Cardiovascular medicines in children — branching viva

Opening — the cyanotic neonate

Examiner: A two-day-old neonate is cyanotic, tachypnoeic and acidotic, with a suspected duct-dependent lesion. Walk me through your immediate pharmacological management. [10]

Candidate (model): I would not wait for echocardiography. I would start an intravenous prostaglandin E1 (alprostadil) infusion immediately at 0.01 to 0.05 microgram per kilogram per minute and titrate upward toward a maximum around 0.1 microgram per kilogram per minute, watching for a rising saturation toward a target of 75 to 85 per cent, a warming perfusion, and a falling lactate. I would secure the airway and have an intubation plan ready, because apnoea is a common adverse effect. I would recognise fever and hypotension as further drug effects, not sepsis, though I would still take cultures and consider antibiotics. Prostaglandin E1 is a bridge to definitive anatomy repair, so I would organise retrieval to a cardiac centre at once. [10]

Branch 1 — why that target saturation

Examiner: Why target 75 to 85 per cent rather than a normal saturation? [10]

Candidate (model): Because in duct-dependent cyanotic disease the systemic and pulmonary circulations share flow across the duct, and excessive pulmonary flow steals blood from the systemic circulation. Pushing the saturation too high with too much prostaglandin can flood the lungs, drop the systemic output, and worsen the metabolic acidosis. A target of around 75 to 85 per cent balances adequate oxygenation against systemic perfusion, which is why I titrate to the perfusion and the lactate as well as to the number. [10]

Branch 2 — the compromised tachycardic child

Examiner: Now a five-year-old, narrow-complex tachycardia at 220 per minute, compromised. Vagal manoeuvres have failed. Talk me through adenosine. [7]

Candidate (model): I would prepare for synchronised cardioversion while I try adenosine, because the child is compromised. Adenosine is given as a rapid intravenous bolus of 0.1 milligram per kilogram, maximum 6 milligrams, chased immediately by a saline flush through a proximal line, on a continuous monitor, because the drug briefly asystoles and is metabolised within seconds. If the first dose fails I give 0.2 milligram per kilogram, maximum 12 milligrams. Adenosine blocks the atrioventricular node, so it terminates a re-entry tachycardia and can reveal the atrial origin of a focal tachycardia — it is diagnostic as well as therapeutic. If the rhythm is broad-complex or the child deteriorates, I move to synchronised cardioversion. [7]

Branch 3 — the post-operative infant and milrinone

Examiner: An infant is on day one after corrective surgery for congenital heart disease, at risk of low cardiac output syndrome. What is the evidence-based prophylactic agent, and at what dose? [6]

Candidate (model): The agent is milrinone, supported by the PRIMACORP randomised trial of Hoffman and colleagues, which showed that prophylactic high-dose milrinone reduced the composite outcome of low cardiac output syndrome or death in infants and children after corrective congenital heart surgery. The regimen is a loading dose of 50 micrograms per kilogram over 30 to 60 minutes, followed by an infusion of 0.75 microgram per kilogram per minute, titrated in the range of 0.25 to 0.75 microgram per kilogram per minute. Milrinone inhibits phosphodiesterase-3, improving inotropy and lusitropy while reducing afterload, and its main adverse effect is hypotension, managed with a fluid bolus or a low-dose vasopressor. [6]

Branch 4 — chronic heart failure and the trial evidence

Examiner: Finally, a child with dilated cardiomyopathy. Your registrar wants to start carvedilol at the full target dose because it works in adults. Defend the correct approach, and tell me honestly what the paediatric trials showed. [2] [3] [4]

Candidate (model): I would start low and titrate slowly, not at the full target dose. Carvedilol is begun at 0.05 to 0.1 milligram per kilogram twice daily and titrated over weeks toward 0.3 to 0.5 milligram per kilogram twice daily, because it lowers heart rate and blood pressure and can destabilise a child if up-titrated too quickly. I would be honest with the registrar: the carvedilol randomised trial of Shaddy and colleagues did not show a significant benefit on its primary composite outcome in children, and the single-ventricle enalapril trial of Hsu and colleagues likewise showed no benefit on the primary outcomes for infants after stage-one palliation. Paediatric heart failure is not adult heart failure, so beta-blocker use is carefully selected, specialist-supervised, and extrapolated from physiology rather than driven by paediatric mortality trials. [2] [3] [4]

Closing — the one-liners examiners reward

Examiner: Give me the three principles you would want every registrar to remember about cardiovascular medicines in children. [4] [10]

Candidate (model): First, prescribe by the current weight, correct for age and organs, and titrate to a named target — the saturation for prostaglandin E1, the rate for a beta-blocker, the blood pressure for a vasodilator. Second, anticipate the named adverse effect for every drug — apnoea for prostaglandin E1, hyperkalaemia for the ACE inhibitor, the QTc for amiodarone and sotalol, the digoxin level and potassium, cyanide for prolonged nitroprusside. Third, recognise the high-risk pairs and traps — amiodarone raises digoxin, verapamil is avoided in infants, sildenafil must never meet nitrate, and the paediatric heart failure trials were negative so we prescribe carefully under cardiology. [4] [10]