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Clinical Application of Bidirectional Glenn Shunt with Off-Pump Technique

Department of Cardiovascular Surgery, Fu Wai Hospital, Peking Union Medical College, Beijing, People’s Republic of China

For reprint information contact: Xin-Jin Luo, MD Tel: 86 10 6831 4466 Fax: 86 10 8770 1652 Email: luoxinjin{at}yahoo.com Department of Cardiovascular Surgery, Fu Wai Hospital, Peking Union Medical College, 167 Beilishi Road, Beijing 100037, People’s Republic of China.

	ABSTRACT

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A study was conducted to evaluate the outcomes of the bidirectional Glenn shunt technique performed off-pump. Between April 1999 and April 2001, 36 patients underwent bidirectional Glenn shunt, unilateral in 28 patients and bilateral in 8 patients, without using cardiopulmonary bypass. The patients consisted of 25 males and 11 females with a mean age of 5.7 ± 5.4 years and a mean body surface area of 0.72 ± 0.34 m². Preoperative percutaneous oxygen saturation was 75% ± 7%, and pulmonary arterial pressure was 14.3 ± 3.6 mmHg. There was no operative mortality. Chylothorax occurred in 1 patient in the early postoperative period. All the other patients were discharged without complications. Mean arterial oxygen saturation at discharge was 92.7% ± 4.0%. This shunt technique is easy to perform and is helpful in the early management of patients with a functionally univentricular heart. However, much remains to be learned about this unusual physiological system.

	INTRODUCTION

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The bidirectional Glenn shunt (BDG) is an operation to divert systemic venous return from the superior vena cava (SVC) directly to both lungs through the right pulmonary artery (RPA), bypassing a hypoplastic or absent right ventricle. This cavopulmonary connection provides excellent palliation in complicated malformations associated with low pulmonary blood flow, low pulmonary arterial (PA) pressure, and low pulmonary vascular resistance. It raises systemic arterial oxygen saturation (SaO₂) by increasing the effective pulmonary blood flow. At the same time, it can relieve the volume load of the single functional ventricle and improve the geometric structure of the ventricle.^1–2 If intracardiac repair is not necessary, the connection could be performed without cardiopulmonary bypass (CPB).^3–4 Moreover, myocardial ischemia need not be applied during construction of the anastomosis outside the heart. Since CPB is known to activate inflammatory mediators, increase lung water, and decrease right ventricular compliance, off-pump surgery offers the advantage of reducing postoperative complications in these patients. In this study, we assessed the results of BDG performed off-pump over a 2-year period.

	PATIENTS AND METHODS

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A total of 36 patients, 25 male and 11 female, underwent BDG without CPB between April 1999 and April 2001. The procedure was the primary operation in all the cases. The patients had a mean age of 5.7 ± 5.4 years (range, 6 months to 24 years), a mean weight of 15.8 ± 9.5 kg (range, 6.5 to 48 kg), and a mean body surface area of 0.72 ± 0.34 m² (range, 0.35 to 1.28 m²). The shunt was unilateral in 28 patients and bilateral in 8. All the patients were examined preoperatively by electrocardiography, chest radiography, and echocardiography. Diagnosis in 33 of them was confirmed by angiocardiography. The diagnoses for these patients are summarized in Table 1. Preoperative percutaneous oxygen saturation ranged from 45% to 83% (mean, 75% ± 7%). PA pressure and SaO₂ were monitored during and after the operation.

In the 28 patients who underwent a unilateral shunt operation, only 1 had bilateral SVCs. In this patient, the tiny left SVC was ligated. In these 28 patients, a temporarily intraoperative SVC-right atrial shunt was established. The SVC was cannulated near the innominate vein with a right-angled venous cannula, which was connected through a short segment of pump tubing to another right-angled venous cannula placed in the right atrium. Care was taken to avoid kinking. With this venous shunt opening, the SVC was occluded to check if blood pressure, SVC pressure, and oxygen saturation would change. Then the SVC was clamped and transected above the cavoatrial junction. The cardiac end of the SVC was closed with 6/0 polypropylene. Care must be taken not to damage the sinus node area. A large side-biting clamp was applied to the RPA, and a longitudinal incision of 1.5 to 2.0 cm was made on the superior aspect of the RPA. The distal end of the SVC was anastomosed end to side to the RPA with a running suture of 6/0 polypropylene in the posterior wall and an interrupted suture of 6/0 polypropylene in the anterior wall to avoid a pursestring effect. The clamp was then released, the temporary shunt removed, and heparin effect reversed. The anastomosis in the anterior wall was widened using the pericardium in 16 patients.

Thick bilateral SVCs were found in 8 patients. Pressure in the proximal SVC on each side was measured while the SVC on the other side was clamped. The pressure did not rise above 28 mmHg with the patient’s head slightly elevated, and no symptoms of edema were observed in the patient’s head. Accordingly, no temporary intraoperative shunt was necessary for SVC decompression. After heparinization, the bilateral SVCs were clamped one by one to allow end-to-side anastomosis to the pulmonary artery on the same side. The anastomosis in the anterior wall was widened in 3 patients.

The data are expressed as mean ± standard deviation and were analyzed using SAS statistical software (SAS Institute, Cary, NC, USA). Student’s t test was used to compare mean values, and differences of p < 0.05 are considered significant.

	RESULTS

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There was no operative mortality. One patient was reoperated 3 hours after the initial operation to stop bleeding from the anastomosis. This patient made a good recovery. All patients had immediate improvement in SaO₂ and showed an excellent postoperative response to the shunt. The mean duration of postoperative ventilatory support was 13.2 ± 7.2 hours (range, 5 to 28 hours). Chylothorax occurred in 1 patient and was treated by a 1-week course of hyperalimentation with nothing by mouth. Mean chest fluid drainage in the other 35 patients was 14.4 ± 6.1 mL·kg^–1. Mean PA pressure rose from 14.3 ± 3.6 mmHg (range, 8 to 20 mmHg) at the beginning of the operation to 16.6 ± 2.6 mmHg (range, 10 to 22 mmHg) in the early postoperative period. All the patients received antiplatelet treatment in the form of a small dose of aspirin (25 to 50 mg·day^–1) for 3 months or longer after the operation. Cyanosis was clearly relieved at discharge from hospital, and SaO₂ had increased to 92.7% ± 4.0% (range, 80% to 96%). There were no neurologic complications; no further arrhythmia occurred and so no antiarrhythmic medication was required.

For comparison, we analyzed the data of the 36 patients in the present study against those of 35 patients who underwent the shunt operation with CPB between 1994 and 2000. The results of the 2 groups are summarized in Table 2.

	DISCUSSION

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There is no consensus on the criteria for performing BDG. Most authors would suggest that the mean PA pressure should be less than 18 mmHg, or ideally below 15 mmHg.¹ In contrast to a systemic pulmonary shunt, the cavopulmonary shunt does not increase ventricular work, thereby avoiding further ventricular hypertrophy and compliance reduction. In comparison with the classic Glenn shunt, BDG provides bilateral pulmonary blood flow, thereby avoiding the mismatch that may occur between the SVC flow volume and the cross-sectional area of the entire right lung.

The role of accessory pulmonary blood flow in the setting of a BDG remains contentious. An additional source of pulmonary blood flow may mitigate some of the benefits of a bidirectional cavopulmonary shunt physiology by offsetting the reduction in ventricular volume load and increasing the likelihood of pulmonary vascular complications. On the other hand, it may offer some advantages over a pure cavopulmonary shunt physiology: the increased SaO₂ may be sufficient to reduce baseline cyanosis, and the additional source of pulmonary blood flow may allow for modestly improved exercise tolerance. In addition, by providing hepatic blood directly to the lungs, introducing an element of pulsatility to the pulmonary flow and increasing flow rates, an additional source of pulmonary flow may in fact reduce the likelihood of pulmonary vascular complications (such as arteriovenous fistulas and aortopulmonary collaterals) and improve pulmonary artery growth.²

CPB plays a vital role in cardiac surgery. However, it may activate inflammatory mediators as well as lead to lung injury and blood cell destruction. These adverse effects can increase pulmonary vascular resistance and decrease pulmonary blood flow after cavopulmonary connection. For this reason, we try, whenever possible, to create the shunt off-pump at normal temperature. The results have so far been satisfactory.

Comparing the results from the present study with those of patients who underwent BDG under CPB, the off-pump group showed better postoperative results in terms of lower PA pressure, shorter duration of ventilatory support, and less thoracic fluid drainage. However, oxygen saturation had increased to the same degree in both groups at discharge. We thus conclude that performing the shunt off-pump offers more benefits than with CPB.

Nevertheless, several issues should be taken into account when using the off-pump technique, including if there are 2 SVCs, if there are communicating branches between the 2 SVCs, and if there is a thick azygous vein continuation of the inferior vena cava (IVC). When 2 thick SVCs are present, both need to be joined to the appropriate pulmonary artery. If there are communicating branches between the SVCs, a temporary intraoperative SVC-right atrial shunt is not necessary for SVC decompression; and the SVCs can be clamped one by one for anastomosis to the pulmonary artery on the same side to be performed. Sometimes one of the SVCs is tiny while the other is thick, in which case the tiny one should preferably be clamped first. As long as no obstruction of the SVCs is observed, which suggests that communicating branches exist between them, the tiny vessel can be ligated. When there is a thick azygous vein continuation of the IVC, the SVC receiving the azygous vein carries over 60% of all systemic venous return.⁸ Because of this, many authors advise keeping the azygous vein open when the shunt is created, believing that the open azygous vein could increase blood flow to the pulmonary artery through the SVC and thus further improve postoperative SaO₂. However, other authors believe that the open azygous vein might allow blood flow intended for the pulmonary artery to be diverted to the lower resistance IVC after the shunt has been created. In our group, the thick azygous vein was ligated. Oxygen saturation improved postoperatively to satisfactory levels in the 6 patients whose azygous vein was ligated.

It is important to keep the anastomosis sufficiently wide in the shunt. Although many authors prefer continuous sutures using absorbable materials or polypropylene, we used interrupted suture on the anterior wall to avoid a pursestring effect, and the pericardium was added to the anterior wall to widen the anastomosis in more than half of the patients studied.

The chylothorax that occurred in a patient in the early postoperative period is assumed to be related to the increase in central venous pressure resulting from the loss of right ventricular pumping after the shunt was created. The development of pulmonary arteriovenous fistulas and systemic venous runoff to the IVC have been of concern in patients with long-standing Glenn shunt.² However, the risk of these late complications are thought by most authors to be lower in BDG, especially when pulsatile antegrade pulmonary blood flow is maintained.^2,9

In conclusion, BDG performed off-pump provides excellent palliation for selected patients with cyanotic congenital heart disease. Nevertheless, long term follow-up is needed for these patients.

	REFERENCES

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1. Freedom RM, Nykanen D, Benson LN. The physiology of the bidirectional cavopulmonary connection. Ann Thorac Surg 1998;66:664–7.[Abstract/Free Full Text]

2. McElhinney DB, Marianeschi SM, Reddy VM. Additional pulmonary blood flow with the bidirectional Glenn anastomosis: does it make a difference? Ann Thorac Surg 1998;66:668–72.[Abstract/Free Full Text]

3. Okabe H, Nagata N, Kaneko Y, Kobayashi J, Kanemoto S, Takaoka T. Extracardiac cavopulmonary connection of Fontan procedure with autologous pedicled pericardium without cardiopulmonary bypass. J Thorac Cardiovasc Surg 1998;116:1073–5.[Free Full Text]

4. Burke RP, Jacobs JP, Ashraf MH, Aldousany A, Chang AC. Extracardiac Fontan operation without cardiopulmonary bypass. Ann Thorac Surg 1997;63:1175–7.[Abstract/Free Full Text]

5. Glenn WW. Circulatory bypass of the right side of the heart. IV. Shunt between superior vena cava and distal right pulmonary artery; report of clinical application. N Engl J Med 1958;259:117–20.[Medline]

6. Abrams LD. Side to side cavopulmonary anastomosis for the palliation of "primitive ventricle" [abstract]. Br Heart J 1977;39:926.

7. Kawashima Y, Kitamura S, Matsuda H, Shimazaki Y, Nakano S, Hirose H. Total cavopulmonary shunt operation in complex cardiac anomalies. A new operation. J Thorac Cardiovasc Surg 1984;87: 74–81.[Abstract]

8. Lamberti JJ, Spicer RL, Waldman JD, Grehl TM, Thomson D, George L, et al. The bidirectional cavopulmonary shunt. J Thorac Cardiovasc Surg 1990;100:22–9.[Abstract]

9. Muster AJ, Zales VR, Ilbawi MN, Backer CL, Duffy CE, Mavroudis C. Biventricular repair of hypoplastic right ventricle assisted by pulsatile bidirectional cavopulmonary anastomosis. J Thorac Cardiovasc Surg 1993;105:112–9.[Abstract]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Qing-Yu Wu Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Luo, X.-J. Articles by Liu, Y.-L. Search for Related Content PubMed PubMed Citation Articles by Luo, X.-J. Articles by Liu, Y.-L. Related Collections Congenital - cyanotic