Review
The Cardiac Malpositions

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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.

Section snippets

Cardiac position

The intrathoracic position of the heart as left sided, right sided, or midline (i.e., levocardia, dextrocardia, or mesocardia).

Cardiac malposition

An abnormal intrathoracic position of the heart.

Situs

Site or position.

Solitus

Normal or usual.

Situs solitus

Normal position (Figure 1).

Situs inversus

Mirror image (Figure 2).

Displacement

An abnormal cardiac position secondary to eventration of a hemidiaphragm, agenesis of a lung, or congenital complete absence of the pericardium.

Ectopia cordis

Location of the heart outside the thoracic cavity (Figure 3).

Chamber designations

Right and left, as in right and left atrium and right and left ventricle.

Great arterial designations

The ascending aorta and pulmonary trunk defined by their ventricle of origin and by their morphology.

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.

Isomerism

From the Greek “isos,” equal, and “meros,” part. The similarity of bilateral structures that are normally dissimilar, such as right and left bronchi and right and left lungs. Isomerism is not an erroneous concept, Van Praagh6 notwithstanding.

Right isomerism

Bilateral structures with morphologic right characteristics, such as bilateral morphologic right bronchi and bilateral trilobed lungs.

Left isomerism

Bilateral structures with morphologic left characteristics, such as bilateral morphologic left bronchi and bilateral bilobed lungs.

Asplenia

Congenital absence of the spleen.

Polysplenia

Multiple spleens, each of which is appreciably smaller than a normal-sized spleen.

Ventricular loop

The straight heart tube of the embryo forms the left ventricle of the definitive heart. Looping is the consequence of the addition of new material at the arterial pole of the developing heart.

D-loop

Rightward (d = “dextro”) bend.

L-loop

Leftward (l = “levo”) bend.

Concordant

From the Latin “concordare,” to agree. A loop that agrees with the visceroatrial situs.

Atrioventricular concordance

Connection of a morphologic right atrium to a morphologic right ventricle and a morphologic left atrium to a morphologic left ventricle.

Ventriculoarterial concordance

Connection of a morphologic right ventricle to a pulmonary trunk and a morphologic left ventricle to an aorta.

Discordant

From the Latin “dis,” apart. Inappropriate.

Transposition of the great arteries

Each great artery arises from an anatomically discordant ventricle, the aorta from a morphologic right ventricle, and the pulmonary trunk from a morphologic left ventricle.

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.

Inversion

Mirror imagery.

Atrioventricular discordance

A morphologic right atrium connects to a morphologic left ventricle, and a morphologic left atrium connects to a morphologic right ventricle.

Ventriculoarterial discordance

A morphologic right ventricle gives rise to the aorta, and a morphologic left ventricle gives rise to the pulmonary trunk.

Double discordance

Atrioventricular discordance together with ventriculoarterial discordance. The result is physiologically correct circulatory flow.

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.

Heterotaxy with right isomerism

Heterotaxy (from the Greek “heteros,” different, and “taxis,” arrangement) is loosely and poorly translated as “another arrangement” or “a different arrangement.” Isomerism (from the Greek “isos,” equal) refers to the similarity of bilateral structures that are normally morphologically asymmetric, such as right and left bronchi, right and left lungs, and right and left atrial appendages. There is strong concordance between a morphologic right bronchus, a trilobed right lung, and a morphologic

Heterotaxy with left isomerism

Heterotaxy with left isomerism is more prevalent in women39 and is characterized by bilateral morphologic left bronchi, bilateral morphologic bilobed lungs, bilateral morphologic left atrial appendages, bilateral superior vena cavae attached to bilateral morphologic left atria, an absent or atretic sinoatrial node, common atrium, common atrioventricular valve, atrioventricular septal defect, and partial anomalous pulmonary venous connection. The pulmonary veins can be connected in a symmetric

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