The Cardiac Malpositions




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).




Cardiac malposition


An abnormal intrathoracic position of the heart.




Cardiac malposition


An abnormal intrathoracic position of the heart.




Situs


Site or position.




Solitus


Normal or usual.




Situs solitus


Normal position ( Figure 1 ) .




Figure 1


Normal heart and abdominal viscera in situs solitus. The stomach (S) is on the left, the liver (L) is on the right, the heart is left sided, the base-to-apex axis points to the left, and the left hemidiaphragm is lower than the right hemidiaphragm. The ascending aorta, the aortic knuckle (unmarked white arrows) , and the pulmonary trunk (PT) are in normal positions. The descending aorta (DAo) is concordant on the left.

Reproduced with permission from Perloff JK. The Clinical Recognition of Congenital Heart Disease . 5th ed. Philadelphia, Pennsylvania: W.B. Saunders, 2003.




Situs inversus


Mirror image ( Figure 2 ) .




Figure 2


The heart and viscera in a 65-year-old woman with complete situs inversus. The stomach (S) is on the right, the liver (L) is on the left, the heart is on the right, and the hemidiaphragm is lower on the side of the right cardiac apex. The ascending aorta, aortic knuckle (unmarked white arrows) , and pulmonary trunk (PT) are in mirror-image positions. The descending aorta (DAo) is concordant on the right.

Reproduced with permission from Perloff JK. The Clinical Recognition of Congenital Heart Disease . 5th ed. Philadelphia, Pennsylvania: W.B. Saunders, 2003.




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 ) .




Figure 3


X-rays from a 2-day-old male infant with ectopia cordis. The external position of the heart is obvious in the lateral projection (right, arrows) but not in the frontal plain (left) .

Reproduced with permission from Perloff JK. The Clinical Recognition of Congenital Heart Disease . 5th ed. Philadelphia, Pennsylvania: W.B. Saunders, 2003.




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 Praagh 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. 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 ).




Figure 4


In situs solitus, the morphologic right bronchus (RB) is short, wide, and straight, and the morphologic left bronchus (LB) is long, thin, and curved (upper left) . In situs inversus (upper right) , the morphologic right bronchus is left sided, and the morphologic left bronchus is right sided. Tomograms (lower and right images) show the morphologic RB and morphologic LB in situs solitus. TR = trachea.

Reproduced with permission from Perloff JK. The Clinical Recognition of Congenital Heart Disease . 5th ed. Philadelphia, Pennsylvania: W.B. Saunders, 2003.


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.




Figure 5


Schematic illustrations of the 4 basic cardiac positions (normal and 3 malpositions) and the relations of the descending aorta (Desc. ao.), cardiac apex, stomach, and liver as viewed on a frontal plain chest x-ray. In situs solitus, the descending aorta, cardiac apex, and stomach are on the left. In situs inversus with a right thoracic heart, the descending aorta, cardiac apex, and stomach are on the right. In situs solitus with a right thoracic heart, the descending aorta and stomach are on the left, and the cardiac apex is on the right. In situs inversus with a left thoracic heart, the descending aorta and stomach are on the right, but the cardiac apex is on the left.

Reproduced with permission from Perloff JK. The Clinical Recognition of Congenital Heart Disease . 5th ed. Philadelphia, Pennsylvania: W.B. Saunders, 2003.


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.


Dec 16, 2016 | Posted by in CARDIOLOGY | Comments Off on The Cardiac Malpositions
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