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]

SAQ 2 (10 marks)

A fourteen-year-old boy is struck in the centre of the chest by a cricket ball while batting during a school match. He collapses instantly, is unresponsive and pulseless, and a bystander begins CPR. The automated external defibrillator at the sports ground advises a shock, which is delivered within three minutes of the collapse. Return of spontaneous circulation is achieved. In the emergency department, his twelve-lead ECG is in sinus rhythm with a normal QTc, his echocardiogram shows a structurally normal heart with normal function, and his troponin is normal. There is no evidence of cardiac contusion on imaging. [4] [3]

1. Give the diagnosis, explain the mechanism, and explain why there is no structural cardiac injury despite the lethal event. (3) [4]
2. Outline the immediate and subsequent management, including the sporting and lifestyle advice. (4) [4] [3]
3. Describe the public health and prevention measures that reduce the mortality from this condition. (3) [4] [1]

Model answer — SAQ 2

(1) Diagnosis and mechanism (3). The diagnosis is commotio cordis — the instantaneous production of ventricular fibrillation by a blunt, non-penetrating blow to the chest wall from a projectile, with no underlying structural cardiac injury. The mechanism is the delivery of the impact precisely on the vulnerable repolarisation window of the cardiac cycle — 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 (impact must land during the narrow repolarisation window), the force (moderate, not necessarily maximal), and the hardness and small diameter of the projectile (a hard, compact ball such as a cricket ball, baseball, or lacrosse ball is most dangerous). There is no structural cardiac injury because the mechanism is purely electrical — the impact does not damage the myocardium, it merely depolarises it at the wrong moment. The structurally normal echocardiogram, the normal troponin, and the absence of cardiac contusion are entirely consistent with the diagnosis. [4]

(2) Management (4). The immediate management was the bystander CPR and the early defibrillation, which were life-saving — the survival rate from commotio cordis 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 admission for cardiac monitoring for at least twenty-four to forty-eight hours, because the risk of re-arrest is highest in the early period. A full cardiac evaluation is mandatory to exclude an underlying substrate that would change the diagnosis and the long-term management: a twelve-lead ECG with manual QTc measurement, an echocardiogram (already done and normal), an exercise stress test, an ambulatory ECG, and — because a small proportion of apparent commotio cordis cases have an underlying channelopathy — genetic testing through an inherited cardiac conditions service. If no underlying condition is identified and the evaluation is entirely normal, the child does not need an ICD, because the event was provoked by a specific external stimulus that is avoidable. The sporting and lifestyle advice centres on avoiding further chest-wall impact: the child should not return to the sport that caused the event (or to any projectile sport) until the full cardiac evaluation is complete and a specialist has cleared him. If the evaluation is normal, a return to non-projectile sports is reasonable, but projectile sports should be avoided or undertaken with appropriate protective equipment and the assurance of AED availability. [4] [3]

(3) Prevention (3). The public health and prevention measures that reduce mortality from commotio cordis operate at several levels. First, the availability of automated external defibrillators at all organised sporting events — schools, clubs, and public sporting venues — is the single most effective intervention, because survival depends on immediate CPR and early defibrillation. Second, the use of age-appropriate safety baseballs (softer, lower-impact balls for younger age groups) reduces the force and the likelihood of the impact landing on the vulnerable window, though chest protectors have not been consistently shown to prevent commotio cordis. Third, education of coaches, teachers, referees, and athletes to recognise the event (instantaneous collapse after a chest-wall impact, with no other explanation) and to respond immediately with CPR and the AED, without waiting for the child to recover. Fourth, the broader framework of preparticipation cardiovascular screening for young athletes, which identifies the underlying cardiac conditions (cardiomyopathies, channelopathies) that produce sudden cardiac death on the sporting field, is part of the same prevention effort. [4] [1]