Electrical Storm

Electrical storm is three or more separate episodes of sustained ventricular tachycardia or ventricular fibrillation (or appropriate defibrillator therapies, shocks or antitachycardia pacing) within 24 hours, each separated by at least 5 minutes and each needing intervention.

Incessant ventricular tachycardia is a related state in which tachycardia recurs at once after termination or persists over several hours. Storm affects roughly 10 to 20% of defibrillator recipients within 3 years of implant, more in secondary prevention, and carries a marked increase in mortality over the following months.

Triggers are acute ischaemia or infarction, decompensated heart failure, hypokalaemia and hypomagnesaemia, QT-prolonging or proarrhythmic drugs, sympathomimetics, cocaine and amphetamine, thyrotoxicosis, sepsis, lead or device problems, and inherited channelopathies (long QT, Brugada syndrome, early repolarisation, short QT, catecholaminergic polymorphic ventricular tachycardia).

Severity grading. There is no validated severity score. These descriptive grades direct escalation:

• Grade 1, stable: recurrent monomorphic ventricular tachycardia or device therapies with preserved consciousness and blood pressure.
• Grade 2, unstable: recurrent ventricular tachycardia or ventricular fibrillation needing shocks, or hypotension, or recurrent polymorphic ventricular tachycardia and fibrillation.
• Grade 3, refractory: recurrences despite beta blockade, amiodarone and deep sedation, or any storm with cardiogenic shock. Needs mechanical support or ablation.

Pathophysiology. Each shock and each episode raises sympathetic outflow, which increases triggered activity and re-entry, producing further episodes. Scar related re-entry, ischaemia, repolarisation abnormalities or calcium handling defects provide the substrate, and autonomic imbalance sustains the loop.

Recognition:

• A patient with a defibrillator reports three or more shocks in a day, or a cluster of shocks within minutes.
• Monitor shows repeated runs of ventricular tachycardia or fibrillation, recurrent syncope or recurrent arrest.
• Anxiety, sweating, chest pain, dyspnoea, hypotension or shock.
• Features of the trigger: ischaemic pain, signs of decompensated heart failure, fever, thyrotoxic signs, drug or alcohol exposure, vomiting and diarrhoea.

Red flags.

• Hypotension, cardiogenic shock or pulmonary oedema
• Two or more shocks within an hour, or ongoing ventricular tachycardia despite shocks
• Ejection fraction under 25%
• Acute ST elevation, or ischaemic symptoms
• Potassium under 3.5 mmol/L or over 5.5 mmol/L, or magnesium under 0.7 mmol/L
• QTc over 500 ms with polymorphic tachycardia
• Patient on sotalol, flecainide, amiodarone or other proarrhythmic drugs

Rapid investigations:

• Continuous ECG monitoring and 12-lead ECG in tachycardia (morphology, rate, monomorphic or polymorphic) and after conversion (ischaemia, QTc, Brugada pattern, J waves, pre-excitation).
• Device interrogation immediately in any patient with a defibrillator: confirm that tachycardia was real and measure cycle length, therapy delivered and lead integrity. A magnet over the device suspends tachycardia therapies without stopping pacing. Apply it only when shocks are confirmed or strongly suspected to be inappropriate (lead noise, supraventricular tachycardia), because it removes rescue from true ventricular tachycardia.
• Bloods: potassium, magnesium, calcium, creatinine, glucose, lactate, blood gases, troponin, natriuretic peptide, thyroid function, digoxin level, drug screen, inflammatory markers.
• Echocardiography for ventricular function, wall motion, tamponade and valve disease. Chest X-ray for lead position and pulmonary oedema.
• Coronary angiography urgently when ischaemia is suspected.
• Later: cardiac MRI, genetic testing and electrophysiology study.

Differential diagnosis.

• Inappropriate shocks (atrial fibrillation or supraventricular tachycardia with rapid conduction, T-wave oversensing, lead fracture or noise, electromagnetic interference)
• Supraventricular tachycardia with aberrancy and pre-excited atrial fibrillation
• Torsades de pointes from acquired long QT
• Hyperkalaemia with sine wave pattern
• Artefact from tremor, shivering or seizure
• Non-sustained ventricular tachycardia bursts that need no shock
• Sinus tachycardia with bundle branch block

Minutes 0 to 5: stabilise and terminate.

• Call for help, apply defibrillator pads, monitor, secure access and airway.
• Pulseless ventricular tachycardia or fibrillation: CPR and defibrillation at 150 to 200 J biphasic, escalating to the device maximum. Adrenaline 1 mg intravenously after the third shock, then every 3 to 5 minutes, using as little as possible because catecholamines feed the storm. Amiodarone 300 mg intravenous bolus after the third shock and 150 mg after the fifth. If amiodarone is unavailable, lidocaine 1 mg/kg intravenously (maximum 100 mg).
• Ventricular tachycardia with a pulse and instability: synchronised cardioversion at 120 to 150 J biphasic, increased to 200 J, under brief sedation if awake (propofol 0.5 to 1 mg/kg intravenously, titrated, with airway support).
• Stop QT-prolonging drugs, sympathomimetics and any proarrhythmic antiarrhythmic. Send point-of-care potassium and magnesium.

Minutes 5 to 30: suppress recurrence.

• Beta blockade, unless cardiogenic shock, severe bradycardia or high grade block without pacing:
  • Esmolol 500 microgram/kg intravenously over 1 minute, then infusion 50 microgram/kg/min, repeating the bolus and increasing the infusion by 50 microgram/kg/min every 4 to 5 minutes. Maximum 200 microgram/kg/min. Use when haemodynamics are uncertain, because the effect wears off within minutes.
  • Propranolol 1 mg intravenously over 1 minute, repeated every 2 minutes if needed, maximum 10 mg. Monitor blood pressure and heart rate.
• Amiodarone 150 mg intravenously over 10 minutes, repeated every 10 minutes for recurrence, then 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours. Maximum 2.2 g in 24 hours. Use a central line when possible. Contraindicated in severe sinus node disease, high grade atrioventricular block and QT prolongation with torsades. Interacts with warfarin and digoxin.
• Magnesium sulphate 2 g (8 mmol) intravenously over 10 minutes, repeated once if recurrence, then 0.5 to 1 g/h. Monitor reflexes, respiratory rate and serum magnesium. Reduce the infusion at creatinine clearance under 30 mL/min.
• Potassium to 4.5 to 5.0 mmol/L: potassium chloride intravenously 10 mmol/h (maximum 20 mmol/h through a central line with ECG monitoring), levels every 2 to 4 hours. Reduce in renal impairment.
• Lidocaine 1 to 1.5 mg/kg intravenously, then 0.5 to 0.75 mg/kg every 5 to 10 minutes to a total of 3 mg/kg, followed by infusion 1 to 4 mg/min, maximum 4 mg/min. Most useful for ischaemia related ventricular tachycardia. Halve the infusion in liver disease, heart failure, shock and older age. Stop for perioral numbness, confusion or seizures. Target level 1.5 to 5 mg/L.
• Deep sedation and ventilation to cut sympathetic drive: propofol infusion 0.3 to 4 mg/kg/h, maximum 4 mg/kg/h, with opioid analgesia. Treat hypotension with fluid and noradrenaline and avoid high dose propofol beyond 48 hours (monitor triglycerides and for infusion syndrome).

Minutes 30 to 60: treat the cause and reprogramme.

• Ischaemia: urgent coronary angiography and revascularisation. Intra-aortic balloon pump for ischaemia with shock.
• Overdrive pacing at 90 to 110/min through a temporary wire or the device for bradycardia dependent or pause dependent polymorphic tachycardia.
• Defibrillator reprogramming: lengthen detection, raise rate zones, and use antitachycardia pacing to avoid shocks. Do not disable therapies unless shocks are inappropriate.
• Percutaneous stellate ganglion block under ultrasound control, left or bilateral: bupivacaine 0.25% 5 to 10 mL at the C6 or C7 level, maximum 2 mg/kg. Complications are Horner syndrome, hoarseness, pneumothorax and intravascular injection.
• Cause specific therapy:
  • Brugada syndrome and early repolarisation: isoprenaline 1 microgram/min intravenously, increased every 5 to 10 minutes to a sinus rate of 90 to 120/min, usual maximum 10 microgram/min, and quinidine sulphate 200 to 300 mg orally every 8 hours, maximum 1,200 mg daily in this setting. Avoid isoprenaline with ischaemia.
  • Long QT syndrome: magnesium, potassium, pacing at 90 to 110/min and beta blockade. Avoid isoprenaline in congenital forms.
  • Catecholaminergic polymorphic ventricular tachycardia: beta blockade (esmolol 500 microgram/kg intravenously over 1 minute then 50 microgram/kg/min, or propranolol 1 mg intravenously over 1 minute repeated every 2 minutes, maximum 10 mg), deep sedation and flecainide 50 mg orally twice daily, increased to 100 mg twice daily, maximum 300 mg daily when structural disease is excluded.
  • Short QT syndrome: quinidine sulphate 200 to 300 mg orally every 8 hours, maximum 1,200 mg daily in this setting, with ECG, full blood count and liver enzyme monitoring.

Beyond 1 hour: refractory storm.

• Urgent catheter ablation of ventricular tachycardia substrate or triggers. Estimate haemodynamic risk with PAINESD (chronic lung disease 5, age over 60 years 3, ischaemic cardiomyopathy 6, NYHA class III or IV 6, ejection fraction under 25% 3, storm 5, diabetes 3): 15 or more is high risk and supports mechanical support before ablation.
• Mechanical circulatory support (intra-aortic balloon pump, left ventricular assist catheter, veno arterial extracorporeal membrane oxygenation) as a bridge to ablation, transplantation or ventricular assist device.
• Surgical or percutaneous left or bilateral cardiac sympathetic denervation.

Special groups.

• Pregnancy: defibrillation is safe. Use amiodarone only for life threatening, refractory arrhythmia.
• Children: defibrillation 4 J/kg, amiodarone 5 mg/kg over 20 to 60 minutes (maximum 300 mg), lidocaine 1 mg/kg.
• Kidney impairment: reduce magnesium infusion and use cautious potassium replacement.

Monitoring. Continuous ECG and arterial pressure. Potassium and magnesium every 2 to 4 hours. QTc daily. Liver and thyroid function on amiodarone. Lidocaine levels at 12 to 24 hours. Lactate and urine output. Device interrogation after every change in programming.

Referral and escalation. Disposition: admit to a cardiac or intensive care unit with continuous monitoring, in a centre with electrophysiology, mechanical circulatory support and cardiac surgery. Transfer early for grade 3 storm. Step down only after 24 to 48 hours free from ventricular arrhythmia, with the trigger treated, drugs and device settings finalised, and outpatient defibrillator and electrophysiology follow up arranged.