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]

The non-secundum defects — primum with a mitral valve cleft, sinus venosus with anomalous venous return, and coronary sinus with a persistent left superior vena cava — are closed surgically. The sinus venosus defect needs a patch that redirects the anomalous vein to the left atrium. [2] [5]

Branch 3: the Eisenmenger contraindication

The examiner asks when closure is contraindicated. The candidate answers that closure is contraindicated when the pulmonary vascular resistance is high and the shunt has reversed, because the defect is acting as a pop off for the right ventricle and closing it causes right heart failure. The threshold is a pulmonary vascular resistance above about eight Wood units with a net right-to-left shunt, and the decision is made at catheterisation when the echocardiographic pulmonary pressures are high. [1] [2]

Branch 4: the scimitar syndrome infant

The examiner closes with a three-month-old infant presenting in heart failure with severe pulmonary hypertension and a chest radiograph showing a curvilinear shadow parallel to the right heart border. The candidate recognises the infantile form of scimitar syndrome, in which the right pulmonary veins drain to the inferior vena cava and the right lung is hypoplastic. The infantile form carries a mortality of up to forty-five per cent and is a surgical emergency, often with an anomalous systemic arterial supply to the right lung that adds a left-to-right shunt. [1]

Closing: transition to adult congenital care

The examiner closes with the same child at eighteen, transitioning to adult congenital cardiology. The candidate explains that even after successful closure, arrhythmia surveillance and pulmonary hypertension screening continue, because atrial fibrillation and flutter remain more common than in the general population. The transition is structured and documented, because the transition point is where young people are most often lost to follow-up. [1] [2]