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Ann Thorac Surg 2004;77:1727-1733
© 2004 The Society of Thoracic Surgeons
a Department of Surgery and Pediatrics,San Francisco, CA, USA
b Department of Pediatric Cardiology, San Francisco, CA, USA
c Critical Care Medicine, University of California, San Francisco Children's Hospital and Pediatric Cardiac Program, University of California, San Francisco School of Medicine, San Francisco, California, USA
Accepted for publication October 2, 2003.
* Address reprint requests to Dr Karl, Division of Pediatric Cardiothoracic Surgery, 513 Parnassus Ave, Rm S-549, Box 0118, San Francisco, CA 94143-0118, USA.
e-mail: karlt{at}surgery.ucsf.edu
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Abstract |
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METHODS: The medical records were retrospectively examined for preoperative demographic and echocardiographic data, operative variables, and postoperative clinical and hemodynamic data. From November 2001 to March 2003, 21 neonates had a modified Norwood procedure (SPA shunt, n = 8; RV-PA conduit, n = 13) at a median age of 5 days (range 1 to 18 days) and a median weight of 2.9 kg (range 1.7 to 4.1 kg). Of the 21 infants, 12 were considered high risk due to presence of low birth weight (n = 4), extracardiac or genetic anomalies (n = 5) or obstruction to pulmonary venous return (n = 5). Nine "high risk" infants were in the RV-PA conduit group.
RESULTS: Overall Norwood operation survival was 90% (19/21) and did not differ between groups. There were 2/19 interstage deaths and Kaplan-Meier survival at 1 year is 79%. Neonates in the RV-PA conduit group had significantly higher diastolic blood pressures at 1, 6, and 24 hours postoperatively (p < 0.05). Neonates in the SPA shunt group had significantly higher heart rates at 1 hour postoperatively (p < 0.05) than those in the RV-PA group. There was a trend to higher number of ventilatory interventions to balance Qp:Qs in the SPA shunt group (p = 0.06).
CONCLUSIONS: In a relatively high-risk group, neonates having an RV-PA conduit as part of the Norwood procedure have favorable postoperative hemodynamics and a good likelihood of stage I survival.
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Introduction |
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The purpose of this study is to determine the outcome of the Norwood procedure at a single institution where both RV-PA conduit and SPA shunt are used for pulmonary blood supply. Specifically, the aim is to determine and compare stage I and interstage survival and outcomes, early postoperative hemodynamics, and critical care resource use in neonates having a Norwood procedure with either right ventricular or systemic arterial origins of pulmonary blood flow.
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Postoperative hemodynamic data were collected by two blinded observers. Details of interventions in the intensive care unit (ICU) for the first 24 hours following operation were obtained retrospectively. Factors that were sought included number of ventilatory changes made to avoid pulmonary overcirculation, resuscitative fluid requirements, number of inotropic agents used, inotrope score, changes in inotrope use, and presence of low output state (defined by rising or persistently elevated serum lactate concentrations, evidence of poor perfusion by physical exam, low urine output, persistent/refractory hypotension, or low [< 30%] mixed venous Hb saturation or elevated arterial to venous Hb saturation differences [> 40%]) [17].
Patients
From November 2001 to March 2003, 21 neonates had a modified Norwood procedure at a median age of 5 days (range 1 to 18 days) and a mean weight of 2.9 kg (range 1.7 to 4.1 kg; 4 low birth weight defined as < 2.5 kg). Fifteen were male.
Morphologic features
Hypoplastic left heart syndrome (HLHS; aortic atresia ± mitral atresia, n = 11) or its variants (aortic stenosis ± mitral stenosis, n = 4) were present in 15 neonates while 6 had a non-HLHS diagnoses (atrioventricular septal defect, n = 4; double outlet right ventricle, n = 1; double inlet left ventricle n = 1). Five neonates had either intact atrial septum (n = 1), restrictive interatrial communication (n = 3), or pulmonary venous obstruction (n = 2), which was demonstrated by echocardiography (n = 5) and diagnostic catheterization (n = 1). Extracardiac or genetic anomalies were identified in 5 patients.
Preoperative echocardiographic data
Ventricular function was assessed echocardiographically as being good in 14 neonates (67%) and fair or depressed/poor in 7 patients (33%). Atrioventricular valve regurgitation was absent in 8 patients, mild in 11 patients, and moderate in 2 patients.
Operative techniques
Following atrial septectomy, arch reconstruction was performed by side-to-side connection between the ascending aorta and the main pulmonary artery and homograft patch augmentation of the arch. A SPA polytetrafluoroethylene (PTFE) shunt was used in 8 patients (size: 3.5 mm in 5 patients, 4 mm in 3 patients). A RV-PA PTFE conduit was used in 13 patients (size: 5 mm in 8 patients, 6 mm in 5 patients). The proximal end of the conduit was beveled and connected to a limited ventriculotomy with resection of subendocardial muscle. The distal end of the conduit was connected to the confluence of the pulmonary arteries which was patched with homograft tissue, autologous pericardium, or PTFE.
Data analysis
Data are described as frequencies, medians with ranges, and means with standard deviations as appropriate. Where there are missing data, the number of non-missing values is given. Characteristics, outcomes, and hemodynamic data of patients having RV-PA conduit or SPA shunt were compared using Fisher's exact tests, t tests, t-Welch tests, and Mann-Whitney U tests as appropriate. Time-dependent analysis of overall survival was calculated using Kaplan-Meier estimates. Cox proportional hazards modeling was used to determine risk factors associated with time-related mortality. The variables assessed as predictors of the above outcome measures include age, gender, weight, presence of mitral or aortic atresia, ascending aortic size, presence of obstruction to pulmonary venous return, genetic or extracardiac anomalies, ventricular function or source of pulmonary blood flow, use of extracorporeal life support (ECLS). All analyses were performed using STATA 7 statistical software (Stata Corporation, TX) or Prism (Graphpad Software, College Station, TX).
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Results |
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Comment |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Stage I mortality, early survival and risk factors for adverse outcome
Stage 1 mortality with the modified Norwood procedure has been reported to range from 20% to 40%, with interstage mortality rates ranging 5% to 15% [3, 4, 6, 7, 18–22]. At the University of Michigan, 303 patients having the Norwood operation for classic hypoplastic left heart syndrome had an overall hospital survival of 76% [1, 2, 19]. Among patients considered at standard risk, survival was significantly higher (86%) than that for those patients with important risk factors (42%). Adverse survival was most strongly associated with significant associated noncardiac congenital conditions and severe preoperative obstruction to pulmonary venous return.
The 15-year experience at the Children's Hospital in Philadelphia (CHOP) with 840 patients having stage I surgery for HLHS has shown 1-, 2-, 5-, 10-, and 15-year survival of 51%, 43%, 40%, 39%, and 39%, respectively [4]. Later era of stage I surgery was associated with significantly improved survival. Age more than 14 days at stage I and weight less than 2.5 kg at stage I were also associated with higher mortality. An analysis of operative outcome for stage I surgery at CHOP in the current era shows a survival of 77% [20]. Multivariable analysis identified birth weight, associated cardiac anomalies, total support time and ECMO or ventricular assist device (VAD) support as predictors of operative mortality. The Kaplan-Meier survival estimate at 1 year was 66% and was not different for patients with HLHS compared to non-HLHS.
For patients who have survived the Norwood procedure, survival to 1 year was 86%. Presence of an extra-cardiac anomaly or genetic syndrome and presence of an additional cardiac defect were predictors of worse survival in the first year of life. In the current study we report a 90% stage I survival (95% CI 70% to 99%) and a Kaplan Meier 1-year survival of 79% for the modified Norwood procedure using either a SPA shunt or RV-PA conduit which compare favorably with most published reports. The majority of patients in this cohort (12/21) would be considered higher risk candidates given the presence of either low birth weight, extracardiac/genetic anomalies, and obstruction to pulmonary venous return. The number of patients in this study is too small too allow us to precisely identify incremental risk factors for perioperative and time-related mortality. A Cox proportional hazards analysis was performed and suggested that the use of ECLS in the postoperative period was indicative of poorer outcome over the follow-up period, consistent with other reports [20].
RV-PA conduit modification
The use of an RV-PA conduit as a source of pulmonary blood flow in the Norwood procedure allows for favorable postoperative hemodynamics and a stable patient in the early postoperative period. The dynamics produced by the RV-PA conduit may prevent hemodynamic instability and allow for a good likelihood of survival. Whether the prevention of early postoperative instability will improve survival compared to neonates having a Blalock-Taussig shunt as part of the Norwood operation is unclear, and cannot be demonstrated by our data and experience thus far. Also, we can only speculate, but not prove that the improved perioperative stability of children who have a successful Norwood operation using an RV-PA conduit may have improved midterm to late outcome. The impact of the ventriculotomy on ventricular systolic, diastolic, and electrical function as well as atrioventricular valve function remains to be determined. A linear incision is made below the valve and subendocardial resection is performed to avoid obstruction of flow into the conduit. Although the ventriculotomy is made at the infundibular region of the ventricle, below the semilunar valve, care must be taken to avoid injuring or distorting the neo-aortic valve.
The potential advantages of improved diastolic perfusion pressure, lower pulmonary to systemic shunt flow, and lower likelihood of postoperative low output syndrome are supported in this study. Furthermore, the modification may be associated with less frequent ventilatory interventions during the first critical 24 hours following stage I palliation. The relative lack of pulmonary blood flow during diastole may allow for improved coronary flow and myocardial perfusion, and lower myocardial oxygen demand because of the reduction in the volume load on the ventricle. One concern with this approach is the possible development of earlier and progressive hypoxia. Also, because the distal anastomosis of the conduit is placed leftward of the arch, proximal right pulmonary artery compression by the aortic arch may be a concern especially when redundant patch or complete ductal excision is used for arch reconstruction.
In our experience, children in both groups presented for second stage palliation at comparable ages, but infants in the RV-PA group had a lower Qp:Qs, higher diastolic blood pressures, and a trend toward lower Hb-oxygen saturations compared to infants who had a SPA shunt. Our current practice is to insert a 5-mm conduit for neonates weighing 2 to 3 kg, and a 6-mm conduit for patients weighing more than 3 kg. As with all decisions regarding pulmonary blood flow one must take into account the state of the pulmonary circulation, ventricle, and atrioventricular valve at the time of operation.
The use of an RV-PA conduit may also facilitate the construction of a bidirectional cavopulmonary anstomosis. The dissection and exposure of the right pulmonary artery is facilitated because no takedown of a shunt is needed. Furthermore, it is possible to perform the operation without cardiopulmonary bypass by having single (left) lung perfusion through the conduit while the superior vena cava return can be passively or actively routed into the right atrium. Management of the RV-PA conduit at the time of cavopulmonary anastomosis can also be tailored to the infant's physiologic needs. If oxygenation is satisfactory with the superior cavopulmonary anastomosis alone then the conduit can be ligated and divided. However, in cases where the pulmonary vasculature requires antegrade flow to allow for adequate oxygenation, then the conduit is left open. In these situations the concern is that the raised mean superior caval pressures and pulsatile flow may produce prolonged pleural effusions. Under these circumstances a snare can be placed around the conduit and left in a subxiphoid position for later tightening and occlusion of the conduit.
In conclusion, in a relatively high-risk group neonates having an RV-PA conduit as part of the Norwood procedure have favorable postoperative hemodynamics and a good likelihood of stage I survival. Neonates having an RV-PA conduit as part of the Norwood procedure, however, may have relatively lower pulmonary blood flow, may need more frequent interstage monitoring and evaluation, and may need earlier catheterization and second stage operation.
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= RV-PA conduit (systolic BP); • = systemic-to-pulmonary shunt; 
RV-PA conduit (diastolic BP); 
= systemic-to-pulmonary shunt (diastolic BP). (BP = blood pressure; RV-PA = right ventricle-to-pulmonary artery conduit; SPA = systemic-to-pulmonary artery shunt.)