Background. In the management of hearts with deranged laterality, it is essential that the left and right atrial chambers are correctly identified. There are two major approaches, which are based on venous connections or on the morphology of the atrial appendages, and there is no consensus as to which is the most useful. We used the iv/iv mouse mutant, which is known to be pertinent to this problem, to evaluate the relations of cardiac defects with atrial, venous, and other visceral morphologies. Methods and Results. The morphology of the heart and other organs was examined in 275 iv/iv mice using criteria based on abnormal laterality in humans. The arrangement of the atrial appendages was determined by morphological examination of the junction between the appendage and the venous component of the atrium. On this basis, 45.1% of cases were shown to have usual atrial arrangement, 50.2% had mirror imagery, 1.5% had right isomerism, and 3.3% had left isomerism. Every case of atrial isomerism had a cardiac lesion; the morphological types were similar to those seen in human cases. Of cases with either usual or mirror-image arrangement of the appendages, 33.2% had abnormal spleens, but only 3.1% had cardiac defects. Similarly, venous abnormalities were much more common (30.1%) than cardiac defects. Conclusions. Study results endorse the importance of the morphology of atrial appendages in predicting cardiac abnormalities and point to the marked inconsistency of the arrangement of other organs, including the spleen and the connections of the systemic veins.
