Echocardiography fundamentals for general paediatricians — formative SAQs

SAQ 1 (10 marks)

A six-year-old boy is referred after a GP heard a heart murmur. He is asymptomatic and growing well. The paediatric cardiologist's report describes a bicuspid aortic valve with a peak continuous-wave Doppler velocity of 4 metres per second across the valve, normal left ventricular dimensions (Z-score 0.8), and a normal aortic root. [1] [9]

1. Outline the systematic approach you would use to read this echo report, and state why every chamber dimension must be interpreted against a Z-score. (3) [1]
2. Calculate the peak pressure gradient across the aortic valve using the modified Bernoulli equation, and interpret the result. (3) [12]
3. What is the significance of the bicuspid aortic valve with this gradient, what needs serial surveillance, and what is the disposition? (4) [9]

Model answer — SAQ 1

(1) Systematic read and Z-scores (3). I read the report in the same order every time — structure, function, valves, flow, pericardium, special findings — and integrate every measurement with the bedside picture. The Z-score is essential because a child's heart grows with the child, so an absolute dimension in millimetres is meaningless without the child's body size. The Z-score expresses a measurement as the number of standard deviations it sits above or below the mean for a child of that body surface area, derived from large normative datasets. A Z-score above positive 2 or below negative 2 is abnormal. In this child the left ventricular Z-score of 0.8 is normal, which reassures me that the ventricle is not dilated or hypertrophied despite the valve lesion. [7] [1]

(2) Bernoulli gradient (3). The modified Bernoulli equation converts a peak Doppler velocity into an estimated peak pressure gradient: the gradient in millimetres of mercury is approximately four times the square of the peak velocity in metres per second. At a peak velocity of 4 metres per second, the gradient is four times 16, which is 64 millimetres of mercury. A peak gradient of this magnitude defines severe aortic stenosis in a child, and the finding changes the child's surveillance and his threshold for intervention. [12]

(3) Significance, surveillance, and disposition (4). A bicuspid aortic valve is the commonest congenital cardiac lesion, and a peak gradient of 64 millimetres of mercury marks this as severe aortic stenosis. The serial surveillance must track the left ventricular hypertrophy and function (the Z-score of the wall thickness and the fractional shortening), the progression of the gradient over time, and the aortic root dimension, because bicuspid valves are associated with aortopathy and progressive root dilation that carries a risk of dissection. The disposition is routine paediatric cardiology referral and serial echocardiographic surveillance at intervals guided by the appropriate-use criteria, with the threshold for balloon valvuloplasty or surgical intervention set by the gradient, the ventricular function, and the symptoms. The family should be advised that the child can remain active but must be reviewed before competitive sport. [9] [1]

SAQ 2 (10 marks)

A three-day-old term infant presents with poor feeding, pallor, and tachypnoea. On examination the child is mottled and cool, the heart rate is 180, the femoral pulses are weak, and the oxygen saturation is 80 percent in air. The blood gas shows a metabolic acidosis. [9] [1]

1. What is the most likely diagnosis, and what echo finding would confirm it? State the lesion class and why it presents on day three. (3) [1]
2. Outline the immediate resuscitation with the drug, the route, and the dose range you would use. (4) [9]
3. After the initial management, what are the next steps, and what complications of the drug must you anticipate? (3) [2]

Model answer — SAQ 2

(1) Diagnosis and echo (3). The most likely diagnosis is a duct-dependent congenital heart lesion, presenting as the ductus arteriosus closes on the third day of life and the systemic or pulmonary circulation that depended on it collapses. The weak femoral pulses, the shock, and the metabolic acidosis raise a duct-dependent systemic circulation such as hypoplastic left heart syndrome, critical aortic stenosis, or a coarctation, and the echo confirms the lesion by showing the obstructed left-heart structures or the aortic arch interruption with a duct-dependent systemic flow. The key teaching is that a duct-dependent lesion and neonatal sepsis share this presentation, and the echo is the discriminator. [1] [9]

(2) Resuscitation and dose (4). I secure the airway and give oxygen, obtain intravenous access, and start intravenous prostaglandin E1 (alprostadil) to reopen and keep the ductus arteriosus patent, because the child's circulation depends on it. The starting dose is 0.005 to 0.01 micrograms per kilogram per minute, titrated up to 0.05 to 0.1 micrograms per kilogram per minute to achieve and maintain ductal patency and an adequate systemic or pulmonary flow. I do not wait for the cardiologist or the echo before the first dose if the clinical picture fits, because the delay risks irreversible shock and acidosis. I arrange transfer to a cardiac centre in parallel. [9]

(3) Next steps and complications (3). Once the duct is patent and the child stabilised, the next steps are a comprehensive paediatric echocardiogram by a paediatric cardiologist to define the anatomy definitively, the transfer to a paediatric cardiac centre for definitive surgical or catheter-based management, and the involvement of paediatric intensive care for the ongoing stabilisation. The complications of prostaglandin E1 I must anticipate are apnoea (which may require intubation and ventilation), fever, hypotension, and hypoglycaemia, so I have full neonatal resuscitation and intubation readiness before and during the infusion, and I monitor the child continuously. [2] [9]