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a Department of Cardiovascular Surgery, Kanagawa Children's Medical Center, Yokohama, Japan
b Intensive Care Unit, Kanagawa Children's Medical Center, Yokohama, Japan
c Department of Pediatric Cardiology, Kanagawa Children's Medical Center, Yokohama, Japan
Accepted for publication September 14, 2009.
* Address correspondence to Dr Kajihara, Kanagawa Children's Medical Center, 2-138-4 Mutsukawa, Minami-ku, Yokohama, Kanagawa, 232-8555, Japan (Email: n-c.kaji{at}f6.dion.ne.jp).
| Abstract |
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Methods: On the basis of our surgical strategy, 68 consecutive patients underwent PAB and were divided into two groups, group 1 (January 1990 to June 2003; n = 30) and group 2 (July 2003 to August 2008; n = 38). The median age at PAB was 45 days in group 1 and 9 days in group 2. The circumference of the bands was significantly shorter in group 2 than in group 1, corresponding to the patient's weight in kg plus 19.0 ± 0.6 mm in group 1 or 17.0 ± 0.3 mm in group 2 (p = 0.003).
Results: Cardiac catheterization before the right heart bypass operation showed that the pulmonary artery index (group 1, 322 ± 29; group 2, 283 ± 27 mm2/m2; p = 0.01), pulmonary resistance index (group 1, 2.4 ± 0.2; group 2, 1.9 ± 0.1 U x m2; p = 0.03), and ventricular end-diastolic volume (group 1, 212 ± 19%; group 2, 166 ± 9%; p = 0.04) were significantly different between the two groups. The rates for achievement of right heart bypass at 12 months (group 1, 19%; group 2, 81%; p < 0.01) and survival at 3 years (group 1, 70%; group 2, 87%; p = 0.04) were significantly higher in group 2 than in group 1.
Conclusions: Our present strategy could prevent volume overload and improve the achievement and survival rates of right heart bypass operations.
| Introduction |
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Because younger patients can tolerate bidirectional cavopulmonary shunt (BCPS), even at 2 months old [3], we believe that PAB in the staged Fontan era should be tighter than that used in the nonstaged Fontan era. To treat functionally single ventricles with unobstructed pulmonary blood flow, our current strategy involves applying a tight PAB in the neonatal period as an initial step, followed by early application of BCPS during infancy. The application of a tighter PAB in the neonatal period might prevent volume overload, protect the pulmonary vascular beds and ventricular function, and improve the BCPS achievement rate and the Fontan completion rate. It seems likely that tighter PABs are empirically performed in many institutes that have adopted the staged Fontan strategy to manage functionally single ventricles with increased pulmonary blood flow. However, we have found no reported evidence to support this approach.
The purpose of this study was to assess the impact of our current surgical strategy for the treatment of functionally single ventricles with unobstructed pulmonary blood flow in terms of protecting pulmonary vascular beds and ventricular function, and consequently achieving successful right heart bypass operation. Accordingly, we compared two groups of patients; patients were treated using the previous strategy before the staged Fontan era and patients treated using our current strategy.
| Patients and Methods |
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Between October 1990 and August 2008, 68 neonates or infants with a functionally single ventricle and unobstructed pulmonary blood flow underwent main PAB at Kanagawa Children's Medical Center. The PAB was the first step performed in all patients. Based on the strategy used to determine the tightness of the pulmonary banding, we divided the patients into two groups: group 1 (n = 30), patients who underwent PAB between 1990 and June 2003; and group 2 (n = 38), patients who underwent PAB after July 2003. The age, body weight, specific anatomic lesions in this series with a functionally single ventricle, and associated anomalies are presented in Table 1. The age ranged from 0 to 367 days (median, 45 days) in group 1, and from 0 to 132 days (median, 9 days) in group 2. Although there was a significant difference in body weight between the two groups, there was no difference in the size of the main pulmonary trunk before PAB (group 1, 11.2 ± 2.4 mm; group 2, 10.8 ± 3.1 mm; p = 0.76). The incidence of associated aortic coarctation was higher in group 2.
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Operative Technique
The chest was entered through an anterolateral thoracotomy or a median sternotomy according to concomitant procedures. We used a 0.6-mm thick, 4-mm wide, expanded polytetrafluoroethylene (ePTFE) patch as a tape to band the main pulmonary artery. Concomitant coarctectomy plus extended aortic arch anastomosis with or without distal arch augmentation from a median sternotomy was performed in 10 patients. In the other patients, concomitant subclavian flap aortoplasty was performed through a posterolateral thoracotomy.
The circumference of the band was calculated as the patient's weight in kilograms plus 20 mm for group 1 or 18 mm for group 2, according to a modified version of Trusler's formula [5]. The tightness of the band was considered appropriate when the oxygen level was around 35 mm Hg at 21% or 40% of fraction of inspired oxygen during surgery in group 1 or at 60% in group 2. As a result, the circumference of the band was tighter in group 2 than in group 1. The final circumference of the band was the patient's weight in kilograms plus 19.0 ± 0.6 mm in group 1 and 17.0 ± 0.3 mm in group 2 (p < 0.01). The circumference of the bands is shown in Figure 1. At discharge, the median percutaneous oxygen saturation was 80% (75% to 90%) in group 2.
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Statistical Analysis
The continuous data in this study are expressed as mean values ± standard error of the mean. Analyses were performed using SPSS software (version 11.0J; SPSS Inc, Chicago, IL). Normally distributed clinical parameters were compared with t tests. The Fisher exact test was used for binary variables. Non-normally distributed clinical parameters were compared with the Mann-Whitney test. The rate of achieving right heart bypass and the survival rate were calculated using the Kaplan-Meier method with log-rank and Breslow comparison of groups.
| Results |
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Group 2
None of the patients died in hospital and none of the patients developed a systemic outflow tract obstruction after PAB. Six surgical interventions were required after the initial PAB in five patients, including repeat PAB in two patients, loosening of the band in one, modification of the BTS due to distortion of the PA in one, repair of the aortic coarctation in one, and creation of an atrial septal defect (ASD) in one.
Cardiac Catheterization Before Right Heart Bypass Operation
Cardiac catheterization before the right heart bypass operation revealed two patients with a significant pressure gradient (>20 mm Hg) between the systemic ventricle and the ascending aorta (systole) in group 1, but none in group 2. There was a significant difference in the pressure gradient of the systemic ventricle-ascending aorta between the two groups (group 1, 6.6 ± 1.7 mm Hg; group 2, 3.4 ± 0.8 mm Hg, p = 0.02). The PA index (group 1, 322 ± 29 mm2/m2; group 2, 283 ± 27 mm2/m2, p = 0.01) and the pulmonary resistance index (group 1, 2.4 ± 0.2 U · m2; group 2, 1.9 ± 0.1 U · m2, p = 0.03) were significantly different between the two groups (Fig 2). The pulmonary to systemic flow ratio (group 1, 1.1 ± 0.1; group 2, 1.2 ± 0.1, p = 0.28) and the pulmonary arterial pressure (group 1, 13.7 ± 0.8 mm Hg; group 2, 15.2 ± 1.2 mm Hg, p = 0.20) were comparable in both groups. With regard to ventricular function, the ventricular end-diastolic volume was significantly smaller in group 2 than in group 1 (group 1, 212 ± 19% of the normal value; group 2, 166 ± 9%, p = 0.04) (Fig 3), although the ejection fraction of the systemic ventricle (group 1, 0.598 ± 0.024; group 2, 0.634 ± 0.025, p = 0.29) and the ventricular end-diastolic pressure (group 1, 8.3 ± 0.5 mm Hg; group 2, 7.3 ± 0.6 mm Hg, p = 0.16) were similar and were stable in both groups.
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The rate of achievement of right heart bypass operation was significantly different (p < 0.01) between the two groups based on the log-rank and Breslow comparisons. In group 2, the right heart bypass operation was accomplished at an earlier stage with a higher rate of achievement compared with that in group 1. Logistic regression analysis revealed that group 2 (p < 0.01) and the band circumference (p = 0.02) were determinants for achievement of the right heart bypass.
Follow-Up
All patients have attended our center for follow-up, with a follow-up interval ranging from 4.5 months to 18.4 years. The survival rate was 80%, 70%, and 63% at 1, 3, and 5 years, respectively, in group 1, and 94% at 1 year and 87% at both 3 and 5 years in group 2 (Fig 5). The survival rates were significantly different (p = 0.04) between the two groups based on the log-rank and Breslow comparisons. In the logistic regression analysis, the results indicated that group 2 was the only independent factor predicting survival with a p value of 0.43.
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| Comment |
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Staged Fontan Strategy
The BCPS plays an important role as a staged procedure in the Fontan operation and has led to a decrease in ventricular volume overload at a younger age [6, 7]. Furthermore, the survival rate after BCPS is high [8–10]. Lee and colleagues [8] reported that the mortality in the pre-Fontan stage was 41.3% in the non-BCPS group and 16.3% in the BCPS group. The BCPS decreased the mortality in the pre-Fontan stage, and increased the likelihood of proceeding to the Fontan procedure. Cochrane and colleagues [9] analyzed the outcome of the Fontan operation at various times to assess the effect of prior BCPS, and reported that the mortality associated with the Fontan operation decreased from 8.5% (1980 to 1987) to 1.8% (1988 to 1995), coinciding with the introduction of the BCPS. Furthermore, Tanoue and colleagues [7] examined cardiac catheterization data before and after the Fontan operation, and reported that the volume reduction achieved with BCPS preceding the Fontan operation allowed for the correction of any after-load mismatch and improved the ventricular energetics after the Fontan operation. These findings prompted us to use the staged strategy for all Fontan candidates.
On the other hand, it was demonstrated that the rate of achieving the right heart bypass operation was low in patients with a functionally single ventricle [11, 12]. For example, Rodefeld and colleagues [11] reported that only 49 of 76 patients (64%) who had previously undergone PAB for a functionally single ventricle underwent a successful right heart bypass operation. The right heart bypass operation tends to be performed at a younger age [3, 13]. We consider that PAB in the staged Fontan era could be tighter than that used in the non-staged Fontan era. Using a tighter PAB during the neonatal period as an initial step may allow us to achieve successful BCPS at an earlier stage and ultimately complete the staged Fontan procedure.
Systemic Outflow Tract Obstruction
To avoid the development of systemic outflow tract obstruction, ventricular dysfunction, or morbidity associated PAB, several reports have demonstrated that a strategy based on the progressive application of DKS or a palliative arterial switch on cardiopulmonary bypass in infancy was effective [14–16]. These reports were based on the hypothesis that the PAB accelerated the systemic outflow tract obstruction secondary to muscular hypertrophy and restriction of the VSD in the subaortic area [11, 17, 18]. However, these reports have also revealed that the patients developed subaortic stenosis at the age of 1.3 to 3 years. This is one reason why we apply the BCPS earlier with aggressive concomitant DKS in infancy.
Despite the early PAB, more patients in group 2 than group 1 in this study required an approach to the subaortic lesion. One reason seems to be that there were many patients with coarctation of the aortic arch in group 2, with a high probability of later development of systemic ventricular outflow tract obstruction; therefore, we frequently applied arch reconstruction and used a tight PAB. Another reason is that our strategy was altered to BCPS in infancy with active DKS actively, if indicated by the morphology, because we found that some patients needed repeated release from the subaortic stenosis after the Fontan operation.
Jensen and colleagues [19] suggested that the high-risk group of patients with subaortic obstruction and a functionally single ventricle could undergo PAB as an initial step, with a subsequent intervention for subaortic obstruction, and that acceptable pre-Fontan hemodynamic parameters could be achieved. Webber and colleagues [20] performed PAB in infants with a double-inlet left ventricle and transposition of the great vessels in the absence of severe subaortic stenosis, and recommended early relief of subaortic stenosis in combination with BCPS in infancy. The benefits of PAB include the relative simplicity and the low mortality associated with the procedure. The PAB offers improved survival rates and does not preclude the performance of more complex surgical interventions in the neonatal period.
As described above (in the "Patients" section), we performed a Norwood operation in five patients with successful outcomes. Although the Norwood or DKS operations offer useful approaches, we consider that these should not comprise the primary step for patients with a functionally single ventricle with unobstructed pulmonary blood flow. The main limitation to the Norwood operation is that it is a complex procedure that entails cardiopulmonary bypass in a neonate [21, 22]. In addition, the patients are at increased risk of shunt thrombosis, pulmonary over-circulation with systemic hypoperfusion, and low diastolic blood pressure with resulting coronary ischemia.
Fiore and colleagues [23] and Daenen and colleagues [24] reported that prior PAB did not appear to cause significant pulmonary insufficiency in patients who required DKS, and the incidence of clinically significant pulmonary insufficiency after the DKS operation was relatively low. Thus, in our patients with potential systemic ventricular outflow tract obstruction, DKS anastomosis or relief of the stenotic systemic outflow tract was performed concomitantly with BCPS in infancy as the second stage.
Conclusion
The findings presented here suggest that our present strategy for treating functionally single ventricles with unobstructed pulmonary blood flow, namely using a tighter PAB in the neonatal period as an initial step and subsequent early application of BCPS in infancy, improves the rate of achieving the right heart bypass operation and the survival rate.
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