Diagnosis and significance of atrial isomerism

Fifty-one patients at the Brompton Hospital were identified as having either right or left atrial isomerism by reviewing the records and catheterization, echocardiographic and, in 17 cases, autopsy data. Every study patient had 1 or more of the following conditions: isomeric bronchial anatomy; angiographic or necropsy evidence of atrial anatomy; echocardiographic diagnosis of isomerism; and anomalies of systemic or pulmonary venous connection. Patients with anomalous venous connections all had additional signs of isomerism. Neither right nor left type was predominant in either sex. The heart was in the left chest slightly more often than the right. Abdominal visceral heterotaxy was the most frequent radiographic finding. An ambiguous and biventricular connection was the commonest type of atrioventricular (AV) connection in left isomerism. A common AV valve was the most frequent mode of connection in both forms. Univentricular AV connection, double-outlet right ventricle, pulmonary atresia and discordant ventriculoarterial connection were commoner in right isomerism. Left isomerism is associated with much longer survival, its constellation of associated malformations frequently being less severe and more amenable to corrective surgery. A precise diagnosis must be made during life in order to select the most appropriate treatment.