Ventricular arrhythmias and sudden cardiac death — branching viva

Examiner opening (Examiner)

You are the general paediatric registrar in the emergency department. A fifteen-year-old boy has been brought in by paramedics after collapsing during a school football match. He was sprinting for the ball, there was no body contact, and he went down suddenly. The paramedics found him in ventricular fibrillation and achieved return of spontaneous circulation after two shocks and CPR. His twelve-lead ECG shows sinus rhythm with deep T-wave inversion in the lateral leads and voltage criteria for left ventricular hypertrophy. His father died suddenly at age thirty-eight. Talk me through your assessment and management. [1]

Exemplar opening (Candidate)

This child has been resuscitated from an out-of-hospital cardiac arrest due to ventricular fibrillation, and the combination of exertional collapse, lateral T-wave inversion, left ventricular hypertrophy on the ECG, and a family history of sudden death at thirty-eight makes hypertrophic cardiomyopathy the most likely diagnosis until proven otherwise. My immediate priorities are, first, to stabilise him in the post-arrest period — he needs a PICU or high-dependency bed, continuous cardiac monitoring, and haemodynamic support, because the risk of re-arrest is highest in the first twenty-four hours. Second, I need to confirm the diagnosis with echocardiography and cardiac MRI. Third, I need to involve the inherited cardiac conditions and electrophysiology service for the ICD decision and the family cascade screening. [1] [3]

Branch 1 — the resuscitation (Examiner)

Let us go back to the field. What is the shockable-rhythm algorithm, and what drug doses would you use? [3]

Exemplar (Candidate)

For ventricular fibrillation or pulseless ventricular tachycardia, the shockable-rhythm loop of the paediatric advanced life support algorithm applies. Begin high-quality CPR immediately — compressions at one hundred to one hundred and twenty per minute, approximately one-third of the anteroposterior chest diameter in depth, full recoil, and minimising interruptions. Defibrillate as soon as possible at two to four joules per kilogram with a biphasic waveform, escalating up to a maximum of ten joules per kilogram or the adult dose. After each shock, resume CPR immediately for two minutes before reassessing the rhythm — pausing to check the rhythm after a shock is a common and damaging error. Give intravenous or intraosseous adrenaline at ten micrograms per kilogram every three to five minutes, starting after the second shock. Give intravenous amiodarone at five milligrams per kilogram after the third shock if the arrhythmia persists — lidocaine at one milligram per kilogram is an alternative, and some guidelines prefer it in children under five years. Throughout, correct the reversible causes: the four Hs — hypoxia, hypovolaemia, hypo- and hyperkalaemia, hypothermia — and the four Ts — thrombosis, tamponade, tension pneumothorax, toxins. Early defibrillation is the single most important determinant of survival. [3] [5]

Branch 2 — the differential of SCD in the young (Examiner)

What are the causes of sudden cardiac death in the young, and how do you classify them? [1]

Exemplar (Candidate)

I classify sudden cardiac death in the young into four cause families. The first is the structurally normal heart, which accounts for approximately thirty-five to forty per cent of cases in the Bagnall prospective cohort. This group is dominated by the inherited arrhythmia syndromes — long-QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, and short-QT syndrome — plus idiopathic ventricular fibrillation and commotio cordis. This is the group most often missed, because the resting ECG may be normal and the heart is structurally normal on imaging. The second family is the cardiomyopathies — approximately twenty-five to thirty per cent — dominated by hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, with dilated, restrictive, and non-compaction cardiomyopathy also contributing. The third is congenital heart disease — twenty to twenty-five per cent — driven by repaired tetralogy of Fallot, transposition of the great arteries after switch, aortic stenosis, and coronary artery anomalies. The fourth is acquired triggers — ten to fifteen per cent — including myocarditis, Kawasaki disease with coronary aneurysms, drug-induced arrhythmia, and severe electrolyte disturbance. This child's presentation — exertional arrest with left ventricular hypertrophy — points firmly to the cardiomyopathy family, and within that, hypertrophic cardiomyopathy. [1] [2]

Branch 3 — the diagnosis (Examiner)

How do you confirm hypertrophic cardiomyopathy in this child, and how do you risk-stratify him? [3]

Exemplar (Candidate)

The echocardiogram is the key initial test: it demonstrates the asymmetric left ventricular hypertrophy, typically affecting the interventricular septum, with a maximal wall thickness above two standard deviations for age, body surface area, or z-score. I would also assess for dynamic left ventricular outflow tract obstruction, systolic anterior motion of the mitral valve, and mitral regurgitation. A cardiac MRI with late gadolinium enhancement characterises the extent of myocardial fibrosis, which is an independent risk factor for sudden cardiac death. Genetic testing for the sarcomeric gene mutations — most commonly MYH7 and MYBPC3 — should be requested through the inherited cardiac conditions service with appropriate pre- and post-test counselling. Risk stratification in hypertrophic cardiomyopathy integrates the history — prior cardiac arrest or sustained VT, unexplained syncope, family history of sudden death, the degree of hypertrophy (maximal wall thickness above thirty millimetres in adults is a major risk factor), the presence of non-sustained VT on ambulatory monitoring, the left ventricular outflow tract gradient, and the extent of late gadolinium enhancement on MRI. This child has already had a cardiac arrest, which is the highest-risk feature, and he will need an ICD for secondary prevention. [3] [5]

Branch 4 — post-arrest care (Examiner)

Tell me about the post-arrest care in the first forty-eight hours. [4]

Exemplar (Candidate)

Post-arrest care is an integral part of the resuscitation, not an afterthought. Targeted temperature management is the neuroprotective strategy: maintain the core temperature at thirty-six degrees Celsius for forty-eight hours after return of spontaneous circulation, with active avoidance of fever. Haemodynamic optimisation is critical — post-resuscitation hypotension is strongly associated with mortality, approximately doubling it in the Topjian cohort, so I would maintain the mean arterial pressure at age-appropriate targets with fluid, inotropes, or vasopressors as needed. I would avoid hyperoxia by weaning the fractional inspired oxygen to the lowest level maintaining adequate saturation, and I would avoid both hypercapnia and hypocapnia, targeting normocapnia. Continuous EEG monitoring is essential because subclinical seizures are common after cardiac arrest. Neurological prognostication should not be attempted before twenty-four hours of normothermia, and should integrate the clinical examination, the EEG, neuroimaging, and biomarkers. Throughout the post-arrest period, the search for the underlying cause continues, because the definitive therapy — the ICD, the disease-modifying medication, the ablation — depends on the diagnosis. [4]

Branch 5 — the ICD and the family (Examiner)

What is the role of the implantable cardioverter defibrillator in this child, and what about his family? [3]

Exemplar (Candidate)

This child needs an implantable cardioverter defibrillator for secondary prevention, because he is a survivor of cardiac arrest due to an underlying condition (hypertrophic cardiomyopathy) that is not reversible, and the recurrence rate is five to fifteen per cent per year without the device. The ICD effectively terminates recurrent VF or VT and reduces arrhythmic death. In children, the threshold for ICD implantation is higher than in adults because of the technical challenges — lead fractures from growth and activity, infection, the need for generator and lead revisions over a lifetime — and the psychological burden of inappropriate shocks, which are more common in young patients whose physiological heart rates may overlap with detection zones. But for secondary prevention, the benefit clearly outweighs the risk. Subcutaneous and extravascular ICD systems are expanding the options for children. Regarding the family: hypertrophic cardiomyopathy is autosomal dominant, so every first-degree relative — his mother, his siblings, and eventually his own children — is at fifty per cent risk. Once a pathogenic sarcomeric mutation is identified in this child, all first-degree relatives need cascade screening with ECG, echocardiography, and targeted genetic testing for the specific mutation. A relative who tests negative for the family mutation is not at risk and does not need further surveillance; a relative who tests positive needs the same management pathway regardless of symptoms. The father who died at thirty-eight almost certainly had the condition, and his death was the index event that, had it been investigated, might have identified the family earlier. [3] [5]

Branch 6 — commotio cordis (Examiner)

Now suppose a different child collapses instantly after being struck in the chest by a cricket ball. The echo is normal, the ECG is normal, and the troponin is normal. What is the diagnosis and the mechanism? [6]

Exemplar (Candidate)

That presentation — instantaneous collapse after a blunt chest-wall impact, with a structurally normal heart and normal ECG — is commotio cordis. The mechanism is the delivery of the impact precisely on the vulnerable repolarisation window of the cardiac cycle, which is the upslope of the T wave, approximately ten to thirty milliseconds before the T-wave peak. The impact generates sufficient local myocardial depolarisation at the moment of maximal electrical vulnerability to trigger ventricular fibrillation. The critical determinants are the timing of the impact on the cardiac cycle, the force, and the properties of the projectile — a hard, compact ball such as a cricket ball or baseball is most dangerous. There is no structural cardiac injury, because the mechanism is purely electrical. The survival rate has risen from under fifteen per cent historically to over sixty per cent with immediate CPR and automated external defibrillator access at sporting venues. After return of spontaneous circulation, the child needs a full cardiac evaluation to exclude an underlying channelopathy (a small proportion of apparent commotio cordis cases have an inherited arrhythmia syndrome), and if the evaluation is entirely normal, he does not need an ICD, because the event was provoked by an avoidable external stimulus. The prevention measures are AED availability at all organised sport, age-appropriate safety baseballs, and education of coaches and referees. [6]

Examiner wrap-up (Examiner)

Thank you. Summarise the three points you most want the examiner to remember. [3]

Exemplar (Candidate)

First, in VF or pulseless VT, defibrillate at four joules per kilogram immediately and follow the shockable-rhythm loop — shock, CPR for two minutes, rhythm check, adrenaline after the second shock, amiodarone after the third shock. Early defibrillation is the single most important determinant of survival. Second, sudden cardiac death in the young has four cause families — structurally normal heart (channelopathies, idiopathic VF, commotio cordis), cardiomyopathy, congenital heart disease, and acquired — and the structurally normal heart group is the one most often missed, because the resting ECG may be normal. Third, post-arrest care is now integral to the resuscitation: targeted temperature management at thirty-six degrees for forty-eight hours, avoidance of hypotension (which doubles mortality), and prognostication only after twenty-four hours of normothermia. [3] [4]