Atrial septal defect and partial anomalous pulmonary venous return — branching viva

Opening: recognise and confirm

The candidate opens by recognising that a soft systolic ejection murmur at the upper left sternal edge with a wide, fixed, split second heart sound is the auscultatory signature of an atrial septal defect. The murmur is the sound of increased right ventricular stroke volume crossing a normal pulmonary valve, not blood crossing the defect. The wide fixed split comes from delayed right ventricular emptying against the increased pulmonary flow. ^[5]

The candidate confirms with echocardiography, which shows the defect, its location, size, rims, and the shunt direction. The right ventricle is dilated, and the Qp to Qs ratio quantifies the shunt, with a ratio above 1.5 to 1 meeting the closure threshold. ^{[5] [1]}

Branch 1: the wide fixed split second heart sound

The examiner probes why the second heart sound is wide and fixed. The candidate explains that the right ventricle takes longer to empty against the increased pulmonary flow, so the pulmonary component is delayed. The split is fixed because the atrial shunt decompresses both atria equally throughout the respiratory cycle, so the right ventricular filling does not vary with respiration as it normally does. ^[5]

The candidate contrasts this with pulmonary stenosis, where the second sound is widely split but varies with respiration, and with the innocent murmur, where the second sound splits normally. The fixed split is the discriminator. ^[5]

Branch 2: device versus surgery

The examiner branches to the closure strategy. The candidate answers that a secundum defect with adequate rims exceeding five millimetres, except the retro-aortic rim, and a stretched diameter under thirty-eight millimetres, is closed with a transcatheter device. The Amplatzer septal occluder or the Gore Cardioform device is placed under general anaesthesia and transoesophageal echocardiographic guidance. ^[3]