Surgical Considerations A majority, up to 85% in some series, of those with isomerism will require functionally univentricular palliation Those in whom a biventricular repair is feasible are more likely have left isomerism For those requiring functionally univentricular palliation, neonatal interventions may be required This may be in the form of a pulmonary artery banding, an aortopulmonary shunt, or a Norwood procedure depending on the specifics on the anatomy and the balance of systemic and pulmonary blood flow Some who will undergo functionally univentricular palliation may not require any neonatal intervention if they have relatively balanced circulations, which may be the case in the setting of doubleoutlet right (or solitary) ventricle with subpulmonary stenosis These patients may be functionally banded, maintaining reasonable relative systemic and pulmonary blood flow The second stage of functionally univentricular palliation will consist of a Glenn or Kawashima procedure Both of these procedures consist of a superior cavopulmonary anastomosis with the difference being primarily functional based on the underlying anatomy Those with an interrupted inferior caval vein that drains into the superior caval vein via an azygos or hemiazygos vein that undergoes a superior cavopulmonary anastomosis are said to undergo a Kawashima procedure This presents an important difference as a larger proportion of the systemic venous return now returns directly to the pulmonary circulation in a passive manner when compared to the Glenn After a Kawashima procedure, the only systemic venous return directly to the heart is likely hepatic venous return while after a Glenn procedure the inferior caval and hepatic venous flow remain, returning directly to the heart Approximately 85% of the systemic venous return is redirected into the pulmonary circulation after a Kawashima procedure With a larger proportion of blood flow being redirected directly to the pulmonary circulation at once, there is concern that patients may fair worse in the postoperative period after a Kawashima procedure when compared to a Glenn anastomosis, although in the modern era this does not appear to be the case If done too early in life, however, either form of superior cavopulmonary anastomosis could be poorly tolerated Anecdotally, patients undergoing the Kawashima procedure between 3 and 6 months of life tolerate the procedure well, although waiting beyond this period will allow for additional pulmonary arterial growth, pulmonary vascular maturation, and pulmonary vascular resistance decrease A study including slightly over 5000 patients undergoing the superior cavopulmonary anastomosis, of which 450 had isomerism, revealed that the median age of those having the Glenn procedure was 10 months in those without isomerism, compared to 13 months in those with isomerism Median length of admission for both groups was 8 days, and median cost of hospitalization did not differ The need for extracorporeal membrane oxygenation also did not differ between the two groups, with approximately 1% requiring extracorporeal membrane oxygenation Inpatient mortality was also comparable between the two groups, with a 2.4% inpatient mortality in those with isomerism.50 There are unique issues that sometimes arise with the superior cavopulmonary anastomosis in those with isomerism due to the frequent finding of systemic venous anomalies Of particular note is the situation in where bilateral superior caval veins are present In this situation, once bilateral superior cavopulmonary anastomoses have been constructed, the portion of the pulmonary arteries that lie between the two superior caval veins may receive limited flow and thus become hypoplastic, atretic, and even discontinuous Some groups have tried to reduce the risk of this by creating a V-shaped superior cavopulmonary anastomoses In this configuration, the ends of the superior caval veins are anastomosed to the pulmonary arteries such that the anastomoses are adjacent to each other This has demonstrated some benefit in preservation of the pulmonary arteries.51 The third stage of palliation for those undergoing functionally univentricular repair consists of an inferior cavopulmonary anastomosis, or Fontan procedure For those with an inferior caval vein returning directly to the heart, the Fontan conversion consists of the traditional inferior cavopulmonary anastomosis For those with an interrupted inferior caval vein, however, the Fontan conversion involves only the hepatic veins Conversion to the Fontan circulation should be done in both patients who have undergone a Glenn anastomosis or a Kawashima procedure The rationale for Fontan completion is the same in both groups The first aim is to further normalize saturations, with the second aim being to allow for the hypothetical hepatic factor to enter the pulmonary circulation The issue of the hepatic factor reaching the pulmonary circulation is of particular importance, as the agent, whatever it is, helps promote regression of and/or prevent the formation of pulmonary arteriovenous malformations The issue of pulmonary arteriovenous malformations is one that is of particular interest in those with isomerism, particularly those with left isomerism who have undergone a Kawashima procedure Nearly a third of these patients will develop pulmonary arteriovenous malformations, experiencing further desaturation as a result Catheterization and bubble echocardiography can help make the diagnosis of such pulmonary arteriovenous malformations Pulmonary arteriovenous malformations generally develop in the first 30 months after the Kawashima procedure Saturations will fall from the mid to high 80% range immediately after the procedure to approximately the mid to high 70% range due to the development of the pulmonary arteriovenous malformations A greater degree of desaturation may be noted, with rare cases of patients having saturations in the 50% range and 60% range In a majority of patients, completion of the Fontan circuit will lead to at least partial resolution of pulmonary arteriovenous malformations, with saturations generally reaching approximately 90% within 1 month of completion in most patients.52–54 Unpublished data have demonstrated that isomerism does independently increase the length and cost of admission for the conversion to the Fontan circulation The presence of isomerism independently increased the length of admission by approximately 1.6 days and increased the total charges for the admission by $31,000 Need for extracorporeal oxygenation and inpatient mortality during the admission did not differ between those with and without isomerism Inpatient mortality in those with isomerism was 3% Competitive flow in the pulmonary circulation from the various systemic venous returns can greatly impact distribution of blood flow after completion of the Fontan circulation In some instances, this may direct a majority of the hepatic venous flow to a single lung, leading to unilateral pulmonary arteriovenous malformations Some groups have tried to model flows using data from magnetic resonance imaging These data can be used to simulate how blood will flow through the circuit with a variety of different geometries Of particular interest has been the Y-graft, in which a single limb bifurcates into two separate limbs, which anastomose into the pulmonary arteries This has been demonstrated to have lesser power loss through the Fontan circuit, and improve hepatic flow distribution in computer modeling studies, but has not shown similar results in the limited clinical studies Y-grafts are more technically demanding and may also be prone to thrombus Such Y-grafts may be helpful in select patients, particularly in the setting of discontinuous pulmonary arteries.55–67 In addition to the Y-graft, other geometries have been developed and have shown benefit in specific patients Direct anastomosis of the hepatic veins into the azygos vein in those with an interrupted inferior caval vein has