Review
Contemporary Management of Electrical Storm

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Cardiac electrical storm (ES) is characterised by three or more discrete episodes of ventricular arrhythmia within 24 hours, or incessant ventricular arrhythmia for more than 12 hours. ES is a distinct medical emergency that portends a significant increase in mortality risk and often presages progressive heart failure. ES is also associated with psychological morbidity from multiple implanted cardioverter defibrillator (ICD) shocks and exponential health resource utilisation. Up to 30% of ICD recipients may experience storm in follow-up, with the risk higher in patients with a secondary prevention ICD indication. Storm recurs in a high proportion of patients after an initial episode, and multiple storm clusters may occur in follow-up. The mechanism of storm remains elusive but is likely influenced by a complex interplay of inciting triggers (e.g., ischaemia, electrolyte disturbances), with autonomic perturbations acting on a vulnerable structural and electrophysiologic substrate. Triggers can be identified only in a minority of patients. An emergent treatment approach is warranted, if possible with emergent transfer to a high-volume centre for ventricular arrhythmia management with a multi-modality approach including ICD reprogramming, sympathetic blockade (sedation, intubation, ventilation, beta blockers), and anti-arrhythmic drugs, and adjunctive intervention techniques, such as catheter ablation and neuraxial modulation (e.g., thoracic epidural anaesthesia, stellate ganglion block). Outcomes of catheter ablation of ES are excellent with resolution of storm in over 90% of patients at 1 year with a low complication rate (∼2%). ES may occur in the absence of structural heart disease in the context of channelopathies, Brugada syndrome, early repolarisation and premature ventricular contraction-induced ventricular fibrillation. There are unique treatment approaches to these conditions that must be recognised. This state-of-the-art review will summarise the incidence, mechanism, and multi-modality treatment of ES in the contemporary era.

Introduction

Electrical storm (ES) is a distinct medical emergency characterised by multiple episodes of sustained ventricular arrhythmia within a short time period, typically 24 hours. In the majority of cases, monomorphic ventricular tachycardia constitutes the primary arrhythmia, however, polymorphic ventricular tachycardia and ventricular fibrillation (VF) are also implicated. In patients without an implantable cardioverter defibrillator (ICD), it is generally accepted that three or more discrete episodes of ventricular arrhythmia within 24 hours, or incessant ventricular arrhythmia for more than 12 hours, constitutes ES [1], [2]. In patients with an ICD, this condition is defined as the occurrence of three or more appropriate device therapies within a 24-hour period, separated from one another by at least 5 minutes [1], [2], [3]. ES predominantly afflicts patients with severe structural heart disease, however, this condition is also reported in those with channelopathies such as Brugada and Long QT Syndrome. Clinical factors associated with a higher incidence of ES include: lower left ventricular ejection fraction, implantation of a secondary prevention ICD, treatment with class I anti-arrhythmic agents, and monomorphic ventricular tachycardia (VT) as the underlying arrhythmia [4]. The development of ES is associated with increased risk of death, heart transplantation and hospitalisation for decompensated cardiac failure [5], [6]. The management of ES requires complex multi-disciplinary care including ICD re-programming, haemodynamic support, the use of antiarrhythmic medications, identification and reversal of precipitating factors, and consideration of catheter ablation and neuraxial modulation. This state-of-the-art review will summarise the contemporary knowledge and treatment of ES.

Section snippets

Incidence Of ES

The overall reported incidence of ES is 10–30% in patients with a secondary prevention ICD, occurring at an average of 4–9 months after ICD implantation [3], [7]. The incidence is 4–7% in patients with a primary prevention ICD, occurring ∼18–24 months after ICD implant [8], [9]. In a longitudinal study of patients with ischaemic cardiomyopathy (ICM) and dilated cardiomyopathy (DCM), storm occurred with similar incidence between the two groups (5.8% vs. 6.9%, respectively). This study showed

Mechanism of ES

The pathophysiological mechanisms which underlie ventricular arrhythmia storm are not well characterised. It is likely that there is a complex interplay between enhanced sympathetic tone, calcium-related signalling abnormalities, dysregulation of protein phosphorylation and a susceptible arrythmogenic substrate [10]. The working theory is that three key factors culminate in storm: a vulnerable heart (i.e., presence of pre-existing heart disease that creates the necessary “substrate”), an

Implications of ES

The occurrence of electrical storm has been associated with a mortality rate of up to 14% in the first 48 hours from presentation [18], [19]. The AVID (Antiarrhythmics Versus Implantable Defibrillators) study, which followed patients with secondary prevention ICDs, demonstrated a 5.6-fold increase in mortality in the first 12 weeks subsequent to the development of ES [18]. Similarly, in a subset analysis of the MADIT (Multicenter Automatic Defibrillator Implantation Trial) II trial, the

Overview

The treatment of electrical storm, regardless of underlying aetiology and electrophysiological substrate, requires a multimodal approach. Several therapeutic modalities have been proposed for the treatment of electrical storm including device reprogramming, pharmacotherapy, sedation, neuraxial modulation and radiofrequency catheter ablation. Radiofrequency catheter ablation is emerging as the standard-of-care in patients with electrical storm refractory to optimal medical management. There is

Conclusions

Electrical storm is a distinct arrhythmic emergency which portends significant morbidity and mortality. In the context of increasing use of ICDs in primary and secondary prevention of sudden cardiac death, the occurrence of this clinical phenomenon is likely to increase. Treatment requires a multi-disciplinary approach involving exclusion and treatment of triggers, optimal ICD and/or CRT programming (including turning off a pro-arrhythmic LV lead), anti-arrhythmic drug therapy, sedation,

Acknowledgements

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Funding Sources

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