Ann Thorac Surg 2002;73:1280-1281
© 2002 The Society of Thoracic Surgeons
Original article: cardiovascular
Invited commentary
Christopher A. Caldarone, MDa
a University of Iowa and Clinics 200 Hawkins Dr, 1616B JCP Iowa City, IA 52242 USA
e-mail: chris-caldarone{at}uiowa.edu
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 Introduction
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Surgical palliation for patients with right atrial isomerism requiring a total cavopulmonary connection presents a formidable technical challenge due to the anatomic variability described in the present report of Aeba and colleagues. Separate orifices for the hepatic veins and inferior vena cava, a single orifice for entry of the pulmonary veins into the left atrium after surgical repair of anomalous venous drainage, and the relative location of the atrioventricular valve comprise the obstacles which must be circumvented to create unobstructed flow from the hepatic veins and inferior vena cava to the pulmonary artery while maintaining unobstructed flow between the pulmonary veins and the atrioventricular valve.
Although the concept of creating an unobstructed connection between the hepatic veins/inferior vena cava and the pulmonary artery is simple, the hemodynamic sequelae are complex. Significant energy losses can occur even with very small pressure gradients due to geometric characteristics of the flow pathway. These energy losses occur in large diameter portions of the pathway as the kinetic energy of the blood is lost to mixing and viscous dissipation prior to being reconverted into kinetic energy in the pulmonary arteries. Collision with the blood from the superior vena cava also contributes to the energy losses. Thus, with the wide variety of anatomic configurations possible in patients with right atrial isomerism, careful consideration of these geometric characteristics, as outlined by Aeba and associates is of critical importance. Such arguments support the concept of an extracardiac conduit which provides a smooth, tubular, energy efficient conduit for inferior vena cava to pulmonary artery flow. Although the authors report that magnetic resonance angiography with gradient-echo and phase contrast techniques was used to evaluate the various cavopulmonary connections, little detail is provided and the tantalizing potential to correlate three dimensional relationships with flow distribution is unrealized.
Separate orifices for the inferior vena cava and the hepatic veins, add a level of complexity to Fontan reconstruction in patients with right atrial isomerism. The separate orifices can be encompassed by the "intra-extra-atrial rerouting" technique described by Aeba and colleagues, thereby exteriorizing the orifices into an extracardiac conduit. In addition to the energy loss-related arguments above, the use of an extracardiac conduit also spares the atrial wall from distension in a high pressure system, and therefore, protects against atrial dilation and may reduce the risk of late atrial arrythmias. In light of the high incidence of early postoperative atrial arrythmias in this population and the unique anatomy of the conduction system in patients with asplenia, this strategy should offer a superior long term result in terms of reduced risk of late atrial arrythmias. This point, however, is far from proven. The data provided by Aeba and associates are inconclusive in demonstrating any short term electrophysiologic benefit with the extracardiac technique.
Doctor Aeba and colleagues also describe using the epicardial surface of the atrial wall as a portion of the Fontan pathway. Other authors have reported using of the epicardial portion of the atrial wall as a portion of a conduit in reconstruction for truncus arteriosus and pulmonary vein stenosis after repair of anomalous pulmonary venous drainage. Although this technique may allow for potential growth of the pathway, it also carries the risk of increased thromogenicity due to blood contact with the epicardium and the potential for dilation of the atrial portion of the high pressure pathway into the remaining low pressure left atrium. This paradoxical dilation of the atrial wall into the left atrial chamber may result in obstruction of the pulmonary veins or the atrioventricular valve.
The ultimate arbiter of these theoretical arguments, however, will be long term freedom from arrhythmia-related and obstruction-related morbidity. As these data become available for the general population of Fontan patients, the unique and widely variable anatomy in the subset of patients with right atrial isomerism may ultimately be the most fruitful in terms of correlating the geometry of surgical reconstruction techniques with long term freedom from arrhythmia-related and obstruction-related morbidity.
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Individualized total cavopulmonary connection technique for patients with Asplenia syndrome
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Ann. Thorac. Surg. 2002 73: 1274-1280.
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