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Congenital right atrial diverticulum, atrial septal defect within the oval fossa, and complex pulmonary valvar obstruction in an infant with chromosome 8(p23.1) deletion
Published online by Cambridge University Press: 03 May 2005
Abstract
We describe an unusual right atrial aneurysm, occurring with progressive obstruction of the right ventricular outflow tract and increasing cyanosis, in a nine-month-old boy with chromosome 8(p23.1) deletion. Surgical resection of the diverticulum, and relief of the right ventricular obstruction, was successful, although impairment of right ventricular compliance persists after 19 months follow-up.
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- © 2005 Cambridge University Press
Aneurysmal dilatation of the right atrium can be seen in a variety of conditions, such as tricuspid stenosis or regurgitation, right atrial tumours, Ebstein's malformation, or cardiomyopathy.1–7 Arrhythmia has been reported as a presenting symptom.2, 5, 7 We report an infant with chromosome 8(p23.1) deletion, initially considered to have Ebstein's malformation with stenosis of the pulmonary valve, who was subsequently found to have an unusually large right atrial diverticulum associated with complex obstruction of the right ventricular outflow tract.
Case report
A nine-month-old dysmorphic boy presented with the initial diagnoses of Ebstein's malformation and an atrial septal defect in the oval fossa with pulmonary valvar stenosis. His karyotype was 46XY, with a small interstitial deletion on the short arm of chromosome 8(p23.1), with resolution of chromosomal analysis greater than the 550 band level. Both parents have a normal karyotype. Clinical evaluation revealed a well-grown child with saturation of oxygen of 82 percent. The echocardiogram demonstrated marked valvar and sub-valvar pulmonary stenosis, the continuous wave Doppler traces showing a gradient of approximately 95 millimetres of mercury. No pre-excitation was present on the electrocardiogram.
The initial angiogram (Fig. 1a,b) demonstrated a smooth-walled, non-contracting inferior chamber from which contrast readily entered the right atrial chamber. Contrast then passed forward and to the left into a trabeculated right ventricular chamber, and into the pulmonary arteries. The ventricular injection (Fig. 1c,d) demonstrated a small, heavily trabeculated, tripartite right ventricle, with a vertically-orientated tricuspid valve having a diameter of 14 millimetres, corresponding with a Z-score of minus 0.5, the valvar leaflets being normally hinged at the atrioventricular groove. The obstruction at the outlet was due to complex sub-valvar stenosis, with additional hypoplasia of the pulmonary valvar orifice, which measured 8 millimetres in diameter, corresponding to a Z-score of minus 2.0.
Figure 1. Antero-posterior (a) and lateral (b) angiograms of the diverticulum. The white arrows in panel (a) point to the annulus of the tricuspid valve. Antero-posterior with cranial angulation (c) and lateral (d) angiograms of the right ventricle. The white arrows in panel (d) point to the complex valvar and sub-valvar obstruction. D: diverticulum; RA: right atrium; RV: right ventricle.
Upon opening the pericardium, a whitish out-pouching was seen leftward of the right atrioventricular groove, which blended into the right ventricular muscle (Fig. 2). The right coronary artery could be seen on the surface of the heart, with a prominent branch passing across the mid-portion of the diverticulum onto the diaphragmatic surface. This vessel appeared to supply an area of the apex of the right ventricle. Spontaneously-converting, narrow complex tachycardia readily occurred with any manipulation of the right atrium. After opening the atrium, the diverticulum was clearly circumscribed by the right coronary artery, and was located posterior to the tricuspid valve. The tricuspid valve, noted to have two orifices, the inferior caval vein, and the coronary sinus, which was of normal size, were separated from the diverticulum by distance of from 1 to 2 milli-metres. Access to the right ventricle was through the normally positioned tricuspid valve. Surgery involved resection of a part of the diverticulum measuring 2.5 by 1.5 centimetres, anterior to the acute marginal branch, along with repair of the obstructed right ventricular outflow tract using a unileaflet pulmonary homograft. Pathologic evaluation of the surgically-excised portion of the diverticulum demonstrated mainly elastic and fibrous tissue, with some myocardium and adjacent adipose tissue.
Figure 2. Surgical (left caudal) view of the diverticulum. The forceps (white arrow) point to the right coronary artery. *: aortic cannula; D: diverticulum; RV: right ventricle.
At follow-up, 19 months after the surgery, the child is growing well, with a systemic saturation of oxygen of 96 percent in room air, and no suggestion of disturbances of rhythm. The orientation of the tricuspid valve remains very unusual on echocardiography, appearing almost vertical in the apical 4-chamber view.
Discussion
Right atrial diverticulum is a rare cardiac condition. It is usually described as a saccular structure originating from the free atrial wall or right atrial appendage.4, 8, 9 In our patient, when viewed through the atriotomy, the orifice of the diverticulum lay posterior to the tricuspid valve, but separate from the orifice of the inferior caval vein and coronary sinus. This location may represent the already thin portion of the atrial wall described as the sub-Thebesian sinus. The diverticulum then occupied an inferior position extending around towards the anterior aspect of the right ventricle (Fig. 2). Histology demonstrated mainly elastic and fibrous tissue with some myocardium and adjacent adipose tissue. The associated pulmonary obstruction included infundibular and discrete pulmonary valve stenosis.
Previously reported cases have been associated with discrete pulmonary valvar stenosis, but without the complex infundibular component seen in our infant. Hypoplasia of the left ventricle has been described in patients where the diverticulum was either posterior to the left ventricle, or arose from the coronary sinus. We speculate that the presence of this diverticulum may have influenced the dynamics of flow during fetal life, contributing to abnormal orientation of the tricuspid valve, development of the right ventricular cavity itself, and the right ventricular outflow tract. Others8, 9 have suggested that incomplete regression of the left sinus horn can result in a diverticum lying posterior to the left ventricle involving the coronary sinus. The cases promoting this speculation, however, were associated with relative hypoplasia of the left ventricle, and were considered a consequence of “compression” of the developing ventricle. Incomplete regression of the sinus horn could not explain the malformation in our patient, as the inferior caval vein entered directly into the floor of the right atrium, and was distinct from the diverticulum.
Infants with right atrial diverticulum can present with cyanosis,1 arrhythmia,2, 3, 5, 7 or generalized cardiomegaly.3 Although our patient was clinically stable, the indication for surgical repair was increasing obstruction and worsening desaturation secondary to right-to-left atrial shunting. The resting electrocardiogram never demonstrated any pre-excitation. There must be great potential, nonetheless, for sub-epicardial muscular atrioventricular connections secondary to the aneurysm.7 The arrhythmogenic potential of the diverticulum was evident when surgical manipulation produced bouts of narrow complex tachycardia, once again confirming the known arrhythmogenic potential of this lesion.
Review of the genetic literature reveals that an interstitial deletion of chromosome 8(p23.1) is associated with congenital heart disease in three-fifths of cases.10 The associated cardiac lesions include atrioventricular septal defect, atrial and ventricular septal defects, double outlet right ventricle, right-sided heart, pulmonary stenosis, and hypoplastic left heart syndrome. Our report extends this spectrum to include the rare lesion of atrial diverticulum. Other phenotypic findings include minor anomalies, such as a broad chest, wide-spaced nipples, retrognathia, and a flat nasal bridge, mild growth delay, microcephaly, developmental delay, behaviour problems, genitourinary anomalies, and seizures.
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Antero-posterior (a) and lateral (b) angiograms of the diverticulum. The white arrows in panel (a) point to the annulus of the tricuspid valve. Antero-posterior with cranial angulation (c) and lateral (d) angiograms of the right ventricle. The white arrows in panel (d) point to the complex valvar and sub-valvar obstruction. D: diverticulum; RA: right atrium; RV: right ventricle.
Surgical (left caudal) view of the diverticulum. The forceps (white arrow) point to the right coronary artery. *: aortic cannula; D: diverticulum; RV: right ventricle.
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