Atrial Septal Defect on ultrasound

Case Study: Defining an Unusual Atrial Septal Defect

This article reviews a case of a middle aged patient who developed increasing dyspnoea on exertion. The patient history included auscultation inferring a split S2 heart sound, a chest x-ray demonstrating cardiomegaly and the resulting referral for an MRI at another institution. The results of this indicated a dilated right heart and a septum primum defect. Our laboratory had been asked to perform a transoesophageal echo to confirm the finding in workup to potential surgical management for the patient. The results of the transoesophageal were immediately surprising as the diagnosis made in the MRI was evidently wrong.

The patient in fact displayed features of an unroofed coronary sinus also known as a coronary sinus atrial septal defect. This congenital malformation comprises of less than 1% of all ASDs and is frequently associated with a persistent left superior vena cava. Morphological classification of the variants are: Type I, completely unroofed with left superior vena cava; Type II, completely unroofed without LSVC, as in our case; Type III, partial unroofed mid portion; and Type IV, partial unroofed terminal portion.

How could our laboratory be sure of this new corrected diagnosis? Septum primum ASDs are a form of atrioventricular septal defects and thus interrogating the cardiac crux can reveal defining features. In a normal heart the anterior mitral valve leaflet and tricuspid septal leaflet both attach to the atiral and ventricular septum. The insertion of the tricuspid leaflet just slightly further apical in relation to the mitral leaflet. This is demonstrated in Figure 1. In a partial atrioventricular canal defect there is absence of fusion between the lower atrial septum and AV valve leaflets, thus creating the septum primum defect. Both valves attach to the crest of the ventricular septum, however at the same level, losing their differential appearance.

Figure 1 also demonstrates that the atrial septum fuses with the cardiac crux and what was thought to be a primum defect is in fact a markedly dilated ostium of the coronary sinus. There is an appearance of a ‘gutter’ in the posterior aspect of the left atrium, until further laterally the coronary sinus becomes enclosed and tapers to a smaller size. Figures 2 and 3. Due to the size of the defect, significant shunting was observed with a predominance of left to right direction.

A persistent LSVC was excluded by performing saline contrast injection into both left and right antecubital veins. No anomalous pulmonary venous connect was observed. The right ventricle was moderately dilated in keeping with a chronic volume overload.

In the absence of a persistent LSVC a procedure which may be performed to correct the defect involves a cannula or obturator introduced into the coronary sinus toward the left atrium. The area is stented while a roof of pericardial tissue is created. The patch runs from a location between the left atrial (LA) appendage and upper pulmonary veins, continuing inferiorly toward the mitral valve, and terminating near the right atrium and right atrial orifice of the coronary sinus. Fortunately the outcome and prognosis for an isolated coronary sinus ASD are excellent.


Figure 1 - The cardiac crux and atrial septum.

Figure 1 - The cardiac crux and atrial septum.

Figure 2 - Markedly dilated coronary sinus with unroofed anterior aspect

Figure 2 - Markedly dilated coronary sinus with unroofed anterior aspect

Figure 3 - Enclosing of the coronary sinus and a relatively normal size.

Figure 3 - Enclosing of the coronary sinus and a relatively normal size.

Figure 4: Large volume of shunting observed due to the defect.

Figure 4: Large volume of shunting observed due to the defect.


References

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  2. Ootaki Y, Yamaguchi M, Yoshimura N, Oka S, Yoshida M, Hasegawa T. Unroofed coronary sinus syndrome: diagnosis, classification, and surgical treatment. J Thorac Cardiovasc Surg 2003;126:1655-6.
  3. Chauvin M, Shah DC, Haïssaguerre M, et al. The anatomic basis of connections between the coronary sinus musculature and the left atrium in humans. Circulation. Feb 15 2000;101(6):647-52.
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Author:

Shae Small
Echocardiographer
CardioVascular Services
Perth, WA
Australia

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