BACKGROUND:Conduction system pacing (CSP) is safe and feasible in congenital heart disease (CHD), but long-term follow-up data remain scarce. OBJECTIVE:This study aimed to evaluate the long-term performance of CSP in patients with CHD. METHODS:This retrospective, multicenter, international study included patients with CHD undergoing CSP-His bundle pacing or left bundle branch area pacing (LBBAP)-with ≥12-month follow-up. The primary endpoint was survival free from CSP lead-related complications (loss of conduction system capture, pacing threshold ≥2.5 V or a ≥2.0 V increase, or lead reintervention). Secondary endpoints included implant success, electrical and echocardiographic outcomes, and clinical status. RESULTS:144 patients were included (88% moderate/complex CHD; 26% systemic right ventricle; 24% with cardiac resynchronization therapy indication), with 29 His bundle pacing and 115 LBBAP. Acute implant success was 95.1%. Over a median follow-up of 32.2 months (interquartile range 18.2-47.1), survival free from CSP lead-related complications was 0.89, with 88% of CSP lead-related events occurring beyond 12 months of follow-up. Device-related complications occurred in 11.8%, and reinterventions in 5.1%. Microdislodgement (14.6%), threshold increase (6.9%), and loss of conduction system capture (5.6%) were less frequent with LBBAP. Left ventricular ejection fraction improved in patients with systemic left ventricle, whereas patients with a systemic right ventricle preserved fractional area change. Among patients with cardiac resynchronization therapy indications, systemic ventricular function improved from 34% ± 10% to 41% ± 13% (P < .001). CONCLUSION:CSP is feasible across a broad spectrum of CHD and is associated with preservation or improvement of systemic ventricular function. Late lead-related complications are not negligible, underscoring the need for long-term follow-up.

Aims Patients with persistent atrial fibrillation (AF) and heart failure (HF) have compromised clinical outcomes. Contemporary management includes rhythm control with AF ablation, or rate control and regularization with conduction system pacing and atrioventricular nodal ablation (CSP + AVNA). These strategies have never been compared in a randomized clinical trial. The study aims to determine whether CSP + AVNA is superior to AF ablation for reducing all-cause mortality and cardiovascular hospitalization, and noninferior with respect to all-cause mortality and heart failure hospitalization. Methods and results ABACUS is a multicentre, investigator-initiated, randomized controlled trial enrolling 220 patients with persistent AF and HF, aged >60 years, who are eligible for both treatment modalities, with at most one previous AF ablation procedure. Participants will be randomized 1:1 to either catheter ablation of AF (with pulmonary vein isolation using any routine technique) or to CSP + AVNA. All patients will undergo at least one year of follow-up. The co-primary endpoints will be tested sequentially. A number of predefined secondary endpoints, including costs, will also be evaluated. Discussion ABACUS compares CSP + AVNA with AF ablation in patients with persistent AF and HF. The results will provide evidence to improve care in this vulnerable patient population.

AIMS:Conduction system pacing (CSP) has emerged as a physiologic alternative to cardiac resynchronization therapy (CRT) with biventricular pacing (BiVP) in heart failure with reduced ejection fraction (HFrEF), yet its comparative effects remain uncertain. This meta-analysis sought to compare outcomes of CSP vs. BiVP in patients with HFrEF undergoing CRT. METHODS AND RESULTS:MEDLINE, Embase, Scopus, and the Cochrane Database were searched through 4 May 2026. Randomized controlled trials (RCTs) were synthesized using random-effects meta-analysis. Thirteen RCTs including 1320 participants were analysed (657 CSP, 663 BiVP). Conduction system pacing was associated with a lower risk of the composite of hospitalization for heart failure (HHF) or all-cause mortality compared with BiVP (46 vs. 83 events; odds ratio [OR] 0.51, 95% confidence interval [CI] 0.28-0.93). No significant differences were observed for HHF alone (OR 0.68, 95% CI 0.36-1.27) or all-cause mortality (OR 0.75, 95% CI 0.36-1.58). Conduction system pacing was associated with greater improvement in the 6-min walk distance (mean difference [MD] 21.53 m, 95% CI 4.33-38.73) and New York Heart Association functional class (standardized mean difference [SMD] -0.27, 95% CI -0.47 to -0.07), but not quality of life. Conduction system pacing also reduced QRS duration compared with BiVP (MD -10.94 ms, 95% CI -17.55 to -4.34), with no significant differences in left ventricular ejection fraction, left ventricular end-systolic volume, overall pacing threshold, total procedure time, fluoroscopy time, any complication, or reintervention. CONCLUSION:In patients with HFrEF undergoing CRT, CSP is associated with lower composite risk of HHF or all-cause mortality compared with BiVP. Conduction system pacing is also associated with improved functional capacity, without significant differences in safety or procedural outcomes.

BACKGROUND AND AIMS:Left bundle branch area pacing (LBBAP) promotes physiological synchronous activation of the left ventricle and may be particularly beneficial in patients with atrioventricular block (AVB), but its mortality benefit remains unclear. This study aims to compare long-term survival in AVB patients receiving either LBBAP or right ventricular pacing (RVP) and to analyse predictors of mortality during LBBAP. METHODS:MELOS RELOADED, a multicentre European collaboration, was a registry-based study of pacemaker patients with AVB, left ventricular ejection fraction (LVEF) >40% and ventricular pacing >20%. The primary outcome was all-cause mortality based on national registries. A 1:1 propensity score matching was performed between the RVP and LBBAP groups. Kaplan-Meier curves and multivariable Cox proportional hazards models were used to estimate survival. RESULTS:In total, 3382 patients receiving LBBAP or RVP were matched. At 4-year follow-up, the Kaplan-Meier curve showed an absolute difference in survival of 11.8% in favour of LBBAP (P < .001). LBBAP was a robust predictor of reduced mortality with a hazard ratio (HR) of 0.53 (95% confidence interval 0.42-0.65, P < .001). Within the LBBAP group, the following independent predictors of increased mortality were identified: lack of confirmed left bundle branch capture (HR 1.85, P < .001), lower percentage of ventricular pacing (HR 1.12), and age. CONCLUSIONS:This is the first large study demonstrating the long-term survival benefit of LBBAP. This strengthens the use of LBBAP in AVB patients with preserved/mildly reduced LVEF while awaiting the results of randomized trials. Confirmation of left bundle branch capture seems advisable to achieve optimal results with LBBAP.

Left bundle branch area pacing is being increasingly adopted in routine clinical practice as a more physiological alternative to right ventricular and biventricular pacing. Understanding the concepts of this pacing modality may be a hurdle for the non-electrophysiologist and specialists alike. This review article aims to explain in a didactic manner the anatomical and electrophysiological principles underlying left bundle branch area pacing.

BACKGROUND:Fibrosis within the interventricular septum hinders the implantation of left bundle branch pacing (LBBP) lead, particularly in candidates for cardiac resynchronization therapy (CRT). OBJECTIVE:This study aimed to report the acute and follow-up outcomes of pacing lead implantation using radiofrequency (RF) current delivered to the lead tip for septal electrosection in challenging LBBP cases. METHODS:Data on lead deployment success, RF power and delivery time, complications, lead stability, proarrhythmia, current of injury, and pacing parameters were collected acutely and at the final follow-up. RESULTS:A total of 37 RF-facilitated lead implantations in 36 patients (average age 71.6 ± 8.8 years), most of whom were CRT eligible (89%), were analyzed. On average, 2.1 ± 1.7 RF applications (resulting in 2.6 ± 2.2 seconds of RF) were used per implantation with a median power of 27 W. RF delivery was used in 85.7% of cases to achieve a current of injury drop that could not be obtained with manual lead rotation alone. Lead implantation was successful in all but 2 cases. The mean follow-up duration was 236 ± 165 days. Lead performance, including pacing parameters and lead stability, was good and did not seem to be affected by RF use (follow-up threshold 0.8 ± 0.3 V; sensitivity: 12.0 ± 5.6 mV). 1 patient experienced sustained ventricular tachycardia, and in all other cases, proarrhythmia was absent or self-limited. No other complications were noted. CONCLUSION:RF-facilitated LBBP lead implantation is a feasible technique with potential cautious use as a bailout in selected cases, especially for failed CRT delivery.

Arrhythmic sudden cardiac death (SCD) remains a major cause of late mortality in adults with congenital heart disease (ACHD), second only to heart failure. Risk prediction is challenging due to the heterogeneity of underlying defects and surgical histories. This review summarizes contemporary evidence on arrhythmic SCD prevention in ACHD, focusing on lesion-specific risk stratification, device-based therapies, and emerging technologies. Traditional markers-ventricular dysfunction, QRS prolongation, and prior arrhythmias-show limited predictive value. Recent models such as PREVENTION-ACHD and the Spanish ACHD Network score offer structured but evolving approaches to individualized risk assessment. Cardiac MRI-derived fibrosis quantification, electro-anatomical mapping, and machine-learning-based tools hold promise for refined prediction. Implantable cardioverter-defibrillators (ICDs) remain the cornerstone of secondary prevention, while subcutaneous ICDs and emerging extravascular systems mitigate lead-related complications. The wearable cardioverter-defibrillator offers a temporary protective option in high-risk patients awaiting definitive therapy. Catheter ablation-particularly in repaired Tetralogy of Fallot-can modify arrhythmic substrates, whereas bradyarrhythmias require vigilant monitoring and timely pacing interventions. In conclusion, effective prevention of arrhythmic SCD in ACHD demands a multidisciplinary, lesion-specific approach integrating advanced imaging, device innovation, and personalized risk modelling. Ongoing refinement of predictive tools and interventional strategies will be crucial to reduce mortality in this growing population.

BACKGROUND:Left bundle branch area defibrillation (LBBAD) therapy is currently an off-label procedure. Nevertheless, it is a promising technique that reduces the number of leads in implantable cardioverter-defibrillator patients who require conduction system pacing. OBJECTIVE:This study aimed to collect real-world data on LBBAD implantation and follow-up. METHODS:Retrospective periprocedural and follow-up data on electrocardiographic and electrical parameters, transthoracic echocardiography data, and clinical outcome were assembled from 12 international centers. RESULTS:In total, 163 patients (age 67 ± 12 years; 137 males) were included. Implantation success rate was 88%. Defibrillation testing was performed in 85 patients and was effective in all cases. Paced unipolar QRS duration was 125 ms (119-135) with a V6 R-wave peak time of 76 ms (70-85) and a V6-V1 interpeak interval of 44 ms (45-54). Capture threshold was 0.8 V/0.4 ms (0.5-1.1), sensing amplitude was 9.0 mV (6.2-12), and pacing and high-voltage impedances were 580 Ω (493-650) and 66 Ω (60-75). Electrical parameters remained favorable over a follow-up of 8 months (3-13). Left ventricular ejection fraction improved from 30% (26%-35%) to 36% (31%-46%) at the last follow-up (P < .001). A total of 13 appropriate and effective shocks were documented, affecting 8 patients (4.9%). No ineffective shocks were reported. 2 LBBAD leads were explanted more than 1 year after implantation without any complication. No deaths were related to LBBAD. CONCLUSION:LBBAD with standard stylet-driven lead is safe and feasible, with stable electrical, electrocardiographic, and echocardiographic parameters at midterm follow-up.

BACKGROUND AND AIMS:Conduction system pacing has emerged as an alternative to biventricular pacing (BiVP) for cardiac resynchronization therapy (CRT). The left-bundle CRT trial evaluated whether left-bundle branch area pacing (LBBAP) is non-inferior to BiVP in patients eligible for CRT. METHODS:The left-bundle CRT trial was a multi-centre, randomized, investigator-initiated, and non-inferiority study. Patients with guideline-based CRT indications and left-bundle branch block per Strauss criteria were randomized to BiVP-CRT or LBBAP-CRT. The primary endpoint was the proportion of patients with a positive CRT response at 6-months, defined as either an improved clinical composite score (CCS) or a ≥15% reduction in left ventricular end-systolic volume. The non-inferiority margin was the lower bound of the 95% confidence interval (CI) and was set at 10%. Patients were followed for 12-months; secondary endpoints included echocardiographic, clinical, and quality-of-life outcomes. RESULTS:The baseline characteristics of the 176 patients randomized to BiVP-CRT (n=84) or LBBAP-CRT (n=92) were similar, except for a wider intrinsic QRS in the LBBAP group: median 172 ms [IQR 158-184] vs. 165 ms [152-180]; P=0.04. Crossovers occurred in 26 patients (14.9%). In the intention-to-treat analysis, the primary endpoint was achieved in 94.6% of BiVP-CRT and 89.7% of LBBAP-CRT patients (RR 0.95; 95% CI 0.88-1.02), not meeting non-inferiority. CCS improved in 77% and 68% of patients randomized to BiVP-CRT and LBBAP-CRT, respectively and 85% and 79% had a ≥15% reduction in left ventricular end-systolic volume. Rates of adverse events and heart failure hospitalization were similar between groups. CONCLUSIONS:In CRT candidates with typical LBBB, LBBAP-CRT was not shown to be non-inferior to BiVP-CRT. Both strategies yielded high response rates and similar clinical outcomes.

BACKGROUND:Ultra-high-frequency electrocardiogram (UHF-ECG) which visualizes electrical ventricular dyssynchrony may be a valuable tool for improving the selection and treatment of patients with indication to cardiac resynchronization therapy (CRT). OBJECTIVE:This study aimed to compare non-invasive assessment of left ventricular (LV) delay using UHF-ECG with invasive QLV in CRT candidates, and to evaluate whether UHF-ECG can identify patients who will achieve resynchronization and LV reverse remodeling after biventricular CRT. METHODS:Consecutive patients undergoing CRT at 2 centers were included. QLV was measured in basal, midventricular, and apical LV segment. UHF-ECG LV delay was measured from QRS onset to local activation in leads V5-V8. Global LV dyssynchrony (lv-DYS) was assessed during spontaneous rhythm and pacing from the earliest activation to the latest activation in leads V5-V8 and was used to identify CRT responders. RESULTS:48 patients were included (75% male, age 67 ± 12 years, LV ejection fraction 31 ± 6%, QRSd 167 ± 20 ms). UHF-ECG in V8, V7, and V6 did not differ from QLV in the basal, midventricular, or apical segments (mean differences: 3 ± 14 ms, P = .52; -3 ± 17 ms, P = .18 and 0 ± 17 ms, P = .92) and strong correlation was observed between them (r = 0.84, P < .001). The lv-DYS strongly correlated with the longest QLV (r = 0.76, P < .001). Patients with baseline lv-DYS >58 ms showed a more significant reduction in lv-DYS and were more often responders to CRT than patients with shorter values (Δlv-DYS -70 ms vs -8 ms, and responders 97% vs 32%). CONCLUSION:UHF-ECG enables non-invasive assessment of QLV and can help with identification of patients who will benefit from CRT.

BACKGROUND:Conduction system pacing (CSP) remains technically challenging because intentional targeting of proximal conduction structures, such as the distal His bundle and proximal left bundle branch (LBB) trunk, is difficult using current implantation techniques. OBJECTIVE:We evaluated a novel computed tomography angiography (CTA)-guided workflow designed to facilitate patient-specific targeting of these structures. METHODS:Conduction-guided intervention (CGI) integrates preprocedural cardiac CTA with patient-specific conduction system reconstruction and real-time fluoroscopic overlay. In this first-in-human prospective study, 40 consecutive patients undergoing CSP were enrolled. Procedural success was defined as implantation at a proximal conduction system target according to predefined anatomical and electrophysiological criteria. Clinical success required proximal conduction system capture with QRS correction at working output. RESULTS:Procedural success was achieved in 38/40 patients (95%). CTA analysis demonstrated substantial inter-individual variability in proximal conduction system anatomy, with marked differences in distances and trajectories along the AVN-His axis between patients. Distal His pacing according to predefined procedural criteria was initially achieved in 26 patients (65%). However, transition to proximal LBB trunk pacing was required in 12 patients because of inadequate QRS correction and/or unfavorable pacing thresholds. Final adjudicated pacing sites included distal His pacing in 14 patients (35%) and proximal LBB trunk pacing in 22 patients (55%), resulting in proximal conduction system pacing in 36/40 patients (clinical success 90%). CONCLUSION:CTA-guided conduction system mapping was feasible and enabled intentional targeting of proximal conduction structures in most patients. Integration of patient-specific anatomical information may complement conventional fluoroscopic and electrophysiological guidance during CSP implantation.

Atrial fibrillation (AF) is sustained by fast driver regions with short atrial fibrillation cycle lengths (AFCL). Successful ablation strategies progressively increase atrial cycle lengths, leading to AF termination. Pulse Field Ablation (PFA) is a promising treatment that achieves targeted substrate modification by disrupting these drivers. Imageless Electrocardiographic Imaging (ECGI) provides a non-invasive, panoramic view of cardiac electrical activity, enabling a real-time assessment of AF substrate modification through AFCL mapping across the atria. This study aims to assess substrate modification in persistent AF patients using ECGI to monitor AFCL before and after the PFA procedure, evaluating its effectiveness in disrupting AF substrates. Seventeen patients (65.4±8.5 years, 10 males) with persistent AF underwent a PFA procedure targeting pulmonary veins (PPV) and the posterior left atrial wall. Imageless ECGI was performed using a 128-electrode vest placed on each patient’s torso and a 3D body surface reconstruction. One-minute ECGI solution segments were selected pre- and post-ablation. In pre-ablation segments, AFCL distributions were tracked on each 4s segment to identify regions with high (dominant) and low (non-dominant) recurrence of short cycle length (Figure 1A), which were then re-evaluated post-ablation to assess substrate changes. Statistical analysis was used to determine the significance of AFCL changes within identified areas, providing insights into the effectiveness of PFA in disrupting AF substrates. ECGI mapping provided a detailed panoramic visualization of AFCL distributions. Isolation of the pulmonary veins and the posterior wall was associated with a general increment in AFCL across the atria. Non-dominant areas identified pre-ablation showed an AFCL increase of 25±14 ms, while dominant regions exhibited a more pronounced AFCL enlargement of 38±14 ms post-ablation. The percentage of increase in AFCL was more significant in dominant areas compared to non-dominant areas (24±9.2 % vs. 14.2±7.3 %, p=0.001), suggesting that PFA effectively alters AF-driving substrates. Non-invasive ECGI mapping could be an effective tool for assessing substrate modification during AF treatment with PFA. By enabling detailed visualization and tracking of cycle length changes across atrial regions, ECGI identified a significant post-ablation increase in AFCL, particularly in recurrent dominant areas. These insights underscore the potential of ECGI to enhance patient-specific ablation strategies and improve treatment outcomes in persistent AF.

BACKGROUND:Radiofrequency (RF) ablation is the technique of choice for treating ventricular tachycardias in ischemic cardiomyopathy. However, recent experimental studies have found it to be ineffective. Poor heat transmission in collagen-rich scar tissue was 1 of the explanations given, even though the thermal properties of infarcted tissue have never been studied. OBJECTIVES:The purpose of the present study was to measure the thermal properties of chronically infarcted myocardium. METHODS:A total of 5 freshly explanted human hearts from patients undergoing heart transplantation with previous chronic myocardial infarction were studied in the operating room. A 2-needle thermal sensor model SH-3 Tempos (Meter Group) was introduced into different infarcted and healthy areas in the left ventricle to measure the thermal conductivity, volumetric heat capacity, and thermal diffusivity. All the measured areas were excised for histological analysis. An in silico model of radiofrequency catheter ablation was then built to evaluate the impact of the thermal parameters obtained. Stiffness, electrical properties, and vascularization were also included to simulate realistic healthy and infarcted myocardium according to previously published data. RESULTS:More than one-half of the area of the infarcted samples was composed of collagen. No significant differences were found between the thermal properties of infarcted and healthy tissue. The RF lesion depths obtained from the computational model did not have any clinically relevant differences (<0.4 mm in depth) between the infarcted and healthy tissue. CONCLUSIONS:Thermal properties of infarcted tissue are not sufficiently different from healthy tissue to justify different RF lesion sizes, according to our computational model.

Pulmonary vein isolation is the best option in most cases for the treatment of atrial fibrillation (AF) due to its clinical and prognostic results. Pulse Field Ablation (PFA) ablation is a proven method with results comparable and even superior in some respects to other energy sources. There are scenarios in which its advantages have not yet been validated by clinical trials, such as in the approach to left flutter, where ablation of substrates other than the pulmonary veins, such as the mitral isthmus (MI), is required. Achieving lateral MI block is technically complex and requires prolonged radiofrequency ablations and often a coronary sinus approach or alcohol ablation of the Marshall vein. The aim is to analyze the initial experience of our center in terms of intraprocedural success, efficacy and safety of PFA in MI ablation in patients with AF and perimitral flutter, compared to radiofrequency. We present a retrospective descriptive study with a consecutive sample of 55 patients ablated for previous AF who underwent a new AF ablation procedure and/or atypical flutter in which mitral isthmus ablation was performed, in them18 by electroporation and in 37 by radiofrequency. The cases were collected from July 2023 to July 2024. We analyzed the baseline characteristics of the patients, the success of the procedure, complication rate, and efficacy at 1 year. Both groups were comparable, with baseline characteristics without significant differences (except for more dyslipidemia in the radiofrequency group). In the group of patients ablated with electroporation, there was a tendency for a higher percentage of patients with persistent arrhythmia (70.5% vs 54.1%). There was a single complication in the radiofrequency group, mitral isthmus block was observed in 94% of cases in both groups, and the electroporation group showed a tendency to have fewer reconnected pulmonary veins (33% vs 56%). The percentage of patients who presented arrhythmic recurrence in the first year was 40.5% in the radiofrequency group vs 23% in the electroporation group, with a p-value of 0.056. In our initial experience, electroporation is a safe, simple and effective method for acutely achieving endocardial MI blockade, which is why we consider it comparable to radiofrequency and even advantageous in some scenarios.

Conduction system pacing (CSP) is being increasingly adopted as a more physiological alternative to right ventricular and biventricular pacing. Since the 2021 European Society of Cardiology pacing guidelines, there has been growing evidence that this therapy is safe and effective. Furthermore, left bundle branch area pacing was not covered in these guidelines due to limited evidence at that time. This Clinical Consensus Statement provides advice on indications for CSP, taking into account the significant evolution in this domain.