Defibrillation Energy Requirements Research Articles

Abstract 13663: 90-day Safety and Performance Outcomes With a Novel Extravascular ICD Lead

Introduction: Long-term transvenous implantable cardioverter defibrillator (ICD) leads have many pitfalls. There is in development a novel extravascular (EV) ICD lead for sensing and defibrillation of ventricular tachyarrhythmias (VT/VF) utilizing commercially available DF-4 ICD pulse generators. We evaluate here 90-day safety and performance outcomes for delivery, stability, sensing, and defibrillation using this prototype EV lead. Methods: 18 patients scheduled to undergo de novo or replacement ICD were enrolled in a prospective, nonrandomized study (SECURE-EV STUDY). Each subject was simultaneously implanted with EV ICD lead (AtaCor, SanClemente, CA) attached to a commercially available ICD pulse generator. Study lead was delivered with a designed tool into left parasternal anterior mediastinum via a selected 4th, 5th or 6th intercostal space. Over 90 days pts were evaluated intermittently for defibrillation energy requirements, matched sensing events between both devices, stability of lead position and adverse events. Results: 16/18 of enrolled subjects received study device. Lead failed implant in 2 due to (1) intercostal ossification and (1) mediastinal adhesions. Prior to 30-days, 4 subjects were withdrawn from study due to pneumothorax, wound dehiscence, death unrelated to IV-ICD implantation and early elective lead removal. Over 90-days of simultaneous sensing, 4 events of VT/VF in 3 pts were detected by both devices. There was 1 AF discrimination error & 1 atrial oversensing event detected by both devices. There were 4 events of non-cardiac noise in 4 pts detected by EV-ICD only. 1 event of Twave oversensing was detected by TV-ICD. 23 conversion tests in 13 subjects were performed at energy (26 to 30 J delivered, 1 tested with 35J) at 30- and 90-day visits, with successful conversion in all 23. Mean time between fibrillation detection and shock delivery was 10.7 seconds. Conclusion: This study showed feasibility of sensing and defibrillating induced VT/VF with intercostal placed prototype extravascular ICD lead. Findings with ICD lead was consistent across 4 commercially available ICDs. Simultaneous sensing of VT/VF in ambulatory pts was matched. Non-cardiac inappropriate sensing with EV-ICD lead is being addressed in new prototype.

The Arrhythmogenicity of Sotalol and its Role in Heart Failure: A Literature Review.

According to the American Heart Association (AHA), approximately six million adults have been afflicted with heart failure (HF) in the United States in 2020 and are more likely to have sudden cardiac death accounting for approximately 50% of the cause of mortality. Sotalol is a nonselective β-adrenergic receptor antagonist with class III antiarrhythmic properties that has been mostly utilized for atrial fibrillation treatment and suppressing recurrent ventricular tachyarrhythmias. The use of sotalol in patients with left ventricular (LV) dysfunction is not recommended by the American College of Cardiology (ACC) or AHA as studies are inconclusive with conflicting results regarding safety. This article aims to review the mechanism of action of sotalol, the β-blocking effects on heart failure, and provide an overview of clinical trials on sotalol use and its effects in patients with heart failure. Small and large scale clinical trials have been controversial and inconclusive about the use of sotalol in heart failure. Sotalol has been shown to reduce defibrillation energy requirements and reduce shocks from implantable cardioverter-defibrillators. TdP is the most life-threatening arrhythmia that has been documented with sotalol use and occurs more commonly in women and HF patients. Thus far, mortality benefits have not been demonstrated with sotalol use and larger multicenter studies are required going forward.

Successful defibrillation verification in subcutaneous implantable cardioverter-defibrillator recipients by low-energy shocks.

BackgroundThe subcutaneous implantable cardioverter‐defibrillator (S‐ICD) is an effective alternative to the transvenous one. Defibrillation efficacy depends on maximum device output and on the optimal device location at device implantation.HypothesisWe sought to investigate the defibrillation safety margin in real life clinical practice.MethodsWe sought to understand what is the efficacy of induced ventricular fibrillation (VF) termination at S‐ICD implantation using lower energies than the recommended 65 J.ResultsSixty‐four consecutive S‐ICD recipients underwent VF termination attempts at implantation with energies ranging from 20 to 50 J. Overall, VF termination occurred in 84% of patients with ≤40 J, in 88% with 45 J, and in 100% with 60 J. Intermuscular S‐ICD placement was associated with 94% VF termination at ≤40 J. An ejection fraction <35% was associated to higher energy requirement for defibrillation; however, an intermuscular S‐ICD placement conferred 90% defibrillation efficacy at 31 ± 5 J in this patients subset.ConclusionsThis is a hypothesis‐generating observation that prompts a methodologically correct investigation to prove that a 60 J output S‐ICD can provide an adequate safety margin to terminate VF in clinical practice. This would enable superior device longevity and/or device downsizing for pediatric/small size patients.

A Novel Defibrillation Tool: Percutaneously Delivered, Partially Insulated Epicardial Defibrillation.

Epicardial defibrillation systems currently require surgical access. We aimed to develop a percutaneous defibrillation system with partially-insulated epicardial coils to focus electrical energy on the myocardium and prevent or minimize extra-cardiac stimulation. We tested 2 prototypes created for percutaneous introduction into the pericardial space via a steerable sheath. This included a partially-insulated defibrillation coil and a defibrillation mesh with a urethane balloon acting as an insulator to the face of the mesh not in contact with the epicardium. The average energy associated with a chance of successful defibrillation 75% of the time (ED75) was calculated for each experiment. Of 16 animal experiments, 3 pig experiments had malfunctioning mesh prototypes such that results were unreliable; these were excluded. Therefore, 13 animal experiments were analyzed - 6 canines (29.8±4.0kg); 7 pigs (41.1±4.4kg). The overall ED75 was 12.8±6.7J (10.9±9.1J for canines; 14.4±3.9J in pigs [P=0.37]). The lowest ED75 obtained in canines was 2.5J while in pigs it was 9.5J. The lowest energy resulting in successful defibrillation was 2J in canines and 5J in pigs. There was no evidence of coronary vessel injury or trauma to extra-pericardial structures. Percutaneous, epicardial defibrillation using a partially insulated coil is feasible and appears to be associated with low defibrillation thresholds. Focusing insulation may limit extra-cardiac stimulation and potentially lower energy requirements for efficient defibrillation.

A shocking past: a walk through generations of defibrillation development.

Defibrillation is one of the most successful and widely recognized applications of electrotherapy. Yet the historical road to its first successful application in a patient and the innovative adaptation to an implantable device is marred with unexpected turns, political and personal setbacks, and public and scientific condemnation at each new idea. Driven by dedicated scientists and ever-advancing creative applications of new technologies, from electrocardiography to high density mapping and computational simulations, the field of defibrillation persevered and continued to evolve to the life-saving tool it is today. In addition to critical technological advances, the history of defibrillation is also marked by the plasticity of the theory of defibrillation. The advancing theories of success have propelled the campaign for reducing the defibrillation energy requirement, instilling hope in the development of a painless and harmless electrical defibrillation strategy.

Is defibrillation testing necessary for implantable transvenous defibrillators?: defibrillation testing is necessary at the time of implantable cardioverter defibrillator implantation.

Clinical trials have documented the efficacy of implantable cardioverter-defibrillators (ICDs) for the primary and secondary prevention of sudden cardiac death.1–7 These trials have typically involved induction of ventricular fibrillation (VF) at the time of implantation to demonstrate effective arrhythmia termination. In fact, defibrillation testing (DT) was also performed at the time of implantation of ICDs in those patients whose data were used to seek approval of the US Federal Drug Administration for general use, and instructions for usage include labeling with DT. This is also the case for the recently approved subcutaneous ICD. Response by Healey et al on p 346 Higher defibrillation thresholds (DFTs) were seen with older ICDs implanted using an epicardial approach, abdominal pulse generators, or monophasic waveforms. In contrast, modern technology now includes devices with biphasic waveform shocks and pectoral active can systems that result in more effective defibrillation.8–11 In addition, devices now have higher output, routinely delivering ≥35 J and also increasing the chance of effective defibrillation. Therefore, it has been suggested that these new defibrillation technologies may eliminate the need for DT. Although the risk of failing defibrillation is now much lower, patients receiving ICDs today may have more comorbidities, more severe heart failure, and a higher risk of failing shocks. If a high defibrillation energy requirement is identified at the time of initial implantation, system revision is typically performed with the intent of increasing the likelihood that the ICD will effectively terminate ventricular tachycardia (VT) or VF when it occurs spontaneously. So, we need to ask ourselves, why would a physician implant this potentially life-saving device without testing? The term DFT refers to the minimum shock strength that defibrillates.12 Historically, a threshold below a specific value has been used as an acceptable criterion for device implantation. …

Abstract 9039: Predictors of High Defibrillation Energy Requirements: Results From the NCDR ICD Registry

Background: Defibrillation testing is typically performed at the time of ICD implantation to establish effective arrhythmia termination. Despite technological advancements, including biphasic waveforms and higher output devices, an inadequate safety margin for defibrillation may still occur. The NCDR ICD Registry was examined to evaluate predictors of a high defibrillation requirement (DER) using modern day devices. Methods: Patients who underwent defibrillation testing in the NCDR ICD Registry were examined to determine characteristics associated with a high DER. This included 45,686 initial ICD implantation procedures from April 2010 to December 2010 performed at 1261 facilities. Patient characteristics were compared using chi-square tests for categorical variables and unbalanced t-tests for continuous variables. Multivariable logistic regression was used to assess independent predictors of a "high" DER, which was defined as &gt;25 joules. Results: A high DER was noted in 4.1% of patients undergoing testing. Patients with a high DER were more often younger, male, on dialysis, and were more likely to have a higher NYHA functional class, lower LVEF, higher creatinine, and wider QRS. Patients on antiarrhythmic drugs and those with nonischemic heart disease were more likely to have a high DER. Independent predictors of a high DER included younger age, higher NYHA class, and increased QRS duration. A high DER was associated with longer post-procedure length of stay (1.6 ± 2.9 vs. 2.1 ± 3.8 days, p&lt;0.001) as well as any complication or death prior to hospital discharge (2.6% vs. 4.0%, p&lt;0.001). Conclusions: A high DER was observed in 4.1% of patients and was associated with more complications and mortality. Several clinical predictors of a high DER were identified, potentially enabling the identification of patients most likely to benefit from testing. Additional study is needed to determine if testing predicts long-term outcome of patients with modern day devices.

Prospective Evaluation of Defibrillation Threshold and Postshock Rhythm in Young ICD Recipients

Adaptation of implantable cardioverter defibrillator (ICD) systems to the needs of pediatric and congenital heart patients is problematic due to constraints of vascular and thoracic anatomy. An improved understanding of the defibrillation energy and postshock pacing requirements in such patients may help direct more tailored ICD therapy. We describe the first prospective evaluation of defibrillation threshold (DFT) and postshock rhythm in this population. We prospectively studied patients ≤ 60 kg at time of ICD intervention. DFTs were obtained using a binary search protocol with three VF inductions. Postshock pacing was programmed using a stepwise protocol, lowering the rate prior to each VF induction. Twenty patients were enrolled: 11 had channelopathy, five congenital heart disease, and four cardiomyopathy. The median age was 16 years, median weight 48 kg. Twelve patients had a transvenous high-voltage coil; eight had pericardial +/- subcutaneous coil(s). Median DFT was 7 J (range 3-31 J); 19/20 patients had DFT ≤ 15 J and all patients <25 kg had DFT ≤ 9 J (n = 6). There was no difference in DFT between patients with transvenous versus pericardial +/- subcutaneous coils (median 7 J vs 6 J, P = 0.59). No patient with normal atrioventricular conduction prior to defibrillation required postshock pacing (n = 16). There were no adverse events. These data suggest that many pediatric ICD patients have low DFTs and adequate postshock escape rhythm. This may help determine appropriate parameters for future design of pediatric-specific ICDs.

Evaluation of shock waveform configuration on the defibrillation capacity of implantable cardioverter defibrillators in dogs

BackgroundImplantable cardioverter defibrillators (ICD) are programmed to detect ventricular arrhythmias and terminate them by delivering an electrical shock. A defibrillation threshold (DFT) at least 10 J below the maximum device output is recommended for successful therapy. Shock waveform configuration is a programmable parameter used to achieve a low DFT. It is hypothesized that a fixed-pulse configuration results in lower defibrillation energy requirements than a fixed-tilt configuration. Animals10 mongrel dogs. Materials and methodsICD generator and transvenous lead were surgically implanted. Defibrillation threshold was determined using a protocol guided by the upper limit of vulnerability. Fixed-pulse and fixed-tilt (50%/50%) waveform configurations were tested in a random order. Plasma cardiac troponin I (cTnI) was measured for signs of myocardial injury. ResultsThe experiment was completed in 9 dogs. Overall mean DFT value was 424 ± 88 V (9.2 ± 3.9 J). Mean differences among voltage, energy and impedance at the DFT for fixed-pulse (422 ± 97 V, 9.1 ± 4.2 J, 62.6 ± 13.8 Ω) and fixed-tilt (426 ± 83 V, 9.3 ± 3.8 J, 62.8 ± 18.5 Ω) configurations were not statistically significant (All P > 0.21). Cardiac TnI concentration changed from 0.03 ng/mL (95% CI: 0.02–0.04) at baseline to 0.11 ng/mL (95 CI: 0.08–0.16) after DFT was obtained with the first waveform configuration and 0.19 ng/mL (95% CI: 0.13–0.28) at the end of the study period. There were no significant changes in heart rate, end-tidal CO2 and blood pressure over time (all P > 0.09). ConclusionThe tested ICD device and lead placement reliably produced acceptable DFT values, based on a 10-J safety margin below the maximum device output. A benefit of fixed-pulse configuration could not be demonstrated over the standard fixed-tilt waveform. Signs of acute myocardial damage from repeated high-voltage shocks and episodes of ventricular fibrillation seemed of limited clinical significance.

Defibrillation Thresholds in Hypertrophic Cardiomyopathy

Defibrillation threshold (DFT) testing is performed in part to ensure an adequate safety margin for the termination of spontaneous ventricular arrhythmias. Left ventricular mass is a predictor of high DFTs, so patients with hypertrophic cardiomyopathy (HCM) are often considered to be at risk for increased defibrillation energy requirements. However, there are little prospective data addressing this issue. To assess DFTs in patients with HCM and evaluate the clinical predictors of elevated DFTs. Eighty-nine consecutive patients with HCM and 600 control patients with ischemic or nonischemic cardiomyopathy underwent a uniform modified step-down DFT testing protocol. DFT was compared between the control and HCM populations. Predictors of elevated DFT were evaluated in the HCM group. There was no difference in DFT between HCM and control groups (10.4 ± 5.8 J vs 11.2 ± 5.6 J, respectively). Among patients with HCM, clinical parameters such as left ventricular ejection fraction, interventricular septal thickness, left ventricular mass, and QRS duration were not predictive of an elevated DFT. Only 3 patients (3.4%) with HCM had a DFT >20 J. Patients with HCM do not have elevated DFTs as compared to more typical populations undergoing implantable cardioverter-defibrillator implant; high-energy devices or complex lead systems are not needed routinely in this population.

Effect of Amiodarone on Signal Characteristics of Ventricular Fibrillation and ICD Shock Success

Introduction: Defibrillation threshold (DFT) testing is routinely performed during implantable cardioverter defibrillator (ICD) implantation to test the effectiveness to terminate ventricular fibrillation (VF). However, with the currently implanted ICDs failure of defibrillation is uncommon and the value of DFT testing is under discussion. Amiodarone alters VF and increases defibrillation energy requirements. In patients using amiodarone DFT testing could be essential to ensure effective therapy.

High defibrillation energy requirements are encountered rarely with modern dual-chamber implantable cardioverter-defibrillator systems

Defibrillation conversion testing to assure a 10 J safety margin is a standard practice during implantable cardioverter-defibrillator (ICD) implantation. Little data are available on the number of patients who do not have a 10 J margin initially and therefore require system revisions, further testing, or a higher energy output device. The INTRINSIC RV study enrolled 1530 new ICD recipients who were not in permanent atrial fibrillation who received a VITALITY AVT (Guidant, St Paul, MN, USA) standard energy (31 J maximum) ICD and underwent defibrillation conversion testing at the time of implantation from 108 centres. Among enrolled patients, 59 (3.9%) did not initially meet the 10 J safety margin criterion. In these 59 patients, a 10 J safety margin was achieved by making at least one system revision: reversing shocking polarity (n = 33, 56%), right ventricular lead repositioning (n = 19, 32%), repeat testing at a later date (n = 1, 2%), adding a subcutaneous array (n = 1, 2%), or other means (n = 10, 17%). Only New York Heart Association class (P = 0.001) and no previous myocardial infarction (P = 0.044) predicted a failed initial conversion test. There were no reported complications from ICD shock testing. Successful defibrillation conversion criteria with the first configuration tested with a standard energy device is almost always met with modern dual-chamber ICD systems. The need for revising the initial ICD shock configuration to achieve a 10 J safety margin appears extremely low and of low risk.

Effect of Drugs on Defibrillation Capacity

Over 300,000 people die of sudden cardiac death (SCD) in the US annually. Implantable cardioverter-defibrillators (ICDs) have been shown to be more effective than antiarrhythmic drugs for the prevention of SCD in specific susceptible populations. Many patients in whom ICDs have been implanted receive concomitant therapy with antiarrhythmic drugs, for the purpose of reducing the frequency of appropriate and inappropriate defibrillation shocks. Drugs may influence defibrillation capacity and therefore influence the function of ICDs. The objective of this article is to review and update the literature regarding the effects of drugs on defibrillation capacity.A literature search was performed using PubMed (1966 to December 2007) to identify clinical studies, case reports and animal studies describing the effects of drugs on defibrillation capacity. Search terms included: antiarrhythmic drugs; cardiovascular drugs; amiodarone; sotalol; flecainide; propafenone; dofetilide; ibutilide; beta-blockers; lidocaine; procainamide; N-acetylprocainamide; mexiletine; disopyramide; moricizine; calcium channel blockers; defibrillation threshold; defibrillation energy requirements; defibrillation energy changes; defibrillation efficacy; implantable cardioverter defibrillators; and external defibrillators. Evidence from clinical studies indicates that amiodarone may increase defibrillation threshold (DFT). In addition, some data indicate that drugs including lidocaine, mexiletine, moracizine (moricizine), verapamil, venlafaxine and anaesthetic agents may increase DFT. In contrast, agents including sotalol, dofetilide and beta-adrenergic receptor antagonists (beta-blockers) may reduce DFT. Propafenone and procainamide appear to have minimal effect on DFT. For those antiarrhythmic drugs with both sodium and potassium channel blockade (e.g. amiodarone), the effect of sodium channel blockade predominates, resulting in an increase in DFT. Numerous drugs may affect defibrillation capacity. These effects must be considered when managing patients who have an ICD and require concomitant pharmacotherapy.

Clinical Study of the Acute Effects of Intravenous Nifekalant on the Defibrillation Threshold in Patients With Persistent and Paroxysmal Atrial Fibrillation

Antiarrhythmic agents are considered to have significant effects on the defibrillation energy requirement, so this study investigated the effects of nifekalant on defibrillation. Forty-two patients with persistent atrial fibrillation (AF) underwent electrical cardioversion via intracardiac electrode catheters prior to and after the intravenous administration of nifekalant. The success rate of the defibrillation and change in the defibrillation threshold using sequential incremental defibrillation energy deliveries was investigated. In addition, the parameters that could predict the beneficial effects of nifekalant were also assessed. Nifekalant significantly decreased the defibrillation energy requirement in 13 of the 42 cases, and nifekalant also converted AF to sinus rhythm with an identical energy to that of the last unsuccessful defibrillation in 21 of 42 cases. The success of defibrillation seemed to be dependent on significant prolongation of the intracardiac atrial electrogram intervals during AF by the nifekalant. Intravenous nifekalant significantly improved the electrical defibrillation efficacy in patients with persistent AF that was resistant to defibrillation, without any serious adverse effects.

Intraoperative hypothermia increased defibrillation energy requirements

We describe two patients with newly implanted automatic implantable cardioverter-defibrillators that had excessive defibrillation thresholds associated with hypothermia at intraoperative defibrillation threshold testing. Normal defibrillation threshold levels were obtained during postoperative non-invasive electrophysiology testing in an electrophysiology laboratory when the patients were normothermic. We hypothesize that inadvertent intraoperative hypothermia during device implantation may increase the defibrillation threshold.

Effect of Amiodarone and Sotalol on Ventricular Defibrillation Threshold

Many patients with implanted cardioverter defibrillators (ICDs) receive adjunctive antiarrhythmic drug therapy, most commonly amiodarone or sotalol. The effects of these drugs on defibrillation energy requirements have not been previously assessed in a randomized controlled trial. The Optimal Pharmacological Therapy in Cardioverter Defibrillator Patients (OPTIC) trial was a randomized clinical trial evaluating the efficacy of amiodarone plus beta-blocker and sotalol versus beta-blocker alone for reduction of ICD shocks. Within OPTIC, a prospectively designed substudy evaluated the effects of the 3 treatment arms on defibrillation energy requirements. Defibrillation thresholds (DFTs) were measured (binary step-down protocol) at baseline and again after 8 to 12 weeks of therapy in 94 patients, of whom 29 were randomized to receive beta-blocker therapy (control group), 35 to amiodarone plus beta-blocker, and 30 to sotalol. In the control group, the mean DFT decreased from 8.77+/-5.15 J at baseline to 7.13+/-3.43 J (P=0.027); in the amiodarone group, DFT increased from 8.53+/-4.29 to 9.82+/-5.84 J (P=0.091). In the sotalol group, DFT decreased from 8.09+/-4.81 to 7.20+/-5.30 J (P=0.21). DFT changes in the beta-blocker and the amiodarone group were significantly different (P=0.006). In all patients, adequate safety margins for defibrillation were maintained. No clinical variable predicted baseline DFT or changes in DFT on therapy. Although amiodarone increased DFT, the effect size with modern ICD systems is very small. Therefore, DFT reassessment after the institution of antiarrhythmic drug therapy with amiodarone or sotalol is not routinely required.

Defibrillation Energy Requirements in an ICD Population Receiving Cardiac Resynchronization Therapy

While defibrillation energy requirements (DERs) have been extensively studied in patients receiving conventional defibrillators, the DERs of patients receiving cardiac resynchronization therapy with defibrillation capability (CRT-D) devices have not been well described. The purpose of this analysis was to characterize DERs (defined as true threshold or the presence of appropriate safety margins) in patients undergoing implant of a CRT-D and to determine whether DERs in this population were similar to those reported for patients undergoing implantation of conventional defibrillators. Data were analyzed retrospectively from the VENTAK CHF/CONTAK CD biventricular pacing study. An appropriate safety margin of at least 10 J was verified with at least two successful conversions with 21 J or less. Multivariate logistic regression was performed to determine baseline predictors of failed DER testing. Of 501 patients enrolled, 444 (89%) had successful DER test outcomes. Of the remaining 57 patients, 34 converted with energies > or = 21J, and 23 had their testing terminated prematurely or were not tested, primarily due to patient condition. Larger left ventricular internal dimension in diastole (P = 0.003) and prolonged procedure time (P = 0.01) were significant predictors of higher energy requirements. Few significant complications arose from DER testing. DER testing can be accomplished safely and successfully in the majority of CRT-D patients. However, safety margins cannot be ascertained in a significant number of these patients. Left ventricular inner diameter in diastole (LVIDd) and prolonged procedure time may predict higher DERs, and could be used to anticipate the need for a high-energy device or inclusion of a subcutaneous array.

Defibrillation energy requirements using a left anterior chest cutaneous to subcutaneous shocking vector: Implications for a total subcutaneous implantable defibrillator

Subcutaneous implantable defibrillators (ICDs) are being developed to facilitate ICD implantation. The purpose of this study was to estimate the human defibrillation energy requirement (DER) using a left chest cutaneous (Q) to subcutaneous (SQ) shocking vector. Twenty patients undergoing implantation of an indicated ICD were enrolled (15 males, age = 63 +/- 12 years; ejection fraction = 0.27 +/- 0.14). Defibrillation testing was performed using an investigational system consisting of an external defibrillator and a constructed connector to deliver a shock between a pectoral SQ can and a cardiac apical Q electrode. Two attempts at defibrillation using this configuration were allowed. Stage 1 testing started at 70 J with a step-down/step-up to 50 or 100 J, respectively. Stage 2 testing began at 50 J with a step-down/step-up to 30 or 70 J. During stage 1, a 70-J shock was successful in 7/9 (78%) patients. A second attempt was successful in 7/7 patients using a 50-J shock. In the two remaining patients, a second attempt using a 100-J shock was successful. During stage 2, a 50-J shock was successful in 10/11 (91%) patients. The protocol could not be completed in 2/11 patients. Of the remaining nine patients, a second defibrillation was successful in seven (78%) using a 30-J shock. The defibrillation energy requirement (DER) of this study vector was 50 J or less in most patients. This low DER supports further investigation of a totally SQ-ICD. However, the DER of 100 J in two patients indicates that further investigation is needed regarding DER variability and safety margins.

Is the ventricular defibrillation threshold higher in patients with the Brugada syndrome?

Dysfunction of the sodium current channel is responsible for distinctive electrophysiologic changes in patients with the Brugada syndrome (BS). High energy requirements for ventricular defibrillation (DF) have been reported in isolated patients with BS, but it has never been systematically studied.

Do biventricular pacemaker defibrillators patients have higher defibrillation thresholds?

Background: Implantable cardioverter-defibrillators (ICDs) have traditionally relied on multiple ventricular fibrillation (VF) inductions with defibrillation conversion testing at implantation. Little data are available assessing the prevalence of high defibrillation energy requirements in cardiac resynchronization pacemakers with defibrillators (CRT-D). The present analysis evaluates the prevalence of high energy requirements in CRT-D patients, in comparison to patients receiving modern single- or dual-chamber ICD systems, from a large ICD patient cohort in the ASSURE Study.