There are five basic anatomic relationships that result in dextrocardia, and five that
result in levocardia. In each case, there are two that exist in venoatrial situs solitus,
one in venoatrial situs inversus, and the remaining two in venoatrial situs ambiguous.
Dextrocardia
Dextrocardia indicates that the cardiac mass is present in the right hemithorax. The
first form of dextrocardia in which situs solitus exists is dextroposition of the
heart, in which an extrinsic factor such as right pulmonary atresia results in the heart
shifting to the right side. A well-described condition, the scimitar syndrome, is
associated with dextroposition of the heart. In this condition there is hypoplasia of the
right lung, partial anomalous pulmonary venous connection to the inferior vena cava, and
right-sided aortopulmonary collaterals. The second form of dextrocardia in which situs
solitus exists is dextroversion, which results from rotational abnormalities of the
cardiac loop during development. Although venoatrial situs solitus exist, there may be
atrioventricular, ventriculoarterial discordance, or a single ventricle. One unique form
of dextroversion is termed the Cantrell syndrome, in which five components are present:
midline epigastric abdominal wall defect often associated with herniation or omphalocele,
a defect of the lower sternum, deficiency of the anterior diaphragm, defect of the
diaphragmatic portion of the parietal pericardium, and diverticulum of the left ventricle.
Dextrocardia associated with venoatrial situs inversus can be associated with tetralogy of
Fallot, double outlet right ventricle, and complete or corrected transposition of the
great arteries. Kartagener's syndrome consists of situs inversus, sinusitis and
bronchiectasis. Subsequent clinical studies indicated that infertility was found in males.
This led to the finding that ciliary action is defective among patients with this
syndrome, leading to the speculation that abnormal ciliary action during embryogenesis may
be a contributing factor to the situs inversus. Dextrocardia associated with situs
ambiguous is present in patients with the atrial isomerism syndromes which are described
above.
Levocardia
The type of situs resulting in levocardia resemble those of dextrocardia, tow being
associated with situs solitus, one with situs inversus, and two with situs ambiguous. The
first of these, the levocardia heart with situs solitus, is simply the normal heart. The
second is that of levoposition of the heart, in which the heart is further displaced into
the left hemithorax because of agenesis of the left lung. Levoversion of situs inversus
represents the opposite of dextroversion of situs solitus. In this condition,
atrioventricular and ventriculoarterial discordance is present, so that the typical
{S,L,L} TGA heart is present with its associated manifestations. Levocardia associated
with situs ambiguous is present in patients with the atrial isomerism syndromes which are
described above. |