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J Thorac Cardiovasc Surg 1994;107:1367-1368
© 1994 Mosby, Inc.

LETTERS TO THE EDITOR

Bidirectional inferior vena cava–pulmonary artery shunt

Department of Cardiothoracic Surgery
UCLA School of Medicine
Los Angeles, CA 90024-1741

Reply to the Editor:

I read with interest the letter from Dr. Luisi's group regarding the Fontan fenestration. We are in agreement that a surgical fenestration as in the partial Fontan operation ¹ can result in an excessive right-to-left shunt with unacceptable desaturation. For this reason, we believe that the adjustable atrial septal defect (ASD) that allows controlled graded adjustments of the right-to-left shunt depending on the arterial oxygen saturation and pressures is preferable to the punched-hole fenestration.

Dr. Luisi's group also comments that the snare-controlled adjustable ASD cannot always be enlarged by releasing the snare. We have found that if one uses the technique that we have described, ² with suturing of the heavy Prolene snare (Ethicon, Inc., Somerville, N.J.) to the edge of the polytetrafluoroethylene patch, the hole can be enlarged by pushing on the heavy Prolene sutures as they emerge from the interatrial septum. Once the chest is closed, however, we have also found that it is more difficult to enlarge the ASD. For this reason, the ASD is left excessively large and is adjusted in slow stages to the desired size after weaning from bypass.

The suggestion of performing an inferior vena cava (IVC) to pulmonary artery (PA) connection in place of a superior vena cava (SVC) to PA connection is an intriguing one. By delivering two thirds of the systemic venous return to the PA, the repair would be closer to a partial Fontan than the bidirectional Glenn shunt and would still be able to decompress via the azygos vein. It is a definite clinical impression that patients undergoing the "Kawashima operation" ³ do well after the operation without the post-Fontan systemic venous hypertension and low cardiac output. In this operation, the SVC with azygos continuity of the IVC is connected to the PA, leaving the hepatic veins draining into the right atrium. These patients thus have more pulmonary blood flow than those with the usual bidirectional Glenn shunt and additionally have a possibility of decompression through venous collaterals via the splanchnic bed to the hepatic veins. However, with the Kawashima operation, the hepatic veins remain at a lower pressure, which may reduce the postoperative fluid shifts and volume requirements caused by hepatic congestion and ascites.

One would expect, therefore, that patients with the IVC-PA connection would do somewhat better than those with an unfenestrated Fontan. The partial Fontan as performed at our institution, by incorporating an appropriately sized and controllable ASD, will allow one third of systemic venous return to shunt right to left and still achieve an arterial oxygen saturation of 85%. Complete separation of the pulmonary and systemic circulations with normalization of arterial saturation can be performed simply by snare closure of the ASD as indicated by improved hemodynamics during the postoperative period. A potential disadvantage of the IVC-PA connection is that it will need to be carried out with the aid of cardiopulmonary bypass with its attendant risks. In contrast, a bidirectional Glenn shunt can usually be performed without cardiopulmonary bypass and provides a small but significant increase in pulmonary blood flow, resulting in an acceptable saturation with only a small volume load. Because of the erect posture, SVC hypertension is better tolerated than is IVC hypertension, perhaps making a bidirectional Glenn shunt more desirable than an IVC-PA connection.

For these reasons, we believe that there would be only limited use for the IVC-PA connection. It would, however, be a more complete partial Fontan than the SVC-PA connection and therefore does have some advantages in terms of safe staging. We would be interested in any clinical experience with this innovative approach that you may aware of.

It may be of interest that we are currently performing what we call a modified Fontan with unidirectional caval connection in selected patients. The SVC is connected to the left PA, thus supplying the smaller left lung. The IVC is connected to the large right lung via a lateral tunnel with a snare-controlled adjustable ASD. This in a sense incorporates Dr. Luisi's idea regarding the matching of IVC flow and right PA size.

References

1. Bridges ND, Lock JE, Castaneda AR. Baffle fenestration with subsequent transcatheter closure: modification of the Fontan operation for patients at increased risk. Circulation 1990;82:1681-9.[Abstract/Free Full Text]
   
2. Laks H, Pearl JM, Haas GS, et al. Partial Fontan: Advantages of an adjustable interatrial communication. Ann Thorac Surg 1991;52:1084-95.[Abstract]
   
3. Kawashima Y, Kitamura S, Matsuda H, Shimazaki Y, Nakano S, Hirose H. Total cavopulmonary shunt operation in complex cardiac anomalies. J THORAC CARDIOVASC SURG 1984;87:74-81.[Abstract]
   

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