Chapter 7

    This malformation of the heart entirely lacks atrial septum due to lack of formation of the septum primum and septum secundum. The main anatomical feature is the existence of a large, common cavity behaving as a single atrium. The superior and inferior vena cava and the four pulmonary veins will drain directly in this common chamber.
    Occasionally other malformations such as cleft mitral valve, cleft mitral and tricuspid valve, etc. can be observed in conjunction.
    The hemodynamics of this malformation are quite similar to the one of a large atrial septal defect.

FROM THE CLINICAL VIEWPOINT

    These patients present, in general, in a similar way as atrial septal defect.
    Clinical evidence of right ventricular hypertrophy with a systolic ejective murmur in the pulmonary artery due to increase of the blood flow across such vessel will be seen. Eventually, as in atrial septal defect or pulmonary stenosis, an early systolic click may be present with splitting of the second sound (many times fixed splitting). The electrocardiogram as in ASD, has normal sinus rhythm with incomplete or complete right bundle branch block. The main axis in the electrocardiogram is typically described as deviated toward the left superior quadrant, with counter-clockwise rotation in the frontal plane of the vectocardiogram. These changes are rather typical of single atrium although they may be eventually found in atrioventricularis comunis and endocardiac cushion defect.

ROENTGENOGRAM

    The chest x-ray will show essentially the same findings as in ASD with increased pulmonary flow, enlargement of the pulmonary artery with right ventricular and right atrium hypertrophy.

CARDIAC CATHETERIZATION AND ANGIOGRAPHY

    The procedure to be performed in these patients does not differ substantially from the one described in atrial septal defect been many times difficult to arrive at the diagnosis of single atrium. The catheter passes toward the left atrium more easily than in ASD and tends to form a loop in the right and left atrium, clearly delineating the contour of the single atrium.
    The injection of contrast in the single atrium may also demonstrate the same sequence of events previously described in ASD.

MEDICAL AND SURGICAL TREATMENT

    There are no significant differences with ASD. A large prosthesis is usually necessary to obliterate the large defect.

Roentgenogram of an infant with Atrioventricularis Comunis.