson correlation coefficient. Exact p values are provided for each analysis to allow the reader to determine statistical and clinical significance.
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Results
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Pulmonary valve preservation was possible in 28 children. Of the 27 children who underwent repair with an intention to preserve the pulmonary valve, 3 children (11%) required a transannular patch due to the presence of an elongated (tunnel-like) infundibulum (n = 1) or a hypoplastic pulmonary annulus (n = 2). There were 10 children who underwent repair at less than 6 months of age, only 1 of whom required a transannular patch (10%) due to a hypoplastic pulmonary annulus. Of the 21 children who underwent repair at greater than 6 months of age, 2 required a transannular patch.
All children were successfully discharged from hospital. One child developed a deep sternal wound infection requiring reexploration. This child was discharged from hospital in good condition on the 34th day after his initial repair. There was no significant morbidity in the remaining children.
Figure 1 illustrates the change in peak gradients with time. Severe (free) pulmonary insufficiency was found in 5 children, or 18% of children with preserved pulmonary valves. Moderate pulmonary insufficiency was found in an additional 5 children. Thus, 68% of children demonstrated pulmonary valve competence at follow-up. There was no effect of age on the subsequent development of pulmonary insufficiency (33% of children under age 6 months compared with 37% of children over age 6 months, p = 0.92). Importantly, only 4 (14%) of the 28 children with preserved pulmonary valves demonstrated a significant RVOT gradient (> 30 mm Hg) at follow-up. Multivariate analysis demonstrated that there was no effect of weight (F = 1.1, p = 0.35), body surface area (F = 0.02, p = 0.90), or age (F = 1.1, p = 0.34) on the peak RVOT gradient at 12 months.
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Fig 1. Right ventricular outflow tract gradients in children with preservation of their pulmonary valve complex.
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Figure 2 demonstrates the relationship between age and the pulmonary annulus to body weight ratio. There was a significant correlation between age and the relative size of the pulmonary annulus (r2 = 0.46, p = 0.02). The three children who required a transannular patch are shown in Figure 2, and are positioned in the lower right hand corner of the graph. For children older than 9 months of age, the mean ratio between the pulmonary annulus and body weight was 0.08 ± 0.01 cm/kg compared with 0.13 ± 0.02 cm/kg for children younger than 9 months (p = 0.009). Figure 3 demonstrates the relationship of pulmonary annulus z-values, age, and the ability to preserve the pulmonary valve.
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Fig 2. The relationship between age and the ratio of pulmonary annulus diameter to body weight. As age increases, the relative size of the pulmonary annulus falls (r = - 0.46, p = 0.02). The asterisks represent the 3 children in whom transannular patching was required. All 3 children presented with a pulmonary annulus-to-weight ratio of less than 0.08 cm/kg.
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Fig 3. The relationship between age and pulmonary annulus z-value. The asterisks represent the 3 children in whom transannular patching was required. The z-value did not correlate with the requirement for transannular patching.
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Comment
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The recent trend towards earlier correction of children born with TOF has been thought to be associated with an increased incidence of pulmonary valve destruction secondary to a transannular patch [1]. Transannular patches have been reported with a frequency as high as 60% to 80% in those performing neonatal repair of this condition. With our recent experience with earlier repair of TOF, an opportunity to refute several ingrained caveats has been provided. Importantly, is there an increased requirement for transannular patching in younger patients? While enlargement of the RVOT is desirable in the early postoperative period, the resultant pulmonary insufficiency remains an important factor contributing to the reduced exercise tolerance reported in these children [3]. Progressive RV dilation with associated tricuspid valve regurgitation is a common indication for pulmonary valve replacement [4, 5].
While residual pulmonary insufficiency is a predictor of ventricular dysrhythmias, there has been no documented relationship between residual pulmonary stenosis and the development of arrhythmias [10–13]. The functional implications of these latter changes have only been recently appreciated. It is with this realization that we decided to attempt pulmonary valve preservation in all patients. Although we commonly accept a 15- to 20-mm Hg valvular outflow gradient postrepair, especially in the neonate and infant, we have found a progressive drop in the RVOT gradient with time. In this study, only 4 children (14%) demonstrated a persistent RVOT gradient greater than 30 mm Hg. Of these 4, 3 children demonstrated gradients in the 30- to 35-mm Hg range, with severe RVOT obstruction (gradient 50 mm Hg) present in only 1 child. This child underwent delayed primary repair at the age of 2.25 years (out of country referral) and demonstrated significant RVOT obstruction with multiple ventricular septal defects at the time of his repair.
Age, weight, and body surface area did not appear to affect our ability to preserve the pulmonary valve. Traditional theory would suggest that pulmonary valve preservation may be more difficult in younger patients due to a less developed pulmonary annulus. Why then operate on neonates if the survival and risk of transvalvular patching remains no different from infants/children 6 to 9 months of age? Our clinical impression is that pulmonary valve preservation is easier in younger children and we are willing to accept higher gradients (20 to 25 mm Hg limited to the pulmonary valve annulus) in this population. The ventricle has been conditioned to the preoperative pressure load, and the relative increase in postrepair "antegrade" blood flow across the RVOT should stimulate growth of the pulmonary valve annulus parallel with somatic development. We believe that this will result in a regression of RVOT obstruction with time (Fig. 1). In fact, of the 2 children who underwent repair at greater that 6 months of age and required a transannular patch, only 1 demonstrated a hypoplastic annulus. The second patient had a tunnel-like infundibulum that necessitated transannular enlargement of the RVOT. Pulmonary valve preservation may have been possible in both of these patients had they undergone operation at an earlier age.
Figure 2 illustrates our hypothesis that advancing age is negatively correlated with the relative size of the pulmonary annulus. All 3 children who required transannular patching demonstrated a pulmonary annulus-to-weight ratio of less than 0.08 cm/kg. Although further larger studies are required to confirm this finding, we believe that children who present for surgery with a pulmonary annulus-to-body weight ratio of greater than 0.08 cm/kg should be candidates for pulmonary valve preservation.
The data from this study indicate that pulmonary valve preservation is possible in most patients presenting for complete repair of tetralogy of Fallot. We continue to recommend the earlier repair of children afflicted with this lesion because we believe that the pulmonary valve will participate in somatic growth and result in a regression of RVOT obstruction. Importantly, the ability to preserve the pulmonary valve in these children should prevent the deleterious effects of free pulmonary insufficiency. We therefore recommend a change in surgical philosophy towards intentional preservation of the neonatal pulmonary valve. With this goal in mind, we recommend against transient palliation afforded by either balloon pulmonary valvuloplasty or systemic-pulmonary shunts. Both of these strategies adversely affect the ability to preserve the pulmonary valve at the time of complete repair, and as such, likely do a disservice to these children in the long term. We hypothesize and provide supporting fetal literature to suggest that semilunar valve development in part depends upon antegrade blood flow. Retrograde blood flow may be associated with maldevelopment of valve leaflets and the remaining components of the valve complex [14, 15]. Our data would suggest that in the asymptomatic patient who is being followed conservatively, surgery should be offered once the ratio of pulmonary annular diameter to body weight falls below 0.1 cm/kg, in order to maximize the probability of successful pulmonary valve preservation.
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References
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Abstract
Introduction
