Atrioventricular septal defect — short-answer question

Part A — Anatomy, classification and ECG (10 marks)

a) Define an atrioventricular septal defect and list its structural components (4 marks)

An atrioventricular septal defect is a congenital malformation in which the atrial and ventricular septa fail to meet at the crux of the heart, producing a common atrioventricular junction with malformed bridging leaflets. The five structural components are a deficient atrioventricular septum, a common atrioventricular junction, a primum atrial septal defect, an inlet ventricular septal defect, and an abnormal left atrioventricular (mitral) valve with a cleft. [1]

b) Describe the three forms of AVSD and the Rastelli classification (4 marks)

The partial form has an ostium primum atrial septal defect, a cleft in the anterior mitral leaflet, two separate atrioventricular orifices, and no ventricular septal defect. The transitional form has a primum defect, two orifices with tethered leaflets, and a small restrictive inlet ventricular septal defect. The complete form has a large primum atrial defect, a large inlet ventricular defect, and a single common atrioventricular valve with bridging leaflets spanning both ventricles. [2]

The complete form is graded by the Rastelli classification of the superior bridging leaflet: type A is divided and attached to the septal crest; type B attaches anomalously to a right ventricular papillary muscle; type C is a free-floating undivided common leaflet, the form commonest in Down syndrome and carrying the highest risk of left atrioventricular valve regurgitation. [2]

c) What is the characteristic ECG finding, and why is it useful? (2 marks)

The signature finding is a superior QRS axis, typically between minus thirty and minus one hundred and fifty degrees, produced by abnormal inferior-to-superior ventricular activation through the deficient septum. It is present across the entire spectrum — partial, transitional, and complete — and is the single bedside feature that distinguishes a primum from a secundum atrial septal defect. [1]

Part B — Pathophysiology and management (10 marks)

a) Explain why this infant has heart failure and pulmonary hypertension (4 marks)

The common atrioventricular junction leaves a primum atrial defect above and an inlet ventricular defect below the valve, so blood shunts left to right at both levels, overloading the right heart and causing massive pulmonary overcirculation. The large ventricular shunt exposes the pulmonary circulation to systemic pressure, raising pulmonary vascular resistance. Down syndrome accelerates this pulmonary vascular remodelling, so the loud pulmonary component of the second heart sound reflects the early pulmonary hypertension that develops in unrepaired complete defects. [2]

b) Outline the definitive management and state the timing and its rationale (4 marks)

Definitive management is surgical — primary repair closing both the primum atrial and the inlet ventricular defects and reconstructing a competent left atrioventricular valve. For the complete form, repair is performed at three to six months of age, before the pulmonary vasculature becomes irreversibly remodelled. Delaying repair past this window risks the development of irreversible pulmonary vascular disease and Eisenmenger physiology, which would render surgery impossible. [2]

c) What is the long-term problem after successful repair, and what follow-up is required? (2 marks)

The dominant long-term problem is left atrioventricular valve regurgitation, the leading cause of reoperation in roughly ten to fifteen percent of patients over the long term. Follow-up is lifelong in a specialist congenital cardiac service, with structured transition to an adult congenital programme in late adolescence for surveillance of valve function, arrhythmia, and pregnancy counselling. [1] [3]