What does an increased atrial-to-ventricular length ratio mean in fetuses with atrioventricular septal defect?
Article first published online: 1 NOV 2004
Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Ultrasound in Obstetrics & Gynecology
Volume 24, Issue 6, pages 597–598, November 2004
How to Cite
Yoo, S.-J. (2004), What does an increased atrial-to-ventricular length ratio mean in fetuses with atrioventricular septal defect?. Ultrasound Obstet Gynecol, 24: 597–598. doi: 10.1002/uog.1773
- Issue published online: 1 NOV 2004
- Article first published online: 1 NOV 2004
Although atrioventricular septal defect (AVSD) is named as such, the septal defect is in fact a variable component of this interesting congenital malformation. Depending on the relationship of the bridging atrioventricular valve leaflets to the defective atrial and ventricular septal edges, the shunt through the septal defect can be both interatrial and interventricular, exclusively interatrial (‘primum defect’), or, very rarely, exclusively interventricular1. When the atrioventricular valves are removed, however, those hearts categorized as having AVSDs look alike regardless of the subtype of defect1. The unifying features of various forms of AVSD are: 1) a deficiency of the atrioventricular septum between the left ventricle and the right atrium and adjacent atrial and ventricular septa showing a scooped-out configuration of the ventricular septal crest; 2) a common atrioventricular annulus with the aortic valve in an ‘unwedged’ position; 3) an abnormal ratio between the inlet and outlet dimensions of the left ventricle due to a short inlet and an elongated outlet (Figure 1).
The diagnosis of AVSD can hardly be missed at echocardiography in children. Surprisingly, however, fetuses with this not uncommon malformation often escape detection2. In this issue, Machlitt, Heling and Chaoui introduced an increased atrial-to-ventricular length (AVL) ratio as a new fetal sonographic marker for AVSD3. In normal fetuses, the mean AVL was 0.47 with a 95% prediction interval of 0.35–0.63; in fetuses with AVSD, the mean AVL was 0.77 with a range of 0.59–0.99. This increased AVL in fetuses with AVSD is a numeric representation of an important common feature of the malformation: shortening of the inlet that results in inlet–outlet disproportion. Alternatively, the inlet–outlet disproportion could be calculated by measuring the inlet and outlet dimensions seen in the four-chamber and left ventricular outflow tract views, respectively. Shortening of the inlet in AVSD is due to the absence of the atrioventricular septum and adjacent ventricular septum. Shortening can be more obvious in a four-chamber echocardiogram as the defective ventricular septal crest characteristically shows a scooped-out appearance and the bridging leaflets of the atrioventricular valve are displaced towards the ventricles against the scooped-out ventricular septal crest, as Machlitt et al.3 explained in their Discussion (Figure 1, upper panel). The rare exceptions would be those AVSDs in which the bridging leaflets are attached to the atrial septal margin.
Unfortunately, measurement of the atrial and ventricular lengths and calculation of the AVL may be cumbersome in daily screening fetal ultrasound, and few will be pleased to have one more parameter to remember. The authors' data, however, provide a firm statistical basis for a very simple message to those who are not fully familiar with AVSD: ‘atrioventricular septal defect should be suspected when the atrial length is more than 50% of the ventricular length in a four-chamber view’. If this simple but important sonographic feature were recognized at fetal screening, few cases with AVSD would escape detection.