Defibrillation Threshold Research Articles

Exploiting SMART pass filter deactivation detection to minimize inappropriate subcutaneous implantable cardioverter defibrillator therapies: a real-world single-centre experience and management guide.

The SMART Pass™ (SP) algorithm is a high-pass filter that aims to reduce inappropriate therapy (IT) in subcutaneous internal cardiac defibrillator (S-ICD), but SP can deactivate due to low amplitude sensed R waves or asystole. The association between IT and SP deactivation and management strategies were evaluated, hypothesizing SP deactivation increases the risk of IT and device re-programming, or lead/generator re-positioning could reduce this risk. Retrospective single-centre audit of Emblem™ S-ICD devices implanted 2016 to 2020 utilizing health records and remote monitoring data. Cox regression models evaluated associations between SP deactivation and IT. A total of 348 patients (27 ± 16.6 months follow-up) were studied: 73% primary prevention. Thirty-eight patients (11.8%) received 83 shocks with 27 patients (7.8%) receiving a total of 44 IT. Causes of IT were oversensing (98%) and aberrantly conducted atrial fibrillation (2%). SP deactivation occurred in 32 of 348 patients (9%) and was significantly associated with increased risk of IT (hazard ratio 5.36, 95% CI 2.37-12.13). SP deactivation was due to low amplitude R waves (94%), associated with a higher defibrillation threshold at implant and presence of arrhythmogenic right ventricular cardiomyopathy. No further IT occurred 16 ± 15.5 months after corrective interventions, with changing the sensing vector being successful in 59% of cases. To reduce the risk of IT, the cause of the SP deactivation should be investigated, and appropriate reprogramming, device, or lead modifications made. Utilizing the alert for SP deactivation and electrograms could pro-actively prevent IT.

Reduction in defibrillation threshold by modifications to the subcutaneous implantable-cardioverter defibrillator coil

The subcutaneous implantable cardioverter defibrillator (S-ICD) is approved as an alternative to the traditional transvenous ICD (T-ICD). The S-ICD has higher average defibrillation threshold (DFT) than the T-ICD, related primarily to greater distance from shocking coil to ventricular myocardium with the S-ICD. The S-ICD therefore utilizes a larger device capable of generating an 80J shock, compared to 35-40J maximal shock output typical for T-ICDs, and defibrillation efficacy testing is generally recommended for the S-ICD 1 Wilkoff B, Fauchier L, Stiles M, et al. 2015 HRS/EHRA/APHRS/SOLAECE expert consensus statement on optimal implantable cardioverter-defibrillator programming and testing. Heart Rhythm 2016;13;e50-86. Google Scholar . We previously published computer modeling of predictors of defibrillation efficacy with the S-ICD, which determined that minimal fat underlying the S-ICD coil and generator (reducing shock impedance), and posterior generator position (better directing the shock vector across the ventricles), are predictors of lower DFT 2 Heist E. Belalcazar A. Stahl W. et al. Determinants of Subcutaneous Implantable Cardioverter-Defibrillator Efficacy. J Am Coll Cardiol EP. 2017; 3: 405-414 Google Scholar . Those findings formed the basis for the PRAETORIAN score, which is utilized in clinical S-ICD implantation to reduce DFT 3 Quast A.-F.B.E. Baalman S.W.E. Brouwer T.F. et al. A novel tool to evaluate the implant position and predict defibrillation success of the subcutaneous implantable cardioverter-defibrillator: The PRAETORIAN score. Heart Rhythm. 2018; 16: 403-410 Abstract Full Text Full Text PDF PubMed Scopus (65) Google Scholar . A previously published computer modeling study examined the impact of dual S-ICD electrodes and electrode arrays, as well as variations in generator and lead location; results demonstrated reduced DFT with some configurations compared to the standard S-ICD 4 Jolley M. Stinstra J. Tate J. et al. Finite Element Modeling of Subcutaneous Implantable Defibrillator Electrodes in an Adult Torso. Heart Rhythm. 2010; 7: 692-698 Abstract Full Text Full Text PDF PubMed Scopus (37) Google Scholar . In this current study, we performed computer modeling to determine whether design modifications to the S-ICD coil could result in reductions to S-ICD DFT.

Propofol dose and efficacy of defibrillation testing during implantation of subcutaneous implantable cardioverter-defibrillators: Aretrospective, single center cohort study.

Defibrillation testing (DFT) is recommended during subcutaneous implantable cardioverter-defibrillator (S-ICD) implantation. Previous studies analyzing the potential interference of propofol with defibrillation threshold are inconsistent. The purpose of this study was to analyze whether propofol affects DFT post S-ICD placement. All patients with S-ICD implantation between 01/2017 and 11/2020 at the University Heart Center Freiburg were retrospectively analyzed. Two groups were generated depending on the success of the first shock during DFT. Implantation characteristics and dose of anesthetics were analyzed. In 12 of the included 80 (15%) patients, first shock during DFT failed. The absolute dose of propofol was significantly higher in patients with first shock failure (median 653 mg [IQR 503-855]) compared to patients with first shock termination (376 mg [200-600]; p = 0.027). Doses of opioids and midazolam as well as type of anesthesia did not differ between the groups. A multivariable binary logistic regression analysis confirmed an independent association of first shock termination and propofol dose (per 100 mg: OR 0.73 (95% CI: 0.56-0.95); p = 0.021). There is an independent association of propofol dose and first shock failure in routineS-ICD defibrillation testing.

Abstract 12958: The Dark Side of Normal Healing: Fibrous Encasement of a Subcutaneous ICD Coil

Introduction: Implantable devices elicit fibrotic and inflammatory responses, which may result in reduced efficacy of the device. Prior literature has addressed thrombus formation and fibrous encapsulation of intravascular leads. This mechanism is at least in part different than subcutaneous fibrosis. However, there have been scarce reports of fibrosis related to subcutaneous leads. Case: A 74 year-old male with long standing ischemic cardiomyopathy and absence of pacing indication met indications for primary prevention S-ICD. After shared decision making, a device was implanted with defibrillation thresholds at 65 joules. He later presented with interventricular dyssynchrony (QRS 160 msec) and symptomatic heart block. Upgrade to a biventricular defibrillator was undertaken with removal of the S-ICD system. S-ICD coil manual traction failed to free the lead from the subcutaneous space of implantation. After extensive blunt dissection and removal of the coil, extensive coil ingrowth and fibrosis was noted (Figure 1). Conclusions: This case describes the occurrence and visually documents extravascular coil fibrosis and ingrowth into the SICD coil, similarly seen in intravascular ICD leads. The S-ICD coil is a necessary component of the shocking vector and extensive fibrosis may contribute to elevated shock impedance and failed defibrillation thresholds. In cases of elevated shock impedance, it is unknown whether failed defibrillation thresholds or elevated high voltage shock impedance is the result of the generator, coil, or both. Further research is warranted to ascertain whether failed defibrillation thresholds and increased shock impedance is due solely from the SICD generator pocket. Advances in coil technology and regenerative medicine may offer insights into mitigation of the inflammatory process.

Defibrillation Threshold Testing and Long-term Follow-up in Chagas Disease.

Sudden cardiac death is the most common cause of death in chronic Chagas cardiomyopathy (CCC). Because most CCC patients who are candidates for implantable cardioverter-defibrillators (ICD) meet criteria for high defibrillation threshold values, a defibrillator threshold test (DTT) is suggested. We investigated the use of DTT in CCC patients, focusing on deaths related to ICD and arrhythmic events, as well as treatment during long-term follow-up. We retrospectively evaluated 133 CCC patients who received an ICD mainly for secondary prevention. Demographic, clinical, laboratory data, Rassi score, and DTT data were collected, with p < 0.05 considered significant. The mean patient age was 61 (SD, 13) years and 72% were men. The baseline left ventricular ejection fraction was 40 (SD, 15%) and the mean Rassi score was 10 (SD, 4). No deaths occurred during DTT and no ICD failures were documented. There was a relationship between higher baseline Rassi scores and higher DTT scores (ANOVA = 0.007). The mean time to first shock was 474 (SD, 628) days, although shock was only necessary for 28 (35%) patients with ventricular tachycardia, since most cases resolved spontaneously or through antitachycardia pacing. After a mean clinical follow-up of 1728 (SD, 1189) days, 43 deaths occurred, mainly related to progressive heart failure and sepsis. A routine DTT may not be necessary for CCC patients who receive an ICD for secondary prevention. High DTT values seem to be unusual and may be related to high Rassi scores.

High Internal Atrial Defibrillation Threshold Is Related to a High Risk of Recurrence After Catheter Ablation for Long-Standing Persistent Atrial Fibrillation But Not for Persistent Atrial Fibrillation.

The atrial defibrillation threshold (ADFT) for internal cardioversion is theoretically related to the critical mass for sustaining atrial fibrillation (AF). This study aimed to investigate the association of ADFT for internal cardioversion with the outcome of catheter ablation for non-paroxysmal AF (non-PAF). We included 368 consecutive patients who underwent first-time catheter ablation for non-PAF. Based on the degree of ADFT recorded by the internal cardioversion before pulmonary vein isolation, we divided the patients into low ADFT (<20 J) and high ADFT (≥20 J) groups and analysed the association between ADFT and atrial tachyarrhythmia recurrence. There were 234 and 134 patients in the low and high ADFT groups, respectively. Of these, 39 patients (16.7%) and 41 (30.6%) patients, respectively, had atrial tachyarrhythmia recurrence during the 2.6±1.0 year follow-up. The high ADFT group showed a significantly higher atrial tachyarrhythmia recurrence than the low ADFT group (p=0.002). This finding was also noted in patients with long-standing persistent AF (p=0.032) but not in patients with persistent AF (p=0.159). The significant predictors of arrhythmia recurrence on multivariate analysis were high ADFT (p=0.004) and long-standing persistent AF (p=0.011). In multivariate analysis within the long-standing persistent AF group, only ADFT remained a significant risk factor for AF recurrence (p=0.035). The high ADFT of internal cardioversion was found to be a risk factor for post-catheter ablation recurrence in patients with long-standing persistent AF but not in those with persistent AF.

Reduced motion external defibrillation: Reduced subject motion with equivalent defibrillation efficiency validated in swine.

External defibrillators are used for arrhythmia cardioversion and for defibrillating during cardiac arrest. During defibrillation, short-duration biphasic pulses cause intense motion due to rapid chest-wall muscle contraction. A reduced motion external defibrillator (RMD) was constructed by integrating a commercial defibrillator with a Tetanizing-waveform generator. A long-duration, low-amplitude, tetanizing waveform slowly stimulated the chest musculature before the biphasic pulse, reducing muscle contraction during the shock. The purpose of this study was to evaluate RMD defibrillation in swine for subject motion during defibrillation pulses and for defibrillation effectiveness. RMD defibrillation can reduce the duration of arrhythmia ablation therapy or simplify cardioversion procedures. The tetanizing unit delivered a triangular 1-kHz pulse of 0.25- to 2.0-second duration and 10- to 100-V peak amplitude, subsequently triggering the conventional defibrillator to output standard 1- to 200-J energy biphasic pulses at the next R wave. Forward limb motion was evaluated by measuring peak acceleration and limb work during RMD (tetanizing + biphasic) or biphasic pulse-only waveforms at 10-3-second sampling rate. Seven swine were arrested electrically and subsequently defibrillated. Biphasic pulse-only and RMD defibrillations were repeated 25-35 times per swine, varying tetanizing parameters and biphasic pulse energy. Defibrillation thresholds (DFTs) were established by measuring the minimum energy required to restore sinus rhythm with biphasic pulse-only or RMD defibrillations. Two forward-limb acceleration peaks occurred during both the tetanizing waveform and biphasic pulse, indicating rapid and slower nociceptic (pain sensation) nerve fiber activation. Optimal RMD tetanizing parameters (25-35 V, 0.25- to 0.75-second duration), relative to biphasic pulse-only defibrillations, resulted in 74% ± 10% smaller peak accelerations and 85% ± 10% reduced limb work. DFT energies were identical when comparing RMD to biphasic pulse-only defibrillations. Relative to conventional defibrillations, RMD defibrillations maintain rhythm restoration efficiency with drastically reduced subject motion.

Subcutaneous and Transvenous ICDs: an Update on Contemporary Questions and Controversies.

While the subcutaneous (S-) implantable cardioverter-defibrillator (ICDs) is an alternative to the transvenous (TV-) ICD in many patients, optimal use remains unclear. In this review, we summarize recent clinically relevant data on sensing algorithms, inappropriate shocks, defibrillation testing, and battery and electrode failures. Changes in sensing algorithms and S-ICD programming have significantly decreased inappropriate shock rates. Avoiding fat below the S-ICD coil and can is key for reducing the defibrillation threshold. While S-ICD battery and electrode failures have resulted in recalls, system components remain commercially availablesince failure rates are low and no other similar devices are available. The S-ICD is a good alternative to the TV-ICD for many patients, and particularly in light of recently developed device algorithms and improvements in implant technique. Future research will need to better understand: the impact of S-ICD electrode and battery failures and the potential for integrating leadless pacing into a modular S-ICD platform.

Failed shocks in hypertrophic cardiomyopathy patients: prevalence, predictors and outcome

Abstract Funding Acknowledgements Type of funding sources: None. Introduction An implantable cardioverter-defibrillator (ICD) is used in selected high-risk hypertrophic cardiomyopathy (HCM) patients in order to prevent sudden arrhythmic death. The unique features of this population raise concerns regarding the reliability of successful defibrillation. Purpose To describe the rate and discover potential predictors of failed shocks in HCM patients. Methods We retrospectively evaluated all HCM patients with an ICD from a single tertiary medical center. Clinical, electrocardiographic and echocardiographic data were collected and compared among patients with and without failed shocks. Results A total of 99 patients (77% male, 45±17 years old) were analyzed. Over a median follow up of 6.3 years (IQR 2.6-10.7), 20 patients developed sustained ventricular arrhythmia (VTA). Of those, 18 patients received appropriate shocks from their ICD. VTA was associated with younger age at diagnosis, history of syncope and thicker maximal LV width. Six patients experienced at least one failed shock. The likelihood of failed shocks was similar when single or dual coil electrodes were used (dual coils in 67% of patients with failed shocks and 50% in those without), and the only predictor was increased wall thickness [OR 1.2 (1.07-1.38) per 1 mm]. All-cause mortality was low and similar in patients with an without failed shocks (0% vs 8%, P=0.5) Conclusions Failed shocks are a rare entity in HCM patients. Increased maximal LV width was the only predictor of those events. Our findings support avoiding defibrillation threshold testing routinely, but may indicate its need in patients with extreme LV wall thickening (≥23 mm).

PO-618-03 REDUCTION IN DEFIBRILLATION THRESHOLD BY MODIFICATIONS TO THE SUBCUTANEOUS ICD COIL

Subcutaneous Implantable Cardioverter Defibrillators (S-ICDs) generally have higher defibrillation thresholds (DFTs) than transvenous ICDs, necessitating larger S-ICD generators and with S-ICD VF conversion testing recommended at implantation. We sought to determine whether modifications to the S-ICD coil configuration or characteristics would reduce DFTs compared to the standard S-ICD coil based on a computer model of defibrillation. We utilized a computer model built from MRI images of a normal thorax and simulation of electrical fields generated by defibrillation. The specific electrical properties of tissues and organs were assigned, as well as other characteristics of the shock circuit, with DFT defined as energy required to achieve an electrical field of 4V/cm in > 95% of ventricular myocardium. Coil configurations examined included a standard parasternal S-ICD coil, dual parallel para-sternal coils, dual coils in series (parasternal and along the left ribcage), and a larger flattened parasternal coil. The standard parasternal S-ICD coil configuration (with < 1mm intervening fat under the coil and generator) resulted in an estimated DFT of 33J. The other coil configurations resulted in marked reductions in DFT by as much as 37% (to 21J) (figure), predominantly related to lower shock impedance and improved electrical field distribution. Our modeling work suggests that modifications to the S-ICD coil design could lead to marked reductions in DFT. This could allow for the creation of S-ICDs with lower energy requirements and correspondingly smaller generators compared to current devices and might obviate the need for VF conversion testing with S-ICDs.

PO-674-05 THE SHOCKING PRACTICES OF PEDIATRIC ELECTROPHYSIOLOGISTS: CONTEMPORARY DFT DATA FROM CIED REGISTRY

Defibrillator threshold (DFT) testing is no longer recommended except in certain circumstances. Data on current national practice pertaining to DFT testing in pediatrics is scarce. To report current implant characteristics, DFT testing practice, and intraprocedural events in pediatric patients undergoing implantable cardiac defibrillator (ICD) placement. We leveraged the pediatric cardiac implantable electronic devices (CIED) registry, a retrospective multicenter study endorsed by PACES, to identify patients (age≤21) who underwent ICD placement between 2017 and 2020. Among 705 patients, 51 underwent new ICD implantation. Median age and median weight at implant were 16 years (IQR 14-18) and 62 kg (53-78) respectively. Cardiomyopathy was diagnosed in 28, congenital heart disease (CHD) in 8, idiopathic VT/VF in 8, channelopathy in 5, and other in 2. An ICD was implanted for secondary prevention in 18 patients. Type of implants were as follows: transvenous in 39, subcutaneous in 8, and epicardial in 4. DFT status was known in 49 patients, of whom 30 (61%) underwent testing. DFT testing was performed in all patients who had a subcutaneous device but there was no difference in those with transvenous vs. epicardial leads (53% vs. 66%, p=0.63). DFT testing was less likely in patients seen at a freestanding Children’s Hospital (48% vs. 87%, p=0.012) but did not vary between diagnoses (CHD 59%, cardiomyopathy 62%, channelopathy 60%, and idiopathic ventricular fibrillation 75%, p=0.68) or type of cardiomyopathy (hypertrophic cardiomyopathy vs. all other types, 62% vs. 55%, p=0.67). Age, weight, mild ventricular dysfunction or greater, history of cardiac arrest, or implant provider were not associated with DFT testing. DFTs failed in 2 patients: inability to induce VT/VF in 1 and inability to defibrillate with an acceptable safety margin in 1. There were no reported complications with DFTs. DFT testing is still performed at implant in the majority of transvenous devices in pediatric patients. Presence of CHD or hypertrophic cardiomyopathy was not associated with higher DFT testing rates. Freestanding children’s hospitals were less likely to perform DFTs.

A Systematic Review and Single-center Experience of Azygos Vein Defibrillator Lead Insertion.

Defibrillation threshold (DFT) testing is performed in individuals with higher predicted risks of defibrillation failure. Many strategies have been explored to overcome the challenge of high DFT, including an insertion of a defibrillator lead into the azygos vein. We performed a systematic review of the literature to evaluate the safety and efficacy of azygos vein implantable cardioverter-defibrillator insertion for high DFT combined with the analysis of a single-center experience of the procedure at our institution. The literature search was performed in PubMed and Embase from database inception to December 2020 to identify all case reports and case series related to azygos vein defibrillator lead insertion. Our search identified 291 records. After excluding duplicate studies and those without DFT thresholds and non-azygos vascular destinations, 12 studies (23 cases) were reviewed from the current database. We also conducted a retrospective analysis of 5 cases performed at our institution, and a total of 28 patients were included in our final analysis. The mean age of the pooled cohort was 47 years (range, 17–88 years). Men composed 92% of the total cases, and the average body mass index was 34 kg/m2. The mean ejection fraction (EF) was 25%, with 78% having non-ischemic cardiomyopathy. The left axillary (36%) or subclavian (48%) vein was the common percutaneous access point. The mean duration of azygos vein access and lead delivery was 22 min (range, 13–60 min). The average DFT prior to azygos coil insertion was 35 J (range, 20–45 J). Fifty-seven percent of cases achieved substantial DFT improvement, whereas 18% achieved relative improvement compared to the pre-procedural threshold. No immediate or remote procedure-related complications were reported in 24 cases where data were available. During an average follow-up period of 18 months, 5 patients had ventricular arrhythmic events requiring device therapy and 4 had successful cardioversion from the device. One patient died from cardiac arrest with variable device therapies of both unsuccessful and successful events. In conclusion, azygos vein defibrillator lead insertion has a considerable rate of success, ease of vascular access with minimal procedural time, and lower risks and complications. Larger studies and longer follow-up periods are warranted to establish its efficacy and safety.

PO-662-02 ACUTE HUMAN DEFIBRILLATION PERFORMANCE OF A SUBCUTANEOUS IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR WITH AN ADDITIONAL COIL ELECTRODE

The subcutaneous implantable cardioverter-defibrillator (S-ICD, EMBLEM®, Boston Scientific Corp) delivers 80 J shocks from an 8 cm left-parasternal coil (LPC) to a 59 cc left lateral pulse generator (PG). A system that defibrillates with lower energy could significantly reduce PG size. Modeling and animal studies suggest a 2nd shock coil either parallel (P) to LPC or transverse (T) from xiphoid to PG pocket would significantly reduce shock impedance and defibrillation threshold (DFT).

The "Defibrillation Testing, Why Not?" survey. Testing of subcutaneous and transvenous defibrillators in the Italian clinical practice.

BackgroundDefibrillation testing (DT) can be omitted in patients undergoing transvenous implantable cardioverter–defibrillator (T-ICD) implantation, but it is still recommended for patients at risk for a high defibrillation threshold and for ICD generator changes. Moreover, DT is still recommended on implantation of subcutaneous ICD (S-ICD). The aim of the present survey was to analyze the current practice of DT during T-ICD and S-ICD implantations.MethodsIn March 2021, an ad hoc questionnaire on the current performance of DT and the standard practice adopted during testing was completed at 72 Italian centers implanting S-ICD and T-ICD.Results48 (67%) operators reported never performing DT during de-novo T-ICD implantations, while no operators perform it systematically. The remaining respondents perform it for patients at risk for a high defibrillation threshold. DT is never performed at T-ICD generator change. At the time of de-novo S-ICD implantation, DT is never performed by 9 (13%) operators and performed systematically by 48 (66%). The remaining operators frequently omit DT in patients with more severe systolic dysfunction. DT is not performed at S-ICD generator change by 92% of operators. DT is conducted by delivering a first shock energy of 65 J by 60% of operators, while the remaining 40% test lower energy values.ConclusionsIn current clinical practice, most operators omit DT at T-ICD implantation, even when still recommended in the guidelines. DT is also frequently omitted at S-ICD implantation, and a wide variability exists among operators in the procedures followed during DT.

Influence of "high" defibrillation thresholds on patient survival and impact of system modification.

To test whether a high defibrillation threshold (DFT) marks patients with poor outcomes which are improved when DFT is decreased by system modification (subcutaneous coil implant; SM). The electrical substrate generating fast ventricular arrhythmias may generate poor outcomes among patients treated with implantable cardioverter-defibrillators (ICDs), even when arrhythmias are treated successfully. Since patients with high DFTs have increased mortality, we contrasted survival among patients with high DFT treated with and without SM. We studied consecutive patients undergoing ICD implantation and DFT testing at Cleveland Clinic over a 14-year period. High DFT was defined as successful defibrillation by shock strength >25 J or ≤10 J of maximal device output. Mortality was recorded using the Social Security Death Index. Survival was compared among those high DFT patients receiving SM versus the remainder. Out of 6353 patients tested, 191 (3%) had high DFT (32.1 ± 3.7 J)versus 13.9 ± 4.9 J in the remainder ("acceptable DFT,"p < .001). One hundred twenty-one high DFT patients (63%; 33.3 ± 3.4 J) underwent SM, which significantly decreased DFT (24.8 ± 5.9 J; p < .001). Seventy patients (37%; 30.3 ± 3.3 J) did not undergo SM. During follow-up, 38% (2363/6162; 7.8 yrs) patients with acceptable DFT died versus 48% high DFT patients (91/191; 5.6 yrs.; p < .001). Concomitantly, 48% patients with SM (58/121) died, as compared to 47% patients (33/70) without SM (p = .91); median follow-up 4.9 yrs). Patients with high DFT have a higher mortality than those with acceptable DFT. The additional subcutaneous coil implant decreases DFT to an acceptable range but does not appear to improve survival. The electrical substrate underlying high DFT appears to determine survival.

Abstract 13691: High Burden of Sensing Changes in Periprocedural TAVR Patients With Pre-Existing CIEDs Presents A Unique Challenge

Introduction: The data on the management of patients undergoing transcatheter aortic valve replacement (TAVR) with pre-existing cardiac implantable electronic devices (CIED) is scarce. Objective: We describe the R wave sensing changes following TAVR in a patient with CIED and describe CIED behavior peri procedurally in a high volume center over 8 years. Results: A 64 year old male patient with a history of non-ischemic cardiomyopathy and a secondary prevention dual-chamber ICD presented for generator change. Six months prior, he underwent TAVR (29mm ES S3). Post TAVR, he developed a new RBBB. Device interrogation revealed a significant drop in sensed R waves from 9mV to 1.5mV which temporally correlated with TAVR (Figure 1). Pacing thresholds and impedance were stable. Chest x-rays showed stable lead position. Given drop in R wave sensing, successful defibrillation threshold testing was performed with generator change. Of the 115 patients with pre-existing CIEDs undergoing TAVR between 2012-2020, 23.5% (27 patients) showed changes in sensing (mean 3.0±2.5mV) peri procedurally with minimal change in impedance or threshold with no correlation with QRS changes. Conclusions: To our knowledge, this is the 1st reported case of a change in sensed R waves due to conduction disturbance following TAVR. We hypothesize this occurred due to a change in the activation wavefront sensed by the right ventricular lead following the development of new RBBB. Up to a quarter of patients have sensing fluctuations in our experience. Consideration of pre and post device interrogation with TAVR could be of value.

Abstract 9615: Predictors of Impedance During Subcutaneous ICD Defibrillation Testing in Hypertrophic Cardiomyopathy

Introduction: Defibrillation threshold testing (DFT) is generally reserved for populations with perceived concern for defibrillation failure, including in hypertrophic cardiomyopathy (HCM). Higher shock impedance has been associated with risk of DFT failure with subcutaneous defibrillators (SICD). The PRAETORIAN score is a chest radiograph based tool that evaluates device positioning to predict risk of DFT failure. Objective: We assessed predictors of impedance during DFT in a single center HCM SICD cohort. Methods: Data was collected from HCM patients who underwent SICD implantation from 2013 to 2021. Predictors of impedance were evaluated with linear and logistic regression. Results: Impedance was reported in 75 HCM SICD patients during DFT with 65J. DFT was successful in 74 patients with mean impedance of 72.7 ohm and septal thickness of 20.6 mm. Ten patients had massive HCM (&gt; 30 mm) with mean impedance of 66.4 ohm. Septal thickness was not predictive of impedance (β 0.37, 95% CI 1.24-0.50; P = .40). Independent predictors of impedance were BMI (β 1.41, 95% CI 0.61-2.21; P = .0008) and PRAETORIAN score (β 0.14, 95% CI 0.05-0.22; P = .0015). Multivariable regression revealed BMI no longer significant and PRAETORIAN score remaining significant (β 0.10, 95% CI 0.01-1.66; P = .038). Conclusion: In this HCM SICD cohort BMI and PRAETORIAN score were predictive of impedance. However, in a multivariable model, BMI was no longer predictive, highlighting importance of implant technique to improve impedance and DFT. Additionally, patients with massive hypertrophy all had successful DFT and septal thickness was not predictive of impedance. HCM has historically been portrayed as a high DFT population. Further prospective trials are necessary to establish whether standard DFT practice can be applied in HCM.

Defibrillation testing of subcutaneous versus transvenous defibrillators in the clinical practice: a nationwide survey in Italy

Abstract Aims According to current guidelines, defibrillation testing (DT) for efficacy can be omitted in patients undergoing transvenous implantable cardioverter–defibrillator (T-ICD) implantation. DT is still recommended for patients at risk for a high defibrillation threshold (e.g. hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, right-sided implantations) and for ICD generator changes. Moreover, a class I recommendation remains to perform DT during the implantation of subcutaneous ICD (S-ICD). The aim of the present survey was to analyze the current practice of DT during T-ICD and S-ICD implantations in Italy. Methods In March 2021, an ad hoc questionnaire on the current performance of DT and the standard practice adopted during testing was completed by 72 operators at Italian centers implanting S-ICD and T-ICD. Results 48 (67%) operators reported never performing DT during de-novo T-ICD implantations, while no operators perform it systematically. The remaining respondents perform it in specific cases: right sided implantations (54%), poor signal sensing (46%), secondary prevention patients (42%), arrhythmic syndromes (13%), hypertrophic cardiomyopathy (8%). DT is never performed at T-ICD generator change. At the time of de-novo S-ICD implantation, DT is never performed by 9 (13%) operators and performed systematically by 48 (66%). The remaining operators perform DT in cases of: secondary prevention patients (73%), sub-optimal S-ICD placement (33%), non-compromised ejection fraction (33%) or obese patients (7%). DT is not performed at S-ICD generator change by 92% of operators. DT is conducted by delivering a first shock energy of 65J by 60% of operators, while the remaining 40% test lower energy values. The most frequently reported conditions for revising the system at the end of de- novo implantation procedure is high shock impedance (54%) and sub-optimal S-ICD placement or high PRAETORIAN score (50%). With adequately low shock impedance and optimal system placement, 37% of operators would accept a defibrillation margin &amp;lt;15J. Conclusion In current clinical practice, the vast majority of operators omit DT at T-ICD implantation, even when still recommended in the guidelines. DT is also frequently omitted at S-ICD implantation. We also report a wide variability among operators in the procedures followed during DT and in the criteria applied for defining the procedural success. Funding Acknowledgement Type of funding sources: None.

The effect of patient weight and amiodarone use on the energy of a successful shock in cardioversion of atrial arrhythmias – single-center experience study

Abstract Background Electrical cardioversion (DCCV) is an effective method of sinus rhythm restitution. Recently published data suggest higher efficiencies of higher discharge energies. The influence of individual parameters on the success of cardioversion is still studying. Purpose To evaluate the influence of individual patient parameters on the energy of a successful external defibrillator shock during cardioversion of atrial arrhythmias Methods The retrospective analysis cohort of all patients treated by DCCV due to atrial arrhythmias between 10/2015 and 1/2020. To evaluate potential predictors for the choice of a higher initial discharge using one-dimensional logistic regression and to include parameters significant at the 10% level of significance (p&amp;lt;0.1) in the multidimensional logistic regression model. Results 1986 electrical cardioversions of 984 patients (382 repeated procedures of the same patients in a cohort). 1292 (65.1%) men and 694 (34.9%) women aged 67.0 (±10.2) years. Mean energy of the first shock 118.9 (±19.2) J with a success rate of 77.8%, energy of the second shock 154.0 (±26.3) J, which increased the overall success to 80.0%, and mean high of the third shock 173.9 (±25.6) J, when the total efficacy of DCCV in sinus rhytm restitution reached 89.8%. From the univariate binary regression, parameters significant at the 10% level of significance (p&amp;lt;0.1) were selected and included in a multidimensional logistic regression model. Only the patient's weight and the use of amiodarone proved to be statistically significant. Weight with OR 1.21 and use of amiodarone with OR 1.43. Conclusion Patient weight and amiodarone use are predictors of the need to use higher energy electric cardioversion. Discussion Amiodarone medication does not appear to increase the defibrillation threshold, but rather is a feature that represents the group of patients treated with more aggressive antiarrhythmic therapy for advanced atrial arrhythmias with more significant structural impairment, but this attitude requires further study. Funding Acknowledgement Type of funding sources: Private hospital(s). Main funding source(s): VAVIA: IGS202009 - Racionální algoritmus při elektivní elektrické kardioverzi fibrilace síní.

Azygos Vein ICD Lead Implantation Lowers Defibrillation Threshold in a Patient with Hypertrophic Cardiomyopathy

A 14-year-old boy with hypertrophic cardiomyopathy (HCM) diagnosed at the age of 1 year and with massive left ventricular hypertrophy suffered an episode of ventricular fibrillation during mild effort. He underwent a dual-chamber implantable cardioverter defibrillator (ICD) implantation. The defibrillation threshold testing (DFT) was ineffective. Subcutaneous multi-coli arrays tunneled into the left postero-lateral position and connected to the superior vena cava (SVC) port of the dual-chamber ICD were added to increase the myocardial mass involved in the defibrillation shock pathway. A new DFT was unsuccessful. The patient was transferred to our hospital for myectomy. An epicardial defibrillation patch was placed on the left ventricular lateral wall, but again, DFT testing was ineffective using the right ventricular (RV) coil to lateral patch as shock pathway. Another epicardial defibrillation patch was then placed on the inferior wall. In this case, DFT testing was effective with a defibrillation pathway between the two patches and the can. In November 2015, a high shock impedance alarm was recorded through remote monitoring, thus compromising the safety of the ICD shock pathway. The patient underwent the implant of a new trans-venous defibrillation coil lead in the azygos vein. After few months, the patient developed symptomatic severe aortic regurgitation and underwent an aortic valve replacement. During the operation, DFT testing was performed and was successful. Our case illustrates that azygous vein ICD lead implantation is efficacious in HCM with massive hypertrophy and high DFT, and prompts further studies to systematically investigate its efficacy in this particular subgroup of the HCM population.