Electrical storm and incessant ventricular tachycardia

INTRODUCTION — Electrical storm, also referred to as arrhythmic storm, refers to multiple recurrences of ventricular arrhythmias over a short period of time. In most instances, the arrhythmia is ventricular tachycardia (VT), but polymorphic VT and ventricular fibrillation (VF) can also result in electrical storm. The arrhythmias can be self-terminating but frequently are terminated using antiarrhythmic drugs or device-related therapies (defibrillation or anti-tachycardia pacing).

In contrast to repetitive ventricular arrhythmias occurring in electrical storm, incessant VT is defined as hemodynamically stable VT which persists for longer than one hour.

This topic will discuss the incidence, triggers, clinical significance and treatment of electric storm and incessant VT. The general approach to the diagnosis and management of VT, as well as the use of implantable cardioverter-defibrillators, are discussed separately in various topics. (See "Sustained monomorphic ventricular tachycardia: Clinical manifestations, diagnosis, and evaluation" and "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis" and "Primary prevention of sudden cardiac death in patients with cardiomyopathy and heart failure with reduced LVEF" and "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy".)

DEFINITION — Electrical storm refers to a state of cardiac electrical instability characterized by multiple episodes of ventricular tachycardia (VT storm) or ventricular fibrillation (VF storm) within a relatively short period of time, typically 24 hours [1]. The clinical definition of electrical storm is varied, somewhat arbitrary, and is a source of ongoing debate [2].

●In patients without an implantable cardioverter-defibrillator (ICD), electrical storm has been variously defined as [1,3-5]:

•The occurrence of three or more hemodynamically stable ventricular tachyarrhythmias within 24 hours

•VT recurring soon after (within five minutes) termination of another VT episode

•Sustained and non-sustained VT resulting in a total number of ventricular ectopic beats greater than sinus beats in a 24-hour period

●In patients with an ICD, the most widely accepted definition of electrical storm is three or more appropriate therapies for ventricular tachyarrhythmias, including antitachycardia pacing or shocks, within 24 hours [2,5-9]. However, this definition is not comprehensive as it fails to account for:

•VT that is slower than the programmed detection rate of the ICD

•VT that fails to terminate with appropriate ICD therapy and remain undetected by the patient

•VT that recurs soon after (within five minutes) a successful therapy are included by only some authors [7,10]

While electrical storm is defined by recurrent ventricular arrhythmia episodes or recurrent ICD therapies, incessant VT is defined as hemodynamically stable VT lasting longer than one hour.

INCIDENCE — The reported incidence of electrical storm varies widely based on the differences in the definition used, characteristics of the study population, device programming, and interpretation of intracardiac electrograms. The indication for implantable cardioverter-defibrillator (ICD) implantation (ie, primary versus secondary prevention) and type of underlying heart disease appear to be the most likely to influence the reported incidence of electrical storm. Most patients with electrical storm or incessant VT have severe underlying structural heart disease, although electrical storm or incessant VT has been less frequently reported in patients with structurally normal hearts (eg, Brugada syndrome or long QT syndrome). (See "Congenital long QT syndrome: Epidemiology and clinical manifestations" and "Brugada syndrome: Clinical presentation, diagnosis, and evaluation".)

When electrical storm is defined by >2 VT/VF episodes requiring device intervention over a 24-hour period, the incidence is approximately 2 to 10 percent per year follow-up period in patients with ICDs [2,6-8,11-17]. As examples:

●In an analysis of 719 patients from the MADIT II study of primary prevention ICD implantation who were followed for an average of 21 months, 4 percent experienced electrical storm (2.3 percent per year) [8].

●In a single-center cohort of 955 patients who received an ICD (81 percent for primary prevention) and were followed for 4.5 years, 6.6 percent experienced electrical storm (1.5 percent per year) [17].

TRIGGERS OF ELECTRICAL STORM — Most patients with electrical storm or incessant VT have severe underlying structural heart disease, and studies have revealed an inciting factor in only a minority of patients with electrical storm. However, careful assessment is required as some of the known triggers are reversible, including [9]:

●Drug toxicity

●Electrolyte disturbances (ie, hypokalemia and hypomagnesemia)

●New or worsened heart failure

●Acute myocardial ischemia

●Thyrotoxicosis

●QT prolongation (which may be related to drug toxicity, electrolyte imbalance, or an underlying syndrome such as long QT syndrome)

A circadian pattern of electrical storm seems likely as well, as shown in a meta-analysis of 246 patients from five cohorts, in which 29 percent of electrical storm episodes occurred between 8 AM and 10 AM (and 61 percent occurred between 8 AM and 4 PM) [18]. These varied triggers highlight the complex interactions among anatomic substrate, autonomic tone, and cellular milieu that result in electrical storm.

CLINICAL PRESENTATION — The clinical presentation of electrical storm is highly variable but rarely if ever asymptomatic. One or more ventricular arrhythmias may be present, but monomorphic VT is the inciting arrhythmia in the vast majority of patients.

Symptoms — The type and severity of symptoms from electrical storm depends on the ventricular rate, the presence of underlying heart disease, the degree of left ventricular systolic dysfunction, and the presence or absence of therapies delivered by an implantable cardioverter-defibrillator (ICD).

●In patients without an ICD, the range of clinical presentations due to electrical storm spans from relatively minor symptoms such as repeated episodes of palpitations, presyncope, or syncope if the patient remains hemodynamically stable to cardiac arrest in those patients with hemodynamically unstable ventricular arrhythmias.

●In patients with a preexisting ICD, electrical storm typically presents with multiple ICD therapies (some combination of anti-tachycardia pacing and ICD shocks depending on how the device is programmed to deliver therapy). However, patients with ventricular arrhythmias that are slower than the detection settings of the ICD may present in similar fashion as patients without an ICD.

Patients with incessant VT may present with similar symptoms (eg, presyncope, syncope, palpitations, chest pain, dyspnea, etc), which again will vary depending on the ventricular rate and hemodynamic instability related to the VT. Rarely, when patients have incessant VT at slower rates (<150 beats per minute), they may remain asymptomatic and hemodynamically stable for days or longer. In such cases, the initial presentation may be heart failure symptoms, suggesting that the incessant VT has resulted in tachycardia-mediated cardiomyopathy. (See "Arrhythmia-induced cardiomyopathy".)

Electrocardiographic monitoring — Electrical storm is not likely to be captured on a standard 12-lead electrocardiogram (ECG), given the brief 10-second window of time recorded with an ECG. Alternatively, continuous monitoring with either surface ECG (continuous ambulatory telemetry monitoring) or intracardiac electrograms (as recorded by an ICD) is required to document the presence, frequency, and duration of VT. A 12-lead ECG during incessant VT should be obtained whenever possible to help identify the mechanism and anatomic site of VT origin in order to help guide treatment.

The electrocardiographic characteristics that are consistent with VT include a wide QRS complex occurring regularly at a rate of more than 100 beats per minute in association with one or more other distinct ECG characteristics (ie, AV dissociation, fusion beats, capture beats, etc). The ECG characteristics of VT are discussed in greater detail elsewhere. (See "Wide QRS complex tachycardias: Approach to the diagnosis", section on 'Evaluation of the electrocardiogram'.)

Type of ventricular arrhythmia — Analyses of stored intracardiac electrograms (in patients with preexisting ICDs) recorded at the time of delivered therapies have provided insight into the arrhythmias responsible for electrical storm. The frequency of various ventricular arrhythmias is as follows [6-8,10-13,15,16,19,20]:

●Monomorphic VT – 86 to 97 percent

●Primary VF – 1 to 21 percent

●Mixed VT/VF – 3 to 14 percent

●Polymorphic VT – 2 to 8 percent

In patients with documented sustained arrhythmias prior to ICD implantation, there exists a significant correlation between the initial arrhythmia and that recorded during electrical storm. Patients with a prior history of VT are more likely to experience VT storm and a similar correlation is reported for patients with VF [8,15].

DIAGNOSIS — The diagnosis of electrical storm is made when a patient has three or more confirmed episodes of ventricular tachyarrhythmia resulting in symptoms or implantable cardioverter-defibrillator (ICD) therapy within a 24-hour period. Typically, the episodes of arrhythmia are confirmed using continuous telemetry monitoring or by reviewing stored intracardiac electrograms from a patient's ICD. Given the likelihood of significant symptoms associated with electrical storm, the diagnosis is usually made in hospitalized patients (or in patients who have presented to the emergency department), though it is possible to make the diagnosis in outpatients whose cardiac activity is being continuously monitored (eg, patients with an ICD or wearing an ambulatory telemetry monitor).

The diagnosis of incessant VT is made by confirming the presence of continuous VT for greater than one hour. As with electrical storm, given the likelihood of significant symptoms with incessant VT, the diagnosis is usually made in hospitalized patients (or in patients who have presented to the emergency department), though it is possible to make the diagnosis in outpatients whose cardiac activity is being continuously monitored (eg, patients with an ICD or wearing an ambulatory telemetry monitor). Rarely, when patients have incessant VT at slower rates (<150 beats per minute), remaining asymptomatic and hemodynamically stable, the initial presentation may be related to tachycardia-mediated cardiomyopathy. (See "Arrhythmia-induced cardiomyopathy".)

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of electrical storm should be thought of differently depending on the presence or absence of an implantable cardioverter-defibrillator (ICD):

●In patients without an ICD, the differential diagnosis includes the usual causes of a wide QRS complex tachycardia (table 1).

●In patients with an ICD who receive multiple ICD shocks, the differential diagnosis includes the usual causes of a wide QRS complex tachycardia as well as the possibility of ICD malfunction (eg, electrical noise, oversensing, lead fracture, etc). (See "Cardiac implantable electronic devices: Long-term complications", section on 'Inappropriate shocks'.)

Differentiating supraventricular tachycardia (SVT) with aberrant conduction from VT can usually be done by identifying P waves associated with every QRS complex (in contrast to the AV dissociation seen with VT) on a surface ECG or atrial activity associated with each ventricular activity on intracardiac electrogram. In patients who have received multiple ICD shock, device interrogation can quickly determine in the shocks were appropriate (in response to ventricular tachyarrhythmia) or inappropriate (ie, in response to an SVT or device malfunction).

The differential diagnosis of incessant VT is similar to that of any wide QRS complex tachycardia (table 1). Most commonly, this would include atrial tachycardia or atrial flutter (with aberrant conduction), although any type of SVT must be considered.

TREATMENT — In patients with an acute and ongoing episode of electrical storm or incessant VT, initial treatment is based on hemodynamic stability or instability [9].

●Patients with hemodynamically unstable ventricular arrhythmias should initially undergo electrical cardioversion according to advanced cardiac life support protocol (algorithm 1) [5]. (See "Advanced cardiac life support (ACLS) in adults", section on 'Pulseless ventricular tachycardia and ventricular fibrillation'.)

●Patients with electrical storm or incessant VT who are hemodynamically stable should be treated with both intravenous (IV) antiarrhythmic therapy and a beta blocker. We recommend IV amiodarone as the initial antiarrhythmic agent given its superior efficacy for terminating most ventricular arrhythmias. Additionally, because of the adrenergic surge associated with frequent ventricular tachyarrhythmias and defibrillator shocks, we recommend co-administration of a beta blocker, usually oral propranolol. (See 'Initial management' below.)

●For patients with electrical storm or incessant VT in whom active myocardial ischemia is felt to be a contributing factor, urgent coronary revascularization should be pursued. (See "Overview of the acute management of non-ST-elevation acute coronary syndromes" and "Overview of the acute management of ST-elevation myocardial infarction".)

Initial management

ACLS and defibrillation — Patients with electrical storm or incessant VT should be rapidly assessed for evidence of hemodynamic stability. Patients without a pulse or with other signs/symptoms of hemodynamic instability (ie, hypotension, active anginal-type chest pain or dyspnea, new changes in mental status, etc) should be promptly treated according to advanced cardiac life support (ACLS) protocol (algorithm 1) with electrical cardioversion/defibrillation [5,21]. ACLS is discussed in greater detail separately. (See "Advanced cardiac life support (ACLS) in adults", section on 'Pulseless ventricular tachycardia and ventricular fibrillation'.)

Patients who are successfully resuscitated from cardiac arrest associated with a ventricular arrhythmia are usually treated with antiarrhythmic therapy as well. (See 'Initial antiarrhythmic medical therapy' below.)

Initial antiarrhythmic medical therapy — While patients with electrical storm or incessant VT who are hemodynamically stable do not usually require emergent electrical cardioversion, urgent therapy is necessary to treat the ventricular arrhythmia(s) and reduce the effect of the adrenergic nervous system on the heart. Patients should be treated with both IV antiarrhythmic therapy and a beta blocker. Our approach to initial medical therapy is as follows:

●We recommend IV amiodarone (150 mg IV over 10 minutes, followed by 1 mg/minute IV infusion for 6 hours, followed by 0.5 mg/minute IV infusion for 18 additional hours), rather than lidocaine, procainamide, or no antiarrhythmic drug, as the initial antiarrhythmic agent given its superior efficacy for terminating most ventricular arrhythmias.

●We recommend oral propranolol (40 mg every 6 hours for the first 48 hours, with additional IV doses as needed for recurrent breakthrough ventricular arrhythmias) rather than a beta-1 selective beta blocker. Once the patient has stabilized, the patient should be transitioned to an oral beta blocker for long-term management. (See 'Maintenance antiarrhythmic therapy' below.)

This approach is in agreement with the 2017 AHA/ACC/HRS guidelines for the management of ventricular arrhythmias and the prevention of sudden cardiac death as well as the 2014 position paper from the European Heart Rhythm Association, both of which included recommendations for the management of electrical storm and incessant VT [5,22]. Following stabilization, options for long-term arrhythmia control include catheter ablation or chronic oral antiarrhythmic therapy. (See 'Subsequent management' below.)

Amiodarone — Amiodarone has been shown in numerous trials to significantly improve survival from cardiac arrest and reduce the frequency of ventricular tachyarrhythmias [23-26]. As examples:

●Among a group of 504 patients with out-of-hospital cardiac arrest due to VF/VT who were not resuscitated following three or more external shocks and who were randomized to either IV amiodarone (300 mg) or placebo, patients who received amiodarone were significantly more like to survive to hospital admission (odds ratio 1.6, 95% CI 1.1-2.4) [23].

●In a randomized, double-blind dose ranging trial of 342 patients with electrical storm who received one of three IV doses of amiodarone (125 mg, 500 mg, or 1000 mg over the first 24 hours, with supplemental 150 mg IV doses as needed for recurrent VF/VT), patients in the 1000 mg group had an 88 percent reduction in ventricular arrhythmias in the initial 24 hours of therapy (compared with the 24 hours preceding therapy with amiodarone) [24].

●Among a group of 273 patients with recurrent VF/VT refractory to therapy with lidocaine, procainamide, and bretylium who received amiodarone, 40 percent survived for 24 hours without any recurrent hemodynamically significant ventricular arrhythmias [25].

Beta blockers — Beta blockers are utilized to reduce the adrenergic surge associated with frequent ventricular tachyarrhythmias and defibrillator shocks. There is extensive evidence of the efficacy of beta blockers in patients with various cardiac conditions (eg, heart failure with reduced left ventricular systolic function, acute myocardial ischemia and/or infarction, etc) in which beta blockers reduced the impact of the sympathetic nervous system on the heart. Patients with electrical storm or incessant VT, particularly those who have received multiple defibrillations, will have increased sympathetic nervous system output, which can further predispose to additional arrhythmias, and they should be treated with a beta blocker along with antiarrhythmic drugs, unless contraindicated [22].

Nonselective beta blockers such as propranolol or nadolol are preferred over selective ones [27]. Propranolol, a nonselective beta blocker, appears to be more effective than metoprolol, which is beta-1 selective. In a single-center, double-blind study of 60 patients with electrical storm, all patients received IV amiodarone and were randomized to propranolol (40 mg every 6 hours) or metoprolol (50 mg every 6 hours) for the first 48 hours [28]. The primary end point (time to termination of ventricular arrhythmias) occurred significantly earlier in patients receiving propranolol (3 versus 18 hours with metoprolol), with 27 of 30 patients receiving propranolol free of ventricular arrhythmias within 24 hours (compared with 16 of 30 receiving metoprolol). Additionally, compared with the patients receiving metoprolol, patients receiving propranolol had significant improvement in several secondary end points, including lower rates of ventricular arrhythmias (incidence rate ratio 0.38, 95% CI 0.21-0.68) and implantable cardioverter-defibrillator (ICD) shocks (incidence rate ratio 0.43, 95% CI 0.23-0.89) during the ICU stay and shorter hospitalizations.

The efficacy of sympathetic blockade was compared with conventional antiarrhythmic drugs in an observational study of 49 patients with electrical storm occurring up to 50 days after an acute myocardial infarction [29]. Patients treated with sympathetic blockade (beta blockers or stellate ganglionic blockade) had a lower overall mortality compared with patients treated with conventional antiarrhythmics both at one week (22 versus 82 percent) and at one year (33 versus 95 percent).

Patients with an ICD — Careful implantable cardiac-defibrillator (ICD) interrogation and assessment of programming are necessary in the setting of electrical storm. This ensures that delivered therapies are appropriate and that the ICD itself is not contributing to the event. Rare cases of pacing "permitted" or "facilitated" ventricular tachycardia (VT) or ventricular fibrillation (VF) have been reported where the pacing mode or programmed rate allows for proarrhythmic pauses or short-long-short sequences. [30]. Anti-tachycardia pacing can also be proarrhythmic in that it may accelerate VT to ventricular flutter or VF.

Coronary revascularization — For patients with electrical storm or incessant VT in whom active myocardial ischemia is felt to be a contributing factor, urgent coronary revascularization should be pursued as revascularization, and restoration of adequate coronary perfusion may be enough to resolve the ventricular tachyarrhythmias [22,31,32]. Urgent coronary revascularization is discussed in greater detail elsewhere. (See "Overview of the acute management of non-ST-elevation acute coronary syndromes" and "Overview of the acute management of ST-elevation myocardial infarction".)

Subsequent management

Catheter ablation — Catheter ablation of ventricular tachyarrhythmias is an important and effective therapy for electrical storm or incessant VT [5,22,33-35]. For patients with electrical storm or incessant VT that persists or recurs in spite of medical therapy with amiodarone and a beta blocker, we recommend catheter ablation. Ablation for these conditions is a complex procedure with significant risk and should be performed in experienced centers capable of treating the recognized complications. Catheter ablation may also be considered in patients whose ventricular tachyarrhythmias are controlled with medical therapy but who are intolerant of medical therapy due to side effects. (See "Overview of catheter ablation of cardiac arrhythmias" and "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis", section on 'Radiofrequency catheter ablation'.)

Elimination of recurrent VT using catheter ablation techniques has long been available. Most reports of catheter ablation in electrical storm or incessant VT have been case reports or small retrospective single-center cohort studies. In a meta-analysis of 471 patients with electrical storm compiled from 39 publications (case reports and cohort studies), there was a high initial success rate for ablation of all ventricular arrhythmias (72 percent) along with a low procedural mortality rate (0.6 percent) and a relatively low recurrence rate of 6 percent over 61 weeks mean follow-up [36]. In this review, the recurrence rate was significantly higher after ablation for electrical storm due to monomorphic VT compared with VF or polymorphic VT with underlying cardiomyopathy (odds ratio 3.8, 95% CI 1.7-8.6).

In a multicenter case series of 1940 patients undergoing VT ablation, which was published after the meta-analysis, 677 patients (35 percent) had electrical storm; patients with electrical storm had a greater number of inducible VTs, required longer procedure times, and had a higher hospital mortality compared with those without storm (6.2 versus 1.4 percent) [37]. At one-year follow-up, the risk of VT recurrence as detected by ICD interrogation was higher in the electrical storm group (32 versus 23 percent). Catheter ablation has also been used with reasonable success in patients with cardiogenic shock and refractory VT that together necessitated mechanical circulatory support; in one single-center experience with 21 such patients, 17 patients were successfully weaned from mechanical circulatory support following ablation, with 15 patients surviving to discharge and 13 surviving for at least one year post-ablation [38].

The impact of catheter ablation on mortality in patients with electrical storm or incessant VT is not as clearly defined. In one single-center retrospective study of 52 patients with a first episode of electrical storm between 1995 and 2011 who were initially treated with pharmacologic therapy alone (29 patients) or catheter ablation (23 patients), the risk of recurrent electrical storm was significantly lower following catheter ablation, but there was no significant difference in survival over a median follow-up of 28 months [39]. Compared with patients undergoing VT ablation in the absence of electrical storm in a large case series of 1940 patients, those with electrical storm had a higher one-year mortality (20.1 versus 8.5 percent; hazard ratio 1.5, 95% CI 1.1-2.1) [37]. The high mortality seen in these patients is most likely related to the severity of underlying cardiac pathology in patients who present with electrical storm or incessant VT.

The potential role of prophylactic catheter ablation for primary prevention of electrical storm in high-risk individuals is discussed separately. (See "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis", section on 'Radiofrequency catheter ablation'.)

Maintenance antiarrhythmic therapy — Antiarrhythmic therapy should be maintained in the following patients:

●Patients who have undergone catheter ablation of their ventricular tachyarrhythmia, until there is evidence of no recurrent arrhythmias following the procedure, at which point the treating clinician may consider stopping the antiarrhythmic medication.

●Patients who have not undergone catheter ablation in whom stopping antiarrhythmic therapy would put them at risk for recurrent arrhythmias.

Maintenance antiarrhythmic therapy is discussed in greater detail separately. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy", section on 'Antiarrhythmic drugs' and "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis", section on 'Antiarrhythmic drugs'.)

ICD implantation — ICD implantation is contraindicated in patients with acute uncontrolled ventricular arrhythmias. However, once the patient has been treated successfully with maintenance antiarrhythmic therapy and catheter ablation, many patients will meet criteria for ICD implantation. (See "Implantable cardioverter-defibrillators: Overview of indications, components, and functions", section on 'Indications'.)

In the small minority of patients with electrical storm due to reversible triggers, eventual ICD implantation will not be necessary once the trigger is removed. These patients should also have no other indication for ICD implantation. (See 'Triggers of electrical storm' above.)

Condition-specific therapies — While general measures are appropriate for most patients, targeted therapies are indicated for specific conditions.

●Specific arrythmias – Pause-dependent torsades de pointes can be effectively treated with pacing, and incessant arrhythmias associated with Brugada syndrome may be suppressed with quinidine or isoproterenol. (See "Congenital long QT syndrome: Epidemiology and clinical manifestations" and "Brugada syndrome or pattern: Management and approach to screening of relatives".)

●Cardiomyopathy – For the majority of patients in whom a cardiomyopathy will be present, appropriate heart failure therapies should be prescribed and titrated to maximally tolerated doses. (See "Overview of the management of heart failure with reduced ejection fraction in adults".)

●Ischemia – For patients in whom myocardial ischemia was the precipitating factor and who underwent revascularization, appropriate antithrombotic and anti-ischemic therapies should be prescribed. (See "Overview of the acute management of non-ST-elevation acute coronary syndromes" and "Overview of the acute management of ST-elevation myocardial infarction".)

●Toxic and/or metabolic factors – Correction of any identified inciting factors should occur. This may include removal of any offending drugs (eg, prescription or illicit drugs that prolong the QT interval) and correction of any electrolyte disturbances (ie, hypokalemia, hypomagnesemia, etc).

Management of refractory cases — Rarely, patients will continue to have refractory electrical storm or incessant VT in spite of medical therapy and catheter ablation attempts. A variety of salvage therapies may be considered, in conjunction with the standard therapies discussed above, when the other treatments have been unsuccessful, including [40-45]:

●Thoracic epidural anesthesia and/or general anesthesia [41,43].

●Insertion of an intraaortic balloon pump or a temporary ventricular assist device. In appropriate patients, these devices may help stabilize patients with refractory recurrent VT until ablation or surgical treatment can be performed. (See "Intraaortic balloon pump counterpulsation", section on 'Refractory ventricular arrhythmias' and "Short-term mechanical circulatory assist devices".)

●Stellate ganglion block (SGB; usually left-sided). In aggregate, case series of patients treated with SGB show a reduction in episodes of VT and ICD shocks [45-50]. In the largest reported case series of 30 patients with drug-refractory electrical storm, among whom 15 underwent left and 15 underwent bilateral SGB, 18 patients (60 percent) were free of VT at 24 hours, with an overall reduction in VT burden of 92 percent over the initial 72 hours [51]. A study of 11 patients who underwent an SGB for electrical storm followed patients for sustained cessation of electrical storm for 24 hours. Cessation of electrical storm for 24 hours was achieved in 90 percent of patients after left SGB. Similarly, 90 percent of patients had no documented episodes of ventricular arrhythmias requiring intervention within six hours after SGB [50]. In a first-in-man case series, transcutaneous magnetic stimulation of the left stellate ganglion significantly reduced episodes of VT and shocks for 48 to 72 hours in five patients with VT storm [52]. SGB is a temporizing measure, and terminal sympathectomy via surgical cardiac sympathetic denervation (CSD) or orthotopic heart transplantation may be needed for eligible non-responders in whom other treatments have also failed.

●CSD, with one series suggesting bilateral CSD, is more efficacious than isolated left CSD [5,40-42,44,46,53-55].

●Cardiac transplantation. (See "Heart transplantation in adults: Indications and contraindications", section on 'Indications for transplantation'.)

●Renal artery denervation (RDN), with one small series of four patients showing marked decrease in the frequency of VT episodes following RDN [56,57].

●In a study of five patients with refractory VT, stereotactic body radiation therapy reduced the number of VT episodes by 99.9 percent, although the benefit was not quite as significant in a second study of 10 patients (88 percent reduction in VT) [58,59].

PROGNOSIS — Electrical storm is generally associated with poor outcomes, with most studies reporting an association between electrical storm and cardiovascular mortality [7,10,15]. As examples:

●In the AVID trial, electrical storm was a significant independent risk factor for cardiac, non-sudden death (relative risk 2.4), which occurred most frequently within three months [7].

●The MADIT II trial found that patients with electrical storm had a 7.4-fold higher risk of death when compared with those without electrical storm, with a 17.8-fold increased risk of death within the first three months after storm onset [8].

What is not clear is whether the ventricular tachyarrhythmias or repeated implantable cardioverter-defibrillator (ICD) shocks themselves contribute to cardiac mortality or are secondary to a degenerating cardiac status. A potential mechanism was suggested by the experimental observation that recurrent ventricular fibrillation (VF) results in increases in intracellular calcium concentrations which might contribute to deterioration of left ventricular systolic function [60,61]. Additionally, repeated shocks can cause myocardial injury leading to acute inflammation and fibrosis [62-64]. Lastly, myocardial injury or stunning from recurrent defibrillations may activate the neurohormonal cascade responsible for worsening heart failure and cardiovascular mortality [29,65,66]. Additional studies are needed to clarify these issues.

Electrical storm, particularly when associated with repeated ICD discharges, may induce long-term anxiety that impacts overall health-related quality of life [6,10,11,13,67]. (See "Cardiac implantable electronic devices: Long-term complications", section on 'Quality of life'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Arrhythmias in adults" and "Society guideline links: Cardiac implantable electronic devices" and "Society guideline links: Ventricular arrhythmias" and "Society guideline links: Catheter ablation of arrhythmias".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics links (see "Patient education: Ventricular tachycardia (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Definition – Electrical storm, also referred to as arrhythmic storm, refers to multiple recurrences of ventricular arrhythmias over a short period of time, while incessant ventricular tachycardia (VT) is defined as hemodynamically stable VT which persists for hours. In most instances, the arrhythmia is monomorphic VT, but polymorphic VT and ventricular fibrillation (VF) can also result in electrical storm. The definition of electrical storm is different in patients with and without an implantable cardioverter-defibrillator (ICD). (See 'Definition' above.)

●Triggers of electrical storm – Common triggers of electrical storm or incessant VT include drug toxicity, electrolyte disturbances, new or worsened heart failure, and acute myocardial ischemia, although a single inciting factor is not identified in the majority of patients. (See 'Triggers of electrical storm' above.)

●Clinical presentation – The clinical presentations of electrical storm and incessant are highly variable but rarely if ever asymptomatic. (See 'Clinical presentation' above.)

•In patients without an ICD, the range of clinical presentations due to electrical storm spans from relatively minor symptoms such as repeated episodes of palpitations, presyncope, or syncope if the patient remains hemodynamically stable to cardiac arrest in those patients with hemodynamically unstable ventricular arrhythmias.

•In patients with a preexisting ICD, electrical storm typically presents with multiple ICD therapies (some combination of anti-tachycardia pacing and ICD shocks depending on how the device is programmed to deliver therapy). However, patients with ventricular arrhythmias that are slower than the detection settings of the ICD may present in similar fashion as patients without an ICD.

●Diagnosis – The diagnosis of electrical storm is made when a patient has three or more confirmed episodes of ventricular tachyarrhythmia resulting in symptoms or ICD therapy within a 24-hour period. Typically, the episodes of arrhythmia are confirmed using continuous telemetry monitoring or by reviewing stored intracardiac electrograms from a patient's ICD. The diagnosis of incessant VT is made by confirming the presence of continuous VT for greater than one hour. (See 'Diagnosis' above.)

●Treatment – The initial treatment approach to patients with electrical storm or incessant VT is based on hemodynamic stability or instability.

•Patients with hemodynamically unstable ventricular arrhythmias should initially undergo electrical cardioversion according to advanced cardiac life support protocol (algorithm 1). (See "Advanced cardiac life support (ACLS) in adults", section on 'Pulseless ventricular tachycardia and ventricular fibrillation'.)

•Patients with electrical storm or incessant VT who are hemodynamically stable should be treated with both intravenous (IV) antiarrhythmic therapy and a beta blocker.

-We recommend IV amiodarone, rather than lidocaine, procainamide, or no antiarrhythmic drug, as the initial antiarrhythmic agent given its superior efficacy for terminating most ventricular arrhythmias (Grade 1B). Amiodarone should be given as 150 mg IV over 10 minutes, followed by 1 mg/minute IV infusion for 6 hours, followed by 0.5 mg/minute IV infusion for 18 additional hours.

-We recommend the nonselective beta blocker propranolol rather than a beta-1 selective beta blocker because of its increased efficacy in terminating VT (Grade 1B). Propranolol should be given as 40 mg oral doses every 6 hours for the first 48 hours, with additional IV doses as needed for recurrent breakthrough ventricular arrhythmias. (See 'Initial management' above.)

•For patients with electrical storm or incessant VT in whom active myocardial ischemia is felt to be a contributing factor, urgent coronary revascularization should be pursued. (See "Overview of the acute management of non-ST-elevation acute coronary syndromes" and "Overview of the acute management of ST-elevation myocardial infarction".)

●Subsequent management – The subsequent management of patients with electrical storm or incessant VT is focused on the prevention of recurrent ventricular tachyarrhythmias.

•For patients with electrical storm or incessant VT that persists or recurs in spite of medical therapy with amiodarone and a beta blocker, we recommend catheter ablation (Grade 1B). (See 'Catheter ablation' above.)

•Most patients will require at least a short course of maintenance antiarrhythmic therapy. (See 'Maintenance antiarrhythmic therapy' above.)

•Patients should also receive medical therapy aimed at the likely underlying cardiac pathology (eg, beta blockers and ACE-inhibitors in patients with heart failure and cardiomyopathy, anti-thrombotic and anti-ischemic therapy for patients with myocardial ischemia). (See 'Condition-specific therapies' above.)