Sudden Cardiac Death

Sudden cardiac death (SCD) is unexpected death from a cardiac cause within 1 hour of symptom onset if witnessed, or within 24 hours of last being seen well if unwitnessed. Sudden cardiac arrest is the same event when circulation is restored.

Incidence is about 50 to 100 in every 100,000 adults each year in high income settings, and about 1 to 2 in every 100,000 each year under 35 years. Survival to discharge after out-of-hospital arrest is about 5 to 10% overall, and 30 to 50% or more where bystander CPR and early defibrillation are in place.

Over 35 years, coronary disease causes about 70 to 80% of cases. Under 35 years the causes are cardiomyopathy (hypertrophic, arrhythmogenic, dilated), channelopathy (long QT, Brugada, catecholaminergic polymorphic ventricular tachycardia, short QT), anomalous coronary origin, myocarditis, aortic rupture and pre-excitation.

A quarter to a half of young victims have a structurally normal heart at autopsy.

Other causes are heart failure with ejection fraction of 35% or less, severe aortic stenosis, pulmonary embolism, potassium disturbance, QT-prolonging drugs, cocaine and commotio cordis.

In sub-Saharan Africa hypertensive heart disease, rheumatic heart disease and cardiomyopathy contribute, and survival is very low because emergency services and defibrillators are scarce.

There is no validated severity score.

Outcome is described by initial rhythm (shockable: ventricular fibrillation or pulseless ventricular tachycardia, now about 20 to 30%; non-shockable: asystole or pulseless electrical activity), bystander CPR, time to first shock, and neurological recovery by cerebral performance category (1 good, 2 moderate disability, 3 severe disability, 4 coma or vegetative state, 5 death).

Pathophysiology. Acute ischaemia, scar re-entry or ion channel dysfunction in a vulnerable substrate produces ventricular tachycardia or fibrillation. Brain injury begins within 4 to 6 minutes of arrest.

Survival falls by about 7 to 10% for each minute without CPR or defibrillation, and about 3 to 4% for each minute with CPR.

Recognition:

• Unresponsive, with absent breathing or only gasping. Lay rescuers do not check a pulse. Health professionals check for no more than 10 seconds.
• Prodrome in about half of cases on review: chest pain, dyspnoea, palpitations or syncope in the preceding hours to weeks.
• Brief seizure like movements from cerebral hypoperfusion, central cyanosis and pallor.
• Circumstances that point to cause: exertion or swimming (long QT type 1, catecholaminergic polymorphic ventricular tachycardia, anomalous coronary, hypertrophic cardiomyopathy), sleep or rest (Brugada, long QT type 3), sudden noise (long QT type 2), recent drugs or stimulants.

Red flags (warning features before arrest in patients seen alive):

• Exertional syncope, or syncope with palpitations
• Family history of sudden death under 40 years
• Ejection fraction of 35% or less, or non-sustained ventricular tachycardia with structural disease
• QTc of 500 ms or more, Brugada type 1 pattern, epsilon waves, or pre-excitation with a short pre-excited RR interval
• Severe left ventricular hypertrophy (wall thickness 30 mm or more)

Rapid investigations during resuscitation:

• Rhythm check every 2 minutes with pauses under 10 seconds.
• Waveform capnography (end tidal CO2 under 1.3 kPa, 10 mm Hg, after 20 minutes of CPR predicts failure).
• Point-of-care ultrasound during rhythm checks for tamponade, right ventricular dilatation (pulmonary embolism), hypovolaemia and absent cardiac activity.
• Blood gas with potassium, glucose, lactate, haemoglobin and pH. Core temperature.

After return of circulation:

• 12-lead ECG at once, high sensitivity troponin, echocardiography, chest X-ray.
• Coronary angiography for ST elevation, and early for other suspected cardiac causes. CT of the head and chest when the cause is unclear.
• Survivors with no cause: cardiac MRI, exercise test, sodium channel blocker challenge, epinephrine challenge, ambulatory ECG, toxicology and genetic testing.
• Death: full autopsy with toxicology, and storage of blood for DNA.

Differential diagnosis.

• Pulmonary embolism, tension pneumothorax and tamponade
• Intracranial haemorrhage and aortic rupture
• Hypovolaemic shock and anaphylaxis
• Hypoglycaemia, opioid or other overdose, hypothermia and drowning
• Seizure and arrhythmic or vasovagal syncope
• Pseudo arrest from monitoring artefact

Minutes 0 to 2: start.

• Shout for help, call emergency services, fetch a defibrillator. Compress the centre of the chest at 100 to 120/min, depth 5 to 6 cm, with full recoil and interruptions under 10 seconds. Ratio 30 compressions to 2 breaths until the airway is secured, then continuous compressions with 10 breaths/min.
• Bag mask ventilation with 100% oxygen. Supraglottic airway or tracheal tube by a skilled operator, confirmed by waveform capnography. Avoid hyperventilation.
• Attach pads. Shockable rhythm: one shock at 150 to 200 J biphasic (or the device maximum), then CPR at once for 2 minutes. Intravenous or intraosseous access.

Drugs and shocks.

• Adrenaline 1 mg intravenously or intraosseously: for non-shockable rhythm as soon as access is gained, and for shockable rhythm after the third shock, then every 3 to 5 minutes.
• Amiodarone 300 mg intravenous bolus after the third shock and 150 mg after the fifth. If amiodarone is unavailable, lidocaine 1 to 1.5 mg/kg intravenously, a further 0.5 to 0.75 mg/kg after 5 to 10 minutes, total maximum 3 mg/kg.
• Torsades de pointes: magnesium sulphate 2 g intravenously over 1 to 2 minutes in cardiac arrest.
• Refractory ventricular fibrillation after 3 shocks: change pad position (anteroposterior) and consider double sequential defibrillation. Evidence is limited. Extracorporeal CPR in selected patients (witnessed, shockable, age under 70 years, under 60 minutes to start, centre with capability).

Reversible causes (hypoxia, hypovolaemia, hypokalaemia or hyperkalaemia, hypothermia, acidosis, tension pneumothorax, tamponade, toxins, thrombosis).

• Hyperkalaemia: calcium chloride 10% 10 mL intravenously, sodium bicarbonate 50 mmol intravenously, and soluble insulin 10 units with glucose 25 g.
• Hypokalaemia: potassium chloride 10 mmol/h intravenously (maximum 20 mmol/h through a central line).
• Suspected pulmonary embolism: alteplase 50 mg intravenous bolus, repeated once after 15 minutes if there is no return of circulation (maximum 100 mg), or tenecteplase by weight band (30 mg under 60 kg to 50 mg at 90 kg or over), then continue CPR for 60 to 90 minutes. Evidence is limited.
• Sodium channel blocker toxicity: sodium bicarbonate 1 to 2 mmol/kg intravenously.
• Local anaesthetic toxicity: 20% lipid emulsion 1.5 mL/kg intravenously over 1 minute, repeated up to twice at 5-minute intervals, then 15 mL/kg/h (cumulative maximum 12 mL/kg for the bolus doses).
• Hypothermia (core under 30 degrees Celsius): up to 3 shocks, withhold adrenaline until over 30 degrees Celsius, then double the dosing interval until over 35 degrees Celsius.
• Tension pneumothorax: decompression. Tamponade: pericardiocentesis or resuscitative thoracotomy. Hypovolaemia: blood and fluid.
• Consider stopping after 20 minutes or more of ALS with a non-shockable rhythm, no reversible cause and persistently low end tidal CO2.

After return of circulation (first hours).

• Oxygen to a saturation of 94 to 98%. PaCO2 4.5 to 6.0 kPa (35 to 45 mm Hg). Mean arterial pressure of 65 mm Hg or more with fluid and noradrenaline 0.05 microgram/kg/min intravenously, titrated, usual maximum 0.5 microgram/kg/min.
• ST elevation: immediate coronary angiography. No ST elevation with a suspected cardiac cause: angiography early, and CT of the head and chest first when the cause is unclear.
• Comatose patients: control temperature at 32 to 37.5 degrees Celsius for at least 24 hours, and prevent fever for 72 hours. Sedation with propofol 0.3 to 4 mg/kg/h intravenously (maximum 4 mg/kg/h, monitor triglycerides) with an opioid.
• Glucose 7.8 to 10.0 mmol/L (140 to 180 mg/dL). Potassium 4.0 to 5.0 mmol/L. Treat clinical seizures with levetiracetam or valproate, with the dose set by neurology. No seizure prophylaxis.
• Prognosis is judged no earlier than 72 hours after normothermia and sedation withdrawal, using at least two concordant findings: absent or extensor motor response, absent pupillary and corneal reflexes, absent bilateral N20 somatosensory responses, neuron specific enolase over 60 microgram/L at 48 or 72 hours, status myoclonus within 72 hours, highly malignant EEG, and diffuse anoxic injury on CT or MRI.

Prevention after survival.

• Implantable cardioverter defibrillator for arrest not due to a reversible cause, with expected survival over 1 year. Primary prevention for ejection fraction of 35% or less with NYHA class II to III after at least 3 months of optimal therapy (at least 40 days after infarction and 90 days after revascularisation). A wearable defibrillator is a bridge.
• Treat the cause: revascularisation, antiarrhythmic and beta blocker therapy by diagnosis, and cascade screening of first degree relatives when the cause is inherited.

Special groups.

• Pregnancy (over 20 weeks): manual left uterine displacement, and emergency delivery within 4 minutes if there is no return of circulation.
• Children: shock 4 J/kg, adrenaline 10 microgram/kg intravenously (0.1 mL/kg of 1 in 10,000), amiodarone 5 mg/kg, ratio 15 to 2 for professionals.
• Region: community training in compression only CPR and public access defibrillators matter most where emergency services are limited.

Monitoring. Continuous ECG and arterial pressure, temperature, lactate, glucose and potassium, neurological examination daily, device interrogation, and echocardiography within 24 hours.

Referral and escalation. Admit to intensive care with cardiac catheterisation and extracorporeal support on site or by early transfer. Refer survivors and families to an inherited cardiac conditions service.