Refractory Ventricular Tachycardia

Refractory ventricular tachycardia is sustained ventricular tachycardia that persists or recurs despite cardioversion and at least one or two intravenous antiarrhythmic drugs. Electrical storm is three or more episodes of sustained ventricular tachycardia or fibrillation, or appropriate defibrillator shocks, within 24 hours.

Epidemiology. Electrical storm affects 10 to 20% of patients with implanted defibrillators within 3 years, and carries a high rate of death and heart failure.

Causes and associations. Ischaemic scar related re-entry, acute coronary ischaemia, dilated and other cardiomyopathies, myocarditis, sarcoidosis, arrhythmogenic cardiomyopathy, channelopathies, electrolyte disturbance (potassium under 4.0 mmol/L, magnesium under 1.0 mmol/L), drug induced QT prolongation, heart failure decompensation, sympathetic surge and ventricular assist device suction events.

Pathophysiology. Re-entry through scar corridors or triggered activity and enhanced automaticity. Sympathetic activation (including from repeated shocks) maintains the arrhythmia in a vicious cycle.

Presentation is palpitations, dizziness, syncope, chest pain, heart failure, hypotension, cardiac arrest, or repeated defibrillator shocks. A wide complex regular tachycardia at 120 to 250 beats/min, with atrioventricular dissociation, fusion or capture beats.

Red flags.

• Haemodynamic instability, altered consciousness or ongoing ischaemia.
• Repeated shocks or three or more episodes in 24 hours.
• Syncope, polymorphic morphology or long QT.

12-lead ECG (morphology, QT interval, Brugada pattern), electrolytes with magnesium and calcium, troponin, drug review (QT-prolonging agents), arterial gas, echocardiography, and coronary angiography if ischaemia is suspected. Check device interrogation. Cardiac MRI, once stable, may show scar.

Differential diagnosis. Supraventricular tachycardia with aberrancy or pre-excitation, atrial fibrillation with a bundle branch block, torsades de pointes, pacemaker mediated tachycardia and artefact.

Unstable (hypotension, ischaemia, heart failure, reduced consciousness). Synchronised cardioversion with sedation: 100 to 200 J biphasic, escalating. Defibrillation at 150 to 200 J for pulseless ventricular tachycardia.

Stable monomorphic ventricular tachycardia.

• Amiodarone 150 mg IV over 10 minutes, repeated once if needed (maximum 2.2 g in 24 hours), then 1 mg/min for 6 hours, then 0.5 mg/min. Monitor hypotension, bradycardia and liver function, and avoid peripheral infusion beyond 2 hours in concentrations over 2 mg/mL.
• Lidocaine 1 to 1.5 mg/kg IV, then infusion 1 to 4 mg/min. Reduce in liver impairment and heart failure. Effective in ischaemia.
• Procainamide 20 to 50 mg/min IV up to 17 mg/kg (maximum 1 g), stopping for hypotension or QRS widening of over 50%. Avoid in heart failure, long QT and renal failure.

Electrical storm.

• Beta blockade: esmolol 500 microgram/kg IV then 50 to 300 microgram/kg/min, or propranolol 0.15 mg/kg IV (about 1 mg every 2 minutes up to 10 mg), unless cardiogenic shock. This suppresses sympathetic tone and is the main therapy.
• Deep sedation, intubation and ventilation (propofol, benzodiazepine) for refractory storm.
• Correct potassium (4.0 to 5.0 mmol/L), magnesium (magnesium sulphate 2 g IV, to over 1.0 mmol/L), calcium and hypoxia. Treat ischaemia with revascularisation.
• Overdrive pacing at 90 to 110 beats/min for pause dependent or torsades related tachycardia.
• Mexiletine 150 to 200 mg orally every 8 hours (up to 300 mg) combined with amiodarone, with monitoring for nausea, tremor and liver injury.
• Stellate ganglion block (bupivacaine 0.25% 5 to 10 mL) or thoracic epidural for refractory cases.

Catheter ablation. Urgent for storm or ventricular tachycardia refractory to drugs, ideally in a specialist centre.

Mechanical support. Intra-aortic balloon pump, percutaneous ventricular assist device or ECMO for haemodynamic collapse and as a bridge to ablation.

Defibrillator reprogramming. Review antitachycardia pacing and shock therapies.

Monitoring. Continuous ECG, QT interval, electrolytes every 4 to 6 hours, arterial pressure and drug levels.

Referral and escalation. Electrophysiology and cardiac intensive care at once for storm.

Special groups. In pregnancy, lidocaine and beta blockers are used, and amiodarone is avoided if possible. In renal impairment, avoid procainamide.