The Blalock-Taussig shunt in the neonate

Computational fluid dynamics characterization of blood flow in central aorta to pulmonary artery connections: importance of shunt angulation as a determinant of shear stress-induced thrombosis

The central aortic shunt, consisting of a Gore-Tex (polytetrafluoroethylene) tube (graft) connecting the ascending aorta to the pulmonary artery, is a palliative operation for neonates with cyanotic congenital heart disease. These tubes often have an extended length, and therefore must be angulated to complete the connection to the posterior pulmonary arteries. Thrombosis of the graft is not uncommon and can be life-threatening. We have shown that a viscous fluid (such as blood) traversing a curve or bend in a small-caliber vessel or conduit can give rise to marked increases in wall shear stress, which is the major mechanical factor responsible for vascular thrombosis. Thus, the objective of this study was to use computational fluid dynamics to investigate whether wall shear stress (and shear rate) generated in angulated central aorta-to-pulmonary artery connections, in vivo, can be of magnitude and distribution to initiate platelet activation/aggregation, ultimately leading to thrombus formation. Anatomical features required to construct the computer-simulated blood flow pathways were verified from angiograms of central aortic shunts in patients. For the modeled central aortic shunts, we found wall shear stresses of (80-200 N/m(2)), with shear rates of (16,000-40,000/s), at sites of even modest curvature, to be high enough to cause platelet-mediated shunt thrombosis. The corresponding energy losses for the fluid transitions through the aorta-to-pulmonary connections constituted (70 %) of the incoming flow's mechanical energy. The associated velocity fields within these shunts exhibited vortices, eddies, and flow stagnation/recirculation, which are thrombogenic in nature and conducive to energy dissipation. Angulation-induced, shear stress-mediated shunt thrombosis is insensitive to aspirin therapy alone. Thus, for patients with central aortic shunts of longer length and with angulation, aspirin alone will provide insufficient protection against clotting. These patients are at risk for shunt thrombosis and significant morbidity and mortality, unless their anticoagulation regimen includes additional antiplatelet medications.

Reappraisal of the prostaglandin E1 dose for early newborns with patent ductus arteriosus-dependent pulmonary circulation

OBJECTIVES

The usual initial dose of prostaglandin E1 (PGE1) for ductal-dependent congenital heart disease (CHD) is 50-100 ng/kg/minute. The aim of this study was to review our experience of a low initial dose of PGE1 treatment in early newborns with congenital heart disease and patent ductus arteriosus (PDA)-dependent pulmonary flow.

METHODS

We reviewed the clinical data of 33 newborns with CHD and PDA-dependent pulmonary circulation who were admitted from January 2005 to December 2010. Clinical parameters were collected, including, PGE1 dosage, oxygenation condition, vital signs, and other related clinical parameters during admission. Echocardiography was employed to assess the status of the PDA as clinically indicated.

RESULTS

Thirty-three newborns, including 17 males and 16 females, with CHD and PDA-dependent pulmonary circulation were enrolled in the study. Their mean age was 2.9 ± 5.1 (within the range of 1-26) days with a median of 1.0 day. Among the 33 cases, 25 were diagnosed with pulmonary atresia and eight with critical pulmonary stenosis. Twenty-five of our patients were treated with the initial low-dosage regimen of 20.0 ± 7.4 ng/kg/minute in our neonatal intensive care unit. None of these 25 patients with had significant apnea necessitating intubation and none had hypotension, fever, convulsion or cortical hyperostosis. Three of the eight patients who were treated with high-dose PGE1 (39 ± 13.2 ng/kg/minute) before referral to our unit had apnea and intubation after PGE1 use. All patients had adequate PDA patency with a low maintenance dose of 10.5 ± 5.3 ng/kg/minute before operation under our protocol.

CONCLUSION

In our experience, adequate PDA flows in early newborns with CHD and PDA-dependent pulmonary circulation could be achieved at a much lower dose than recommended in the literature. The lower dose of PGE1 also causes much fewer complications, such as apnea, fever, and hypotension. For early newborns with CHD and PDA-dependent pulmonary circulation, treatment with a lower initial dose of PGE1 of 20 ng/kg/minute and a maintenance dose of 10 ng/kg/minute is recommended.

Sternotomy Approach for Modified Blalock-Taussig Shunt: Is it a Safe Option?

Central aorta-pulmonary artery shunts have fallen into disfavor because of shunt thrombosis and congestive heart failure, and a modified Blalock-Taussig shunt via thoracotomy can lead to pulmonary artery hypoplasia and distortion. We reviewed the outcomes of a modified Blalock-Taussig shunt by a sternotomy approach in 20 infants from July 2007 to October 2009. Their mean age was 5.79 months, and median weight was 5.4 kg. A 4-mm graft was placed in 11 patients, a 5-mm graft in 8, and a 3.5-mm graft in 1. There was no incidence of sepsis, seroma, or phrenic nerve palsy. There was one hospital death. The mean hospital stay was 10.4 ± 4.3 days (range, 8–15 days). The mean oxygen saturation at discharge was 89% (range, 81%–93%). The sternotomy approach is technically easier to perform, cosmetically preferable, and probably hemodynamically superior. Correction of branch pulmonary stenosis is easily incorporated into this procedure. The theoretical disadvantage of this method is a potential technical difficulty with sternal reentry for subsequent procedures.

Blalock-Taussig shunt: Experience from the developing world

BACKGROUND

Palliative procedures have a role in congenital cardiac malformations that do not permit a complete early repair, and in centres where facilities for complete early repair do not exist. The lack of data on modified Blalock-Taussig shunt from developing countries prompted this analysis.

METHODS

We report a retrospective study of 70 Blalock-Taussig shunt procedures in 63 patients over an 8-year period. Most of the procedures (54.0%) were done on children less than 4 months of age. Thirty-nine (58%) patients had Tetralogy of Fallot; the remaining patients had a wide spectrum of lesions.

RESULTS

In the first year of the review period, the classical Blalock-Taussig shunt was done in six patients (9.5%) and the modified Blalock-Taussig shunt was used thereafter. In 49 patients who were followed up long term, clinical congestive cardiac failure developed in three (6%) and shunt failure was reported in 10 (14%). Of the 16 (33%) total deaths, six had serious comorbid conditions preoperatively.

CONCLUSIONS

The Blalock-Taussig shunt is a relatively safe palliative procedure, requiring fewer resources and less expertise than corrective surgery, making it a suitable option in developing countries.

Sternotomy approach for the modified Blalock-Taussig shunt

BACKGROUND

Since 1990, sternotomy has been the preferred approach for construction of a modified Blalock-Taussig shunt (MBTS) at Children's Hospital, Boston, Mass. In retrospect, we sought to test the hypothesis that this approach yields less mortality and morbidity than the traditional thoracotomy approach.

METHODS AND RESULTS

One hundred four primary MBTSs with polytetrafluoroethylene grafts were constructed in patients from January 1988 through December 1992. Fifty-two shunts were constructed by thoracotomy approach and 52 by sternotomy approach. Fifteen of the thoracotomy patients were less than one month of age (8 less than 7 days), while 36 of the sternotomy patients were less than 1 month of age (20 less than 7 days). There were 10 shunt failures and 3 hospital deaths in the thoracotomy group and 4 shunt failures with 6 hospital deaths in the sternotomy group. The overall hospital mortality rate for the group was 8.7% (9 of 104). The operative route was not a significant predictor of hospital mortality (P = .30). However, there was a significant difference between the two operative approaches in shunt failure, with shunts that were created by thoracotomy four times more likely to fail than those created by the sternotomy route (odds ratio, OR, 3.88; 95% CI, 1.01 to 15.03; P = .049). The side of the shunt was also a significant predictor of failure with left-side MBTSs foru times more prone to failure (OR, 4.02; 95% CI, 1.19 to 15.25; P = .025).

CONCLUSIONS

The sternotomy route is technically less challenging and is associated with fewer shunt failures than the classic thoracotomy approach. The potential theoretical disadvantages of this method for future sternal reentry for subsequent procedures was not apparent but requires prospective analysis.

The Blalock-Taussig shunt in infants: standard versus modified

In recent years, the modified Blalock-Taussig shunt--a polytetrafluoroethylene graft from the subclavian artery to the pulmonary artery--has been preferred over the standard shunt by some surgeons because (1) it requires less dissection and (2) length of native vessels is not critical. From January, 1979, to June, 1985, we operated on 51 infants less than 1 year of age, including 26 less than 1 week of age, to palliate severe complex cyanotic congenital cardiac malformations. Twenty-four modified Blalock-Taussig shunts and 29 standard Blalock-Taussig shunts were created. The groups were concurrent. We reviewed all available cineangiograms and measured branch pulmonary and subclavian arteries. Pulmonary artery index was not different preoperatively in patients given a modified versus a standard Blalock-Taussig shunt (144 +/- 118 and 118 +/- 59 mm2/m2, respectively), but it was greater postoperatively in patients with a modified shunt (431 +/- 188 and 189 +/- 106 mm2/m2) (p = 0.07). Distortion of the pulmonary artery occurred less often after a modified Blalock-Taussig shunt (4/11) than a standard Blalock-Taussig shunt (6/8) (p = 0.06), though none of the distortions was severe. Early and late shunt failure occurred less often with a modified shunt (5/24) than with a standard shunt (15/29) (p less than 0.05). The modified Blalock-Taussig shunt had advantages over the standard Blalock-Taussig shunt in our series: pulmonary artery growth was greater, distortion of pulmonary arteries was less commonly seen, and shunt failure occurred less often. Thus, in infants, we believe the modified Blalock-Taussig shunt should be considered a reasonable alternative to the standard Blalock-Taussig shunt.

Pulmonary hemodynamics and maintenance of palliation following polytetrafluoroethylene shunts for cyanotic congenital heart disease

Subclavian-to-pulmonary artery anastomoses with interposition polytetrafluoroethylene (PTFE) conduits provide excellent early palliation for many forms of cyanotic heart disease. It is important to assess whether patients with this condition maintain adequate arterial oxygenation without developing pulmonary artery distortion or hypertension. From October, 1980, to December, 1982, 29 PTFE shunts were performed. There were no hospital deaths or shunt failures. Catheterization was performed in 14 patients from 2 months to 2.5 years (mean 13.4 months) following operation. All shunts were patent. Arterial Po2 at the late study ranged from 33 to 96 torr (mean 57.1 +/- 17.3 torr) and was not significantly different from values obtained before hospital discharge at the time of the shunt procedure (mean 47.6 +/- 5.9 torr). Only one patient demonstrated moderate pulmonary hypertension (44/25 mm Hg), believed to be secondary to ventricular dysfunction. No patient demonstrated pulmonary artery distortion or kinking, and none required a second shunt because of inadequacy of the original procedure. The results in these patients, as well as the continued excellent clinical course of the patients not as yet recatheterized, have prompted us to use this shunt as our procedure of choice in neonates.

A comparison of Blalock-Taussig, Waterston, and polytetrafluoroethylene shunts in children less than two weeks of age

Results obtained with Blalock-Taussig, Waterston, and polytetrafluoroethylene (PTFE) shunts were compared in 67 cyanotic infants less than 2 weeks of age. A different shunt was preferably used at each of three institutions. The incidences of early shunt failure (3 out of 21, 14%), mortality after revision of early shunt failure (0 out of 3), and overall hospital mortality (1 out of 21, 5%) were all lowest for the PTFE shunt. Incidence of congestive heart failure secondary to excessive flow was comparable for the Blalock-Taussig and PTFE shunts, both of which were lower than the Waterston shunt. Cumulative probabilities of late shunt adequacy were calculated for hospital survivors. At 1 year, all shunts provided comparable adequate palliation (greater than 80%). Probability of late shunt failure was significantly higher (p = 0.04) for the PTFE shunt at 3.5 years. Results suggest that the PTFE shunt may be the safest and most effective shunt in neonates, but that elective shunt replacement or total repair may be warranted in the first or second year of life.

Aneurysmal degeneration of Blalock-Taussig shunts: identification and surgical treatment options

Many Blalock-Taussig shunts (subclavian to pulmonary artery anastomoses) have been created and a significant number are still being done. Two cases of aneurysmal degeneration of a Blalock-Taussig shunt and their management are described. Development of this rare complication may be related to large shunt flow and long duration. Large, symptomatic or enlarging aneurysms should be repaired and smaller ones studied by serial computed axial tomography. A simple and safe approach to correct this lesion is division and oversewing of the proximal subclavian artery through an anterior approach, assuming adequate pulmonary blood flow is already present or can be established concomitantly.

Use of saphenous vein allografts for aortopulmonary artery anastomoses in neonates with complex cyanotic congenital heart disease

A saphenous vein allograft was used to create an aortopulmonary communication in 16 infants with cyanotic congenital heart disease and ductus-dependent pulmonary blood flow. These grafts measured from 3 to 8 mm in diameter and were placed between the aorta and main pulmonary artery in eight patients, between aorta and right pulmonary artery in eight, and between aorta and left pulmonary artery in one (one child had two grafts). Before heparin was used, early in the series, four of these grafts occluded and three of the four infants died during attempted revision. Another infant died early from renal failure. Late mortality has claimed four: one from cerebral hemorrhage, two from hypoxia, and one at open-heart surgery for repair. There are eight late survivors (50%). Most of the allografts were used before small diameter Gore-Tex was available; in more recent patients, 4- to 6-mm Gore-Tex grafts have been used. In our most recent patient, however, the attempt to place a Gore-Tex graft was unsuccessful, but the more pliable saphenous vein graft was readily placed and an adequate shunt obtained. Both the saphenous vein graft and the Gore-Tex have the advantage of providing pulmonary flow without the higher risk of congestive failure or pulmonary hypertension seen in patients with a Waterston or Potts anastomosis. They are easier to perform, require less anesthesia time than the Blalock-Taussig shunt, last as long as the Blalock-Taussig when done under similar conditions, and are easy to take down at the time of total repair.

Subclavian-pulmonary artery shunts with polytetrafluorethylene interposition grafts

Systemic-pulmonary artery shunts remain an important treatment in cyanotic patients. Central shunts continue to pose early and late problems when standard Blalock-Taussig shunts are not possible. Twenty patients underwent subclavian-pulmonary artery shunt procedures with polytetrafluoroethylene (PTFE) prostheses between October, 1980, and August, 1982. Their ages ranged from 1 day to 15 years; 11 patients were less than 14 days old. The arterial oxygen tension rose from 30.7 +/- 11.9 mm Hg to 51.3 +/- 9.1 mm Hg (standard deviation; p less than 0.001) and from 26.4 +/- 7.5 mm Hg to 50.5 +/- 9.3 mm Hg (p less than 0.001) among the 11 neonates. There were no hospital deaths and only 2 late deaths (not shunt related). All patients have patent shunts and excellent relief of cyanosis. The 18 survivors have been followed for an average of 19 months (range, 7 to 29 months). No patient has required reoperation for shunt inadequacy or thrombosis. Recatheterization in 11 patients has demonstrated normal pulmonary pressures and good pulmonary artery growth without vessel distortion. Subclavian-pulmonary shunts using PTFE provide long-term palliation in cyanotic patients. This type of shunt appears to offer important advantages over other shunt procedures, including the classic Blalock-Taussig operation, in newborns.

Maintaining patency of the ductus-arteriosus for palliation of cyanotic congenital cardiac malformations. The use of prostaglandin E1 and formaldehyde infiltration of the ductal wall

We have used two methods to maintain ductal ppatency in 13 newborns during surgery for congenital cardiac malformations: prostaglandin E1 (PGE1) infusion for the short-term and formaldehyde infiltration of the ductus arteriosuos (FID) for the longer term. PGE1 increased the arterial oxygen saturation, leading to stable intraoperative hemodynamics in the six infants in whom it was used. FID was used in all 13 patients. Four of these patients died in the hospital, all with the ductus open. Of the nine early survivors, all required an additional shunt procedure. The five long-term survivors had the second palliative operation immediately, three hours, three days, two and one-half months, and four and one-half months after FID. We continue to use PGE1 to maintain ductal atency through operation, but use aortopulmonary anastomosis in the newborn period rather than FID.

The prosthetic (Teflon) central aortopulmonary shunt for cyanotic infants less than three weeks old: results and long-term follow-up

The expanded microporous polytetrafluoroethylene (PTFE) 4 mm vascular prosthesis has been used to create a central aortopulmonary shunt in 20 critically ill infants less than 3 weeks old. The infants ranged from 1 to 18 days old (5.25 days), and from 1.5 to 4.0 kg (2.9 kg). Conduit length ranged from 2 to 6 cm (4 cm). Sixteen patients had atresia of the tricuspid or pulmonary valve. There were 6 early deaths (30%), only 1 of which was shunt related. The mean preoperative arterial oxygen saturation was 62% (range, 33 to 80%), and mean postoperative saturation was 87% (range, 78 to 90%). There were 5 late deaths, 1 probably caused by shunt failure. Nine long-term survivors have done well. Follow-up ranges from 1 to 36 months (18 months). Factors influencing conduit function are length, technical considerations, and pulmonary vascular resistance. Late restudy in 5 of 9 survivors confirms patency and demonstrates bidirectional pulmonary blood flow. Since PTFE shunt flow capability is fixed, the infant may require repair or a second shunt within 24 months of the initial procedure.

Classic shunting operations as part of two-stage repair for tetralogy of Fallot

One hundred forty-nine consecutive patients with tetralogy of Fallot, with or without pulmonary atresia, underwent Blalock-Taussig or Waterston operation for initial palliation. Of these patients, 45 were less than 6 months old, and 63 were less than 1 year old. The type of shunt, and the presence or absence of pulmonary atresia did not have a significant effect (p greater than 0.2) on hospital mortality. Parametric analysis showed a significant effect of age (p = 0.03), the risk of hospital death being 6% at 1 month of age, 4% at 3 months, 3% at 6 months, and 2.5% at 12 months. No late deaths occurred before the age of 3 years. Six patients (4.2% of the hospital survivors) required another operation before they were 3 years old. Severe arm ischemia occurred after a Blalock-Taussig shunt in 1 infant with Down's syndrome.