Congenital dextrocardia. Clinical, angiocardiographic, and autopsy studies on 50 patients.

Summary Fifty cases of congenital dextrocardia were studied and classified into 5 major types. In Type I dextrocardia (mirror-image dextrocardia) the anatomic right atrium and right ventricle are situated to the left of an anterior to the corresponding systemic chambers. A mirror-image arrangement of the cardiac chambers is present since the frontal relationship of the chambers is reversed, yet, the anteroposterior arrangement is normal. In Type II dextrocardia (dextroversion complex) the relations of the cardiac chambers are normal; the right atrium and right ventricle are situated to the right of and posterior to the corresponding systemic chambers. In complete dextroversion the cardiac apex is situated anteriorly and to the right; in incomplete dextroversion or mesoversion, it is located in the substernal region and the longitudinal axis of the heart is parallel to the midsagittal axis of the chest. Type III dextrocardia (mixed dextrocardia) is characterized by inversion of the atria alone or of the ventricles alone. The arrangement of the cardiac chambers is therefore in part similar to that of Type I and of Type II dextrocardia. In Type IV dextrocardia (congenital dextroposition) the heart is in the midchest, but the arrangement of the chambers is normal and the cardiac apex is still directed to the left and anteriorly. Types I, II, III, and IV represent the intrinsic group of dextrocardia, since the cardiac heterotaxy is caused by a developmental anomaly of the primitive heart tube. In Type V dextrocardia (congenital extrinsic) the abnormal position of the heart is due to its displacement by congenital anomalies of the lungs, diaphragm, or chest cage. The rightward displacement may be in the frontal plane only (simple dextroposition) or may occur in both the frontal and horizontal planes (dextroposition with pivotal rotation). The various types of dextrocardia are illustrated by angiocardiograms. The incidence of cardiac anomalies in theintrinsic group was 79 per cent, and in the extrinsic group 24 per cent. These anomalies were, as a rule, multiple and severe and together formed specific anatomic syndromes usually characterized clinically by dextrocardia, cyanosis, and diminished pulmonary blood flow. The most common entities encountered were tetralogy, single ventricle with pulmonary stenosis, and tricuspid atresia or stenosis. The chest roentgenologic findings in Types I, II, and III are similar in most respects, consisting of an elevated left diaphragm and identical cardiac configurations in the posteroanterior and in the oblique views which are the reverse of the normal. A right aortic arch is common in Type I dextrocardia. Situs inversus always accompanies this type. The previously reported cases of isolated mirror-image dextrocardia are probably Type II or possibly Type III dextrocardia. In Type IV dextrocardia the heart shadow is medially located in the frontal view and assumes normal configuration in the oblique chest roentgenograms. Negative P waves in Lead I generally indicate atrial inversion, as occurs in Type I and occasionally in Type III dextrocardia, but they may be observed in other conditions not associated with atrial inversion as in nodal rhythm, in levocardia, and in atrial tachycardia. On 2 occasions we have observed slightly negative P I waves in dextroversion with marked right atrial enlargement. The rSr′ ventricular pattern in Lead I as well as the interchanged tracings of Leads aVR and II with those of Leads aVL and III, respectively, is typical of uncomplicated Type I dextrocardia. In the presence of right ventricular hypertrophy a constantly observed change is a relatively tall R wave in Lead I of the QR or qR pattern. The tracings in complete dextroversion characteristically consist of flattened but upright P waves in Lead I and deep Q waves in Leads I, II, and aVL with negative T waves. Similar tracings are seen in Type V dextrocardia when the dextroposition is accompanied by severe pivotal rotation. The T waves in these cases are, however, more often upright than negative. Only 1 of the 5 cases with incomplete dextroversion had similar abnormal Q waves in Leads I and aVL; a qRs pattern in V 2 through V 6 was present in 3. There are no typical electrocardiographic findings in Type III dextrocardia. The tracings in Type IV dextrocardia are normal. Most of the electrocardiographic changes described may be explained by the abnormal position and location of the cardiac chambers. These are demonstrated by means of schematic vector analysis and illustrated by actual vectorcardiograms.