Atypical form of atrioventricular septal defect without left axis deviation: relation between morphology and unusual QRS axis.

OBJECTIVE

To clarify the morphological features relating to an intermediate axis or a right axis deviation in atrioventricular septal defect (AVSD).

SUBJECTS: 135 patients with typical AVSD and with nine patients with atypical AVSD, characterised by a well formed atrial septum, a milder downward displacement of the atrioventricular valves, and a shorter length of the ostium primum defect.

MAIN OUTCOME MEASURES: Relation between morphology and electrocardiographic and vectorcardiographic findings; prevalence of Down's syndrome and of other cardiac anomalies.

RESULTS

All nine patients with atypical AVSD had an unusual mean frontal QRS axis compared with six of the 135 patients (4%) with typical AVSD (p < 0.01). All eight patients who underwent the vector analyses showed atypical movement of the QRS loop--that is, an initial left inferior movement in the frontal loop (eight patients) and counter-clockwise rotation in the sagittal loop (seven). The corresponding values for 119 patients with typical AVSD were 20 and 22 patients (p < 0.01). Seven patients with atypical AVSD (78%) and 55 (41%) with typical AVSD had Down's syndrome (p < 0.05). None of the twenty one patients with additional cardiac anomalies had atypical AVSD, an unusual QRS axis, or unusual movement in the QRS loop.

CONCLUSIONS

The atypical morphology, supposedly related to the degree of posteroinferior displacement of the conduction system, was one of the causes of unusual movement of the QRS loop in AVSD.