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Ann Thorac Surg 2008;86:1299-1304. doi:10.1016/j.athoracsur.2008.06.016
© 2008 The Society of Thoracic Surgeons
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Original Articles: Pediatric Cardiac

Development of the Pulmonary Arteries After the Norwood Procedure: Comparison Between Blalock-Taussig Shunt and Right Ventricular–Pulmonary Artery Conduit

Joseph Caspi, MD*, Timothy W. Pettitt, MD, Theodorus Mulder, MD, Aluizio Stopa, MD

Division of Cardiothoracic Surgery and Pediatric Cardiology, Louisiana State University and Children's Hospital, New Orleans, Louisiana

Accepted for publication June 2, 2008.

* Address correspondence to Dr Caspi, Children's Hospital, 200 Henry Clay Ave, New Orleans, LA 70118 (Email: caspij{at}aol.com).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 References
 
Background: The Norwood-Sano procedure for hypoplastic left heart syndrome (HLHS) has been associated with improved postoperative hemodynamics and outcome. This study compared the effect of a Blalock-Taussig shunt with right ventricular-pulmonary artery (RV-PA) conduit before bidirectional Glenn on the development of the PAs.

Methods: Between January 2000 and June 2007, 42 patients with HLHS underwent bidirectional Glenn: 19 (mean age, 7 ± 1.5 months) had a Blalock-Taussig shunt (3.5 mm in 15; and 4 mm in 4); 23 patients (mean age, 5 ± 1 month) had RV-PA conduit (5-mm tube). Patients underwent postoperative cardiac catheterization and echocardiograms.

Results: Total PA (Nakata) index was 192 ± 10 mm2/m2 in the Blalock-Taussig group and 238 ± 18 mm2/m2 in the RV-PA conduit group (p = 0.03). In the RV-PA conduit patients, the left and right PAs had comparable diameters. In the Blalock-Taussig group, the left PA was smaller than the right (p = 0.02). The mean PA pressure at the end of the operation was 14 ± 2 mm Hg in the Blalock-Taussig group and 11 ±1 mm Hg in the RV-PA conduit group (p = 0.06). Persistent pleural effusion occurred in 4 Blalock-Taussig patients (21%) and in 1 (4%) with RV-PA conduit (p < 0.05). Postoperative arterial oxygen saturation was 80% ± 2% in the RV-PA conduit group and 74% ± 2% in the Blalock-Taussig group (p < 0.05).

Conclusions: The Norwood procedure with RV-PA conduit may have favorable effects on the development of the PA due to even distribution of pulmonary blood flow.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 References
 
The operative mortality associated with the Norwood procedure for hypoplastic left heart syndrome (HLHS) has decreased during the past 20 years because of better prenatal diagnosis and intraoperative management, including the use of newer surgical techniques and myocardial protection strategies [1, 2]. Despite improved surgical outcome, substantial operative mortality, between 15% and 40%, and interstage mortality, between 5% and 20%, still exists [3].

A modification of the Norwood procedure with right ventricular to pulmonary artery (RV-PA) conduit has been shown to improve the immediate surgical outcome compared with the classic Norwood procedure with a Blalock-Taussig (BT) shunt [4, 5]. The advantages of the Norwood procedure with RV-PA conduit are better coronary perfusion due to higher postoperative diastolic blood pressure and more favorable balance between the pulmonary and systemic circulations, resulting in improved systemic perfusion.

Underdevelopment of the pulmonary arteries after the Norwood procedure has been found as an independent risk factor predicting a higher late morbidity and mortality after subsequent bidirectional Glenn shunt and Fontan procedures [6]. Left pulmonary artery hypoplasia and bifurcation stenosis range between 40% and 77% [7]. Extrinsic compression by the neoaorta, distortion of the right pulmonary artery by the BT shunt, preferential flow to the right pulmonary artery, and technical issues related to the method of repairing the central segment of the pulmonary arteries may all be contributing factors [8]. The use of the RV-PA conduit as an alternative source of pulmonary blood flow can promote the development of the pulmonary arteries after the Norwood procedure [9].

Central pulmonary artery stenosis still remains a significant problem, however. This study compared the size of the pulmonary arteries of patients after BT shunt or RV-PA conduit who underwent bidirectional Glenn shunt, with special emphasis on postoperative hemodynamics and clinical course.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 References
 
We retrospectively reviewed the clinical records, echocardiographic studies, cardiac catheterizations, and surgical records of 42 patients with HLHS syndrome who underwent a bidirectional Glenn shunt between January 2000 and June 2007. The Ethics Committee on Human Research at Louisiana State University approved the study with a waiver of parental consent.

First-stage repair (Norwood procedure) was performed in the newborn period using standard techniques: atrial septectomy, pulmonary artery to ascending aorta anastomosis with pulmonary homograft, or bovine pericardial patch augmentation of the transverse aortic arch in all patients.

Patients were divided into two groups according to the era of operation. In the BT group (n = 19), a polytetrafluoroethylene (PTFE) tube, 3.5 mm in 15 patients and 4 mm in 4 patients, was placed between the right innominate artery and the right pulmonary artery (Fig 1). All patients with a BT shunt were operated on before 2004.


Figure 1
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  		Fig 1. A polytetrafluoroethylene tube graft of an appropriate size (3.5 to 4.0 mm) is anastomosed to the proximal innominate artery using a running 7-0 monofilament suture. The distal end of the tube graft is anastomosed close to the origin of the right pulmonary artery.

 
After 2004, RV-PA conduit has been used in all patients with HLHS. Patients with a RV-PA conduit (n = 23) received a 5-mm PTFE tube. The defect in the central pulmonary arteries was repaired with a large oval-shaped patch of bovine pericardium, which helped to decrease the development of central pulmonary artery stenosis. The distal end of the PTFE conduit was anastomosed to the patch after the creation of a 5-mm hole in the center of the patch. The proximal anastomosis to the right ventricle was augmented with a pericardial hood (Figs 2 and 3). Go


Figure 2
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  		Fig 2. A 5-mm tube of polytetrafluoroethylene material is anastomosed to the center of a large oval-shaped pericardial patch that is used to repair the central pulmonary arteries.

 

Figure 3
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  		Fig 3. (A) After the appropriate length of the tube graft has been trimmed, the proximal right ventricular anastomosis is constructed and augmented with a pericardial hood. (B) Lateral view of the completed proximal anastomosis. (C) Angiographic view of the right ventricular to pulmonary artery shunt. The proximal anastomosis is augmented with a small pericardial hood that prevents early stenosis at the ventricular mouth level.

 
The mean age at the time of the bidirectional Glenn shunt was 7 ±1.5 months (range, 5 to 9 months) in the BT group and 5 ±1 months (range, 4 to 7 months) in RV-PA conduit group (p = 0.7). The mean weight was 5 ± 0.7 kg (range, 4.1 to 7 kg) in the BT group and 5.2 ± 0.6 kg (range, 4.5 to 6 kg) in the RV-PA conduit group (p = 0.8). Mean preoperative systemic arterial saturation was 73% ± 4% (range, 65% to 81%) in the BT group and 70% ± 3% (range, 63% to 75%) in the RV-PA conduit group (p = 0.3).

All patients were evaluated with cardiac catheterization and two-dimensional and Doppler echocardiograms before the bidirectional Glenn shunt. The digital images were studied, and the diameter of right and left pulmonary arteries proximal to the first bifurcation was measured on the anteroposterior view. All values were obtained during ventricular systole and, when possible, from the same angiographic frame. Narrowing of the central segment greater than 50% of the luminal diameter or distortion related to the shunt was recorded. Angiographic catheter sizes were used to determine the magnification coefficient to adjust for measured vs actual size.

For the quantitative assessment of the pulmonary arteries, the following variables were calculated: (1) total pulmonary (Nakata) index, the combined cross-sectional area of the branch pulmonary arteries per square meter [10] and (2) the ratio between the diameter of the left and right pulmonary artery, expressed as a percentage. Preoperative echocardiograms were used to assess ventricular function by calculating ejection fraction. Tricuspid valve regurgitation was graded as mild, moderate, or severe. Hemodynamic variables were derived from cardiac catheterizations and included ventricular systolic and end-diastolic pressures, aortic pressures, partial arterial oxygen tension, and superior vena cava, and aortic saturation. The pulmonary/systemic blood flow ratio was calculated with the Pick principle. Balloon dilation of arch narrowing was performed in 3 patients in the BT group and in 2 patients in the RV-PA conduit group at the time of cardiac catheterization before the operation. Tricuspid valve annuloplasty was performed in 2 patients in the BT group and 1 in the RV-PA conduit group.

Surgical Technique
All operations were performed through a median sternotomy approach using cardiopulmonary bypass with a normothermic beating heart. A short period of moderate hypothermia (28°C) with blood cardioplegic arrest was used in 3 patients who required tricuspid annuloplasty. The superior vena cava was anastomosed in an end-to-side fashion to the right pulmonary artery using standard techniques after the BT shunt was ligated and divided. The RV-PA conduit was ligated and divided after institution of cardiopulmonary bypass.

After the patients were weaned from cardiopulmonary bypass, the pressure was directly measured in the pulmonary artery after introducing a 3F monitoring catheter (Medtronic, Minneapolis, MN) in the superior vena cava at the cannulation site. All pressure measurements were performed at normothermia with the patient in sinus rhythm and receiving 50% inspired oxygen. Pulmonary artery catheters were removed before chest closure.

All patients were mildly sedated in the intensive care unit postoperatively. Right atrial pressure and systemic arterial pressure were monitored continuously.

Statistical Analysis
Preoperative and postoperative data were analyzed and compared between groups. Data are expressed as mean ± standard deviation. A two-tailed Mann-Whitney U test was used to compare variables between groups, and the {chi}2 test was used to compare the frequency of postoperative complications using SPSS software (SPSS Inc, Chicago, IL). The difference was considered statistically significant at p ≤ 0.05.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 References
 
Table 1 summarizes preoperative hemodynamic and angiographic variables. The difference in the ejection fraction or in the severity of tricuspid regurgitation obtained by echocardiographic studies between the groups was not significant. Cardiac catheterization data demonstrated no significant difference in right ventricular systolic or end-diastolic pressure. The mean aortic oxygen saturation and pulmonary/systemic flow ratio were higher in the BT group, but these findings did not reach statistical difference.


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  		Table 1 Hemodynamic and Angiographic Variables After Blalock-Taussig Shunt and Right Ventricular to Pulmonary Artery Conduit
 
The diameter of the left and right pulmonary arteries was comparable in the RV-PA conduit group, but in the BT group, the left pulmonary artery was smaller than the right pulmonary artery, with significantly lower left to right pulmonary artery ratio (p = 0.02; Fig 4). A left to right pulmonary artery ratio of 0.5 or less was found in 4 patients (21%) in the BT group compared with none in the RV-PA conduit group (p < 0.01). The total pulmonary artery (Nakata) index was 192 ±10 mm2/m2 in the BT group compared with 238 ± 18 mm2/m2 in the RV-PA conduit group (p = 0.03; Fig 4).


Figure 4
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  		Fig 4. (A) A pulmonary arteriogram before the bidirectional Glenn shunt demonstrates relatively small branch pulmonary arteries after construction of the 3.5-mm Blalock-Taussig shunt. (B) A pulmonary arteriogram after the right ventricular to pulmonary artery conduit has been placed demonstrates well-developed branch pulmonary arteries.

 
Significant narrowing occurred at the insertion site of the BT shunt in 2 patients (10%), and central branch stenosis occurred at the distal insertion of the RV-PA conduit in 1 patient (4%). Left pulmonary patch arterioplasty was performed in 4 patients in the BT group, but in only 1 patient in the RV-PA conduit group (p < 0.05). No early or late deaths occurred.

Table 2 summarizes the postoperative hemodynamic data after the bidirectional Glenn shunt in both groups. The mean pulmonary artery and atrial filling pressures were comparable between the groups. After extubation and before discharge, the arterial oxygen saturation on room air was significantly higher in the RV-PA conduit group compared with the BT group (p = 0.03). One patient in the BT group required the addition of a central shunt to the left pulmonary artery because of low arterial oxygen saturation at the end of the procedure. Duration of mechanical ventilation was significantly longer in the BT group (p =0.04). The incidence of transient postoperative supraventricular tachyarrhythmias was similar in both groups. Persistent pleural effusion lasting longer than 10 days occurred in 4 patients (21%) in the BT group and in 1 patient (4%) in the RV-PA conduit group (p = 0.04). The groups had comparable predischarge ejection fractions: 0.57 ± 0.03 in the BT shunt group and 0.59 ± 0.02 in the RV-PA conduit group.


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  		Table 2 Hemodynamic Variables After Bidirectional Glenn Shunt
 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
References
 
Since the introduction of the Norwood procedure for HLHS in 1983, the surgical outcome has significantly improved because of better perioperative management and the advent of new surgical techniques. The Norwood procedure still remains a surgical challenge, however, with surgical mortality between 20% and 40% and interstage mortality rates between 5% and 15% [11].

Recently, there has been renewed interest in the RV-PA conduit as an alternative source of pulmonary blood flow [12]. Compared with the BT shunt, the RV-PA conduit provides a more stable hemodynamic state in the immediate postoperative period [13, 14]. The advantages of the RV-PA conduit are better coronary artery flow and myocardial perfusion due to higher diastolic blood pressure, more balanced pulmonary to systemic blood flow, and better systemic perfusion and cardiac output [15]. Also, patients after RV-PA conduit placement required fewer ventilatory interventions during the immediate postoperative course.

The ventriculotomy, however, may have adverse effects on myocardial systolic and diastolic function, the atrioventricular valve function, and the incidence of ventricular arrhythmias [16]. Our data show that the ventriculotomy was not associated with a higher incidence of diminished ventricular function and significant tricuspid regurgitation. Although we have not found a higher incidence of ventricular or supraventricular dysrhythmias in patients after RV-PA conduit placement, we still believe that a longer follow-up is required.

Structural abnormalities of the pulmonary arteries, such as hypoplasia or left pulmonary artery stenosis, after the Norwood procedure are independent risk factors predicting poor outcome after bidirectional Glenn shunt and Fontan procedures [9]. Different mechanisms may be narrowing at the ductal remnant site, extrinsic compression by the neoaorta on the left pulmonary artery, and distortion of the right pulmonary artery by the BT shunt [12]. Less than optimal growth of the contralateral pulmonary vessel after the BT shunt, especially in the absence of antegrade pulmonary blood flow, can occur [10, 16, 17]. To address this finding, a modified technique of BT construction in which the shunt anastomosis was directed leftward into the retroaortic pulmonary artery avoided development of left pulmonary artery stenosis [9].

Others have suggested that the RV-PA conduit may have more favorable effects on the development of the branch pulmonary arteries than the BT shunt because it is more centrally located and creates more pulsatile flow [11, 18]. This is in agreement with a multivariate analysis that found that the discrepancy in the size of the pulmonary arteries after the Norwood procedure was directly related to the location of the BT shunt and not the HLHS itself [11].

In this study we compared the size of the branch pulmonary arteries of patients after the Norwood procedure with either a BT shunt or RV-PA conduit. Our results support those of other studies that the RV-PA conduit promotes better growth of the pulmonary arteries and less discrepancy in size. The sizes of the left and right pulmonary arteries were comparable in the RV-PA conduit group, but the left pulmonary artery in the BT group was smaller than the right pulmonary artery. Also, the total pulmonary artery (Nakata) index was significantly higher, supporting the notion that the RV-PA conduit provides even distribution of blood flow to the pulmonary arteries.

A major concern is the late development of central pulmonary artery stenosis at the site of insertion of the RV-PA conduit. Griselli and colleagues [9] reported significant central pulmonary artery stenosis in 43% of their patients. Multivariable analysis found that the use of the RV-PA conduit was the only major risk factor for the need of central pulmonary artery arterioplasty. Also, 18% of their patients required catheter-based reintervention on branch pulmonary arteries between stages II and III or after stage III. This high incidence of central pulmonary artery stenosis was not correlated with the operative technique used to repair the defect in the pulmonary artery or to a modified technique of placing the distal end of the RV-PA conduit on the right side of the neoaorta.

Some have suggested that the neoaorta may compress the retroaortic distal RV-PA conduit anastomosis, resulting in central pulmonary artery stenosis or left pulmonary artery hypoplasia [8]. In contrast, our data show that the location of the distal RV-PA conduit anastomosis to the left side of the neoaorta was not associated with significant narrowing of the central pulmonary artery. Interestingly, despite the presence of significant central pulmonary artery stenosis, the RV-PA conduit promotes the growth of the pulmonary arteries better than the BT shunt [19]. Only 1 patient in our study with central pulmonary artery stenosis after an RV-PA conduit required patch pulmonary arterioplasty.

We attribute the low incidence of central pulmonary artery stenosis to the use of a relatively large pericardial patch to repair the defect in the pulmonary artery and anastomosing the conduit in the center of the patch, avoidance of tension on the conduit, and augmenting the proximal anastomosis with a pericardial hood. The use of this modified technique may help to reduce the frequently observed stenosis at the ventriculotomy level.

Our experience with the 5-mm PTFE shunt has been very favorable, and it is the standard size that we use in all patients. Early in our series, patients with the RV-PA conduit demonstrated worsening cyanosis soon after the operation that necessitated an earlier bidirectional Glenn shunt. Modification of the surgical technique with patch augmentation of the proximal anastomosis and careful coring out of the myocardium has eliminated this problem.

The method of establishing the pulmonary blood flow combined with the Norwood procedure remains controversial. Modifications of the surgical techniques, such as the location of the distal BT shunt anastomosis, patch augmentation of the proximal and distal RV-PA conduit anastomoses, and avoidance of compression on the left pulmonary artery by the neoaorta may explain the variation of the results among institutions. The interval between the two palliative procedures was not statistically different between the 2 groups in this study and therefore was not included in our analysis of the results. To determine the effect of the time interval between the Norwood procedure and the Glenn shunt on the development of the pulmonary artery, a larger age-matched comparative study is required.

In summary, the RV-PA conduit provides better distribution of pulmonary blood flow, which may have favorable effects on the development of the pulmonary arteries. As this series illustrates, the lower incidence of structural abnormalities of the pulmonary arteries may also facilitate the recovery after second stage repair.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 References
 

  1. Tabbutt S, Dominguez TE, Ravishankar C, et al. Outcomes after the stage 1 reconstruction comparing the right ventricular to pulmonary artery conduit with the modified Blalock Taussig Ann Thorac Surg 2005;80:1582-1590discussion 1590–1.[Abstract/Free Full Text]
  2. Bove EL. Current status of staged reconstruction for hypoplastic left heart syndrome Pediatr Cardiol 1998;19:308-315.[Medline]
  3. Cua CL, Thiagarajan RR, Taeed R, et al. Improved interstage mortality with modified Norwood procedure: a meta-analysis Ann Thorc Surg 2005;80:44-49.[Abstract/Free Full Text]
  4. Imoto Y, Kado H, Shiokawa Y, Fukae K, Yasui H. Experience with the Norwood procedure without circulatory arrest Ann Thorac Surg 1999;68:559-561.[Abstract/Free Full Text]
  5. Norwood WI, Lang P, Hansen DD. Physiologic repair of aortic atresia-hypoplastic left heart syndrome N Engl J Med 1983;308:23-26.[Medline]
  6. Knott-Craig CJ, Julsrud PR, Schaff HV, Puga FJ, Danielson GK. Pulmonary artery size and clinical outcome after the modified Fontan operation Ann Thorac Surg 1993;55:646-651.[Abstract]
  7. Azakie A, Martinez D, Sapru A, Fineman J, Teitel D, Karl TR. Impact of right ventricle to pulmonary artery conduit on outcome of the modified Norwood procedure Ann Thorac Surg 2004;77:1727-1733.[Abstract/Free Full Text]
  8. Januszewska K, Kolcz J, Mroczek T, Procelewska M, Malec E. Right ventricle-to-pulmonary artery shunt and modified Blalock-Taussig shunt in preparation to hemi-Fontan procedure in children with hypoplastic left heart syndrome Eur J Cardiothorac Surg 2005;27:956-961.[Abstract/Free Full Text]
  9. Griselli M, McGuirk SP, Ofoe V, et al. Fate of pulmonary arteries following Norwood procedure Eur J Cardiothorac Surg 2006;30:930-935.[Abstract/Free Full Text]
  10. Nakata S, Imai Y, Takanashi Y, et al. A new method for the quantitative standardization of cross-sectional areas of the pulmonary arteries in congenital heart diseases with decreased pulmonary blood flow J Thorac Cardiovasc Surg 1984;88:610-619.[Abstract]
  11. Hughes ML, Shekerdemian LS, Brizard CP, Penny DJ. Improved early ventricular performance with right ventricle to pulmonary artery conduit in stage I palliation for hypoplastic heart syndrome: evidence from strain Doppler echocardiography Heart 2004;90:191-194.[Abstract/Free Full Text]
  12. Sano S, Ishino K, Kawada M, et al. Right ventricular-pulmonary artery shunt in first stage palliation of hypoplastic left heart syndrome J Thorac Cardiovasc Surg 2003;126:504-509.[Abstract/Free Full Text]
  13. Waldman JD, Karp RB, Gittenberger-de Groot AC, Agarwala B, Glagov S. Spontaneous acquisition of discontinuous pulmonary arteries Ann Thorac Surg 1996;62:161-168.[Abstract/Free Full Text]
  14. Maher KO, Pizarro C, Gidding SS, et al. Hemodynamic profile after the Norwood procedure with right ventricle to pulmonary artery conduit Circulation 2003;108:782-784.[Abstract/Free Full Text]
  15. Bichell DP, Lamberti JJ, Pelletier GJ, et al. Late left pulmonary artery stenosis after the Norwood procedure is prevented by a modification in shunt construction Ann Thorac Surg 2005;79:1656-1661.[Abstract/Free Full Text]
  16. Batra AS, Starnes VA, Wells WJ. Does the site of insertion of a systemic-pulmonary shunt influence growth of the pulmonary arteries? Ann Thorac Surg 2005;79:636-640.[Abstract/Free Full Text]
  17. Ullom RL, Sade RM, Crawford Jr FA, Ross BA, Spinale F. The Blalock-Taussig shunt in infants: standard versus modified Ann Thorac Surg 1987;44:539-543.[Abstract]
  18. Malec E, Januszewska K, Kolez J, Mroczek T. Right ventricle-to-pulmonary artery shunt versus modified Blalock-Taussig shunt in the Norwood procedure for hypoplastic left heart syndrome-influence on early and late haemodynamic status Eur J Cardiothorac Surg 2003;23:728-733.[Abstract/Free Full Text]
  19. Godart F, Qureshi SA, Simha A, et al. Effects of modified and classic Blalock Taussig shunt on pulmonary arterial tree Ann Thorac Surg 1998;66:512-518.[Abstract/Free Full Text]




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