Atrioventricular nodal reentry tachycardia treatment using CARTO 3 V7 activation mapping: a new era of slow pathway radiofrequency ablation is under coming.

Background: Slow pathway (SP) ablation is the cornerstone for atrioventricular nodal reentry tachycardia (AVNRT) treatment, and a low-voltage bridge offers a good target during mapping using low x-ray exposure. We aimed to assess a new tool to identify SP by activation mapping using the last CARTO3® version, i.e., CARTO PRIME® V7 (Biosense Webster, Diamond Bar, CA, USA). Methods and results: Right atrial septum and triangle of Koch 3D-activation map were obtained from intracardiac contact mapping during low x-ray CARTO 3® procedure. In 60 patients (mean age 60.3 ± 14.7, 61% females) undergoing ablation for AVNRT, an automatic activation map using a DECANAV® mapping catheter and CARTO® Confidense™, Coherent, and FAM DX software modules were obtained. The SP was identified in all patients as the latest atrioventricular node activation area; RF catheter ablation (RFCA) in that region elicited junctional beats. The mean procedural time was 150.3 ± 48.3 min, the mean fluoroscopy time exposure was 2.9 ± 2 min, the mean dose-area product (DAP) was 16.5 ± 2.7 cGy/cm2. The mean number of RF applications was 3.9 ± 2, the mean ablation index was 428.6 ± 96.6, and the mean contact force was 8 ± 2.8 g. There were no adverse event during the procedure, and no AVNRT recurrences occurred during a mean follow-up of 14.3 ± 8.3 months. Conclusion: Ablation of the SP by automatic mapping using Confidense™, Coherent, and FAM DX software modules is an innovative, safe, and effective approach to AVNRT ablation. The CARTO3® V7 system shows on a 3D map the latest AV node activation area during sinus rhythm allowing low fluoroscopy time and highly effective RFCA.

[2020 Catheter Ablation Registry of the Italian Association of Arrhythmology and Cardiac Pacing]. / Registro Italiano Ablazioni 2020. Associazione Italiana di Aritmologia e Cardiostimolazione.

BACKGROUND: This report describes the findings of the 2020 Italian Catheter Ablation Registry of the Italian Association of Arrhythmology and Cardiac Pacing (AIAC). METHODS: Data collection was retrospective. A standardized questionnaire was completed by each of the participating centers. RESULTS: A total of 10 378 ablation procedures were performed by 66 institutions. Most centers (70%) have an electrophysiology laboratory, and 23% a hybrid cardiac surgery laboratory. All centers have a 3D mapping system. The median number of electrophysiologists and nurses involved in the electrophysiology laboratory was 3.5 and 3, respectively. An electrophysiology technician was involved in 35% of all centers. In 88.2% of cases, catheter ablation was performed for supraventricular arrhythmias; the most frequently treated arrhythmia was atrial fibrillation (39.4%), followed by atrioventricular nodal reentrant tachycardia (18.6%), and common atrial flutter (10.6%). In 72.9% of patients, catheter ablation was performed using a 3D mapping system, with a "near-zero" fluoroscopic approach in 37.7% of all patients. CONCLUSIONS: The 2020 Italian Catheter Ablation Registry confirmed that the electrophysiology activity was markedly affected by the COVID-19 pandemic; atrial fibrillation is the most frequently treated arrhythmia with an increasing number of procedures performed with a 3D mapping system and a "near-zero" approach.

Five waves of COVID-19 pandemic in Italy: results of a national survey evaluating the impact on activities related to arrhythmias, pacing, and electrophysiology promoted by AIAC (Italian Association of Arrhythmology and Cardiac Pacing).

BACKGROUND: The subsequent waves of the COVID-19 pandemic in Italy had a major impact on cardiac care. METHODS: A survey to evaluate the dynamic changes in arrhythmia care during the first five waves of COVID-19 in Italy (first: March-May 2020; second: October 2020-January 2021; third: February-May 2021; fourth: June-October 2021; fifth: November 2021-February 2022) was launched. RESULTS: A total of 127 physicians from arrhythmia centers (34% of Italian centers) took part in the survey. As compared to 2019, a reduction in 40% of elective pacemaker (PM), defibrillators (ICD), and cardiac resynchronization devices (CRT) implantations, with a 70% reduction for ablations, was reported during the first wave, with a progressive and gradual return to pre-pandemic volumes, generally during the third-fourth waves, slower for ablations. For emergency procedures (PM, ICD, CRT, and ablations), recovery from the initial 10% decline occurred in most cases during the second wave, with some variability. However, acute care for atrial fibrillation, electrical cardioversions, and evaluations for syncope showed a prolonged reduction of activity. The number of patients with devices which started remote monitoring increased by 40% during the first wave, but then the adoption of remote monitoring declined. CONCLUSIONS: The dramatic and profound derangement in arrhythmia management that characterized the first wave of the COVID-19 pandemic was followed by a progressive return to the volume of activities of the pre-pandemic periods, even if with different temporal dynamics and some heterogeneity. Remote monitoring was largely implemented during the first wave, but full implementation is needed.

The Interplay of PR Interval and AV Pacing Delays Used for Cardiac Resynchronization Therapy in Heart Failure Patients: Association with Clinical Response in a Retrospective Analysis of a Large Observational Study.

Background. Cardiac resynchronization therapy (CRT) is a treatment for heart failure (HF) patients with prolonged QRS and impaired left ventricular (LV) systolic function. We aim to evaluate how the baseline PR interval is associated with outcomes (all-cause death or HF hospitalizations) and LV reverse remodeling (>15% relative reduction in LV end-systolic volume). Methods. Among 2224 patients with CRT defibrillators, 1718 (77.2%) had a device programmed at out-of-the-box settings (sensed AV delay: 100 ms and paced AV delay: 130 ms). Results. In this cohort of 1718 patients (78.7% men, mean age 66 years, 71.6% in NYHA class III/IV, LVEF = 27 ± 6%), echocardiographic assessment at 6-month follow-up showed that LV reverse remodeling was not constant as a function of the PR interval; in detail, it occurred in 56.4% of all patients but was more frequent (76.6%) in patients with a PR interval of 160 ms. In a median follow-up of 20 months, the endpoint of death or HF hospitalizations occurred in 304/1718 (17.7%) patients; in the multivariable regression analysis it was significantly less frequent when the PR interval was between 150 and 170 ms (hazard ratio = 0.79, 95% confidence interval (CI): 0.63−0.99, p = 0.046). The same PR range was associated with higher probability of CRT response (odds ratio = 2.51, 95% CI: 1.41−4.47, p = 0.002). Conclusions. In a large population of CRT patients, with fixed AV pacing delays, specific PR intervals are associated with significant benefits in terms of LV reverse remodeling and lower morbidity. These observational data suggest the importance of optimizing pacing programming as a function of the PR interval to maximize CRT response and patient outcome.

Complete Percutaneous Revascularization in Patients Aged ≥85 Years With Acute Coronary Syndrome and Multivessel Coronary Artery Disease.

Multivessel coronary disease is frequent in older patients who underwent coronary angiography for acute coronary syndrome. Whether a complete revascularization or a culprit-only approach is preferable in these patients is still debated. We included consecutive patients aged ≥85 years, presenting with acute coronary syndrome and showing multivessel coronary disease at coronary angiography. Patients were grouped according to complete (residual SYNTAX score [RSS] 0 to 8) or incomplete (RSS >8) revascularization. Primary end point was the rate of major adverse cardiovascular events (MACEs, the composite of cardiovascular death, re-myocardial infarction [re-MI], clinically driven percutaneous coronary intervention, and rehospitalization because of cardiac disease) at 2 years follow-up. A total of 166 patients met the criteria for enrollment; 108 patients had a final RSS 0 to 8 (complete revascularization) and 58 patients had a final RSS >8 (incomplete revascularization). The rate of MACE was reduced in patients who underwent complete revascularization (35.2% vs 51.7%, p = 0.039, adjusted hazard ratio 0.60, 95% confidence interval 0.37 to 0.98, p = 0.04), a difference mainly driven by a reduction in re-MI (8.3% vs 19.0%, p = 0.045), clinically driven percutaneous coronary intervention (2.8% vs 19.0%, p <0.001), and rehospitalization for cardiac disease (9.3% vs 24.1%, p = 0.009). Other independent predictors of MACE were active malignancy, previous MI, left ventricle ejection fraction <35% (increasing risk of events), and radial access (reducing risk of events). In conclusion, in patients aged ≥85 years, a complete revascularization is associated with a better prognosis, especially in terms of nonfatal events.

Long-term follow-up of patients with a quadripolar active fixation left ventricular lead: An Italian multicenter experience.

INTRODUCTION: Left ventricular (LV) lead optimal positioning is one of the most important determinants of cardiac resynchronization therapy (CRT) success. LV quadripolar active fixation (QAF) leads have been designed to ensure stable LV pacing in the target area and reduce the likelihood of phrenic nerve stimulation (PNS). The aim of this analysis is to compare performances, safety, and clinical outcomes of QAF with those of quadripolar passive fixation leads (QPL) and bipolar active fixation (BAF) leads in a real-world cohort of CRT patients. METHODS AND RESULTS: This retrospective analysis compared the procedure and follow-up data of 117 QAF included in the One Hospital ClinicalService project from nine Italian hospitals with two historical cohorts of 261 BAF and 124 QPL. QAF enabled basal pacing more frequently than QPL (24.1% vs. 6.5%, p < .001) but not differently from BAF (p = .981). At implant, mean QAF LV myocardial threshold (LVMT) was 1.21 ± 0.8 V at 0.4 ms, not different from that of BAF (p = .346) and QPL (p = .333). At a median follow-up of 22 months, LVMT was 1.37 ± 0.90 V (p = .036 vs. implant). Acute LV lead dislodgment occurrence was low in all cohorts: 1 (0.9%) in QAF, 4 in BAF (1.5%), and none (0.0%) in QPL. During follow-up, total LV-related complication rate was lower in QAF (0.5/100 patient-years) than in BAF (4.2/100 patient-years, p = .014) and QPL (3.6/100 patient-years, p = .055). QAF, BAF, and QPL annual rate of heart failure hospitalization were respectively 6.1/100 patient-years, 2.5/100 patient-years (p = .081), and 3.6/100 patient-years (p = .346). CRT responders' rate in QAF was 69.9%, with no difference in comparison to BAF (p = .998) and QPL (p = .509). During follow-up, mean left ventricular ejection fraction (LVEF) of QAF increased from 31.8 ± 10.1% to 40.3 ± 10.7% (p < .001). The average degree of echocardiographic response (ΔLVEF) did not differ between QAF and other cohorts; however, LVEF CRT responder's distribution of QAF differs from those of BAF (p = .003) and QPL (p = .022), due to a higher percentage of super-responders. CONCLUSIONS: QAF with short interelectrode spacing resulted in non-inferior clinical outcomes and CRT responders' rate in comparison to BAF and QPL, while reducing complication rate during follow-up and increasing the possibilities of electronic repositioning to manage PNS or to optimize resynchronization therapy.

Chronic Kidney Disease with Mild and Mild to Moderate Reduction in Renal Function and Long-Term Recurrences of Atrial Fibrillation after Pulmonary Vein Cryoballoon Ablation.

The aim of this research was to evaluate if patients with chronic kidney disease (CKD) and mild or mild to moderate depression of renal function have an increased risk of atrial fibrillation (AF) recurrences after cryoballoon (CB) ablation. We performed a retrospective analysis of AF patients undergoing pulmonary vein isolation (PVI) by CB. The cohort was divided according to the KDIGO CKD-EPI classification into a (1) normal, (2) mildly decreased, or (3) mild to moderate reduction in estimated glomerular filtration rate (eGFR). Freedom from AF recurrences was the primary endpoint. A total of 1971 patients were included (60 ± 10 years, 29.0% females, 73.6% paroxysmal AF) in the study. Acute success and complication rates were 99.2% and 3.7%, respectively, with no significant differences among the three groups. After a follow-up of 24 months, AF recurrences were higher in the mildly and mild to moderate CKD groups compared to the normal kidney function group (23.4% vs. 28.3% vs. 33.5%, p < 0.05). Mild to moderate CKD was an independent predictor of AF recurrences after the blanking period (hazard ratio:1.38, 95% CI 1.02−1.86, p = 0.037). In conclusion, a multicenter analysis of AF patients treated with cryoablation revealed mild to moderate reductions in renal functions were associated with a higher risk of AF recurrences. Conversely, the procedural success and complication rates were similar in patients with normal, mildly reduced, or mild to moderate reduction in eGFR.

Determinants of worse prognosis in patients with cardiac resynchronization therapy defibrillators. Are ventricular arrhythmias an adjunctive risk factor?

AIMS: Cardiac resynchronization therapy (CRT) is indicated in patients with systolic heart failure (HF), severe left ventricle (LV) dysfunction and interventricular dyssynchrony.In prospective observational research, we aimed to evaluate whether CRT-induced LV reverse remodelling and occurrence of ventricular arrhythmias (VT/VF) independently contribute to prognosis in patients with CRT defibrillators (CRT-D). METHODS: In 95 Italian cardiological centres, after a screening period of 6 months, patients were categorized according to VT/VF occurrence and CRT response, defined as LV end-systolic volume relative reduction >15% or LV ejection fraction absolute increase >5%. The main endpoint was death or HF hospitalizations. RESULTS: Among 1308 CRT-D patients (80% male, mean age 66 years), at 6 months, follow-up 71% were identified as CRT responders and 12% experienced appropriate VT/VF detections. The main endpoint was significantly and independently associated with previous myocardial infarction, New York Heart Association Class, VT/VF occurrence and with CRT response. CRT nonresponder patients who suffered VT/VF in the screening period had a risk of death or HF hospitalizations [HR = 7.82, 95% confidence interval (CI) = 3.95-15.48] significantly (P < 0.001) higher than CRT responders without VT/VF occurrence. This risk is mitigated without VT/VF occurrence (HR = 3.47, 95% CI = 2.03-5.91, P < 0.001) or in case of CRT response (HR = 3.11, 95% CI = 1.44-6.72, P = 0.004). CONCLUSION: Our data show that both CRT response and occurrence of VT/VF independently contribute to the risk of death or HF-related hospitalizations in CRT-D patients. Early VT/VF occurrence may be identified as a marker of disease severity than can be mitigated by CRT response both in terms of all-cause mortality and long-term VT/VF onset. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifier: NCT00147290 and NCT00617175.

Estimate and reporting of longevity for cardiac implantable electronic devices: a proposal for standardized criteria.

BACKGROUND: Cardiac implantable electronic devices (CIEDs) are widely used according to consensus guidelines in various patient categories. The longevity of CIED is a major determinant of the frequency with which patients require device replacement. Given the mismatch between the useful life of the devices and patient survival, device replacement is often needed. There is a great variability in the criteria used by manufacturers to determine the longevity of pacemakers (PM), implantable defibrillators (ICDs), and devices for cardiac resynchronization therapy (CRT). Thus, a fair comparison and an effective device evaluation is often difficult. METHODS: The objective of this paper is to provide standardized criteria based on typical clinical settings for estimating the longevity of single and dual chamber ICDs, cardiac resynchronization defibrillators (CRT-D), single and dual chamber PMs, and cardiac resynchronization PMs (CRT- P) to be used in health technology assessment for an appropriate comparison among different devices. RESULTS: The proposed parameters, if applied to the current marketed devices, provide longevity values in the range 5-17.2 years. CONCLUSION: The values of longevity with the non-standardized criteria used by the manufacturers result in higher maximum values respect to the proposed standardized criteria for CRT-D, CRTD-MPP, CRT-P, and Dual-chamber PM.

The Practice of Deep Sedation in Electrophysiology and Cardiac Pacing Laboratories: Results of an Italian Survey Promoted by the AIAC (Italian Association of Arrhythmology and Cardiac Pacing).

The aim of this survey, which was open to all Italian cardiologists involved in arrhythmia, was to assess common practice regarding sedation and analgesia in interventional electrophysiology procedures in Italy. The survey consisted of 28 questions regarding the approach to sedation used for elective direct-current cardioversion (DCC), subcutaneous implantable cardioverter-defibrillator (S-ICD) implantation, atrial fibrillation (AF) ablation, ventricular tachycardia (VT) ablation, and transvenous lead extraction procedures. A total of 105 cardiologists from 92 Italian centres took part in the survey. The rate of centres where DCC, S-ICD implantation, AF ablation, VT ablation and lead extraction procedures were performed without anaesthesiologic assistance was 60.9%, 23.6%, 51.2%, 37.3%, and 66.7%, respectively. When these procedures were performed without anaesthesiologic assistance, the drugs (in addition to local anaesthetics) commonly administered were benzodiazepines (from 64.3% to 79.6%), opioids (from 74.4% to 88.1%), and general anaesthetics (from 7.1% to 30.4%). Twenty-three (21.9%) of the 105 cardiologists declared that they routinely administered propofol, without the supervision of an anaesthesiologist, in at least one of the above-mentioned procedures. In current Italian clinical practice, there is a lack of uniformity in the sedation/analgesia approach used in interventional electrophysiology procedures.

[2019 Catheter Ablation Registry of the Italian Association of Arrhythmology and Cardiac Pacing]. / Registro Italiano Ablazioni 2019. Associazione Italiana di Aritmologia e Cardiostimolazione.

BACKGROUND: This report describes the findings of the 2019 Italian Catheter Ablation Registry of the Italian Association of Arrhythmology and Cardiac Pacing (AIAC). METHODS: Data collection was retrospective. A standardized questionnaire was completed by each of the participating centers. RESULTS: A total of 15 201 ablation procedures were performed by 91 institutions. Most (78%) of the centers has one electrophysiology laboratory, and 17% of them has a hybrid cardiac surgery laboratory. Almost all (98%) centers have a 3D mapping system. The median number of electrophysiologists and nurses involved in the electrophysiology laboratory was 3 and an electrophysiology technician was involved in 30% of all centers. In 88.4% of cases, ablations were performed for supraventricular arrhythmias, and among these the most frequently treated arrhythmia was atrial fibrillation (32.9%), followed by atrioventricular nodal reentrant tachycardia (23.9%), and common atrial flutter (11.7%). In 10 256 (67.4%) patients catheter ablation was performed by means of a 3D mapping system, with a "near-zero" fluoroscopic approach in 4626 (30.4%) of all patients. CONCLUSIONS: The 2019 Italian Catheter Ablation Registry confirmed that atrial fibrillation is the most commonly treated arrhythmia in the ablation centers with an increasing number of procedures performed with a 3D mapping system and a "near-zero" approach.

Arrhythmic manifestation in ß-thalassemia cardiomyopathy: a complex management.

A young male with ß-thalassemia major was implanted with a single-chamber Implantable cardioverter-defibrillator (ICD) for a cardiac arrest due to ventricular fibrillation. He received multiple inappropriate shocks due to atrioventricular nodal re-entrant tachycardia (AVNRT) treated with radiofrequency catheter ablation and then to high-rate atrial tachycardia refractory to amiodarone and not inducible during electrophysiological study. He refused empirical pulmonary vein isolation. Upgrading to biventricular ICD and performing atrioventricular node ablation avoided further inappropriate shocks.

AV junction ablation and cardiac resynchronization for patients with permanent atrial fibrillation and narrow QRS: the APAF-CRT mortality trial.

AIMS: In patients with atrial fibrillation (AF) and heart failure (HF), strict and regular rate control with atrioventricular junction ablation and biventricular pacemaker (Ablation + CRT) has been shown to be superior to pharmacological rate control in reducing HF hospitalizations. However, whether it also improves survival is unknown. METHODS AND RESULTS: In this international, open-label, blinded outcome trial, we randomly assigned patients with severely symptomatic permanent AF >6 months, narrow QRS (≤110 ms) and at least one HF hospitalization in the previous year to Ablation + CRT or to pharmacological rate control. We hypothesized that Ablation + CRT is superior in reducing the primary endpoint of all-cause mortality. A total of 133 patients were randomized. The mean age was 73 ± 10 years, and 62 (47%) were females. The trial was stopped for efficacy at interim analysis after a median of 29 months of follow-up per patient. The primary endpoint occurred in 7 patients (11%) in the Ablation + CRT arm and in 20 patients (29%) in the Drug arm [hazard ratio (HR) 0.26, 95% confidence interval (CI) 0.10-0.65; P = 0.004]. The estimated death rates at 2 years were 5% and 21%, respectively; at 4 years, 14% and 41%. The benefit of Ablation + CRT of all-cause mortality was similar in patients with ejection fraction (EF) ≤35% and in those with >35%. The secondary endpoint combining all-cause mortality or HF hospitalization was significantly lower in the Ablation + CRT arm [18 (29%) vs. 36 (51%); HR 0.40, 95% CI 0.22-0.73; P = 0.002]. CONCLUSIONS: Ablation + CRT was superior to pharmacological therapy in reducing mortality in patients with permanent AF and narrow QRS who were hospitalized for HF, irrespective of their baseline EF. STUDY REGISTRATION: ClinicalTrials.gov Identifier: NCT02137187.

Ventricular activation patterns during intrinsic conduction and right ventricular pacing in cardiac resynchronization therapy patients.

BACKGROUND: Cardiac resynchronization therapy (CRT) involves stimulation of both right ventricle (RV) and left ventricle (LV). LV pacing from the sites of delayed electrical activation improves CRT response. The RV-LV conduction is typically measured in intrinsic rhythm. The differences in RV-LV conduction patterns and timing between intrinsic rhythm and during paced RV activation, these differences are not fully understood. METHODS: Enrolled patients were implanted with a de novo CRT device and quadripolar LV lead, with lead implant locations at the implanting physician's discretion. QRS duration and conduction delay between the RV lead and each of the four LV electrodes (D1, M2, M3, and P4) were measured during intrinsic conduction and RV pacing. RESULTS: Conduction measurements were collected from 275 patients across 14 international centers (68 ± 13 years of age, 73% male, 45% ischemic, 158 ± 22 ms QRS duration). Mean RV-LV conduction time was shorter during intrinsic conduction versus RV pacing by 59.6 ms (106.5 ± 36.5 versus 166.1 ± 32.1 ms, p < 0.001). The intra-LV activation delay between the latest and earliest activating LV electrode was also shorter during intrinsic conduction versus RV pacing by 6.6 ms (20.6 ± 13.1 vs. 27.2 ± 21.2 ms, p < 0.001). Intrinsic conduction and RV pacing resulted in a different activation order in 72.7% of patients, and the same LV activation order in 27.3%. CONCLUSIONS: Differences in RV-LV conduction time, intra-LV conduction time, and activation pattern were observed between intrinsic conduction and RV pacing. These findings highlight the importance of evaluating intrinsic versus paced ventricular activation to guide LV pacing site selection in CRT patients.

Organization and procedures in contemporary catheter ablation centres: data from the 2018 Italian Catheter Ablation Registry.

AIMS: This report describes the findings of the 2018 Italian Catheter Ablation Registry of the Italian Association of Arrhythmology and Cardiac Pacing (AIAC). METHODS: The Italian Catheter Ablation Registry systematically collects data on the ablation procedures performed in Italy. Data collection was retrospective. A standardized questionnaire was completed by participating centres. RESULTS: We collected data on 15 714 catheter ablation procedures performed in Italy during 2018 in 94 electrophysiology centres. In most centres (75/94, 80%), a single electrophysiology laboratory was available, and a hybrid electrophysiology laboratory was available in 15% (14/94) of centres. In most (93%) centres, at least two electrophysiologists were involved in the catheter ablation procedures. In only 13 out of 94 (14%) electrophysiology laboratories, an anaesthesiologist assists every electrophysiology procedure; in most cases (74/94, 79%), an on-demand anaesthesiology service was available. On-site cardiothoracic surgery was reported in 43 out of 94 (46%) centres.Nonfluoroscopic navigation systems were available in most centres (88/94, 93%). Intracardiac echocardiography was used in 59 out of 94 (63%) electrophysiology laboratories. Atrial fibrillation (31%) was the most frequently treated ablation target, followed by atrioventricular nodal re-entrant tachycardia (20%) and cavo-tricuspid isthmus (15%). In 61.7% of all procedures, a 3D mapping system was used. In about one-third of procedures, a near-zero approach was performed. CONCLUSION: In most Italian electrophysiology centres, a single electrophysiology laboratory was available and at least two electrophysiologists were involved in the ablation procedures. An increasing number of procedures were performed by means of a nonfluoroscopic mapping system with a near-zero approach.

Is 40 Joules Enough to Successfully Defibrillate With Subcutaneous Implantable Cardioverter-Defibrillators?

OBJECTIVES: This study evaluated the efficacy of conversion test performed at 40 J (defibrillation margin ≥40 J), and factors potentially associated with test failure were identified. BACKGROUND: Current subcutaneous implantable cardioverter-defibrillator (S-ICD) devices deliver a maximum of 80 J. Functional defibrillation testing is recommended at S-ICD implantation, and it is usually conducted by delivering a shock energy of 65 J to ensure a safety defibrillation margin ≥15 J. Although high rates of successful conversion were reported at 65 J, limited data exist on the defibrillation margin extent. METHODS: Ventricular fibrillation was induced and conversion test was performed by delivering a 40-J shock in 308 patients. Success was defined as termination of ventricular fibrillation by the first shock delivered in standard polarity. The S-ICD system positioning was evaluated with the PRAETORIAN score using bidirectional chest X-rays. RESULTS: The generator was positioned in an intermuscular pocket in 301 patients (98%) and the lead was implanted by means of a 2-incision technique. The PRAETORIAN score was <90 (low risk of conversion failure) in 293 (95%) patients. Overall, ventricular fibrillation termination occurred in 259 (84%) patients with 40 J. Male gender (odds ratio [OR]: 3.79; 95% confidence interval [CI]: 1.09 to 13.14; p = 0.036), body mass index (OR: 1.09; 95% CI: 1.01 to 1.19; p = 0.036), dilated cardiomyopathy with reduced ejection fraction (OR: 0.42; 95% CI: 0.20 to 0.87; p = 0.019), and PRAETORIAN score >50 (OR: 2.93; 95% CI: 1.26 to 6.83; p = 0.013) were independently associated with conversion failure. CONCLUSIONS: The authors showed a high rate of defibrillation success with 40-J shocks in S-ICD systems implanted by means of modern surgical techniques. The variables associated with shock failure were male gender, higher body mass index, and suboptimal device position according to the PRAETORIAN score.