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(Circulation. 1995;92:294-297.)
© 1995 American Heart Association, Inc.

Articles

Bidirectional Glenn

Is Accessory Pulmonary Blood Flow Good or Bad?

Presented in part at the 67th Scientific Sessions of the American Heart Association, Dallas, Tex, November 16, 1994, and published in abstract form (Circulation. 1994;90[pt 2]I-421).

Richard D. Mainwaring, MD; John J. Lamberti, MD; Karen Uzark, PHD; Robert L. Spicer, MD

From the Divisions of Cardiac Surgery and Cardiology, Children's Heart Institute, Children's Hospital-San Diego, Calif.

Correspondence to Richard D. Mainwaring, MD, 3030 Children's Way, Suite 310, San Diego, CA 92123.

	Abstract

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Background The bidirectional Glenn (BDG) is frequently used in the staged surgical management of single ventricle patients. Controversy exists whether accessory pulmonary blood flow (APBF) sources should be left at the time of the BDG to augment systemic saturation or should be eliminated to reduce volume load of the ventricle. The present study was a retrospective review to assess the influence of APBF on outcome after the BDG.

Methods and Results Ninety-two patients have undergone BDG at our institute during the interval from 1986 through 1994. At the time of BDG, 40 patients had either a systemic-to–pulmonary artery shunt or patent right ventricular outflow tract as an additional source of pulmonary blood flow. Fifty-two patients had elimination of APBF. There were three operative deaths (two with and one without APBF) and four procedures (two in each group) that failed and required subsequent revision. Thus, there were 85 patients who underwent successful operation. Effusions (defined as chest tube drainage exceeding 7 days' duration) occurred in 8 of 85 patients; this complication was seen in 7 of 36 patients (19%) with APBF and 1 of 49 patients (2%) without APBF (P<.05). There were 11 deaths, including 6 patients (17%) with APBF, 2 patients (4%) without APBF, and 3 of the patients (75%) who had a failed BDG.

Conclusions The data suggest that morbidity and mortality are lower in patients in whom APBF is eliminated at the time of the BDG.

Key Words: shunts • ventricles • blood flow

	Introduction

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The bidirectional Glenn (BDG) procedure is frequently performed as part of the staged surgical management of single ventricle patients who will ultimately undergo a Fontan operation.^{1 2} The use of this approach has a number of theoretical advantages, including the early elimination of volume load,³ reducing reliance on palliative procedures, such as systemic-to–pulmonary artery shunts and pulmonary artery bands,^{4 5} and simplifying the operative procedure at the time of the Fontan.⁶ Several centers have reported reduced morbidity and mortality of the Fontan procedure in those patients who have undergone BDG, supporting the efficacy of this concept.^{7 8} As a result, the BDG has assumed an increasingly important role in the management of the single ventricle patient.⁹

Although many centers endorse the staged surgical approach to single ventricle patients, certain controversies still exist. There is considerable debate concerning the timing of the BDG, as well as the ideal interval between BDG and the Fontan procedure.¹⁰ In addition, there is a divergence of opinion as to the merits of leaving an accessory source of pulmonary blood flow (eg, a systemic-to–pulmonary artery shunt or a patent right ventricular outflow tract) at the time of the BDG. Proponents suggest that a dual source of pulmonary blood flow results in more satisfactory levels of arterial saturation, but opponents emphasize the merits of eliminating volume loads to the heart.¹¹

At Children's Hospital-San Diego, we began performing the BDG in 1986.¹² For several years, accessory sources of pulmonary blood flow were left in the majority of operations performed, whereas in more recent years we have favored eliminating these additional sources of blood flow. The present study reviews our experience to assess the impact of accessory pulmonary blood flow on outcome after the BDG.

	Methods

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This study was a retrospective review of our institutional experience with the BDG procedure. From February 1986 through September 1994, 92 BDG operations were performed. Two groups were formulated on the basis of the presence or absence of accessory pulmonary blood flow, which included either a systemic-to–pulmonary artery shunt or a patent right ventricular outflow tract. Aortopulmonary collateral vessels were excluded from our definition as a source of accessory pulmonary blood flow. Fig 1 summarizes the number of cases performed per year over this interval.

View larger version (38K): [in this window] [in a new window]   Figure 1. Bar graphs indicating the number of bidirectional Glenn (BDG) procedures performed at our institute each year from February 1986 through October 1994. The shaded portion of each bar represents number of patients who underwent BDG with an accessory source of pulmonary blood flow (BDG+APBF). The open portion of each bar represents number of patients who underwent BDG as the sole source of pulmonary blood flow (BDG).

Forty patients had a shunt or patent right ventricular outflow tract as an additional source of pulmonary blood flow augmenting the BDG. The median age of these patients at operation was 11 months (range, 2.5 to 195 months; 10th to 90th percentile, 3 to 53 months) and the median weight was 7.4 kg (range, 3.9 to 37 kg; 10th to 90th percentile, 4.8 to 13.1 kg). Thirty of these patients (75%) had undergone a previous palliative procedure (see Table 1). Concomitant procedures performed in this group are summarized in Table 2.

View this table: [in this window] [in a new window]   Table 1. Previous Palliative Procedures: Bidirectional Glenn With Accessory Pulmonary Blood Flow

View this table: [in this window] [in a new window]   Table 2. Concomitant Procedures: Bidirectional Glenn With Accessory Pulmonary Blood Flow

Fifty-two patients had no accessory pulmonary blood flow at the time of the BDG. Median age was 8.6 months (range, 2.2 to 46 months; 10th to 90th percentile, 4 to 14 months) and the median weight was 6.9 kg (range, 3.9 to 15.8 kg; 10th to 90th percentile, 5.2 to 10.3 kg). Thirty-two of the 52 patients had undergone a previous palliative procedure (see Table 3). Concomitant procedures are summarized in Table 4.

View this table: [in this window] [in a new window]   Table 3. Previous Palliative Procedures: Bidirectional Glenn Without Accessory Pulmonary Blood Flow

View this table: [in this window] [in a new window]   Table 4. Concomitant Procedures: Bidirectional Glenn Without Accessory Pulmonary Blood Flow

The results of this study are reported as either the mean±SEM or, where appropriate, the median with the range and 10th to 90th percentile limits. Statistical comparison of the two groups was performed using a Mann-Whitney test. Kaplan-Meier survival curves were constructed using the product-limit method. To test for an association between survival and year of follow-up, a two-tailed Fisher's exact test was used. A value of P<.05 was considered significant.

	Results

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Comparison of the two groups demonstrated no differences with respect to age, weight, incidence of previous operation, or number of concomitant procedures. The groups did differ with regard to surgical date, with patients having accessory pulmonary blood flow undergoing operation significantly earlier in this series (P<.05).

There were three operative deaths (3.3%), two occurring in the group with accessory pulmonary blood flow and one without accessory pulmonary blood flow. Causes of operative death included failure to oxygenate, leading to myocardial dysfunction in two patients, and primary myocardial dysfunction in one.

Four patients (two from each group) underwent a BDG that failed to provide satisfactory palliation and subsequently required surgical revision. Each of these patients had significant hypoplasia of one branch pulmonary artery and underwent attempted pulmonary artery reconstruction at the time of the BDG. Two patients had acute thrombosis of the BDG managed by insertion of a systemic-to–pulmonary artery shunt on the side of the discontinuous pulmonary artery. One patient had late thrombosis and also underwent systemic-to–pulmonary artery shunt. The fourth patient on follow-up had severe stenosis of one pulmonary artery and underwent revision and patch enlargement. This attempt resulted in thrombosis, and subsequently a shunt was performed to the discontinuous pulmonary artery.

Eighty-five patients underwent successful BDG (36 with accessory pulmonary blood flow and 49 without). Effusions (defined as chest tube drainage exceeding 7 days) occurred in 7 patients (19%) in the former group and in 1 (2%; P<.05) in the latter group (Fig 2).

View larger version (32K): [in this window] [in a new window]   Figure 2. Bar graphs indicate incidence of pleural effusions after BDG. Abbreviations as in Fig 1.

Length of hospital stay for the two groups is shown in Fig 3. There were 3 patients (6%) who underwent BDG with no accessory pulmonary blood flow whose hospital stay exceeded 14 days. In contrast, 11 patients (31%) in the group with accessory pulmonary blood flow had a hospital stay in excess of 2 weeks (P<.05). More than half of the prolonged hospitalizations were attributable to the development of effusions. Other causes of prolonged stay included poor oxygenation (n=2), low cardiac output (n=2), sepsis (n=1), and sick sinus syndrome requiring pacemaker insertion (n=1).

View larger version (12K): [in this window] [in a new window]   Figure 3. Plot shows hospital length of stay for patients undergoing BDG with and without accessory pulmonary blood flow. Abbreviations as in Fig 1.

There were 11 late deaths including 6 patients (17%) with accessory pulmonary blood flow, 2 patients (4%) without accessory pulmonary blood flow (P<.05), and 3 of the patients (75%) who had a failed BDG. Causes of late death are listed in Table 5.

View this table: [in this window] [in a new window]   Table 5. Causes of Late Death After Bidirectional Glenn

Actuarial analysis was performed for patients undergoing BDG with and without accessory pulmonary blood flow (Fig 4). This evaluation indicates 1-, 2-, and 3-year survival rates of 92%, 84%, and 77% with accessory pulmonary blood flow versus 98%, 91%, and 86%, respectively, without accessory pulmonary blood flow.

View larger version (13K): [in this window] [in a new window]   Figure 4. Actuarial analysis of patients undergoing BDG with and without accessory pulmonary blood flow. This analysis includes operative mortality at the time of BDG. Abbreviations as in Fig 1.

Fifty-three of the 85 patients who underwent successful BDG have subsequently undergone completion of their Fontan procedure. This includes 22 of 36 patients with accessory pulmonary blood flow and 31 of 49 patients without accessory pulmonary blood flow. There were 3 (6%) early and 3 (6%) late deaths after the Fontan procedure.

	Discussion

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Patients with single ventricle must eventually undergo Fontan procedure if they are to achieve separation of their systemic and pulmonary circulations. Although this goal is widely accepted, the method of achieving this goal continues to evolve. The BDG is commonly used as an intermediate step in this strategy. The present study was undertaken to assess the influence of accessory pulmonary blood flow on outcome after the BDG. The data demonstrate that patients undergoing BDG with no other sources of accessory pulmonary blood flow had a lower incidence of pleural effusions, and fewer of these patients required prolonged hospitalizations. In addition, overall survival appears to be improved in patients in whom accessory pulmonary blood flow was eliminated.

Effusions are one of the principal causes of extended hospital stay after BDG. This complication was seen in 9% of patients who underwent successful operation, an incidence comparable to previous reports.¹³ However, in our series, the incidence of effusions was ninefold higher in the group with accessory pulmonary blood flow. The cause of pleural effusions after BDG remains uncertain but clearly must be associated with an increased left-to-right shunt. The single patient who developed an effusion after BDG without accessory pulmonary blood flow had a large aortopulmonary collateral vessel that served as the major source of pulmonary blood flow preoperatively. When this patient developed an effusion postoperatively, catheter embolization was performed with resolution of this complication.

Combined early and late deaths occurred in 21% of patients with accessory pulmonary blood flow compared with 6% of patients without accessory pulmonary blood flow. Several deaths were likely unrelated to the BDG (eg, the patient who died of tracheal complications), although others may be more directly related (such as those after the Fontan procedure). The actuarial analysis does suggest a survival advantage for patients without accessory pulmonary blood flow. The reason for this difference is unknown, but potentially early relief from volume load could result in either improved preservation of ventricular function¹¹ or a reduction in changes in pulmonary vascular resistance.⁴

Mendelsohn et al¹⁴ have demonstrated that the BDG may result in impaired growth of the pulmonary arteries. Potentially, this could have an adverse effect at the time of the Fontan, and some authors have emphasized the importance of pulmonary artery size in this operation.¹⁵ Others have found that pulmonary artery size does not predict survival after the Fontan procedure.^{16 17} Certainly, if pulmonary artery size were universally accepted as an important predictive factor, then one might speculate that the addition of accessory pulmonary blood flow to the BDG might facilitate pulmonary artery growth and improve outcome after the Fontan. From our data, one could infer that pulmonary artery growth does not appear to be a significant clinical problem because patients undergoing BDG without accessory pulmonary blood flow demonstrate a level survival curve, at least through 3 years of follow-up, with a significant number having completed the Fontan.

Pulmonary arteriovenous (AV) fistulas after the BDG procedure have been a theoretical concern. The development of pulmonary AV fistulas has been noted after the classic Glenn shunt¹⁸ and after the Kawashima operation.^{19 20} Both of these operations exclude hepatic venous circulation to the lungs on first pass, suggesting a "hepatic factor" in the etiology of pulmonary AV fistulas.²¹ Since the BDG also excludes hepatic circulation to the lungs, it is plausible that pulmonary AV fistulas could develop in this setting. This rationale has been put forth as an argument in favor of including a source of accessory pulmonary blood flow.²¹ However, we have not observed the development of pulmonary AV fistulas after BDG except in the specific circumstance of interrupted inferior vena cava with azygous continuation. There were 4 patients included in our series with this systemic venous anatomy, 2 of whom have subsequently developed fistulas. In contrast, none of the 88 patients with a continuous inferior vena cava have developed pulmonary AV fistulas. Thus, the argument to leave accessory pulmonary blood flow to prevent pulmonary AV fistulas does not seem to be well founded for the vast majority of patients. Whether a source of accessory pulmonary blood flow would prevent pulmonary AV fistulas after the Kawashima operation is unknown.

The BDG procedure failed in 4 of 92 patients; each of these patients had severe stenosis and hypoplasia of the left pulmonary artery. Attempts at reconstruction of the pulmonary arteries may increase the risk of thrombosis after BDG secondary to the low pressure venous flow. Each of these patients subsequently had a shunt placed to the discontinuous pulmonary artery. One patient developed pleural effusions after this procedure and eventually died of sequelae of the effusion. Two other patients in this group died, resulting in an overall mortality rate of 75% for failed procedures. On the basis of this experience, it is our current recommendation to address severe pulmonary artery stenosis or hypoplasia well in advance of the BDG using either surgical or stent techniques.²²

In summary, patients undergoing the BDG and having no accessory pulmonary blood flow had lower morbidity and mortality than patients with accessory pulmonary blood flow. It is our belief that relief from volume loading will aid in preserving both pulmonary and ventricular function. Further study is required to determine whether this strategy will improve long-term outlook after the Fontan procedure.

	Acknowledgments

 
The authors would like to thank Patricia Silva, MS, for her assistance with the statistical analysis.

	References

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