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Management and outcome of heterotaxy (isomerism of the atrial appendages)

Alexander Lowenthal, MD
Theresa Tacy, MD
Rajesh Punn, MD
Section Editors
David R Fulton, MD
Candice Silversides, MD, MS, FRCPC
Deputy Editor
Carrie Armsby, MD, MPH


Heterotaxy, also referred to as isomerism of the atrial appendages, is defined as an abnormal assembly of the thoracic and abdominal organs from the normal arrangement known as "situs solitus." It is caused by disruption of left-right axis orientation during early embryonic development. Cardiac malformations are a major component of heterotaxy syndrome, resulting in significant morbidity and mortality. Abnormal cardiac development typically leads to atrial appendage isomerism, resulting in either bilateral paired right atria (right atrial isomerism [RAI]) or paired left atria (left atrial isomerism [LAI]).

This topic will review the management and outcome of patients with heterotaxy (isomerism). The anatomical variation, clinical manifestations, and diagnosis of heterotaxy (isomerism) are presented separately. (See "Anatomy, clinical manifestations, and diagnosis of heterotaxy (isomerism of the atrial appendages)".)


In patients with heterotaxy, the normal asymmetry of the thoracic and abdominal organs is lost, resulting in an unusual degree of symmetry of organs and veins. The term "isomerism," derived from Greek (iso, meaning "equal," and meros, meaning "part"), refers to this abnormal developmental symmetry in which morphologic structures that normally develop on one side or the other of the body are found on both sides of the body, and is the currently accepted term used to describe hearts with isomeric atria and atrial appendages [1]. So, in affected patients, instead of a distinct left and right side, individuals with isomerism will have either two right sides or two left sides resulting in either two right atria or two left atria (atrial isomerism) [2]. Atrial isomerism is a major component of heterotaxy and causes significant morbidity and mortality because of discordance among the heart, systemic and pulmonary vessels, and other organs, and also among components of the heart.

Atrial isomerism

Right atrial appendage isomerism — Right atrial appendage isomerism, also referred to as right atrial isomerism (RAI), results in two right sides with bilateral right atria and atrial appendages, and an absence of left-sided structures (eg, coronary sinus). These patients usually have pulmonary venous anomalies, such as anomalous pulmonary venous connections or small pulmonary veins. Single ventricle physiology is predominant in RAI, as patients usually have a hypoplastic left ventricle. These patients also typically have asplenia, as the spleen is a left-side abdominal organ. (See "Anatomy, clinical manifestations, and diagnosis of heterotaxy (isomerism of the atrial appendages)", section on 'Right atrial isomerism'.)

In general, patients with RAI most often present during the neonatal period with cyanosis due to right-to-left shunting as a result of pulmonary outflow obstruction and septal defects between the atria and ventricles. In severely affected neonates, survival is dependent on maintaining a patent ductus arteriosus. In other cases, respiratory distress may develop because of pulmonary congestion due to pulmonary venous obstruction.


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Literature review current through: Sep 2016. | This topic last updated: Mar 31, 2016.
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