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Ann Thorac Surg 1999;67:1397-1399
© 1999 The Society of Thoracic Surgeons

Original Articles

Does the modified Blalock-Taussig shunt cause growth of the contralateral pulmonary artery?

Marjan Jahangiri, FRCSa, Christopher Lincoln, FRCSa, Elliot A. Shinebourne, FRCPb

a Department of Cardiothoracic Surgery, Royal Brompton Hospital, London, England, UK
b Department of Paediatric Cardiology, Royal Brompton Hospital, London, England, UK

Accepted for publication October 7, 1998.

Address reprint requests to Miss Jahangiri, Department of Cardiothoracic Surgery, Royal Brompton Hospital, Sydney St, London SW3 6NP, England


   Abstract
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 Footnotes
 Abstract
Introduction
 Material and methods
 Results
 Comment
 References
 
Background. Although some pediatric cardiology departments have a policy of adopting primary correction of tetralogy of Fallot in all symptomatic infants, we and others still palliate neonates and infants. Effective palliation should ameliorate symptoms and allow growth of the pulmonary arteries. Although studies on the growth of the ipsilateral and contralateral pulmonary arteries after a classic Blalock-Taussig shunt have been reported, pulmonary artery growth after a modified Blalock-Taussig shunt has not been studied as thoroughly. Therefore, we examined whether there is equal growth of the contralateral pulmonary artery after a modified Blalock-Taussig shunt.

Methods. We retrospectively analyzed the records of 140 patients with symptomatic tetralogy of Fallot who had a modified Blalock-Taussig shunt between October 1985 and October 1995. The median age at the time of the Blalock-Taussig shunt was 1.6 months. All patients had corrective procedures at a median age of 1.7 years. Cineangiography was done before the corrective procedure. From the angiograms the diameter of the right and left pulmonary arteries before their first lobar branches and the diameter of the descending thoracic aorta at the level of the diaphragm were measured. For each patient the ratios of right pulmonary artery to descending thoracic aorta and left pulmonary artery to descending thoracic aorta were determined and compared using Student’s t test.

Results. Of the 140 patients, 114 had a left-sided Blalock-Taussig shunt, 20 had a right-sided shunt, and 6 patients had bilateral shunts. The mean right pulmonary artery to descending thoracic aorta ratio was 1.10 and the mean left pulmonary artery to descending thoracic aorta ratio was 0.98. This difference was not significant.

Conclusion. We showed equal growth of the right and left pulmonary arteries with no distortion after a modified Blalock-Taussig shunt. If palliation is considered, the modified Blalock-Taussig shunt remains our choice.


   Introduction
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 Abstract
 Introduction
Material and methods
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Although a classic Blalock-Taussig (BT) shunt has been the established systemic-to-pulmonary shunt for many years [1], the modified BT shunt using polytetrafluroethylene for anastomosis has become popular, especially for palliation of congenital heart disease in neonates [2, 3]. Studies on the growth of the ipsilateral and contralateral pulmonary arteries after a classic BT shunt have been reported. However, pulmonary artery growth after a modified BT shunt has not been studied as thoroughly.

After a classic BT shunt, Guyton and colleagues [1] found growth of both the ipsilateral and contralateral pulmonary arteries, particularly in small pulmonary arteries. Laas and colleagues [4] found growth of the ipsilateral pulmonary artery but did not find significant growth of the contralateral pulmonary artery. With improvement in operative techniques, the role of shunting as a preliminary procedure rather than primary repair has been questioned. Some recent reports suggested that, when an operation is required in early life, preliminary shunting operations rather than primary repair do not improve outcome in patients with tetralogy of Fallot (TOF) [5, 6].

We examined whether there is equal growth of the contralateral pulmonary artery after a modified BT shunt and whether it is still the preferred method as a preliminary procedure before corrective procedures.


   Material and methods
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 Footnotes
 Abstract
 Introduction
 Material and methods
Results
 Comment
 References
 
We retrospectively analyzed the records of all patients with symptomatic TOF who had a modified BT shunt between October 1985 and October 1995. Patients with pulmonary atresia, absent pulmonary valve, and those who had a prior surgical procedure were excluded. We identified 140 patients who met inclusion criteria and whose records were complete. The male-to-female ratio was 1.5:1. The median age at the time of the shunt was 1.6 months (range, 1 day to 13 months). Forty-four (31%) patients were neonates.

Associated cardiac anomalies included multiple ventricular septal defects in 6 (3.3%), left-sided superior vena cava in 5 (2.7%), and a persistent arterial duct in 12 (6.6%) patients. The initial diagnosis before the shunt procedure was confirmed by transthoracic echocardiography. High-parasternal, short-axis views were used to image the right and left pulmonary arteries, and lateral resolution allowed differences of 2 mm to be detected. All pulmonary arteries were confluent. There was no disparity in size between the right and left pulmonary arteries. All patients had cineangiography before the corrective procedure. The median time from the shunt operation to corrective operation was 1.7 years (range, 7 months to 2.6 years). Before corrective operations, cardiac catheterization and angiography were done. Selective injections into the shunt were done using a cranio-caudal tilt and approximately 20-degree left anterior oblique projection. An aortogram in 45-degree caudo-cranial, 30-degree left anterior oblique projection (to visualize coronary arteries) and lateral projections was also done [7].

From the angiograms, the diameter of the right pulmonary artery (RPA) and left pulmonary artery (LPA) before their first lobar branches and the diameter of the descending thoracic aorta (DTA) at the level of the diaphragm were measured. All measurements were taken during ventricular systole and, when possible, from the same angiographic frame. For each patient the ratios of RPA to DTA and LPA to DTA were determined and compared using Student’s t test. This method was used for normalization of the pulmonary artery size to the size of the patient, and the diameters of the cardiac catheters were used to account for any magnification factor.

The salient operative techniques include using the largest interposition graft possible (4 or 5 mm) in all patients, and excising an ellipse of tissue from the pulmonary artery. Before the vessels are clamped, heparin is given at a dose of 1 mg/kg. At completion of both anastomoses the clamps are removed simultaneously.


   Results
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 Footnotes
 Abstract
 Introduction
 Material and methods
 Results
Comment
 References
 
Of the 140 patients, 114 patients had a left-sided BT shunt, 20 patients had a right-sided shunt, and 6 patients had bilateral shunts. There were no hospital deaths. Narrowing of the shunt at the site of the anastomosis was present in 2 (1.4%) patients, and narrowing along the conduit was present in 9 (6.4%) patients. There was no pulmonary artery stenosis present. Of the 6 patients who had bilateral BT shunts, all had narrowing along the interposition graft. Four of the 6 patients were less than 1 month old, and 1 patient who was 5 months old had a particularly small left subclavian artery.

For all patients (n = 140) who had a modified BT shunt and subsequently had correction for TOF, the mean RPA to DTA ratio was 1.10 and the mean LPA to DTA ratio was 0.98. This difference was not significant. For the 114 patients who had a left-sided BT shunt there was no significant difference between the RPA to DTA and LPA to DTA ratios. Similarly, there was no significant difference in the ratios for the 20 patients who had a right-sided shunt (Table 1).


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  		Table 1. Comparison of the Diameter of the Right and Left Pulmonary Arteries

 

   Comment
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 Footnotes
 Abstract
 Introduction
 Material and methods
 Results
 Comment
References
 
If palliation rather than primary correction is to be done, the procedure should allow adequate development of the pulmonary arteries as well as improvement in oxygenation and the general symptomatic status of the patient. In this group of patients we compared the size of the RPA with LPA to determine whether there was any differential growth before corrective procedures. The magnification factor was accounted for by using the diameter of the DTA in each patient. This method also allows for normalization of the pulmonary artery size to the size of the patient. This method of normalization of pulmonary artery size was used by Piehler and associates [8] to assess pulmonary artery distortion. Honda [9] also reported similar results from clinical and angiographic data in 60 patients with modified BT shunts. In Honda’s study the ipsilateral pulmonary artery grew to the same extent as the contralateral pulmonary artery. Similarly, in a study by Bove and colleagues [10], no pulmonary artery distortion was observed in the 32 patients who had angiographic follow-up. These findings are in contrast to those of Gladman and colleagues [11], who reported significant distortion of the pulmonary arteries in one third of the children who had a single right-sided shunt. In their study, 38% had palliation as neonates. They showed that the neonates had significantly smaller distal right pulmonary arteries at follow-up angiography than infants who had initial palliation at a later age. Surgical technique and operator-dependent factors might account for those differences, but Gladman and colleagues did not associate those factors with outcomes. Because all our shunt procedures followed the same surgical protocol, we believe that differences in results might be dependent on technical factors. The treatment of children, particularly infants with symptomatic TOF, is still controversial. Some investigators have reported that a palliative shunt does not improve outcome in TOF and where possible primary repair should be attempted [5, 6]. The aim of the present study was not to compare the outcome of a one-stage as opposed to a two-staged procedure for TOF. Instead, we demonstrated that if a choice is made to palliate rather than correct TOF in infants, then a modified BT shunt remains our choice. It is not an incremental risk factor for death and results in growth of both pulmonary arteries, which remained undisturbed.


   Footnotes
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 Footnotes
Abstract
 Introduction
 Material and methods
 Results
 Comment
 References
 
This article has been selected for the open discussion forum on the STS Web site: http:/www.Sts.org/section/atsdiscussion/


   References
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 Footnotes
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 References
 

  1. Guyton R.A., Owens J.L., Waumett J.D., Dooley K., Hatcher C.R., Williams W.H. The Blalock-Taussig shunt. J Thorac Cardiovasc Surg 1983;85:917-922.[Abstract]
  2. Ilbawi M.N., Grieco J., DeLeon S.Y., et al. Modified Blalock-Taussig shunt in newborn infants. J Thorac Cardiovasc Surg 1984;88:770-777.[Abstract]
  3. DeLeval M.R., McKay R., Jones M., et al. Modified Blalock-Taussig shunt use of subclavian artery orifice as flow regulator in prosthetic synthetic systemic-pulmonary shunts. J Thorac Cardiovasc Surg 1981;81:112-118.[Abstract]
  4. Laas J., Engesser U., Meisner H., et al. Tetralogy of Fallot. Development of hypoplastic pulmonary arteries and palliation. J Thorac Cardiovasc Surg 1984;32:113-138.
  5. Kirklin J.W., Blackstone E.H., Jonas R.A., et al. Morphologic and surgical determinants of outcome events after repair of tetralogy of Fallot and pulmonary stenosis. J Thorac Cardiovasc Surg 1992;103:706-723.[Abstract]
  6. Shimazaki Y., Blackstone E.H., Kirklin J.W., Jonas R.A., Mandell V., Colvin V.E. The dimensions of the right ventricular outflow tract and pulmonary arteries in tetralogy of Fallot and pulmonary stenosis. J Thorac Cardiovasc Surg 1992;103:692-705.[Abstract]
  7. Carvalho J.S., Silva C.M., Rigby M.L., Shinebourne E.A. Angiographic diagnosis of anomalous coronary artery in tetralogy of Fallot. Br Heart J 1993;70:75-78.[Abstract/Free Full Text]
  8. Piehler J.M., Danielson G.K., McGoon D.C., Wallace R.B., Fulton R.B., Mair D.D. Management of pulmonary atresia with ventricular septal defect and hypoplastic pulmonary arteries by right ventricular outflow obstruction. J Thorac Cardiovasc Surg 1980;80:552-567.[Medline]
  9. Honda J. Growth of the pulmonary arteries and morphological assessment after Blalock-Taussig shunts. J Jpn Surg 1993;41:569-577.
  10. 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):III1923.
  11. 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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This Article
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