The cardiac malpositions

The history

Situs inversus with dextrocardia and a structurally normal heart is usually discovered by chance in a chest x-ray that is often considered normal because the film is inadvertently reversed when first read. Situs inversus with dextrocardia is the malposition most likely to occur with an otherwise structurally normal heart and with normal longevity. Symptoms caused by coexisting acquired cardiac or noncardiac disease may lead to the discovery of hitherto unsuspected situs inversus . The pain of ischemic heart disease is located in the right anterior chest with radiation to the right shoulder and right arm. The pain of appendicitis is referred to the left lower quadrant, and the pain of biliary colic presents in the left upper quadrant ( Fig. 3.12 ).

In 1933 Kartagener called attention to the association of sinusitis, bronchiectasis, and situs inversus , a combination subsequently called Kartagener syndrome or triad. In 1986 a study of cilia ultrastructure in Kartagener syndrome found a widespread inherited ciliary disorder that included the upper and lower respiratory tracts including bronchitis, bronchiectasis, and sinusitis. Associated abnormalities of the testis with sperm immobility and infertility are commonly described associations in men, although Kartagener syndrome has been described in women. Kartagener syndrome is sometimes familial. One family of six siblings included two cases of Kartagener syndrome and two cases of isolated bronchiectasis.

Situs solitus with dextrocardia occasionally occurs without coexisting congenital heart disease and escapes recognition. A routine chest x-ray may provide the first evidence (see Fig. 3.9 ). As a rule, accompanying congenital cardiac malformations bring the patient to medical attention. Situs inversus with levocardia (see Fig. 3.10 ) invariably occurs with coexisting congenital heart disease that leads to the discovery of the cardiac malposition.

Physical appearance, the arterial pulse, and the jugular venous pulse

These features are determined by coexisting congenital heart disease rather than the cardiac malposition . The left testicle in the normal upright male is lower than the right testicle, whereas the opposite is the case in situs inversus . Poland syndrome, which is characterized by absence of a pectoralis major muscle (usually right-sided), ipsilateral syndactyly, brachydactyly, and hypoplasia of a hand, has been reported with situs solitus and dextrocardia and the Goldenhar syndrome (oculoauricular vertebral dysplasia, hemifacial microsomia) has been reported with complete situs inversus .

Percussion and palpation

A right anterior chest bulge with asymmetry arouses suspicion of dextrocardia. Percussion and palpation are useful in the clinical recognition of cardiac malpositions because these physical signs are influenced by the malposition per se and establish the right or left thoracic location of the heart and the abdominal location of hepatic dullness and gastric tympany. If the stomach is not sufficiently air-filled to generate a tympanitic percussion note, a carbonated beverage or deliberate aerophagia (an infant can suck an empty bottle) solves the problem. Percussion begins over the sternum and then compares left and right parasternal sites. The side of major cardiac dullness is more accurately established by percussing with the patient turned moderately to the left and then moderately to the right. The heart tends to fall to the side toward which the base to apex axis points. Situs inversus with dextrocardia is characterized by gastric tympany on the right, hepatic dullness on the left, and cardiac dullness on the right (see Figs. 3.3 and 3.6 ). Situs solitus with dextrocardia is characterized by normal locations of gastric tympany and hepatic dullness and by cardiac dullness on the right (see Figs. 3.6 and 3.9 ). Situs inversus with levocardia is the converse of situs solitus with dextrocardia (see Figs. 3.6 and 3.10 ).

Palpation is undertaken with the patient supine and then in both left and right lateral decubitus positions. The normal situs solitus heart (see Fig. 3.1 ) is represented by a morphologic left ventricle that occupies the apex and a morphologic right ventricle that underlies the lower left sternal border. Situs inversus with dextrocardia (see Fig. 3.3 ) is represented by a morphologic left ventricle that occupies the apex in the right hemithorax and a morphologic right ventricle that underlies the lower right sternal border. Situs solitus with dextrocardia is represented by a right thoracic apical low-pressure morphologic right ventricle that retracts and a high pressure systemic morphologic left ventricle that generates outward systolic movement adjacent to the lower right sternal border (see Figs. 3.8 and 3.9 ). Situs inversus with levocardia and l-bulboventricular loop is represented by a left thoracic apical low pressure morphologic right ventricle that retracts and a high-pressure systemic morphologic left ventricle that generates outward systolic movement adjacent to the lower left sternal border (see Fig. 3.10 ).

Auscultation

The relative prominence of auscultatory events should be compared in the left and right anterior hemithorax, more specifically along the left and right sternal borders and at the apices ( Fig. 3.13 ). The stethoscope should alternate from one side to the other to compare analogous right and left thoracic sites. With dextrocardia, the first and second heart sounds are louder in the right anterior chest (see Fig. 3.13 ); splitting of the second sound in the second right intercostal space is a feature of dextrocardia just as splitting of the second heart sound in the second left interspace is a feature of a left thoracic heart. In situs solitus with dextrocardia and a d-bulboventricular loop (see Figs. 3.8 and 3.9 ), the position of the pulmonary valve results in splitting of the second sound in the second right interspace, and the anterior position of the aorta results in amplification of the aortic component ( Fig. 3.14 ). In situs inversus with levocardia, splitting of the second sound is more prominent in the second left interspace.

The location and radiation of murmurs are governed by the type of cardiac malposition. In situs inversus with dextrocardia, murmur sites are the mirror images of normal. In situs solitus with dextrocardia, a pulmonary stenotic murmur is louder to the right of the sternum ( Fig. 3.15 ) and radiates upward and to the left because of the direction taken by the pulmonary trunk (see Fig. 3.8 A).

The electrocardiogram

In situs inversus with dextrocardia, a mirror image sinus node lies at the junction of a left superior vena cava and the mirror image left-sided morphologic right atrium. The right and left bundle branches supply their corresponding mirror image right and left ventricles. It is essential to be certain that the limb leads are properly attached before proceeding with interpretation of the 12-lead electrocardiogram. Interpretation in mirror image dextrocardia is easier when the arm leads are intentionally reversed and when right precordial leads are intentionally recorded from locations that are the exact opposites of standard left precordial lead positions ( Fig. 3.16 ). In situs solitus with dextrocardia , the limb leads are best left unchanged while the precordial leads are recorded from the right anterior chest ( Fig. 3.17 ). This recommendation is appropriate because atrial situs is normal (sinus node is at the junction of the right superior vena cava and morphologic right atrium on the right) and because the base to apex axis points to the right whether the bundle branches supply their corresponding ventricles as d-loop or l-loop. In situs inversus with levocardia , standard limb lead and precordial lead positions suffice ( Fig. 3.18 ).

Analysis of the electrocardiogram starts with the P wave. In situs solitus with either levocardia or dextrocardia, atrial depolarization proceeds from a normally positioned right sinus node, so upright P waves appear in leads 1 and aVL and an inverted P wave appears in lead aVR ( Fig. 3.19 ). Conversely, in situs inversus with either dextrocardia or levocardia, atrial depolarization proceeds from a left sinus node, so inverted P waves appear in leads 1 and aVL and an upright P wave appears in lead aVR (see Figs. 3.16 and 3.18 ). In the presence of a right sinus node, the direction of the P wave can be altered by a left atrial ectopic focus. The Valsalva maneuver, ocular pressure, or exercise may transiently shift the ectopic focus to the right sinus node. Left atrial ectopic rhythm is manifested by a negative P wave in lead 1 and isoelectric or negative P waves in left precordial leads (see Fig. 3.17 ). A less common but more distinctive configuration is the dome and dart P wave in lead V1 ( Fig. 3.20 ). A negative P wave in lead 1 or lead V1 does not distinguish situs solitus with a left atrial ectopic rhythm from situs inversus , but a dome and dart P wave in lead V1 or V2 confirms a left atrial ectopic focus irrespective of atrial situs.

In situs inversus with dextrocardia , ventricular activation and repolarization are the reverse of normal, as predicted in 1889 (see Fig. 3.16 ). In lead 1, the major QRS deflection is negative and the T wave is inverted; lead aVR resembles lead aVL and vice versa, and right precordial leads resemble leads from corresponding left precordial sites (see Fig. 3.16 ). Septal Q waves appear in right lateral precordial leads rather than in left lateral precordial leads because septal depolarization proceeds from right to left (see Fig. 3.16 ). The electrocardiogram can be “corrected” when limb leads are reversed and chest leads are recorded from right precordial sites (see earlier).

In situs solitus with dextrocardia and a d-loop, the left ventricle is relatively anterior and the right ventricle lies to the right (see Fig. 3.9 ); left ventricular electrical activity is directed anteriorly and right ventricular activity is directed to the right. Depolarization in the frontal plane is counterclockwise, so Q waves appear in leads 1 and aVL (see Figs. 3.17 and 3.19 ). Precordial leads display relatively prominent R waves in leads V1 and V2 (anterior left ventricular forces) and display prominent RS complexes in most of the remaining right precordial leads (see Fig. 3.17 ). Normal left to right septal depolarization (d-loop) results in Q waves in standard left precordial locations (see Figs. 3.17 and 3.19 ). The converse is the case for an l-loop with which Q waves are absent in left precordial leads and are present in right precordial leads, indicating right-to-left septal depolarization ( Fig. 3.21 ). Left ventricular hypertrophy is manifested by tall R waves in leads V1 and V2, whereas right ventricular hypertrophy is manifested by tall R waves in leads V5R and V6R and deep Q waves in lead 1 (see Figs. 3.17 and 3.19 ). In situs inversus with levocardia and l-loop, septal depolarization is right-to-left, so precordial Q waves are present at right sites and are absent on the left.

The x-ray

The x-ray permits confident recognition of cardiac malpositions. ^{, , ,} The first necessity is to identify the orienting letters L and R or analogous symbols that designate left and right. From the radiologic point of view, this is all that is required to diagnose situs inversus with dextrocardia (see Fig. 3.3 ). The aorta is in its inverted position with the arch deviating the trachea toward the left , the descending thoracic aorta runs as a fine line along the right vertebral border, and the major cardiac shadow to the right of midline (see Figs. 3.3 and 3.22 A). Situs inversus is missed if the film is inadvertently read in a reversed position, because it then appears correct except for the L and R designations that are on the wrong side (see Fig. 3.22 B). Complete situs inversus implies atrial situs inversus (visceroatrial concordance) (see Figs. 3.7 and 3.22 ), which is established by identifying the inverted morphologic right and left bronchi (see Fig. 3.4 ).

Situs solitus with dextrocardia (see Figs. 3.8 , 3.9 , and 3.23 A) is represented by normal positions of the stomach, liver, descending thoracic aorta, and right and left bronchi, by the major cardiac shadow to the right of midline, and by the right hemidiaphragm lower than the left hemidiaphragm because the cardiac apex is on the right. ^, The position of the ascending aorta permits identification of a d-bulboventricular loop (see Fig. 3.23 A).

Situs inversus with levocardia is represented by inverted positions of the stomach, liver, descending aorta, and bronchi, while the major cardiac shadow is to the left of midline and the left hemidiaphragm is lower than the right hemidiaphragm because the cardiac apex is on the left (see Figs. 3.10 , 3.24 , and 3.25 ). When the bulboventricular loop is discordant for situs inversus (d-loop), the ascending aorta forms a smooth contour at the left basal aspect of the heart (see Fig. 3.24 ).

A midline cardiac position —mesocardia—is uncommon and is usually represented by situs solitus with a d-bulboventricular loop that stops at midline as it pivots from right to left (see Fig. 3.11 ). A hump-shaped contour of the right cardiac border is due to superimposition of right ventricular and right atrial shadows (see Fig. 3.11 B ).

The echocardiogram

Echocardiography with color flow imaging lends itself to systematic segmental analysis of visceroatrial situs, atrioventricular connections, ventricular locations, and the spatial relationships and ventricular alignments of the great arteries. Atrial morphology and atrial situs are established by identifying the right atrial appendage with its broad junction and the left atrial appendage with its narrow junction. However, it is easier to infer atrial morphology and situs from the abdominal echocardiogram. The normal situs solitus with left thoracic heart is represented by an aorta on the left side of the spinal column and an inferior cava on the right side of the spinal column ( Fig. 3.26 ). The morphologic right atrium resides on the same side as the inferior vena cava (atrial situs solitus). The inferior vena cava and aorta are distinguished from each other by color flow imaging because the aorta pulsates. The liver is on the right and the stomach on the left —normal positions (see Fig. 3.26 ). Hepatic venous connections to the inferior vena cava can be identified as well as the course of the inferior vena cava to the right-sided morphologic right atrium.

Situs inversus with dextrocardia is the reverse—mirror image—of the normal arrangements. The short-axis view recognizes the left atrial appendage with its narrow junction to the right of the aorta and recognizes the right atrial appendage with its broad junction to the left of the aorta. The abdominal echocardiogram identifies the aorta to the right of the spinal column and identifies the inferior vena cava to the left of the spinal column ( Fig. 3.27 A). Color flow imaging refines identification of the aorta and inferior vena cava (see Figs. 3.27 B and C). The echocardiogram then determines hepatic venous connections to the inferior vena cava and determines the course of the left-sided inferior vena cava to the left-sided morphologic right atrium. Situs solitus with dextrocardia has echocardiographic features of normal atrial situs. Situs inversus with levocardia has the echocardiographic features of atrial situs inversus. Once atrial situs is established, echocardiography focuses on the atrioventricular junction, ventricular morphology, ventricular location, and ventricular/great arterial connections.