Heterotaxy and Isomerism

HeterotaxyHeterotaxy refers to an abnormality of situsSitus or left–right patterning within the body, which is often associated with congenital heart diseaseCongenital heart disease and/or arrhythmiasArrhythmia. There are two main types: classic right isomerismIsomerism with asplenia and classic left isomerismIsomerism with polysplenia. Right isomerismIsomerism typically involves right ventricular outflow tract obstructionRight ventricular outflow tract obstruction, which is often ductal-dependent, and complete atrioventricular septal defectAtrioventricular septal defect (AVSD) with ventriculoarterial discordance that is often treated with staged univentricular palliation. The presence of obstructed total anomalous pulmonary venous connectionTotal anomalous pulmonary venous connection (TAPVC) portends a worse outcome. Classic left isomerismIsomerism with polysplenia, on the other hand, typically manifests with less significant structural congenital heart diseaseCongenital heart disease, often amenable to a biventricular repair. However, this form may present with potentially life-threatening bradyarrhythmias, particularly in the fetus. Mixed or disharmonious arrangements may occur in up to 20%. Extracardiac manifestations, such as poor splenic function, intestinal malrotation, and biliary atresia, are common and important to consider for comprehensive management. Outcomes of heterotaxyHeterotaxy patients are highly variable; survivalSurvival is lower compared to non-heterotaxyHeterotaxy patients with the same congenital heart defects. Risk factors for mortality from birth include right isomerismIsomerism/asplenia, obstructed pulmonary venous return, complete atrioventricular septal defectAtrioventricular septal defect (AVSD), and common atrioventricular valveCommon atrioventricular valve regurgitation.