Effect of Blalock Taussig shunt on clinical parameters, left ventricular function and pulmonary arteries.

H Kulkarni, R Rajani, B Dalvi, KG Gupta, A Vora, P Kelkar 
 Dept of Cardiology, KEM Hospital, Bombay, Maharashtra.

Correspondence Address:
H Kulkarni
Dept of Cardiology, KEM Hospital, Bombay, Maharashtra.

Full Text

::   Introduction

In the recent years, increasing emphasis has been placed on the early primary intra-cardiac repair of congenital heart defects. This is the optimal approach, if it can be accomplished with an acceptable morbidity and mortality. Nevertheless, some patients are not suitable for early total correction and systemic pulmonary artery shunts continue to play an important role in the management of such defects, either as temporary palliation before total correction or as a means of permanent palliation. In an effort to increase the blood flow to the lungs, a number of systemic pulmonary artery anastomoses have been described. These include subclavian  pulmonary artery shunt (Blalock Taussig), direct aortopulmonary anastomoses between the descending aorta and left pulmonary artery (Potts) and between the ascending aorta and right pulmonary artery (Waters-on). These conventional shunts are associated with certain problems, like kin-king and distortion of the pulmonary arteries, excessive pulmonary blood flow and preferential flow to one lung.

A modification of Blalock  Taussig shunt with inter-positioning of expanded polytetrafluoroethylene (PTFE) graft has averted these difficulties and rendered palliation easy, safe and an effective procedure. The present followup study deals with 20 patients with cyanotic congenital heart defects in whom modified BT shunts were performed using PTFE grafts and evaluates effects of shunt procedures on various clinical and laboratory parameters.

::   Methods

The indications for BT shunts in 20 children with congenital cyanotic heart disease were 1. cyanotic spells and 2. Hypo-plastic pulmonary arteries as seen on angiocardiography. All the patients underwent clinical, laboratory, radiological, electrocardiographic, echocardiographic and angiocardiographic analysis before and 6 months to one year after the shunt.

On twodimensional echocardiography, left ventricular end diastolic volumes were calculated using the arealength method considering the left ventricle as a pro-late ellipse averaging the apical 4 chamber and apical 2 chamber views. Left atrial systolic volumes were measured in apical 4 chamber and apical 2 chamber views using the area length method'. A pulsed gated Doppler study was done in all the patients to demonstrate patency of the shunt by observing continuous turbulence across the left subclavian artery.

The cardiac catheterisation and angiocardiography was performed under intravenous ketamine and diazepam anaesthesia. The right heart catheterisation was performed by percutaneous femoral vein puncture technique using 6 or 7 F NIH catheter. The catheterisation protocol included right heart pressure measurements, oximetry and right ventriculography in frontal and lateral views followed by femoral artery puncture for pressure measurements and oximetry. Six months to 1 year after the BT shunt, the catheterisation study was repeated in all the patients. In 2 patients, the aorta was entered antegradely from venous side and a hand injection with 76% urograffin (Sodium meglumine diatriozate) was made by keeping the tip of 5 F USCI high flow right coronary artery catheter at the mouth of the left subclavian artery to demonstrate the patency of the shunt.

The maximal systolic diameters of the right and the left pulmonary arteries were measured just before the origin of the first branch in frontal view and the pulmonary valve annulus was measured in, systole[2]. The main pulmonary artery was measured at its narrowest point and the descending thoracic aorta was measured just above the level of the diaphragm[3]. All the measurements were corrected for magnification.

All patients underwent left modified BT shunt using 5 mm expanded PTFE graft, interposed, side to side between left subclavian and left pulmonary artery. The postoperative period was uneventful in all the patients without any death.

Statistical analysis: The data obtained in the study are expressed as mean + standard deviation. A paired students ‘t’ test was performed for comparison of data. A p value less than 0.05 was considered significant.

There were 20 patients (boys 14, girls 6) with a mean age of 3.25 years (range 5 months to 11 years). The morphological diagnoses were tetralogy of Fallot in 16, double outlet right ventricle with ventricular septal defect (VSD) and pulmonary stenosis (PS) in 2; corrected transposition of great vessels, VSD with PS in 1 and tricuspid atresia type 1 B in 1.

The best common indication for modified BT shunt was cyanotic spell (n = 15, 75%). After the BT shunt, none had a cyanotic spell during the followup period. The BT shunt was patent in all the cases on pulsed gated Doppler study at followup period varying from 6 months to 1 year.

As shown in [Table:1], there was a significant tall in packed cell volume (PCV) and haemoglobin (Hb)

The arterial oxygen saturation improved significantly and the cardiothoracic ratio increased. The left atrial systolic volume (LASV) and the left ventricular end diastolic volume (LVEDV) increased significantly during followup study. The ratio of LASV to body surface area (BSA) and LVEDV/BSA increased from 15.82 + 6.37 to 20.83 + 8.91 ml/sq. cm (p = 0.006) and from 36.13 + 16.08 to 41.08 + 20.47 ml/sq. cm (p = 0.01) respectively. [Table:2] shows the significant growth in size of right pulmonary artery, left pulmonary artery and the pulmonary annulus.

::   Discussion

Modification of the Blalock  Taussig shunt in which a Teflon prosthetic tube is anastomosed end to side to the undivided subclavian artery and end to side to the pulmonary artery was first described by Klinner and colleagues[4]. To avoid the problems of growth retardation of the limb associated with the ligation of the subclavian artery, this modification was introduced. Since the introduction of expanded polytetrafluoroethylene (PTFE) graft as a vascular prosthesis by Soyer et al[5], there have been several encouraging reports documenting the long term patency of this graft material used for systemic  pulmonary shunts in all ages. In this study the modified BT shunt was performed for cyanotic spells in 15 (75%) and hypo-plastic pulmonary arteries in 5 (25%) patients. None of the patients had cyanotic spell after the shunt and there was marked improvement in cyanosis in 10 (50%) patients. There was significant increase in the arterial saturation and decrease in the hematocrit following the shunt.

In the present study, after the shunt the left atrial systolic and left ventricular end diastolic volumes increased significantly. These changes appear to be secondary to increase in pulmonary blood flow (Qp) after the shunt. Graham et al[6] have reported that the left ventricular and diastolic volume of less than 55% of the normal for age in tetra-logy of Fallot is an in hospital incremental risk factor for intra-cardiac repair. Nomoto et al[7] have also mentioned that a smaller left ventricular volume is a risk factor for late post-operative deaths following intra-cardiac repair.

In our study, there was significant growth of the main, right and left pulmonary arteries, and pulmonary valve annulus following the shunt. The growth of the ipsilateral pulmonary artery was marginally more than the contra-lateral pulmonary artery. Guyton et al[8], and Gale et al[9] have also observed symmetrical growth of the pulmonary arterial tree widening the pulmonary annulus following the shunt and postulated that increase in the pulmonary blood flow is the main stimuli for the growth of the pulmonary arteries. However. Lass et al[10] showed that significant growth occurs only in the ipsilateral pulmonary artery.

The main pulmonary artery, Contra-lateral pulmonary artery and pulmonary valve annulus do not grow to the same extent. As the BT shunt increases the pulmonary artery size and left ventricular volume. it would possibly help in reducing mortality following intra-cardiac repair in patients with tetra-logy of Fallot with smaller pulmonary arteries and reduced left ventricular volumes.

::   Acknowledgment

We sincerely thank our secretary Mr. Kadav in helping us to prepare this manuscript.

References