Dextrocardia was known in the 17th century and was 1 of the first congenital malformations of the heart to be recognized. Fifty years elapsed before Matthew Baillie published his account of complete transposition in a human of the thoracic and abdominal viscera to the opposite side from what is natural. In 1858, Thomas Peacock stated that “the heart may be congenitally misplaced in various ways, occupying either an unusual position within the thorax, or being situated external to that cavity.” In 1915, Maude Abbott described ectopia cordis, and Richard Paltauf’s remarkable illustrations distinguished the various types of dextrocardia. In 1928, the first useful classification of the cardiac malpositions was proposed, and in 1966, Elliott et al’s radiologic classification set the stage for clinical recognition. The first section of this review deals with the 3 basic cardiac malpositions in the presence of bilateral asymmetry. The second section deals with cardiac malpositions in the presence of bilateral left-sidedness or right-sidedness. Previous publications on cardiac malpositions are replete with an arcane vocabulary that confounds rather than clarifies. Even if the terms themselves are understood, inherent complexity weighs against clarity. This review was designed as a guided tour of an unfamiliar subject.
Dextrocardia was 1 of the first congenital malformations of the heart to be recognized. The malposition was mentioned by Hieronymus Frabricius in 1606 and by Aurelio Severino in 1643. A century and a half then elapsed before Matthew Baillie published his account of “complete transposition in the human subject, of the thoracic and abdominal viscera to the opposite side from what is natural.” In 1858, Thomas Peacock wrote, “The heart may be congenitally misplaced in various ways, occupying either an unusual position within the thorax, or being situated external to that cavity.” In 1915, Maude Abbott described ectopia cordis. Richard Paltauf’s remarkable illustrations, also in 1915, distinguished the various types of dextrocardia, and in 1928, Mandelstam and Reinberg proposed the first useful classification of cardiac malpositions. Estimated prevalence is 0.10 per 1,000 live births.
In 1931, Maria de la Cruz, 1 of the world’s foremost cardiac embryologists, began to shed light on the embryologic basis of the malpositions, and the landmark observations of Van Praagh appeared in 1977. Campbell’s practical diagrams and Elliott et al’s radiologic classification in 1966 set the stage for the clinical recognition of the malpositions.
The first section of this review deals with the 3 basic cardiac malpositions in the presence of bilateral asymmetry. The second section deals with malpositions in the presence of bilateral left-sidedness or bilateral right-sidedness. The bronchi and lungs are bilateral but asymmetric. The liver is unilateral but transverse. The atria are asymmetric, but their appendages are symmetric.
The published research on cardiac malpositions is replete with an arcane vocabulary that confounds rather than clarifies. Even if the terms themselves are understood, inherent complexity weighs against clarity. So let me begin with definitions that may at least make the terms accessible.
Cardiac position
The intrathoracic position of the heart as left sided, right sided, or midline (i.e., levocardia, dextrocardia, or mesocardia).
Situs solitus
Normal position ( Figure 1 ) .
Situs inversus
Mirror image ( Figure 2 ) .
Ectopia cordis
Location of the heart outside the thoracic cavity ( Figure 3 ) .
Heterotaxy
From the Greek “heteros,” different, and “taxis,” arrangement. Loosely and poorly translated as “another arrangement” or “a different arrangement.” The internal thoracic organs and the abdominal organs exhibit abnormal left-right relations. The concept of bilateral right- and left-sidedness as it applies to the heart is a good mnemonic but is not supported by developmental or embryologic observations.
Malposition of the great arteries
Abnormal spatial relations of the aorta and pulmonary trunk to each other. Each of the abnormally related great arteries arises above the anatomically correct ventricle. The definition applies more accurately to anatomically corrected malposition, because the great arteries are also malposed in double-outlet left or right ventricle, but they do not arise from concordant ventricles.
Systematic analysis
Sequential attention to the atria, atrioventricular valves, atrioventricular connections, ventricles, ventriculoarterial connections, great arteries, and position or malposition of the heart and abdominal viscera.
I shall first deal with normal cardiac and abdominal visceral positions, then with the 3 major cardiac malpositions.
The embryonic straight heart tube initially bends to the right (d-loop), then moves to the left until the ventricular portion occupies a normal left thoracic position. Situs solitus can be inferred from the physical examination by percussing a left-sided heart, a left-sided stomach, and a right-sided liver. Chest x-ray confirms these positions ( Figure 1 ) and identifies concordant bronchial morphology ( Figure 4 ) . Chest x-ray also establishes a leftward base-to-apex axis, which is appropriate for situs solitus ( Figure 1 ).
The relative levels of the 2 hemidiaphragms are determined by the location of the cardiac apex, not by the location of the liver. In situs solitus, the left hemidiaphragm is lower than the right hemidiaphragm and vice versa. The ascending aorta is convex at the left basal aspect of the heart, and the descending thoracic aorta runs a course parallel to the left border of the vertebral column ( Figure 1 ). Situs inversus with a structurally normal right thoracic heart is usually a chance discovery on a routine chest x-ray that had been read as normal because the film was reversed.
There are 4 basic cardiac positions, normal and 3 malpositions ( Figure 5 ) : (1) situs solitus with a right thoracic heart, (2) situs inversus with a right thoracic heart, and (3) situs inversus with a left thoracic heart. A midline heart (mesocardia) is sometimes regarded as a fourth malposition.
In the general population, the incidence of situs inversus with a right thoracic heart is about 1 in 8,000. The thoracic and abdominal viscera are mirror images of normal, a morphologic right bronchus is concordant with the morphologic right atrium and a trilobed lung, and a morphologic left bronchus is concordant with the morphologic left atrium and a bilobed lung ( Figure 4 ). The heart is right sided; the right hemidiaphragm is lower than the left hemidiaphragm ( Figure 2 ); the ascending aorta, aortic knuckle, and pulmonary trunk; are in mirror image positions; and the aorta descends on the right.
In situs solitus with a right thoracic heart ( Figure 5 ), the lungs and abdominal viscera are normally positioned, the ascending aorta and aortic knuckle are normally located, the descending aorta runs its normal course along the left side of the vertebral column, but the major cardiac shadow lies to the right of midline. The base-to-apex axis points to the right, so the right hemidiaphragm is lower than the left hemidiaphragm. In situs solitus with a right thoracic heart, the embryonic straight heart tube initially bends rightward (d-loop) but fails to move into the left chest. In situs inversus with a left thoracic heart ( Figure 6 ) , the lungs and abdominal viscera are mirror images of normal. The left hemidiaphragm is lower than the right hemidiaphragm; the bronchi, atria, and lungs are inverted; the stomach is on the right; and the liver is on the left.
