Asian Cardiovasc Thorac Ann 2001;9:196-199
© 2001 Asia Publishing EXchange Pte Ltd
Bidirectional Glenn Shunt: 170 Cases
Xie Bin, MD,
Zhang Jin Fang, MD,
Devi Prasad Shetty, MS
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Manipal Heart Foundation Bangalore, Karnataka, India
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For reprint information contact: Xie Bin, MD Tel: 86 20 8382 7812 Fax: 86 20 8387 5453 email: leoxie{at}21cn.com Department of Cardiac Surgery, Guangdong Cardiovascular Disease Research Institute, Dongchuang Road, Guangzhou, Guangdong 510100, People's Republic of China.
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Abstract
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Between June 1997 and July 2000, 170 patients aged 0.5 to 20 years received a bidirectional Glenn shunt without the use of a temporary shunt or cardiopulmonary bypass. Arterial oxygen saturation rose from 78% ± 8.5% preoperatively to 90% ± 4.3% postoperatively. Hemodynamic studies showed a mean postoperative superior vena cava pressure of 13 ± 2 mm H2O. One patient had desaturation and the shunt was taken down, 5 required reexploration for bleeding, and 8 needed prolonged drainage of 9 to 19 days, 2 of whom had chylothorax. Hospital stay was 9.3 ± 3.5 days. There were 3 late operative deaths (1.8%) from low output syndrome. In 20 patients, bilateral bidirectional Glenn shunts were instituted. Three patients under-went a subsequent Fontan procedure without cardiopulmonary bypass. The bidirectional Glenn shunt remains an excellent palliative procedure as a preliminary step to a Fontan operation, or as an integral part of a Fontan or modified Fontan operation when the procedure is deferred because of age, weight, or cardiac malformations characterized by a hypoplastic right or left ventricle.
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INTRODUCTION
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Current surgical approaches in congenital heart disease that is characterized functionally as single ventricle are based on diverting systemic venous return to the lungs. The classic Glenn shunt has been performed for nearly 40 years and has provided excellent long-term palliation of complex cardiac malformations associated with low pulmonary blood flow, low pulmonary arterial pressure, and low pulmonary vascular resistance.1–3 This procedure improves oxygen saturation by increasing effective pulmonary blood flow without increasing total pulmonary blood flow, pulmonary artery (PA) pressure, or cardiac work, and it does not produce PA distortion as with the systemic-pulmonary shunt. After initial widespread use, the disadvantages of this procedure became evident with the discovery of pulmonary arteriovenous fistulas on the side of the Glenn anastomosis, and difficulties in application of the technique in small children.4 Thus, it was largely replaced by the classic Fontan operation in the mid 1970s.5 However, some patients are not ideal candidates for the Fontan operation. To overcome these problems, a modification of the Glenn shunt, bidirectional cavopulmonary anastomosis, has been widely used. Like the classic Glenn shunt, it improves systemic arterial oxygen saturation and volume unloads the ventricle by increasing the effective pulmonary flow; it also alters ventricular geometry whether it is of right or left ventricular morphology.6,7 In the 1980s, there were several favorable reports on the bidirectional Glenn shunt, stressing that the pulmonary arteries were left in continuity and could be easily incorporated into a Fontan or modified Fontan procedure.6,8 Cavopulmonary anastomosis was identified as a natural step in these procedures.9 It decreases operative risk in a subsequent Fontan procedure and ensures better long-term ventricular function. Recently, cavopulmonary anastomosis has been included as part of total right heart bypass in both the intracardiac and extracardiac procedures.10,11 In this setting, superior vena cava-pulmonary artery anastomosis could be considered both as an intermediate step and as part of the procedure of total right heart bypass.
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PATIENTS AND METHODS
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Between June 1997 and July 2000, 170 patients received a bidirectional Glenn shunt at this institution. Their records were reviewed retrospectively. There were 88 males and 82 females, aged 0.5 to 20 years (mean, 7.3 years). Weights ranged from 6 to 42 kg (mean, 19.3 kg). Primary diagnoses are listed in Table 1
. Associated anomalies are shown in Table 2. A sternotomy was performed under general anesthesia with monitoring lines in place. The superior vena cava (SVC) was dissected intra- and extra-pericardially up to the innominate vein junction, after ligation of the azygous vein. Heparin was administered (2 mg•kg–1), and after mobilization of the SVC and the right PA, all right PA branches were occluded. A large side-biting clamp was applied to the right PA, a long incision was made in its superior aspect, and the opening was extended centrally. The SVC was clamped proximally and distally, and transected at the level of the right PA. Anastomosis of the SVC to the right PA was performed with running 6/0 polypropylene sutures. Four quadrant sutures were used to avoid the pursestring effect. The clamp was released when the anastomosis was completed. The cardiac end of the SVC was closed with 6/0 polypropylene sutures. Care was taken to avoid damaging the sinus node. The procedure was repeated when there was a left SVC; 20 patients received bilateral bidirectional Glenn shunts. Concomitant procedures are listed in Table 3. Three patients underwent a subsequent Fontan procedure without cardiopulmonary bypass (2 with an intracardiac tube, and 1 with an extracardiac tube).
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RESULTS
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There were 3 late operative deaths because of low cardiac output; mortality was 1.8%. Hemodynamic studies showed a mean postoperative SVC pressure of 13 ± 2 mm H2O. Arterial oxygen saturation rose from 78% ± 8.5% preoperatively to 90% ± 4.3% postoperatively. One patient diagnosed with transposition of the great arteries associated with a ventricular septal defect, pulmonary stenosis, and patent ductus arteriosus, had desaturation and the shunt was taken down 24 hours after the operation. Prolonged drainage (9 to 19 days) was required in 8 patients, 2 of whom had chylothorax. Reexploration was carried out in 5 patients because of bleeding. Hospital stay was 9.3 ± 3.5 days (range, 5 to 23 days). The postoperative course was uneventful in all other patients, echocardiography demonstrated no stenosis of the cavopulmonary anasto-moses, and electrocardiography showed no arrhythmias. Echocardiography and cardiac catheterization were performed to evaluate left ventricular volume, mass, ejection fraction, diameter of the PA ipsilateral to the shunt, and PA indices (cross-sectional areas including left, right, total, and lower lobe branch of the right and left PA at each point of measurement were indexed to body surface area) before subsequent Fontan procedures. Three patients had significant decreases in indexed end-diastolic volume (from a mean of 115 mL•m–2 to 70 mL•m–2) and moderate decreases in indexed ventricular mass (from 212 g•m–2 to 135 g•m–2) with no significant change in ejection fraction and PA indices after institution of the shunt.
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DISCUSSION
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There is certainly no unanimity on the criteria for per-forming a bidirectional cavopulmonary connection.6,12,13 Most authors would suggest that mean PA pressure should be less than 18 mm Hg, ideally less than 15 mm Hg, with a calculated pulmonary vascular resistance of less than 2.0 units•m–2. Although there are some general guidelines as to the caliber of PA acceptable for cavopulmonary anastomosis, it is acknowledged that these measurements do not take into consideration the compliance of the vascular bed, the so-called maturity of the pulmonary bed, or the most peripheral and intraparenchymal pulmonary arteries. PA distortion defined as peripheral PA stenosis, hypoplasia, or discontinuity, remains a risk factor for suboptimal operative outcome. The timing of cavopulmonary anastomosis is poorly defined. We believe it can be performed at approximately 6 months of age; others have indicated that it can be carried out at any age after the pulmonary vascular resistance has reached its nadir.14 Some have applied the technique in very young patients.15 It was found to facilitate ventricular volume unloading and regression of ventricular mass in younger children (< 1 year old), and the beneficial effect on ventricular end-diastolic volume and mass is clearly age-dependent, with older patients benefiting less in terms of enhanced systemic oxygen saturation.16 Older age might be a risk factor for postoperative cyanosis because of the lower proportion of caval return from the SVC relative to the inferior vena cava in the older child.17
Although the bidirectional Glenn shunt is widely used for a variety of complex congenital heart diseases, there are several concerns with this procedure as a long-term palliation. These include progressive desaturation, disparity with patient size, and pulmonary vascular changes such as arteriovenous fistulas, aortopulmonary collateral arteries, systemic venous collaterals, and potentially poor PA growth. However, these potential complications might be reduced or eliminated by allowing antegrade flow through the main PA, which provides pulsatility, increased absolute volume and flow rate, and hepatic venous blood to both lungs. The role of accessory pulmonary blood flow in the setting of a shunt is contentious; there is a trend toward improved survival when it is eliminated, whereas patients with accessory pulmonary flow have increased risks of effusion and prolonged hospital stay, higher central venous pressures, and late development of chylothorax.18 Mendelsohn and colleagues19 observed a significant decrease in mean PA pressure and a 32% decrease in indexed cross-sectional PA area. A decrease in the size of the central PA contralateral to the shunt reflects diminished blood flow to that lung, so it is questionable whether the shunt should be used as a staging maneuver when the PA size is a risk factor in the Fontan operation. Reddy and colleagues20 suggested the indexed cross-sectional area of the lower lobe branches of the right and left PA as more appropriate measures of PA growth; these PA indices do not change significantly after shunting and do not correlate with the outcome of a Fontan operation. In some patients, gradual enlargement of collateral venous channels between the SVC and the inferior vena cava occurs with diminished flow through the anastomosis and an increase in pressure in the SVC; these decompress the SVC system into the inferior caval system and contribute to progressive cyanosis. Coil embolization of multiple venous collaterals is necessary to increase arterial oxygen saturation. However, if not all venous collaterals are accessible for coil embolization, the cavopulmonary anastomosis must be taken down.8
Staging the Fontan operation by performing a bidirectional Glenn shunt first may allow some patients who would not otherwise qualify for a full Fontan procedure to show an improvement in ventricular function or a decrease in pulmonary vascular resistance after removal of the volume load. In this study, 3 patients were selected for a Fontan operation because follow-up examinations showed they had significant decreases in indexed end-diastolic volume and moderate decreases in indexed ventricular mass. Some patients did not report for follow-up because of economic or other reasons; others who will need a subsequent Fontan procedure are still being followed up.
Temporary shunts were not used in this study because central venous pressures did not increase excessively when the SVC was clamped. However, if the central venous pressure increases to a dangerous level, a temporary shunt should be used to avoid neurological damage and problems related to cardiopulmonary bypass. It can also provide excellent venous drainage with improvement in oxygen saturation during SVC clamping.21 The bidirectional Glenn shunt remains an excellent palliative procedure as a preliminary step to a Fontan operation or as an integral part of a Fontan or modified Fontan operation when the procedure is deferred because of age, weight, or cardiac malformations characterized by a hypoplastic right or left ventricle. Although the mortality and morbidity associated with a cavopulmonary connection have decreased in recent years, problems can still be identified.
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REFERENCES
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Abstract
INTRODUCTION
