Electrical storm aborted by automated shock polarity reversal in implantable cardioverter-defibrillator

Key Teaching Points.

• •Cardiac sarcoidosis is associated with an increased risk of ventricular arrhythmias, and high-risk patients warrant primary prevention implantable cardioverter-defibrillator implantation for prevention of sudden cardiac death.
• •Modern implantable cardioverter-defibrillator programming involves biphasic defibrillation, which has consistently shown improved efficacy over monophasic defibrillation.
• •Nominal programming of the right ventricular coil serving as the anode vs cathode varies by manufacturer. Unique programming algorithms, which include reverse shock polarity features, can be useful in select cases.

Introduction

Implantable cardioverter-defibrillators (ICDs) are important mainstays in the prevention of sudden arrhythmic cardiac death among high-risk patients. We describe a case of a 58-year-old woman with cardiac sarcoidosis who experienced refractory ventricular fibrillation (VF) and whose life was saved by an automatic shock polarity reversal feature that is available in many, but not all, ICD models.

Case report

A 58-year-old woman with a history of heart failure with reduced ejection fraction (left ventricular ejection fraction 35%) in the setting of multisystem cardiopulmonary sarcoidosis, complicated by ventricular tachycardia (VT) and status post Incepta dual-coil, dual-chamber implantable cardioverter-defibrillator (Boston Scientific, Marlborough, MA; implanted in 2013) with left-sided prepectoral implantation site, was admitted with numerous ICD shocks. In addition to her history, the patient had known paroxysmal atrial fibrillation, functional severe mitral regurgitation, and hypertension. At the time of her event, she had been on stable doses of amiodarone 200 mg, metoprolol succinate 12.5 mg, apixaban 5 mg twice daily, empagliflozin 10 mg, spironolactone 25 mg, and sacubitril-valsartan 24–26 mg twice daily.

Regarding the patient’s history of multisystem sarcoidosis, she first presented with recurrent VT in 2013. At the time, chest imaging revealed diffuse mediastinal lymphadenopathy, and subsequent endobronchial, ultrasound-guided, transbronchial, fine-needle aspiration revealed noncaseating granulomas, pathognomonic for the diagnosis of sarcoidosis in this clinical context. Later imaging studies, most recently fluorodeoxyglucose F-18 positron emission tomography/computed tomography in 2021, revealed no evidence of active sarcoidosis. At the time of the electrical storm event, she had been on a stable long-term glucocorticoid regimen of prednisone 5 mg and 7.5 mg on alternating days.

While the patient was sleeping, the patient’s ICD appropriately detected the onset of VF (ventricular rates 240–260 beats/min). The patient received 8 consecutive 41-J shocks, which eventually converted the patient into an atrial-paced, ventricular-paced rhythm. The patient was not aware of these shocks and woke from sleep to the beeping tone from her device that it had reached elective replacement indicator.

Evaluation of the device transmission revealed that the first 7 ICD shocks were unsuccessful; however, with an automated lead polarity reversal feature, the eighth ICD shock successfully terminated the VF (Figure 1).

Figure 1.

Intracardiac electrograms at the time of electrical storm show rapid, low-amplitude ventricular signals, with atrioventricular dissociation, consistent with ventricular fibrillation. A: Initiation of the rhythm. B: The patient received 7 appropriate but ineffective shocks. C: The eighth shock with polarity inversion terminated the ventricular fibrillation and restored atrial-paced, ventricular-paced rhythm.

The patient was admitted and underwent ICD generator replacement with a Boston Scientific Vigilant El ICD generator, as well as intensification of anti-arrhythmic regimen, with reloading 10 g oral amiodarone and the addition of mexiletine 200 mg twice daily. Surface electrocardiogram revealed sinus rhythm, with known chronic right bundle branch block and left anterior fascicular block (Figure 2). Evaluation of the intracardiac electrograms and continuous telemetry while admitted did not demonstrate a consistent premature ventricular complex trigger that could be a viable target for ablation. Programmed sensitivity on the right ventricular lead was 0.6 mV (nominal), with stable right ventricular pacing and defibrillation impedances of 508 Ω and 55 Ω, respectively. Posterior-anterior and lateral chest radiograph projections demonstrated unchanged lead position (Figure 3). Repeat positron emission tomography/computed tomography protocolized for cardiac sarcoidosis found no evidence of active inflammation. Due to minimal troponin elevation (peak 214 pg/mL; reference range 0–15 pg/mL), no anginal symptoms, and no significant changes on echocardiogram, an ischemic evaluation was deferred. In the 6 months after the electrical storm event, the patient has been electrically stable and has not experienced further events.

Figure 2.

12-lead surface electrogram demonstrating sinus rhythm with right bundle branch block and left anterior fascicular block, which are stable chronic findings. The QT interval was within normal limits.

Figure 3.

Upright posterior-anterior and lateral chest radiographs demonstrating stable lead and generator position compared with prior imaging.

Discussion

Due to their superiority in aborting ventricular tachyarrhythmias, biphasic—as opposed to monophasic—ICDs have become the standard of care. Biphasic defibrillation is thought to mitigate this risk and improve the success of terminating ventricular tachyarrhythmias, while reducing proarrhythmic wavefronts, either by reversing the polarity of the virtual electrodes and/or redistributing them in the second phase of the shock¹ or by way of the “burping theory.” The latter postulates that the initial wavefront of biphasic shock extends the refractory period of ventricular cardiomyocytes in range, and the subsequent reverse wavefront removes excess charge from the remaining cardiomyocytes, thereby terminating an arrhythmia and resetting the electrical properties of the tissue.²

In patients who require ICD for secondary prevention of sudden cardiac death due to monomorphic VT, as was the case for this patient, it is common for providers to program different sequences of therapy for arrhythmias that fall into the VT and VF zones. These zone cutoffs describe the rates of the arrhythmia only, sensed by the ICD, rather than providing true insight into their mechanism.

Within the VF zone, ICDs manufactured by Boston Scientific have nominal programming that mandates shock polarity reversal after the patient had received 7 unsuccessful shocks for ventricular tachyarrhythmias with the initial polarity configuration. In this programming, the nominal relationship is for the right ventricular coil to serve as the cathode for the first 7 shocks. Historical studies have demonstrated lower defibrillation threshold (DFT) when the right ventricular coil serves as the anode; however, this configuration may be less important in the days of biphasic defibrillation.² The existence of patients who appeared to achieve much lower DFT from one polarity over the other, whether anodal or cathodal, may be at least somewhat probabilistic and is impossible to predict for any individual patient.

The feature of shock polarity reversal is not available in all manufacturers’ ICDs, including some models manufactured by Medtronic and Abbott.³ Thoughtful programming has become even more important in the current landscape of ICD management, wherein routine DFT testing at the time of implantation or generator replacement has been phased out of practice. Multiple randomized controlled trials have found that routine DFT testing in patients with left-sided ICD implantation does not improve long-term mortality or improve shock efficacy.^4,5 To protect against the possibility that the nominal configuration is unsuccessful in terminating the arrhythmia, some have recommended programming shock polarity reversals into tachyarrhythmia treatment sequences.⁶

At the time of this patient’s initial ICD implantation, DFT was performed. Shock-on-T was delivered to induce VF, with successful defibrillation to sinus rhythm with a single 23-J shock in the nominal configuration (right ventricular coil served as the cathode). Repeat DFT was not performed at the time of generator replacement after the patient’s electrical storm event.

With regard to this patient’s underlying cardiomyopathy, ventricular tachyarrhythmias are not uncommon in the presence of cardiac sarcoidosis. Although VT occurs in the setting of reentry within areas of scar and is amenable to catheter ablation, VF is not routinely managed with catheter ablation.⁷ As such, the primary approaches of management include anti-arrhythmic medical therapy and immunosuppression. In refractory and select cases, sympathectomy or cardiac transplantation can be considered.⁸

Conclusion

Electrical storm is an uncommon but serious complication of cardiac sarcoidosis. While anti-arrhythmic medical therapy and immunosuppression remain the standard of care for first-line therapy, ICDs have an important role in the prevention of sudden cardiac death. In the vast majority of cases, biphasic waveforms generated by ICDs have obviated the need for specific programming of the right ventricular ICD coil to serve preferentially as either the anode or cathode. In addition, some ICDs are programmed for automatic shock polarity reversal if several appropriate shocks with the nominal configuration fail to terminate a ventricular tachyarrhythmic event. In these rare cases, an automatic shock polarity reversal feature may terminate an arrhythmia and provide life-saving treatment.

Disclosures

Mr Brinkhaus is an employee of Boston Scientific; the rest of the authors have no conflicts of interest.