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]}