Ventricular septal defect — formative SAQs

SAQ 1 — The six-week-old infant in overcirculation (20 marks, ~15 minutes)

A six-week-old term infant presents with a three-week history of worsening tachypnoea, taking 40 minutes to finish 60 mL of feeds while sweating, and crossing two weight centiles downward. On examination there is a pansystolic murmur at the lower left sternal border, an apical mid-diastolic murmur, a hyperactive precordium, and hepatomegaly. Oxygen saturations are 98 percent in air. ^[1]

Questions

1. Give the most likely diagnosis and the pathophysiology that explains why it has presented now, at six weeks, rather than at birth. (4 marks) ^[1]
2. Outline your immediate investigations and the definitive test that confirms and sizes the lesion. (3 marks) ^{[1] [9]}
3. Outline your immediate medical management, including the specific drug doses you would use as a bridge. (5 marks) ^[1]
4. State the indications for definitive closure and the usual timing, and outline the options (surgical versus device). (4 marks) ^[9]
5. State the one complication that the entire management strategy is designed to prevent, and why closure is harmful once it has occurred. (4 marks) ^{[6] [9]}

Model answer (must-hit)

1. The most likely diagnosis is a moderate-to-large ventricular septal defect with pulmonary overcirculation and left-heart failure. The pathophysiology is a left-to-right shunt whose volume depends on the defect size and the pulmonary vascular resistance. At birth the resistance is high and the shunt is small, so the infant looks well; as the resistance falls over the first six to eight weeks, the shunt grows, the left ventricle (which pumps to the body and across the defect to the lungs) dilates and fails, and the infant presents with tachypnoea, poor feeding, sweating and failure to thrive. The apical flow rumble signals a large shunt dilating the left atrium. ^[1]

2. The definitive test is echocardiography, which confirms and locates the defect, measures the shunt (Qp:Qs) and the gradient, estimates the pulmonary artery pressure from the tricuspid regurgitation jet, and assesses the aortic valve for cusp prolapse. A chest radiograph is expected to show cardiomegaly with pulmonary plethora, and an ECG left atrial and left ventricular overload. ^{[1] [9]}

3. Immediate medical management is a bridge to closure: a loop diuretic such as furosemide 1 to 2 mg/kg/day to relieve pulmonary congestion; an angiotensin-converting-enzyme inhibitor (captopril or enalapril) to reduce afterload and therefore the shunt; and increased caloric density of feeds (with nasogastric supplementation if needed) to overcome the metabolic cost of the extra cardiac work. Oxygen is used cautiously because it lowers pulmonary resistance and can increase the shunt; intercurrent infection and anaemia are treated promptly. ^[1]

4. The indications for closure are a symptomatic child with a significant shunt, a Qp:Qs above roughly 1.5 to 2 with left ventricular overload, recurrent infective endocarditis, or aortic regurgitation from cusp prolapse. The usual timing is within the first year. Surgical patch closure is the standard for most perimembranous, inlet and large muscular defects; transcatheter device closure is an alternative for selected muscular and perimembranous defects with favourable anatomy. ^[9]

5. The complication to be prevented is fixed pulmonary vascular disease progressing to Eisenmenger syndrome. Once the resistance is fixed, the right ventricle depends on the defect as a pressure pop-off, and closing the defect removes that pop-off and is harmful and potentially fatal. This is why the whole strategy of paediatric VSD care is to close the defect before the resistance becomes fixed. ^{[6] [9]}