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Ann Thorac Surg 2001;71:899-905
© 2001 The Society of Thoracic Surgeons

Original article: cardiovascular

Development of pulmonary arteries after central aortopulmonary shunt in newborns

Evgenij V. Potapov, MDa, Vladimir V. Alexi-Meskishvili, MD, PhDa, Ingo Dähnert, MDa, Ekaterina A. Ivanitskaia, MDa, Peter E. Lange, MD, PhDa, Roland Hetzer, MD, PhDa

a Deutsches Herzzentrum Berlin, Berlin, Germany

Accepted for publication September 24, 2000.

Address reprint requests to Dr Potapov, Deutsches Herzzentrum Berlin, Augustenburger Platz 1, 13353 Berlin, Germany
e-mail: potapov{at}dhzb.de


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 Acknowledgments
 References
 
Background. Central shunt (CS) is frequently used to treat diminished pulmonary blood flow in newborns. We analyzed the impact of CS on the growth of the pulmonary arteries (PAs).

Methods. Twenty-two consecutive newborns underwent a CS procedure. In 15 newborns the preoperative angiograms and angiograms taken before undergoing anatomic or hemodynamic correction procedures were analyzed. The patients were divided retrospectively into two groups by the size of the PA in the preoperative angiogram: group I, patients with PAs more than 4 mm (n = 10), group II, PAs 4 mm or less (n = 5). To compare the development of the PAs in the groups, the Nakata index, McGoon ratio, and lower lobe indices were calculated from angiograms.

Results. The indices were significantly higher in group I before CS, but no differences was found between the groups before anatomic or hemodynamic correction. The postoperative Nakata indices and the McGoon ratios in the groups were higher when compared with preoperative values (group I, p = 0.037 and p = 0.013; group II, p = 0.043 and p = 0.043, respectively). The significant increase of the lower lobe indices only in group II (p = 0.043) suggests faster growth of the PA in this group.

Conclusions. Optimal diameters of the CS promote growth of the PAs, which was confirmed by the increased Nakata and McGoon indices. The benefit in smaller PAs is greater.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 Acknowledgments
 References
 
Primary repair is feasible, but not always possible, in all newborns with critically diminished pulmonary blood flow. In such cases an anastomosis between systemic circulation and pulmonary arteries (PAs) has to be established. Modified or classic Blalock-Taussig shunts are still in widespread use. The disadvantages of asymmetric shunts are an unequal flow between right and left PAs and the risk of kinking, stenosis, or even complete occlusion of shunts at the distal anastomosis with the child’s growth [1–5]. Especially in neonates, the modified Blalock-Taussig shunt is associated with an increased incidence of iatrogenic PA deformation [4]. Elevated pressure or deformation of one PA may preclude the subsequent Fontan procedure [1]. Incidence of iatrogenic PA deformations after modified Blalock-Taussig shunt was reported as between 35% and 65% [4, 6, 7].

Treatment strategies for patients with a congenital univentricular cardiac anatomy or right ventricular outflow tract hypoplasia depend on a well-developed PA system. Today, the creation of a central shunt (CS) from the aorta ascendens to the main PA or to the pulmonary bifurcation is an established procedure [5, 8–10]. The most important advantage of the CS is antegrade flow to both lungs, which promotes symmetrical growth of the hypoplastic central and hilar pulmonary vessels. This shunt minimizes iatrogenic deformations of the PA branch and reduces the frequency of PA stenosis [9, 11]. In patients awaiting subsequent Fontan procedures, well-developed PAs without distortion are crucial. In this paper we analyzed the development of the PA in newborns after a CS was performed.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 Acknowledgments
 References
 
Twenty-two consecutive newborns (10 boys, 12 girls) with diminished pulmonary blood flow received a CS between January 1, 1991, and January 1, 1999, as a primary procedure performed by one surgeon (V.A.-M.). Three patients died postoperatively (< 30 days), and in 4 patients no preoperative angiogram was performed. The remaining 15 patients were included in the analysis. In these 15 patients preoperative angiograms and subsequently 14 angiograms were performed before anatomic or hemodynamic correction procedures, and in 1 patient awaiting operation, the angiogram was performed 5.9 years after the CS. These patients were divided into two groups on the basis of the measurement of the diameters of the right and left PAs in preoperative angiograms: group I, both PAs more than 4 mm (n = 10); group II, both PAs 4 mm or less (n = 5). Infusion of prostaglandin E1, at a rate of 0.01 to 0.05 µg · kg-1 · min-1, was used in each neonate to keep the ductus arteriosus open and effec-tively relieve severe hypoxia until the CS was performed. The diagnoses are shown in Table 1. No special treatment was necessary to balance the circulation early postoperatively except adjustment of arterial CO2 tension by changing the ventilator settings. The mean arterial diastolic pressure was kept in all patients between 30 and 40 mm Hg.


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  		Table 1. Preoperative Characteristics and Follow-up of Patients

 
Cross-sectional area of the left and right PAs (Nakata index) [12], lower lobe PAs index (LL–Nakata), McGoon ratio [13], and lower lobe ratio (LL–McGoon) [14] were calculated from pulmonary angiograms. Increases of diameters of pulmonary and lower lobe arteries were calculated in groups and compared between groups.

The mean pressure in the left and right PAs was measured during catheterization only before corrective surgical procedures. The mean values were calculated and compared between left and right PAs in the groups and between left and right sides.

Operative technique
One surgeon (V.A.-M.) performed all the operations according to the technique described by Amato and associates [9]. After median sternotomy the main PA was dissected from the ascending aorta and occluded at the bifurcation in patients with pulmonary valve atresia, or a side-biting clamp was applied in patients with the main PA. If the patient’s hemodynamics and gas exchange remained stable, a 3.5- or 4-mm-diameter and 4- to 6-mm-long Gore-Tex (W.L. Gore & Associates, Flagstaff, AZ) prosthesis was anastomosed end-to-side to the incision at the main PA or pulmonary bifurcation with continuous 7-0 polypropylene suture. The other end of the prosthesis was anastomosed to the ascending aorta after the application of the side-biting clamp. After completion of the anastomosis, heparin was given intravenously (50 to 100 IU/kg body weight) to obtain an activated clotting time of approximately 200 seconds. In 4 patients (27%), after partially clamping off the PA, hemodynamic instability developed, and the distal ascending aorta and right atrium were cannulated and the operation was performed using normothermic cardiopulmonary bypass. The mean perfusion time was 50 ± 32.4 minutes (range, 23 to 105 minutes). Additionally, cardioplegia was used in patient 1 because of the necessity to close the tricuspid valve. According to the size of the great arteries, a 3.5-mm shunt was used in 7 patients and a 4-mm one in 8 patients. There was no postoperative bleeding or need for reexploration. In 1 patient, delayed chest closure was performed 2 days after the procedure. Ligation of the patent ductus arteriosus was performed in 4 patients. In patients with a small ductus without significant impact on the circulation, the ductus was not ligated and closed spontaneously, usually after the cessation of prostaglandin infusion.

Statistical analysis
Statistical analysis of the data was performed with SPSS 9.0 for Windows (SPSS, Chicago, IL). The data were expressed as mean ± standard deviation and additionally as medians and ranges. A Wilcoxon’s test in groups and a Mann-Whitney U test between groups confirmed significance. A p value of less than 0.05 was considered significant.


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 Acknowledgments
 References
 
There were no intraoperative deaths. The overall 30-day mortality was 13.6% (n = 3). In all 3 patients, cardiopulmonary bypass was used during performance of the shunt. The mean age at the time of the first surgical procedure was not different (p = 0.6) between group I (5.2 ± 3.9 days; median, 4; range, 2 to 21 days) and group II (6 ± 3.8 days; median, 8 days; range, 1 to 10 days). The mean weight was similar (p = 0.81) in both groups (group I: 3.14 ± 0.63 kg; range, 1.82 to 3.92 kg; group II: 3 ± 0.6 kg; range, 2.3 to 3.9 kg).

Anatomic or hemodynamic corrections were performed in 14 patients (Table 1). Nine patients of group I had corrective procedures after CS after a mean interval of 1.1 ± 0.7 years (median, 225 days; range, 106 days to 2.1 years). One patient (No. 2) is still awaiting corrective operation. This interval was similar (p = 0.99) when compared with the mean interval of 1.1 ± 0.9 years (median, 197 days; range, 126 days to 2.8 years) in group II.

The follow-up angiograms were performed in group I after a mean of 476 ± 613 days (median, 268 days; range, 92 days to 5.9 years), which were not significantly different (p = 0.41) when compared with group II, in which the follow-up angiograms were taken after a mean of 290 ± 214 days (median, 174 days; range, 116 days to 1.6 years). Figure 1 shows an example of the development of small PAs in patient 11.



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  		Fig 1. Development of small pulmonary arteries in patient 11. (A) Before central shunt was performed, the Nakata index was 64 and the McGoon ratio was 0.82. (B) One hundred seventy-four days after operation, the Nakata index rose to 89 and the McGoon ratio to 1.1.

 
All indices, calculated from angiograms before performing the CS, were significantly lower in group II (Table 2). There were no differences, except for the Nakata index, of these indices between the groups in the angiograms performed immediately before anatomic or hemodynamic correction and in 1 patient awaiting operation 5.9 years after CS was performed (Table 2).


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  		Table 2. Differences of Nakata Indices, McGoon Ratios, and Lower Lobe Indices Between Groups Preoperatively and Before Subsequent Procedures

 
A significant difference was found between the preoperative and postoperative Nakata indices in group I (p = 0.037) and in group II (p = 0.043). The postoperative McGoon ratios in the groups were significantly higher when compared with the preoperative value (group I: p = 0.013; group II: p = 0.043). The values of LL–Nakata indices postoperatively increased in both groups, but were statisti-cally significant only in group II (p = 0.11 and p = 0.043, respectively). The LL–McGoon ratios increased postoperatively in both groups, but a statistically significant difference was reached only in group II (p = 0.051 and p = 0.043, respectively). The values of the indices are presented in Table 2 and the individual changes in Figures 2–5.



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  		Fig 2. Changes of Nakata indices in both groups compared preoperatively and before subsequent procedures. The horizontal lines represent normal ranges for the Nakata index.

 


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  		Fig 3. Changes of McGoon ratios in both groups compared preoperatively and before subsequent procedures. The horizontal lines represent normal ranges for the McGoon ratios.

 


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  		Fig 4. Changes of lower lobe Nakata indices in both groups compared preoperatively and before subsequent procedures. The horizontal lines represent normal ranges for the lower lobe Nakata index.

 


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  		Fig 5. Changes of lower lobe McGoon ratios in both groups compared preoperatively and before subsequent procedures. The horizontal lines represent normal ranges for the lower lobe McGoon ratios.

 
No differences in growth of pulmonary and lower lobe arteries were found between the right and left sides in both groups (Table 3).


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  		Table 3. Growth of Left and Right Pulmonary and Left and Right Lower Lobe Arteries

 
The mean values of mean pressure in both PAs are given in Table 4. No significant differences were found in the groups between the left and right PAs. However, the mean pressures were lower in group II when compared with group I, but a significant difference was reached only for pressure in the right PA.


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  		Table 4. Mean Pressures in the Left and Right Pulmonary Arteries Before Corrective Proceduresa

 
In group I there was 1 patient with postoperative deformation of the origin of the left PA. Two other patients (1 from group I and 1 from group II) had stenosis of the origin of the left PA because of ductal sling, before CS was performed. In all 3 patients, the left PA had to be reconstructed during subsequent elective surgical procedures. In patient 9, the growth of the PA was not successful, and the patient received a left-sided Blalock-Taussig shunt (Table 1).


   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
Acknowledgments
 References
 
Central shunt as a primary procedure in newborns with diminished pulmonary blood flow provides symmetrical and bidirectional blood flow and promotes growth of the PA. Depending on the weight of the patients and the size of the PAs, we used short (4 to 6 mm) Gore-Tex prostheses of 3.5 or 4.0 mm diameter. In our series these shunts allow sufficient pulmonary blood flow without the risk of pulmonary edema or subsequent pulmonary hypertension.

The presented results demonstrate the symmetrical growth of PAs after installation of a CS (Fig 1, Tables 3 and 4). In only 1 patient (No. 9) with insufficient growth of the PAs, was an additional Blalock-Taussig shunt necessary. Later at the age of 2.4 years the patient successfully underwent bidirectional cavopulmonary connection.

Central shunt allows easier subsequent access for diagnostic catheterization procedures for the better definition of PA anatomy. Because of the easy identification and accessibility of the CS, its closure during subsequent procedures is much easier than closure of peripheral shunts. Further, the CS is unlikely to be injured during repeated sternotomy [11].

In our series there was only 1 patient of group I with postoperative deformation of the left PA, which required a patch enlargement during a subsequent establishment of a bidirectional cavopulmonary connection. Creation of a CS is mostly possible without cardiopulmonary bypass. In 15 patients, 4 patients, all from group II, underwent operation with cardiopulmonary bypass because of hemodynamic instability or the necessity for intracardiac repair.

The early postoperative mortality in our patients was comparable with mortality reported by other authors [8, 9, 11]. In all patients who died early postoperatively, cardiopulmonary bypass was used, which carries additional risks. This may be explained by a larger number of other cardiac and noncardiac defects in these patients.

Many authors report an indirect correlation between the size of the PAs and postoperative mortality after a Fontan procedure as well as corrective operation for pulmonary atresia [15–17]. However, neither the McGoon ratio nor the Nakata index can be considered as optimal methods for the evaluation of PAs, probably because the diameters of the left and right PAs are sometimes smaller than their prebranching part [15]. Our series suggests that lower lobe indices might be of more prognostic value, but statistical significance was not reached because of the small number of patients. The lower lobe indices were more informative than the Nakata index or the McGoon ratio for the evolution of the PA tree because they are not influenced by congenital or iatrogenic central PA deformations. However, the qualitative judgment of angiograms is also important to recognize any circumscript stenosis or other local deformities that are not in the area where the diameter of the PA for calculation of the indices was measured.

Pulmonary arteries developed well after the CS procedure. Rising Nakata and LL–Nakata indices as well as McGoon and LL–McGoon ratios demonstrate this clearly (Figs 2–5). Despite the small number of patients and a shorter period between evaluations of indices in group II [1], the difference between preoperative and postshunt indices (except lower lobe indices in group I) reached a significant level. As expected all preoperatively calculated indices were significantly diminished in group II compared with group I and normal values. There were no significant differences of postshunt indices between groups (Table 2), indicating that the potential benefit for smaller PAs is greater. After CS was performed, these indices rose significantly and, except for the Nakata index, reached normal values (Figs 2–5). Moreover, no pressure differences between groups were found before corrective operation. Because of these facts, we suggest that CS enables symmetrical growth of PAs in newborns with diminished pulmonary blood flow with normal and even small PAs, which showed even more improvement.

In our series 14 of 15 patients (93%) underwent subsequent procedures without any deaths (Table 1). One patient is still awaiting operation.

We believe that CS is a first choice of treatment of newborns with diminished pulmonary blood flow, especially with small PAs, and CS is the standard procedure in our institution in such patients, especially in view of subsequent anatomic or hemodynamic corrections. This study has some limitations owing to the small number of patients as well as the lack of comparison between patients with a CS and those with modified Blalock-Taussig shunt.

Implementation of a CS is a safe and easily performed primary procedure in newborns with complex cyanotic congenital cardiac defects. In comparison with other aortopulmonary shunt procedures, the CS has fewer complications. An optimal diameter of the CS provides sufficient and bidirectional symmetrical pulmonary blood flow and promotes growth of the PAs. Good development of PAs, even in patients with small PAs, is confirmed by increasing Nakata and McGoon indices. The potential for smaller PAs is greater.


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 Acknowledgments
References
 
We are grateful for editorial assistance from Tonie Derwent. We are indebted to Helge Haselbach who provided the illustrations.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Godart F., Qureshi S.A., Simha A., et al. Effects of modified and classic Blalock-Taussig shunts on the pulmonary arterial tree. Ann Thorac Surg 1998;66:512-518.[Abstract/Free Full Text]
  2. Ebert P., Gay W., Oldham N.H. Management of aorta-pulmonary artery anastomosis during total correction of tetralogy of Fallot. Surgery 1972;71:231-234.[Medline]
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  4. Gladman G., McCrindle B.W., Williams W.G., Freedom R.M., Benson L.N. The modified Blalock-Taussig shunt: clinical impact and morbidity in Fallot’s tetralogy in the current era. J Thorac Cardiovasc Surg 1997;114:25-30.[Abstract/Free Full Text]
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  6. Ullom R.L., Sade R.M., Crawford F.A., Jr, Ross B.A., Spinale F. The Blalock-Taussig shunt in infants: standard versus modified. Ann Thorac Surg 1987;44:539-543.[Abstract]
  7. Bove E.L., Kohman L., Sereika S., et al. The modified Blalock-Taussig shunt. analysis of adequacy and duration of palliation. Circulation 1987;76(Suppl 2):III19-III23.
  8. Gazzaniga A., Lamberti J.J., Siewers R.D., et al. Arterial prosthesis of microporous expanded polytetrafluoroethylene for construction of aorta-pulmonary shunts. J Thorac Cardiovasc Surg 1976;72:357-363.[Abstract]
  9. Amato J.J., Marbey M.L., Bush C., Galdieri R.J., Cotroneo J.V., Bushong J. Systemic-pulmonary polytetrafluoroethylene shunts in palliative operations for congenital heart disease. Revival of the central shunt. J Thorac Cardiovasc Surg 1988;95:62-69.[Abstract]
  10. Gates R.N., Laks H., Johnson K. Side-to-side aorto-Gore-Tex central shunt. J Thorac Cardiovasc Surg 1976;72:357.
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