Ventricular arrhythmias and sudden cardiac death — formative SAQs

SAQ 1 (10 marks)

A fifteen-year-old boy collapses without warning during a school football match. He was sprinting for the ball, there was no body contact, and he is now unresponsive, apnoeic, and pulseless. A teacher begins cardiopulmonary resuscitation. The paramedics arrive within four minutes, and the monitor shows a chaotic, irregular rhythm with no discernible QRS complexes — ventricular fibrillation. A single 150-joule biphasic shock is delivered, and return of spontaneous circulation is achieved after two minutes of CPR and a second shock. On arrival in the emergency department, 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. ^{[1] [3]}

1. Describe the immediate resuscitation of this child, giving the shockable-rhythm algorithm and the drug doses you would use. (4) ^{[3] [6]}
2. Give the likely diagnosis based on the history, the ECG findings, and the family history, and outline the diagnostic workup that confirms the cause. (3) ^{[1] [6]}
3. Outline the post-arrest care in the first forty-eight hours, including the haemodynamic targets and the neurological prognostication. (3) ^{[5] [3]}

Model answer — SAQ 1

(1) Immediate resuscitation (4). This child is in cardiac arrest from ventricular fibrillation, a shockable rhythm. The resuscitation follows the shockable-rhythm loop of the paediatric advanced life support algorithm. Begin high-quality CPR immediately (compressions at one hundred to one hundred and twenty per minute, compression depth approximately one-third of the anteroposterior chest diameter, full recoil between compressions, minimising interruptions). Defibrillate as soon as possible at two to four joules per kilogram using a biphasic waveform, escalating up to a maximum of ten joules per kilogram or the adult dose if required. After each shock, resume CPR immediately for two minutes before reassessing the rhythm — do not pause compressions to check the rhythm after a shock, as this is a common and damaging error. Give intravenous or intraosseous adrenaline at ten micrograms per kilogram every three to five minutes after the second shock. Give intravenous amiodarone at five milligrams per kilogram after the third shock if VF or pulseless VT persists (lidocaine at one milligram per kilogram is an alternative, and is preferred in children under five years by some guidelines). Throughout the resuscitation, identify and 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] [6]}

(2) Likely diagnosis and workup (3). The combination of sudden cardiac arrest during exertion, left ventricular hypertrophy with deep T-wave inversion on the ECG, and a family history of sudden death at thirty-eight is most consistent with hypertrophic cardiomyopathy. The diagnostic workup includes an echocardiogram to demonstrate the asymmetric left ventricular hypertrophy (typically affecting the interventricular septum, with a wall thickness above two standard deviations for age, body surface area, or z-score), an assessment for left ventricular outflow tract obstruction, and a cardiac MRI with late gadolinium enhancement to characterise the extent of fibrosis. Genetic testing for the sarcomeric gene mutations that underlie hypertrophic cardiomyopathy (most commonly MYH7 and MYBPC3) should be requested through an inherited cardiac conditions service with appropriate counselling. The family history of sudden death mandates a detailed three-generation pedigree and cascade screening of first-degree relatives with ECG and echocardiography. ^{[1] [6]}

(3) Post-arrest care (3). Post-arrest care is now an integral part of the resuscitation. Targeted temperature management at thirty-six degrees Celsius for forty-eight hours after return of spontaneous circulation is the recommended strategy, with active avoidance of fever. Haemodynamic optimisation is critical: post-resuscitation hypotension is strongly associated with mortality (approximately doubling it in the Topjian cohort), and the mean arterial pressure should be maintained at age-appropriate targets with fluid, inotropes, or vasopressors. Avoid hyperoxia by weaning the fractional inspired oxygen to the lowest level maintaining adequate saturation, and avoid both hypercapnia and hypocapnia (target 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. The patient will need an ICD for secondary prevention once the diagnosis is confirmed and a reversible cause has been excluded. ^{[5] [3]}