Successful Defibrillation Research Articles

The risk of failure of subcutaneous implantable cardioverter defibrillator therapy: from PRAETORIAN score to clinical practice.

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an alternative to traditional ICDs. The PRAETORIAN score, based on chest radiographs, has been validated to predict the probability of successful S-ICD defibrillation testing by assessing factors like fat thickness between the coil and sternum and generator placement. This study evaluated the correlation between the PRAETORIAN score and clinical characteristics, as well as implantation variables. We retrospectively analyzed data from 1253 patients who had undergone implantation of an S-ICD across 33 centers. The intermuscular positioning of the pulse generator was adopted in all patients. Post-implantation posterior-anterior and lateral chest radiographs were analyzed to calculate the PRAETORIAN score. 95.7% of patients had a PRAETORIAN score <90, indicative of a low risk of conversion failure. Body mass index (BMI) was the only independent predictor of a score ≥90, and all patients with BMI <25kg/m2 (normal weight or underweight) had a score <90. The intermuscular positioning technique resulted in optimal posterior placement of the device in all patients and significant sub-generator fat in only 3% of cases. A shock impedance value >88Ohm enabled to detect a PRAETORIAN score ≥90 with 98% (95% CI 97%-99%) negative predictive value. In contemporary practice, the PRAETORIAN score can be simplified. By adopting an intermuscular approach, two of the three steps of the score-evaluating the adequate posterior positioning of the generator and measuring the sub-generator fat-become superfluous, and impedance may serve as a reliable surrogate of sub-coil fat thickness. Furthermore, our data suggest that for non-obese patients, a favorable PRAETORIAN score is assured, making the score evaluation potentially unnecessary.

Abstract Su503: Relationships Between Quantitative ECG Measures and Defibrillation Success in Early Ventricular Fibrillation

Introduction: Rapid termination of ventricular fibrillation (VF) has long been recognized as the cornerstone of effective cardiac arrest resuscitation. In recent years, amplitude spectral area (AMSA) has been shown to be highly associated with defibrillation success, and AMSA has been experimentally used to personalize defibrillation timing and strategy. However, questions remain about whether the interpretation of AMSA holds uniformly in varied conditions, such as ultra-early or prolonged cardiac arrest or after anti-arrhythmic administration. Hypothesis: AMSA is greater after 20 seconds of untreated VF compared to 50 seconds of untreated VF; a higher AMSA predicts greater first-defibrillation success. Methods: VF was induced in adult swine (n = 3) with a bipolar pacing catheter placed in the right ventricle. Animals were randomized to 20- or 50-second-long episodes of VF (n = 123), followed by standard 150 J biphasic defibrillation. In MATLAB, AMSA was calculated as the summed product of frequency and square root of power after Fast Fourier Transform for the four second period of VF immediately prior to defibrillation. Results were analyzed by a two-sided Chi-squared test or ANOVA with Tukey’s HSD in R; a p-value &lt; 0.05 was considered significant. Results: First shock success was lower in the 20-second-VF group compared to the 50 second group (31/78 (39.7%) vs 31/45 (68.8%), p = 0.003). The AMSA at 20 seconds was significantly higher for successful compared to unsuccessful first defibrillation (8.20 vs. 7.31 mV-Hz, p = 0.034). The AMSA at 50 seconds was not statistically different between successful and unsuccessful defibrillations (6.32 vs. 5.67 mV-Hz, p = 0.470). Evaluating the AMSA after a duration of VF irrespective of shock success, AMSA was higher at 20 seconds compared to 50 seconds (7.66 vs 6.12 mV-Hz, p &lt; 0.001). Conclusion(s): AMSA decreases from 20 to 50 seconds of untreated VF, and higher AMSA at a given time point is associated with greater first defibrillation success. However, first defibrillation success was higher after 50 seconds of untreated VF compared to 20 seconds, raising questions about special cases, such as edge effects, that may influence AMSA interpretation.

Amplitude spectrum area is dependent on the electrocardiogram magnitude: evaluation of different normalization approaches

Objective.Amplitude Spectrum Area (AMSA) of the electrocardiogram (ECG) waveform during ventricular fibrillation (VF) has shown promise as a predictor of defibrillation success during cardiopulmonary resuscitation (CPR). However, AMSA relies on the magnitude of the ECG waveform, raising concerns about reproducibility across different settings that may introduce magnitude bias. This study aimed to evaluate different AMSA normalization approaches and their impact on removing bias while preserving predictive value.Approach.ECG were recorded in 118 piglets (1-2 months old) during a model of asphyxia-associated VF cardiac arrest and CPR. An initial subset (91/118) was recorded using one device (Device 1), and the remaining piglets were recorded in the second device (Device 2). Raw AMSA and three ECG magnitude metrics were estimated to assess magnitude-related bias between devices. Five AMSA normalization approaches were assessed for their ability to remove detected bias and to classify defibrillation success.Main results.Device 2 showed significantly lower ECG magnitude and raw AMSA compared to Device 1. CPR-based AMSA normalization approaches mitigated device-associated bias. Raw AMSA normalized by the average AMSA in the 1st minute of CPR (AMSA1m-cpr) exhibited the best sensitivity and specificity for classification of successful and unsuccessful defibrillation. While the optimal AMSA1m-cprthresholds for balanced sensitivity and specificity were consistent across both devices, the optimal raw AMSA thresholds varied between the two devices. The area under the receiver operating characteristic curve for AMSA1m-cprdid not significantly differ from raw AMSA for both devices (Device 1: 0.74 vs. 0.88,P= 0.14; Device 2: 0.56 vs. 0.59,P= 0.81).Significance.Unlike raw AMSA, AMSA1m-cprdemonstrated consistent results across different devices while maintaining predictive value for defibrillation success. This consistency has important implications for the widespread use of AMSA and the development of future guidelines on optimal AMSA thresholds for successful defibrillation.

Defibrillation success with a second generation intercostal extravascular ICD lead and commercially available left pectoral pulse generator

Abstract Background/Introduction An investigational intercostal extravascular ICD lead has been developed for compatibility with commercially available pulse generators (PGs) that are placed in a left pectoral position in appropriate patients. This is substantially different from currently available extravascular ICD systems that require a custom PG placed in a left lateral position. Purpose The purpose of this analysis was to evaluate sensing and defibrillation of a second-generation intercostal, extravascular defibrillation lead (EV-ICD Lead) when used with currently available ICD PGs in a traditional left pectoral location. Methods Patients (n=20) undergoing an ICD implant or replacement underwent acute VF EV-ICD Lead connected to a left pectoral pulse generator. Induced VF was sensed and shocked using a 10 J safety margin, with subsequent higher-energy shocks delivered if required. Testing was also conducted in the left lateral pocket for a paired analysis with patients serving as their own control. Results Automatic sensing of acute, induced VF episodes from the left pectoral PG was successful in 19 of 20 patients (95%) whose pre-induction R-waves were greater than 1.0 mV and unsuccessful in one subject with a pre-induction R-wave of 0.3 mV. VF was successfully terminated with a 10 J safety margin in 17 of 20 (83%) patients, a 5 J safety margin in 2 of 20 (10%) patients and failed to convert one patient (BMI 32.9) from the pectoral pocket (however, conversion was successful from a lateral pocket with a 10 J shock, which provides a 30 J safety margin. With a left lateral ICD, 100% of patients demonstrated successful VF termination with ≥10 J safety margin. Conclusion(s) Sensing and defibrillation using a left pectoral PG location is feasible with a new intercostal, extravascular defibrillation lead.

Regional results of the lead evaluation for defibrillation and reliability (LEADR) trial

Abstract Introduction ICD/CRT-D patients are living longer, and interest in reliable leads with targeted placement is growing. The Lead EvaluAtion for Defibrillation and Reliability (LEADR) trial was designed to assess the novel small-diameter, lumenless, catheter-delivered, defibrillation study lead. The study lead is based on the SelectSecure SureScan MRI Model 3830 lumenless pacing lead delivered by catheter that has a simplified durable construction with improved long-term reliability (97.2% 12-year RV lead survival). Purpose The LEADR trial assessed the efficacy and safety of the novel defibrillation lead. Methods The global LEADR Pivotal trial (NCT04863664) enrolled patients with ACC/AHA/ESC guideline-directed indications for de novo implant of a primary or secondary prevention ICD/CRT-D. The primary efficacy and safety endpoints were defibrillation success at implant and freedom from study lead-related major complications at 6-months, respectively. Results A total of 643 patients were successfully implanted (61.9±12.9 years, 26% female, 28.5±6.4 kg/m2 BMI, and 80.9% NYHA Class II) with the study lead placed in the desired RV location in 99.5%. The estimated freedom from study lead-related major complications was 97.1% at 6- and 12-months. Defibrillation testing was successful in 116/119 (97.5%) patients. The prespecified primary efficacy and safety thresholds (88% and 90%, respectively) were exceeded. There were zero study lead fractures and electrical measurements were stable through 12.7±4.8-month mean follow-up. Approximately 20% of patients were in Asia, 9% in Australia, 21% in Europe, and 50% in North America (Table). The estimated freedom from study lead-related major complications at 6- and 12-months per region were 96.2% in Asia, 100% in Australia, 96.4% in Europe, and 97.2% in North America (Figure), P=0.82 across regions. There were 19 study lead-related major complications (5 in Asia, 0 in Australia, 5 in Europe, 9 in North America), with the most common being lead dislodgement across regions. Defibrillation testing was successful in 116/119 patients with 33/33 in Asia, 32/32 in Australia, 7/8 in Europe, and 44/46 in North America, P=0.11 across regions. Among the 3 patients with unsuccessful testing, 2 (North America) remained in the study at physician discretion after successful conversion outside of protocol requirements, and 1 (Europe) was exited. Pacing capture threshold, pacing impedance, and R-wave amplitude were chronically stable across regions. Conclusion The LEADR Pivotal trial demonstrated the safety, efficacy, and reliability of the novel defibrillation lead, exceeding prespecified efficacy and safety thresholds. There were no notable differences in primary endpoints between regions. The trial has met its endpoints and ongoing follow-up will provide long-term performance. This trial demonstrated the ability to place the lead in targeted RV locations; a study of this lead for conduction system pacing is forthcoming.TableFigure

Association Between Delay to First Shock and Successful First-Shock Ventricular Fibrillation Termination in Patients With Witnessed Out-of-Hospital Cardiac Arrest.

In patients with out-of-hospital cardiac arrest who present with an initial shockable rhythm, a longer delay to the first shock decreases the probability of survival, often attributed to cerebral damage. The mechanisms of this decreased survival have not yet been elucidated. Estimating the probability of successful defibrillation and other factors in relation to the time to first shock may guide prehospital care systems to implement policies that improve patient survival by decreasing time to first shock. Patients with a witnessed out-of-hospital cardiac arrest and ventricular fibrillation (VF) as an initial rhythm were included using the prospective ARREST registry (Amsterdam Resuscitation Studies). Patient and resuscitation data, including time-synchronized automated external defibrillator and manual defibrillator data, were analyzed to determine VF termination at 5 seconds after the first shock. Delay to first shock was defined as the time from initial emergency call until the first shock by any defibrillator. Outcomes were the proportion of VF termination, return of organized rhythm, transportation with return of spontaneous circulation, and survival to discharge, all in relation to the delay to first shock. A Poisson regression model with robust standard errors was used to estimate the association between delay to first shock and outcomes. Among 3723 patients, the proportion of VF termination declined from 93% when the delay to first shock was <6 minutes to 75% when that delay was >16 minutes (Ptrend<0.001). Every additional minute in VF from emergency call was associated with 6% higher probability of failure to terminate VF (adjusted relative risk, 1.06 [95% CI, 1.04-1.07]), 4% lower probability of return of organized rhythm (adjusted relative risk, 0.96 [95% CI, 0.95-0.98]), and 6% lower probability of surviving to discharge (adjusted relative risk, 0.94 [95% CI, 0.93-0.95]). Every minute of delay to first shock was associated with a significantly lower proportion of VF termination and return of organized rhythm. This may explain the worse outcomes in patients with a long delay to defibrillation. Reducing the time interval from emergency call to first shock to ≤6 minutes could be considered a key performance indicator of the chain of survival.

Ventricular fibrillation during thoracoscopic pericardiectomy in a St. Bernard dog

AbstractVentricular fibrillation is one of the known complications of pericardiectomy in veterinary medicine. We present a case of ventricular fibrillation occurring during thoracoscopic pericardiectomy in a 2‐year‐old St. Bernard dog. Despite prompt recognition, immediate resuscitation efforts‐based chest compressions and mechanical ventilation, drug administration and defibrillation (external using 200 J, using 50 J internally subsequently), the dog died. The suspected cause of ventricular fibrillation was related to the use of an electrosurgical device. The challenges encountered during resuscitation and possible reasons for the delayed success of defibrillation are discussed in this report. Electrical safety and the implications during thoracoscopy underscore the importance of the development and the mechanisms underlying ventricular fibrillation during thoracoscopic pericardiectomy.

A manual synchronous low energy shock impedance as a predictor of successful defibrillation testing during subcutaneous ICD implantation.

Guidelines recommend defibrillation testing (DFT) during subcutaneous implantable cardioverter-defibrillator (S-ICD) implantation. Implant position, patient characteristics and device factors, such as shock impedance, influence defibrillation success. To evaluate the shock impedance, a manual synchronous 10J shock (low energy synchronous shock [LESS]) can be delivered, without the need to induce ventricular fibrillation (VF). To compare LESS and DFT impedance values and to evaluate the diagnostic accuracy of LESS impedance for predicting a successful DFT during S-ICD implantation. Consecutive S-ICD implantations were included. Shock impedances were compared by paired t-tests. Univariate analysis was performed to investigate factors associated with successful DFT. A prediction model of successful DFT based on LESS impedance was assessed by logistic regression. Receiver operating characteristic (ROC) curve, area under the ROC curve and the Hosmer-Lemeshow tests were used to evaluate the accuracy of LESS impedance. Sixty patients were included (52±14years; 69% male). LESS and DFT impedance values were highly correlated (r2=0.97, p<.01). Patients with a failed first shock had higher body mass index (BMI) (30±3vs. 25.7±4.3, p=.014), higher mean LESS (120±35Ω vs. 86.±23Ω, p=.0013) and DFT impedance (122±33Ω vs. 87±24Ω, p=.0013). ROC analysis showed that LESS impedance had a good diagnostic performance in predicting a successful conversion test (AUC 84% [95% CI: 0.72-0.92]) with a cutoff value of <94Ω to identify a successful DFT (sensitivity 71%, specificity 73%). LESS impedance values without the need to induce VF can intraoperatively predict a successful DFT.

Feasibility of Single-lead Cardiac Resynchronization and Defibrillation Therapy in an Animal Model.

Conduction system pacing (CSP) has emerged as an alternative to cardiac resynchronization therapy (CRT); however, there is limited experience with CSP using implantable cardiac defibrillator (ICD) leads. The achievement of CSP with an ICD lead may yield comparable results to cardiac resynchronization therapy defibrillator (CRT-D) therapy using fewer leads. We implanted the Biotronik Linox DX "VDD"-programmable ICD lead in a swine model to investigate the feasibility of "single-lead" CRT-D implantation. With the lead embedded in the basal right ventricular septum, morphologic criteria for CSP were achieved, and successful defibrillation was performed while maintaining atrial sensing. Future work may assure reproducibility of these findings and further determine the feasibility of a single-lead CRT-D.

Feasibility, safety, and short-term follow-up of defibrillator lead at left bundle branch area pacing location: A pilot study

BackgroundLeft bundle branch area pacing (LBBAP) has been increasingly adopted as an alternative modality to cardiac resynchronization therapy (CRT). The feasibility and safety of using an LBBAP lead to provide sensing of ventricular arrhythmia in patients receiving an implantable cardioverter-defibrillator (ICD) with CRT has been demonstrated recently. ObjectivesThe purpose of our study was to analyze the feasibility, safety, and short-term follow-up of a traditional defibrillator lead at the LBBAP location. MethodsPatients who underwent successful LBBAP defibrillator using DF-1/DF-4 lead and delivery catheter were included in the study. Defibrillation threshold (DFT) testing was performed after implantation to assess the ability of the LBBAP defibrillator lead to sense and provide appropriate therapy for ventricular arrhythmia. ResultsAlthough the ICD lead could be successfully deployed in the left bundle branch area in 7 of 8 patients, it was repositioned to the right ventricular (RV) apex because of atrial oversensing in 1 patient and cheesy septum in another patient. Acute procedural success was 62.5% (5/8 patients). Mean patient age was 62.6 ± 21.6 years. Mean procedural duration was 115.6 ± 38.1 minutes, with LBBAP defibrillator lead fluoroscopy duration of 10.6 ± 3.5 minutes. Mean capture threshold was 0.58 ± 0.23V/0.4 ms, sensed R-wave amplitude 9.6 ± 2.2 mV, pacing impedance 560 ± 145 Ω, and shock impedance 65.4 ± 5.5 Ω. Defibrillation testing was successful in inducing ventricular fibrillation and could be sensed and reverted promptly by the shock delivered through the lead. During mean follow-up of 3.8 ± 2.2 months, pacing parameters remained stable. No episodes of inappropriate arrhythmia detection or therapy delivery occurred during follow-up. ConclusionLBBAP defibrillator is feasible, safe, and effective during short-term follow-up. DFT testing at the time of implantation will help to ensure appropriate sensing and treatment of ventricular arrhythmias.

Safety, efficacy, and reliability evaluation ofa novel small-diameter defibrillation lead: Global LEADR pivotal trial results

BackgroundImplantable cardioverter-defibrillators last longer, and interest in reliable leads with targeted lead placement is growing. The OmniaSecure defibrillation lead is a novel, small-diameter, catheter-delivered lead designed for targeted placement, based on the established SelectSecure SureScan MRI Model 3830 lumenless pacing lead platform. ObjectiveThis trial assessed safety and efficacy of the OmniaSecure defibrillation lead. MethodsThe worldwide LEADR pivotal clinical trial enrolled patients indicated for de novo implantation of a primary or secondary prevention implantable cardioverter-defibrillator or cardiac resynchronization therapy defibrillator, all of whom received the study lead. The primary efficacy end point was successful defibrillation at implantation per protocol. The primary safety end point was freedom from study lead–related major complications at 6 months. The primary efficacy and safety objectives were met if the lower bound of the 2-sided 95% credible interval was >88% and >90%, respectively. ResultsIn total, 643 patients successfully received the study lead, and 505 patients have completed 12-month follow-up. The lead was placed in the desired right ventricular location in 99.5% of patients. Defibrillation testing at implantation was completed in 119 patients, with success in 97.5%. The Kaplan-Meier estimated freedom from study lead–related major complications was 97.1% at 6 and 12 months. The trial exceeded the primary efficacy and safety objective thresholds. There were zero study lead fractures and electrical performance was stable throughout the mean follow-up of 12.7 ± 4.8 months (mean ± SD). ConclusionThe OmniaSecure lead exceeded prespecified primary end point performance goals for safety and efficacy, demonstrating high defibrillation success and a low occurrence of lead-related major complications with zero lead fractures.

A His bundle pacing protocol for suppressing ventricular arrhythmia maintenance and improving defibrillation efficacy

Background:The excitable gap (EG), defined as the excitable tissue between two subsequent wavefronts of depolarization, is critical for maintaining reentry that underlies deadly ventricular arrhythmias. EG in the His-Purkinje Network (HPN) plays an important role in the maintenance of electrical wave reentry that underlies these arrhythmias. Objective:To determine if rapid His bundle pacing (HBP) during reentry reduces the amount of EG in the HPN and ventricular myocardium to suppress reentry maintenance and/or improve defibrillation efficacy. Methods:In a virtual human biventricular model, reentry was initiated with rapid line pacing followed by HBP delivered for 3, 6, or 9 s at pacing cycle lengths (PCLs) ranging from 10 to 300 ms (n=30). EG was calculated independently for the HPN and myocardium over each PCL. Defibrillation efficacy was assessed for each PCL by stimulating myocardial surface EG with delays ranging from 0.25 to 9 s (increments of 0.25 s, n=36) after the start of HBP. Defibrillation was successful if reentry terminated within 1 s after EG stimulation. This defibrillation protocol was repeated without HBP. To test the approach under different pathological conditions, all protocols were repeated in the model with right (RBBB) or left (LBBB) bundle branch block. Results:Compared to without pacing, HBP for >3 seconds reduced average EG in the HPN and myocardium across a broad range of PCLs for the default, RBBB, and LBBB models. HBP >6 seconds terminated reentrant arrhythmia by converting HPN activation to a sinus rhythm behavior in the default (6/30 PCLs) and RBBB (7/30 PCLs) models. Myocardial EG stimulation during HBP increased the number of successful defibrillation attempts by 3%–19% for 30/30 PCLs in the default model, 3%–6% for 14/30 PCLs in the RBBB model, and 3%–11% for 27/30 PCLs in the LBBB model. Conclusion:HBP can reduce the amount of excitable gap and suppress reentry maintenance in the HPN and myocardium. HBP can also improve the efficacy of low-energy defibrillation approaches targeting excitable myocardium. HBP during reentrant arrhythmias is a promising anti-arrhythmic and defibrillation strategy.

Predictive value of the PRAETORIAN score for defibrillation test success in patients with subcutaneous ICD: A subanalysis of the PRAETORIAN-DFT trial

BackgroundThe PRAETORIAN score estimates the risk of failure of subcutaneous implantable cardioverter-defibrillator (S-ICD) therapy by using generator and lead positioning on bidirectional chest radiographs. The PRospective randomized compArative trial of subcutanEous implanTable cardiOverter-defibrillatoR ImplANtation with and without DeFibrillation Testing (PRAETORIAN-DFT) investigates whether PRAETORIAN score calculation is noninferior to defibrillation testing (DFT) with regard to first shock efficacy in spontaneous events. ObjectiveThis prespecified subanalysis assessed the predictive value of the PRAETORIAN score for defibrillation success in induced ventricular arrhythmias. MethodsThis multicenter investigator-initiated trial randomized 965 patients between DFT and PRAETORIAN score calculation after de novo S-ICD implantation. Successful DFT was defined as conversion of induced ventricular arrhythmia in <5 seconds from shock delivery within 2 attempts. Bidirectional chest radiographs were obtained after implantation. The predictive value of the PRAETORIAN score for DFT success was calculated for patients in the DFT arm. ResultsIn total, 482 patients were randomized to undergo DFT. Of these patients, 457 (95%) underwent DFT according to protocol, of whom 445 (97%) had successful DFT and 12 (3%) had failed DFT. A PRAETORIAN score of ≥90 had a positive predictive value of 25% for failed DFT, and a PRAETORIAN score of <90 had a negative predictive value of 99% for successful DFT. A PRAETORIAN score of ≥90 was the strongest independent predictor for failed DFT (odds ratio 33.77; confidence interval 6.13–279.95; P < .001). ConclusionA PRAETORIAN score of <90 serves as a reliable indicator for DFT success in patients with S-ICD, and a PRAETORIAN score of ≥90 is a strong predictor for DFT failure.

Defibrillation threshold in elective subcutaneous implantable defibrillator generator replacements: Time to reduce the size of the pulse generator?

IntroductionThe first step-down defibrillation studies in the subcutaneous implantable cardioverter-defibrillator (S-ICD) described a defibrillation threshold (DFT) of 32.5 ± 17.0 J and 36.6 ± 19.8 J. Therefore, the default shock output of the S-ICD was set at 80 J. In de novo implants, the DFT is lower in optimally positioned S-ICDs. However, a retrospective analysis raised concerns about a high DFT in S-ICD replacements, possibly related to fibrosis. ObjectiveWe aimed to find the DFT in patients undergoing S-ICD generator replacement. MethodsThis prospective study enrolled patients who underwent S-ICD generator replacement with subsequent defibrillation testing. A pre-specified defibrillation testing protocol was used to determine the DFT, defined as the lowest shock output that effectively terminated the induced ventricular arrhythmia. ResultsA total of 45 patients were enrolled, 6.0 ± 2.1 years after initial implant. Mean DFT during replacement in the total cohort was 27.4 ± 14.3 J. In patients with a body mass index (BMI) 18.5–25 kg/m2 (N = 22, BMI 22.5 ± 1.6), median DFT was 20 J (IQR 17.5–30). In 18/22 patients, the DFT was ≤30 J and 5/22 patients were successfully defibrillated at 10 J. One patient with hypertrophic cardiomyopathy had a DFT of 65 J. In patients with a BMI >25 kg/m2 (N = 23, BMI 29.5 ± 4.2), median DFT was 30 J (IQR 20–40). In 15/23 patients, the DFT was ≤30 J and 4/23 patients had a successful defibrillation test at 10 J. ConclusionsThis study eases concerns about a high DFT after S-ICD generator replacement. The majority of patients had a DFT ≤30 J, regardless of BMI, suggesting that the shock output of the S-ICD could be safely reduced.

Dissolution of spiral wave's core using cardiac optogenetics.

Rotating spiral waves in the heart are associated with life-threatening cardiac arrhythmias such as ventricular tachycardia and fibrillation. These arrhythmias are treated by a process called defibrillation, which forces electrical resynchronization of the heart tissue by delivering a single global high-voltage shock directly to the heart. This method leads to immediate termination of spiral waves. However, this may not be the only mechanism underlying successful defibrillation, as certain scenarios have also been reported, where the arrhythmia terminated slowly, over a finite period of time. Here, we investigate the slow termination dynamics of an arrhythmia in optogenetically modified murine cardiac tissue both in silico and ex vivo during global illumination at low light intensities. Optical imaging of an intact mouse heart during a ventricular arrhythmia shows slow termination of the arrhythmia, which is due to action potential prolongation observed during the last rotation of the wave. Our numerical studies show that when the core of a spiral is illuminated, it begins to expand, pushing the spiral arm towards the inexcitable boundary of the domain, leading to termination of the spiral wave. We believe that these fundamental findings lead to a better understanding of arrhythmia dynamics during slow termination, which in turn has implications for the improvement and development of new cardiac defibrillation techniques.

Efficacy of bepridil as a periprocedural support drug in atrial fibrillation patients with left ventricular systolic dysfunction undergoing catheter ablation

Abstract We previously reported that sinus restoration either with drugs or DC cardioversion prior to catheter ablation (CA) was associated with a better outcome in persistent atrial fibrillation (AF). As an antiarrhythmic agent for persistent AF, amiodarone is recommended for patients with structural heart disease. Bepridil, a unique multichannel inhibitor, has a comparable defibrillation efficacy and fewer extracardiac complications than amiodarone, although safety and efficacy of bepridil has not been established in those with left ventricular (LV) systolic dysfunction. We compared the safety and efficacy of bepridil and amiodarone as periprocedural support drugs for CA in patients with persistent AF with LV systolic dysfunction. Method and result: Persistent AF patients with LVEF ≤50% taking bepridil or amiodarone as periprocedural support drugs for CA were retrospectively analyzed; 51 patients in the bepridil group and 17 patients in the amiodarone group. There were 20 (39%) in the bepridil group and 17 (100%) in the amiodarone group with LVEF less than 40%. The amiodarone group had more history of heart failure hospitalizations, higher BNP, and lower LVEF than the bepridil group (HF; Bep 35.8% vs Amio 94.1% [p&amp;lt;0.01], BNP; Bep 306.4±422.8 pg/ml vs Amio 645.2±456.3 [p&amp;lt;0.01], LVEF; Bep 39.9±8.4% vs Amio 26.7±7.9% [p&amp;lt;0.01]). Bepridil was used at a dose of 126±39 mg and amiodarone at 153±60 mg before CA. Successful pharmacological defibrillation before CA was more prevalent in the bepridil group (Bep; 15:29.4% vs Amio; 2:11.8%, p=0.14). The time from drug induction to CA was 41±38 days in the bepridil group and 66±59 days in the amiodarone group. At 1-year after CA, doses of both drugs could be reduced (Bep: 72±53mg, Amio: 67±49mg), and 12 (23.5%) in the bepridil group and 3 (17.6%) in the amiodarone group were able to discontinue the drug. AF recurred in 6 (11%) in the bepridil group, and 2 (11%) in the amiodarone group. QTc was the longest immediately before CA in the both groups (Bep: 462±36ms, Amio: 462±32ms), but was shortened at 1-year with the drug dose reduction (Bep: 435±40ms, Amio: 444±29ms). LVEF significantly improved following maintenance of sinus rhythm in the both groups (Bep: 39.9±8.4% to 52.6±10.2% [p&amp;lt;0.01], Amio: 26.7±7.9% to 49.5±14.5% [p&amp;lt;0.01]), which was comparable between the 2 groups. Fatal ventricular arrhythmia occurred in 1 (5%) in the amiodarone group but not in the bepridil group. Hospitalization for heart failure occurred in 2 (3.9%) in the bepridil group. Discussion: Bepridil could be used safely at a short-term high dose before ablation and then reducing the dose after ablation. There is also a trend toward selecting bepridil in patients with relatively preserved cardiac function and less severe conditions. Conclusion: Bepridil can be used rather safely in AF patients with LV systolic dysfunction undergoing CA as a periprocedural support drug.

Abstract 311: Accuracy of Automated External Defibrillator Pad Placement During Out-of-Hospital Cardiac Arrest Resuscitation Simulations

Introduction: Out-of-hospital cardiac arrest (OHCA) victims receiving defibrillation from an automated external defibrillator (AED) placed early in the chain of survival are more likely to survive. Aim: We sought to explore the accuracy of AED pad placement for lay rescuers (LR) and first responders (FR). Methods: We conducted a secondary analysis of data collected during randomized OHCA simulation trials involving LR and FR. LR received hands-only CPR and AED guidance from a simulated 9-1-1 telecommunicator. FRs did not receive telecommunicator instruction. Participants were surveyed about medical training and experience. Correct AED pad placements (anterior: AP, lateral: LP) were individually determined from video abstraction based on manufacturer’s recommendations and distance to anatomical landmarks (mid, nipple, and naval lines). Incorrect AP placement was defined as more than 6 cm medial or 10 cm inferior. Incorrect LP placement was defined as more than 6 cm superior, 9 cm inferior, or 10 cm medial. We examined the association between correct pad placement and previous CPR training (current, expired, or never) for LR and correct pad placement and self-reported recent field experience (&lt; 1 year) with AED application for FR using Chi-square tests. Results: LR correctly placed the AP in 30/38 (79%) and the LP 30/38 (79%) simulations. Application did not differ significantly based on previous CPR training (AP p= .187, LP p=.578). The most common incorrect placement was too low for both AP (5/8, 63%) and LP (4/8, 50%). FRs applied the AP correctly in 31/36 (86%) and the LP in 22/36 (61%) simulations. Among FRs, correct pad application did not differ significantly based on recent field experience (AP p=.29, LP p=.563). The most common incorrect placement was too low for both AP (5/5, 100%) and LP (12/14, 86%). Conclusion: Both LRs and FRs may not apply AEDs per manufacturer’s recommendations. Further research is needed to improve instructions and follow-up training to ensure appropriate placement of AEDs, and to understand how improper AED placement impacts the accuracy of rhythm analysis and defibrillation success.

Abstract 15009: Extra-Low Energy Defibrillation With Epicardial Implantable Cardioverter Defibrillator Networks With Electrically Conductive Fibers in Disease Models

Introduction: We previously reported that extra-low energy (&lt;0.6J) defibrillation is possible with the epicardial ICD net lead system (Ep-ICD) in normal canine hearts. Hypothesis: The aim of this study was to test whether the Ep-ICD can terminate ventricular fibrillation (Vf) with the same energy in two disease models (heart failure and long QT syndrome (LQT)). Methods: 1. Ep-ICD was constructed by fine tungsten fibers at the top and bottom of the cardiac mesh (Figure 1), connected to the RV and SVC coils of the DF-1 lead, respectively. 2. Heart failure was induced by rapid right ventricular pacing (170 bpm, 8 weeks). 3. Vf was induced by placing a 9V battery on the surface of the heart. DC shock was delivered with a minimum energy of 0.4J (Medtronic Viva XT). 4. Defibrillation threshold (DFT) was defined as 75% of defibrillation success. 5. LQT was simulated by reducing the conductance (Gk) of the IKS current by (x 1.0(CTL) or 0.8(LQT)) by computer simulation. Results: 1. DFT(J) of Ep-ICD in the canine HF model: 0.8, 1.2, 1.2. 3, Minimum DF energy(J): 0.6, 0.6, 0.8, 2. Maximum DF energy(J): 1.2, 1.6, 5, 52. Immediate return to sinus rhythm (SR) was achieved in most cases after DC delivery. In a small number of cases, brief periods of VT occurred, with rapid return to SR. No tachycardic arrhythmias occurred after return to SR. 3. The DFT was 0.39 for LQT and 0.52 for CTL. Conclusions: 1. DFT of Ep-ICD increased from 0.6 J in normal canine heart to 1.2 J in canine HF model, but still much lower energy used in current ICD system (36 J). 2. The Ep-ICD lead system is the least traumatic and still within the acceptable range while conscious. 3. DFT of LQT with Ep-ICD is 25% lower than normal heart. 4. Ultra-low energy DC can avoid conduction abnormalities or malignant arrhythmias after shock. Hearts return to SR immediately. 5. Ep-ICD can deliver the DC shock before loss of consciousness, improving quality of life and safety of ICD therapy.

Acute human defibrillation performance of a subcutaneous implantable cardioverter-defibrillator with an additional coil electrode

The subcutaneous implantable cardioverter-defibrillator (S-ICD) delivers 80 J shocks from an 8 cm left-parasternal coil to a 59 cm3 left lateral pulse generator (PG). A system that defibrillates with lower energy could significantly reduce PG size. Computer modeling and animal studies suggested that a second shock coil either parallel to the left-parasternal coil or transverse from the xiphoid to the PG pocket would significantly reduce the defibrillation threshold. The purpose of this study was to acutely assess the defibrillation efficacy of parallel and transverse configurations in patients receiving an S-ICD. Testing was performed in patients receiving a conventional S-ICD system. Success at 65 J was required before investigational testing. A second electrode was temporarily inserted from the xiphoid incision connected to the PG with an investigational Y-adapter. Phase 1 (n = 11) tested the parallel configuration. Phase 2 (n = 21) tested both parallel and transverse configurations in random order. This study enrolled 35 patients (28 males (80%); mean age 51 ± 17 years; left ventricular ejection fraction 40% ± 15%; body mass index 26 ± 4 kg/m2; prior myocardial infarction 46%; congestive heart failure 49%; cardiomyopathy 63%). Compared to the conventional S-ICD system, mean shock impedance decreased for both parallel (69 ± 15 Ω vs 86 ± 20 Ω; n = 33; P < .001) and transverse (56 ± 14 Ω vs 81 ± 21 Ω; n = 20; P < .001) configurations. Shock success rates at 20, 30, and 40 J were 55%, 79%, 97%, and 25%, 70%, 90% for parallel and transverse configurations, respectively. Defibrillation threshold testing was well tolerated with no serious adverse events. Adding a second shock coil, particularly in the parallel configuration, significantly reduced the impedance and had a high likelihood of defibrillation success at energies ≤40 J. This may enable the development of a smaller S-ICD.

Amplitude spectral area of ventricular fibrillation and defibrillation success at low energy in out-of-hospital cardiac arrest.

The optimal energy for defibrillation has not yet been identified and very often the maximum energy is delivered. We sought to assess whether amplitude spectral area (AMSA) of ventricular fibrillation (VF) could predict low energy level defibrillation success in out-of-hospital cardiac arrest (OHCA) patients. This is a multicentre international study based on retrospective analysis of prospectively collected data. We included all OHCAs with at least one manual defibrillation. AMSA values were calculated by analyzing the data collected by the monitors/defibrillators used in the field (Corpuls 3 and Lifepak 12/15) and using a 2-s-pre-shock electrocardiogram interval. We run two different analyses dividing the shocks into three tertiles (T1, T2, T3) based on AMSA values. 629 OHCAs were included and 2095 shocks delivered (energy ranging from 100 to 360J; median 200J). Both in the "extremes analysis" and in the "by site analysis", the AMSA values of the effective shocks at low energy were significantly higher than those at high energy (p = 0.01). The likelihood of shock success increased significantly from the lowest to the highest tertile. After correction for age, call to shock time, use of mechanical CPR, presence of bystander CPR, sex and energy level, high AMSA value was directly associated with the probability of shock success [T2 vs T1 OR 3.8 (95% CI 2.5-6) p < 0.001; T3 vs T1 OR 12.7 (95% CI 8.2-19.2), p < 0.001]. AMSA values are associated with the probability of low-energy shock success so that they could guide energy optimization in shockable cardiac arrest patients.