Heart Rhythm

BackgroundThe Aveir leadless pacemaker employs an active fixation method, enabling real-time monitoring of electrical parameters during implantation. However, comprehensive studies regarding the electrical parameters during this procedure are rare. ObjectiveThis study aims to analyze the electrical characteristics to further guide the implantation strategy and improve device stability and safety. MethodsThis multi-center retrospective study enrolled 119 patients (mean age 70.18 years; 59.58% female) who received the Aveir VR leadless pacemaker from November 2024 to May 2025 across ten centers in China. Intraprocedural variations in commanded electrogram (CEGM), current of injury (COI), impedance, pacing threshold, and sensing parameters were meticulously documented. ResultsCEGM mapping demonstrated various morphologies (R, RS, QR, QRS, and QS) aiding localization. During fixation, 58.82% of patients exhibited an increased COI from mapping to 0.5 turns, which was associated with reduced short-term pacing thresholds. From 0.5 to 1 turn, 52.94% showed further COI increases. ROC analysis revealed that an impedance increase has predictive value for short-term pacing thresholds, with an AUC of 0.634 and a cut-off value of 230 {Omega} (sensitivity 0.622, specificity 0.41). Lead stability showed a moderate correlation with impedance increase ({rho}=0.44, P<0.001), while the correlation with COI was weak. ConclusionDuring Aveir implantation, CEGM variations guide site localization. Initial COI increases (0-0.5 turns) are linked to optimal short-term thresholds. Monitoring impedance increase is vital, as a threshold of 230 {Omega} serves as a key indicator of device stability and fixation quality.

BackgroundDuring atypical atrioventricular nodal reentrant tachycardia (AVNRT), the earliest atrial activation site following retrograde slow pathway (SP) conduction is at the atrial exit of the left inferior extension of the compact node (LIE) in the coronary sinus (CS) or the right inferior extension (RIE) on the tricuspid annulus (TA). We tested the validity of conventional electrode placement-based mapping of the atrial ends of these extensions. MethodsWe retrospectively evaluated the efficiency of the two catheter (His bundle and CS) mapping method for localization of LIE and RIE in atypical AVNRT patient using electroanatomical 3D mapping validation. ResultsAmong 19 atypical AVNRTs (15 fast/slow and 4 slow/slow) in 14 patients (9 females, age 59{+/-}17), 8 AVNRTs had LIE involvement and 11 had RIE. The 8 LIE exits were inside the CS, and localization by 3D mapping and CS electrode catheter matched in all. In contrast, RIE exits were on the posterior TA where electrode catheters are conventionally not placed. All RIE exits required 3D mapping for accurate localization. During retrograde RIE conduction, comparison of the activation time of the CS ostium and HBE showed that the CS ostium was earlier in 7 RIEs, HBE was earlier in 1, and they were simultaneous in 3, resulting in the presence of RIE being missed in 4/11 (36%) AVNRTs using current diagnostic criteria. Activation time of the CS ostium and His bundle were determined by their relative closeness to the RIE exit. ConclusionsConventionally placed electrode catheter mapping in atypical AVNRT was able to identify 100% of LIE, but only 64% of RIE. It is critical to place a catheter on or use a 3D mapping system for the posterior TA in cases of suspected atypical AVNRT, so that all inferior extensions of the AV node can be identified and targeted for treatment.

BACKGROUNDThe short-term safety, feasibility, and performance of the Medtronic SelectSecure 3830-69 cm pacing lead for conduction system pacing (CSP) has been reported; however, its longer-term performance is not well established. OBJECTIVEThe purpose of this study is to examine the long-term performance of the 3830 lead for His Bundle Pacing (HBP) and Left Bundle Branch Area Pacing (LBBAP). METHODSWe retrospectively reviewed all cases of CSP performed with the Medtronic SelectSecure 3830-69 cm pacing lead at Cleveland Clinic Florida between May 2016 and October 2021. RESULTSOf 515 attempts, HBP achieved an 85% success rate (340 cases), while LBBAP demonstrated a higher success rate of 97.4% (150 cases). The mean follow-up was 28 months for HBP and 14 months for LBBAP, with patient ages averaging 75 and 77 years, respectively. Only 7% of the cohort had an ejection fraction below 50%. The primary indications for HBP were sick sinus syndrome (35.5%), atrioventricular block (35.2%), cardiac resynchronization therapy (10%), and refractory atrial fibrillation (18.8%), with similar distributions for LBBAP. The HBP groups capture threshold at implant was 1.3 {+/-} 0.8 V at 0.8 {+/-} 0.2 ms, which significantly increased at chronic follow-up to 1.68 {+/-} 1.3 V at 0.7 {+/-} 0.3 ms (p <0.001), whereas the LBBAP groups capture threshold remained stable from 0.8 {+/-} 0.5 V at 0.5 {+/-} 0.3 ms to to 0.9 {+/-} 0.5 V at 0.5 {+/-} 0.3 ms, (p= 0.35). Lead revisions were more common in the HBP group (50 cases) than in the LBBAP group (5 cases), with exit block rates of 11.7% and 3%, respectively. CONCLUSIONUsing the 3830 lead for HBP can result in significantly elevated thresholds, loss of His-bundle capture, and frequent lead revision rates at long-term follow-up. These issues are less commonly seen when the lead is used for LBBAP.

BackgroundThe ventricular tachycardia (VT) substrate map is influenced by the rhythm during mapping. This study aimed to elucidate the effects of different pacing sites on substrate mapping using decrement-evoked potential (DEEP) mapping in patients with scar-related VT. MethodsPatients with ischemic cardiomyopathy (ICM) or nonischemic cardiomyopathy (NICM) who underwent substrate mapping and ablation for scar-related VT were included. DEEP mapping was performed during right ventricular apex (RVA) and left ventricular outflow tract (LVOT) pacing. We analyzed the number, location, shape, and timing of lines of conduction block (LOB) using substrate maps obtained during RVA and LVOT pacing. ResultsA total of 19 patients (mean age, 62.7 {+/-} 16.6 years; 17 males; 10 with ICM and 9 with NICM) were studied. DEEP mapping during RVA and LVOT pacing was performed in 16 patients. The number of pacemap-matching LOBs identified from the RVA S1, RVA S2, LVOT S1, and LVOT S2 maps were 0.61 {+/-} 0.70, 1.24 {+/-} 1.09, 1.00 {+/-} 0.85, and 1.50 {+/-} 1.17, respectively. The number of final pacemap-matching LOBs was 1.58 {+/-} 1.07. Two LOBs were visible only during RVA pacing because they were parallel to the conduction direction. Six LOBs were visible only during LVOT pacing--five LOBs were parallel to the conduction direction, and one LOB was located at the wavefront collision area. During a mean follow-up of 7.6 {+/-} 3.9, VT recurred in 26.3% of patients. ConclusionA high number of LOBs on critical substrates can be identified using two-site pacing DEEP mapping.

BackgroundDuring permanent deep septal pacing, it is important to confirm left bundle branch (LBB) capture.\n\nObjectiveThe effective refractory period (ERP) of the working myocardium is different than the ERP of the LBB; we hypothesized that it should be possible to differentiate LBB capture from septal myocardial capture using programmed extra-stimulus technique.\n\nMethodsIn consecutive patients undergoing pacemaker implantation who received pacing lead in a deep septal position programmed pacing was delivered from this lead. Responses to programmed pacing were categorized on the basis of QRS morphology of the extrastimuli as: myocardial (broader QRS, often slurred), selective (narrower QRS, preceded by an isoelectric interval) or non-diagnostic (unequivocal change).\n\nResultsProgrammed deep septal pacing was performed 269 times in 143 patients; in every patient with the use of an 8-beat basic drive train of 600 ms and when possible also during supraventricular rhythm. Responses diagnostic for LBB capture were observed in 114 (79.7%) of patients. Selective LBB paced QRS was more often seen when premature beats were introduced during the intrinsic rhythm rather than after the basic drive train. The average septal-myocardial refractory period was significantly shorter than the LBB refractory period: 263.0{+/-}34.4 ms vs. 318.0{+/-}37.4 ms.\n\nConclusionsA novel maneuver for the diagnosis of LBB capture during deep septal pacing, was formulated, assessed and found as diagnostically valuable. This method, based on the differences in refractoriness between LBB and the septal myocardium is unique in enabling the visualization of components of the usually fused, non-selective LBB paced QRS complex.\n\nGraphical abstract O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

BackgroundThe limited effectiveness of pulmonary vein isolation (PVI) alone using cryoballoon ablation (CBA) led to addictive ablation in procedures of persistent atrial fibrillation (AF) ablation. Roof line (RL) ablation in addition to PVI hold great promise for reduction of AF recurrence after CBA. The randomized controlled CARFI-PerAF trial aimed to prospectively investigate the efficacy of a novel CBA strategy for block of RL and reduction of AF recurrence. MethodsOne hundred and ten patients who were diagnosed with persistent AF were randomized into PVI group and PVI+RL group. Quarter balloon ablation technique and roof distortion technique were used to improve quality of RL ablation. Conduction block of RL was confirmed by both voltage mapping and upper right atrial septum pacing. Primary effectiveness was freedom from AF or atrial tachycardia absent class I/III antiarrhythmic drugs through 12-month follow-up according to ECGs collected by portable device and 24-hour Holter. ResultsThere was no significant difference in AF recurrence between PVI group and PVI+RL group (63.5% vs 76.2%, P = 0.296) after 532.7 {+/-} 171.0 days of follow-up. However, blocked RL was associated with a significant reduction in risk of AF recurrence in the PVI+RL group (84.0% vs 45.5%, P = 0.025). The shape of RL was the only factor affecting the success rate of RL block. Patients with Regular shape of RL predicted a higher rate of RL block than other types (89.7% vs 56.3%, P = 0.014). ConclusionsBlocked roof line ablation was associated with a significant reduction in risk of atrial fibrillation recurrence after cryoballoon ablation. Patients with Regular shape of roof line may benefit more from roof line ablation.

Background Accurate assessment of the QT interval is challenging in the presence of QRS prolongation, such as during ventricular pacing or bundle branch block. Current correction methods are heterogeneous and lack consensus. To evaluate the relationship between QRS duration and QT interval during ventricular pacing and to develop a practical correction method for QT assessment. Methods In this prospective single-centre study, 94 patients undergoing electrophysiology study for supraventricular tachycardia were included. Standardised pacing was performed at the same cycle length from the right ventricular (RV) apex, high output and low output pacing from His catheter, and coronary sinus (reference). QRS and QT intervals were measured from 12-lead ECGs. Changes in QT (QT) and QRS duration (QRS) were analysed using linear regression and mixed-effects modelling. QT correction formulas of the form QT corrected = QT N x QRS were evaluated using Bland-Altman analysis across multiple coefficients. Results A significant positive correlation between QRS and QT was observed across all pacing sites (r = 0.52-0.74, p < 0.001). In mixed-effects modelling, QRS was a strong independent predictor of QT (0.59, p < 0.001), with no significant interaction between pacing site and QRS, supporting a consistent relationship across pacing locations. Bland-Altman analysis demonstrated that correction coefficients of 0.65-0.70 minimised systematic bias compared with lower coefficients, with similar precision across models (SD 16 ms) and no evidence of proportional bias. A coefficient of 0.65 provided the most balanced performance between bias and variability. Conclusion QT prolongation during ventricular pacing is primarily driven by QRS widening and follows a consistent linear relationship across pacing sites. A simple correction using QT corrected = QT 0.65 x (QRS 100 ms) provides a practical and accurate method for QT assessment, with potential clinical applicability in patients with conduction abnormalities or ventricular pacing.

BackgroundMultielectrode mapping catheters, such as the OCTARAY and OPTRELL, are essential in creating myocardial electroanatomical mapping in arrhythmias. The OCTARAY is a multi-spline mapping catheter with 48 closely spaced multielectrodes that enables high-resolution electroanatomical mapping, while the OPTRELL is a multi-electrode catheter with 36 electrodes arranged on eight radiating splines. However, only a few studies have compared their performance. In this study, we aimed to compare the OCTARAY and OPTRELL catheters in two areas: left atrial (LA) mapping during atrial fibrillation (AF) ablation; and premature ventricular contraction (PVC) mapping. MethodsTwenty patients (Ten patients for LA mapping and ten for PVC mapping) were enrolled. LA voltage mapping was performed twice, alternating between catheters post-AF ablation. Parameters compared included mapping time, mapping points, catheter-induced premature atrial contraction (PACs), tissue proximity indication, low voltage area, and fluoroscopy time. For PVC mapping, comparisons included mapping time, catheter-induced PVCs, earliest activation time measured from the onset of PVC QRS, earliest activation point, and fluoroscopy time. ResultsCompared with THE OCTARAY, mean voltage using the OPTRELL was higher (0.192 mV[0.072, 0.48] vs. 0.126 mV[0.042, 0.378]; P = .001) and the percentage of tissue proximity indication positive was also higher (14.97% vs. 11.45%; P < .001). However, there were no significant differences in low voltage area between the two groups (39.5 m2[16.5, 66.8] vs. 40[23.6, 61]; P = .861), and in other LA parameters. In PVC mapping, catheter-induced PVCs using OPTRELL were significantly fewer than the OCTARAY (100 [32, 337] vs. 247 [110, 745], P = .039), with fewer catheter induced PVCs per minute (15 [6, 23] vs. 35 [20, 71], P = .039). However, no significant differences were observed in other PVCs mapping parameters. ConclusionThe OPTRELL catheter demonstrated higher voltage recordings in LA mapping and fewer catheter-induced PVCs compared with the OCTARAY catheter. However, no significant difference was observed in other mapping parameters.

BackgroundPulsed-field ablation (PFA) is becoming more widely used as its efficacy and safety. However, the durability of pulmonary vein isolation (PVI) is not necessarily satisfactory even with PFA. This study aimed to investigate whether post-PFA residual tiny pulmonary vein potentials (PVPs) on a high-resolution map may serve as a predictor of late-phase reconnection between the left atrium and pulmonary vein. MethodsFifteen patients who underwent PFA-based PVI, and the second ablation for recurrent atrial tachyarrhythmias were enrolled. The association between residual tiny PVPs ([&ge;] 0.03 mV) on a post-PFA high-resolution map and reconnected PVPs observed during the second ablation were studied. The presence or absence of PVPs in 270 pulmonary vein segments from 15 cases was compared between the post-PFA map of the initial ablation and the map from the second ablation. ResultsAmong 42 post-PFA residual tiny PVPs, 34 (81%) showed locational concordance with the late-phase reconnected PVPs identified at the second ablation. Thirty-four (52%) out of 66 late-phase reconnected PVPs at the second ablation were located at sites concordant with the post-PFA residual tiny PVPs. Post-PFA residual tiny PVPs defined as bipolar voltage of [&ge;] 0.03 mV well predicted late-phase reconnected PVPs (sensitivity=52%, specificity=96%, positive predictive value=81%, negative predictive value=86%). ConclusionThe presence of post-PFA residual tiny PVPs can be used as late-phase reconnection between the left atrium and pulmonary vein. Condensed abstractThis observational study aimed to investigate whether post-PFA residual tiny pulmonary vein potentials (PVPs) on a high-resolution map may serve as a predictor of late-phase reconnection between the left atrium and pulmonary vein. Fifteen patients were who underwent pulmonary vein isolation using pulse field ablation and the second ablation for recurrent atrial tachyarrhythmias were enrolled. Residual tiny PVPs defined as bipolar voltage of [&ge;] 0.03 mV well predicted late-phase reconnected PVPs (sensitivity=52%, specificity=96%, positive predictive value=81%, negative predictive value=86%). In conclusion, the presence of post-PFA residual tiny PVPs can be used as late-phase reconnection between the left atrium and pulmonary vein

BackgroundCurrently, splitting of electrogram (EGM) or electrocardiogram (ECG) under threshold test are used as the gold standard to assess Left bundle branch (LBB) capture in LBB area pacing. However, discrete intracardiac ventricular EGM has not been reported until now. This study aims to explore the clinical significance and possible mechanism of different pacing ventricular EGM morphologies in selective LBB pacing. MethodsOnly patients with evidence of selective LBB pacing (splitting of EGM under threshold test) were included. According to the differences between intrinsic and paced ventricular EGM morphologies, the participants were further divided into three groups: concordant EGM (CE) group, similar EGM (SE) group and discordant EGM (DE) group. Baseline characteristics, indications for pacing, pacing parameters, and V6 R-wave peak time were analyzed. Results274 patients (85.6%) achieved successful selective LBB pacing. After excluding 34 LBBB patients, LBB potential was recorded in 192 (80%) of 240 patients. In patients with LBB potential, the correlation between V-V6(P) RWPT and V-V6(S) RWPT in CE group (r=0.083, P<0.0001) and SE group (r=0.766, P<0.0001) were strong. V-V6(S) RWPT was significantly shorter than V-V6(P) RWPT (38.14{+/-}9.42 vs. 43.68{+/-}6.72, P<0.01) in DE group. In patients without LBB potential, V-V6(S) RWPT was significantly shorter than V-V6 RWPT (38.14{+/-}11.60 vs. 46.15{+/-}11.81, P<0.05) in DE group. There was a strong correlation (r=0.943, P<0.0001) between V-V6 RWPT and V-V6(S) RWPT in CE group, a possible correlation (r=0.564, P=0.07) in SE group, while poor correlation (r=0.259, P=0.27) in DE group. ConclusionThe continuous recording technique combined with High Pass-200 Hz filter setting was feasible and effective for confirming selective LBB pacing by discrete EGM. Concordant or similar intrinsic and pacing ventricular EGM indicated that the electric conduction shared the same pathway, while discordant intrinsic and pacing ventricular EGM indicated that the electrical stimulation is conducted through different pathway. WHAT IS KNOWN?1. Left bundle branch (LBB) pacing is a novel physiological pacing strategy. 2. Double transition in QRS morphology during threshold testing was considered as the criteria for LBB capture, and splitting of EGM under threshold test was used as the gold standard to assess selective LBB pacing. 3. Identifying discrete local ventricular EGM is still a challenging task. WHAT THE STUDY ADDS1. The continuous recording technique combined with High Pass-200 Hz filter setting was feasible and effective for confirming selective LBB pacing by discrete EGM. 2. Different pacing ventricular EGM morphologies compared with intrinsic EGM accounted for clinical significance and possible mechanism: concordant or similar intrinsic and pacing ventricular EGM indicated that the electric conduction shared the same pathway, while discordant intrinsic and pacing ventricular EGM indicated that the electrical stimulation is conducted through different pathway. 3. The anatomical structure of LBB and its fascicular branch was complex, which could not be adequately recorded by 12-lead ECG and EGM.

BackgroundLeft bundle branch area pacing (LBBAP) is increasingly being used for cardiac resynchronization therapy (CRT); however an additional left ventricular (LV) lead is required when resynchronization remains incomplete. This study evaluates whether lead V8 can provide a simple, non-invasive marker of persistent posterolateral LV delay during LBBAP. MethodsConsecutive patients undergoing LOT-CRT implantation were included. Standard 12-lead ECGs were obtained with the V5 electrode repositioned to the V8 location. Local activation time was measured as the steepest negative downslope of the QRS (negative derivative activation time, NDAT) and compared with the LV electrical delay (LVED) determined from the LV lead during LBBAP. ResultsThirty consecutive patients undergoing LOT-CRT implantation were included with a total of 106 ECG recordings with corresponding LVED measurements. The NDAT-V8 demonstrated a strong correlation with the LVED during intrinsic conduction (r = 0.95) and during all LBB pacing subtypes: combined r = 0.922; mean difference 2.5 {+/-} 8 ms; RV septal pacing, r = 0.89; LV septal pacing, r = 0.92; non-selective LBBP, r = 0.91; and selective LBBP, r = 0.81. The correlation of LVED during intrinsic conduction and all LBBAP pacing subtypes was significantly weaker for NDAT-V6 and the RWPT in V6 and V8 (r=0.681, 0.626 and 0.726, respectively). ConclusionThe NDAT-V8 provides a reliable non-invasive surrogate for the LV posterolateral wall delay during LBBAP, outperforming NDAT-V6 and the RWPT in V6 and V8 and establishes the groundwork for future studies evaluating NDAT-V8 as a tool to guide adequate resynchronization during LBBAP. Clinical PerspectiveO_ST_ABSWhat is KnownC_ST_ABS- Although left bundle branch area pacing (LBBAP) is increasingly being used as an alternative resynchronization strategy, complete resynchronization is not always achieved. - The negative derivative activation time in lead V8 (NDAT-V8) has been shown to provide a non-invasive marker of the left ventricular electrical delay- also referred to as QLV - at the LV postero-lateral wall in patients with left bundle branch block, intraventricular conduction delay, and right bundle branch block. What the Study Adds- This study shows that the NDAT-V8 provides a non-invasive surrogate for the left ventricular posterolateral wall delay during LBBAP. - This study establishes the groundwork for future studies evaluating NDAT-V8 as a tool to guide adequate resynchronization therapy during LBBAP to determine when the addition of a coronary sinus lead is needed.

Background and AimsLeft bundle branch pacing (LBBP) is a novel pacing strategy that improves ventricular synchrony by utilizing the native conduction system. However, the current standard practices limit continuous monitoring of paced electrocardiogram (ECG) and intracardiac electrogram (EGM) transition, which may result in overlooked or misinterpreted subtle transitions. This study aimed to explore the electrophysiological characteristics of the lead-position-dependent EGM continuous transition and evaluate their clinical significance. MethodsThis observational study included patients referred for LBBP due to symptomatic bradyarrhythmia. A continuous pacing and recording technique was employed, allowing real-time monitoring of progressive alterations in the paced QRS complex as the lead penetrates deeper into the ventricular septum. EGM and ECG parameters were continuously monitored and analyzed. ResultsThe study encompassed 105 patients, with selective LBBP achieved in 88 patients (83.8%). The amplitude of ventricular EGM predictably changed with radial interventricular septum depth and peaked in the mid-septum. As the lead was inserted into the left ventricular subendocardium, the ventricular current of injury (COI) declined to a level approximating that of the right septum. Continuous recording technique enabled real-time monitoring of the entire perforation process and the subtle variations that exist among different perforation modalities. The discernment of discrete was feasible through the examination of unfiltered EGM, suggesting that selective LBB capture can also be confirmed by observing the subtle morphological transitions within the ventricular COI. ConclusionsThe continuous recording technique provides a more detailed understanding of the radial depth of the pacing lead throughout the implantation process. It simplifies the implantation procedures and facilitates the prevention or early detection of perforations. Future studies are needed to validate these findings and explore their clinical implications. Whats new?O_LIUtilization of Ventricular Electrogram (EGM) for Lead Positioning: The amplitude of ventricular EGM changes predictably with radial interventricular septum depth, peaking in the mid-septum. This provides a useful way to determine whether the lead is located on the left, right, or middle of the ventricular septum. C_LIO_LIReal-time Monitoring of Perforation Process: The continuous recording technique enables real-time monitoring of the entire perforation process. This feature helps to distinguish the subtle variations that exist among different perforation modalities, facilitating early detection and prevention of perforations. C_LIO_LIConfirmation of Selective Left Bundle Branch Pacing (SLBBP): The emergence of a discrete ventricular current of injury (COI) may serve as a novel characteristic of SLBBP. This suggests that SLBBP can be confirmed by observing the subtle morphological transitions within the ventricular COI. C_LI

BackgroundOne of the most common modes of lead failure is outer insulation breach which may result in myopotential noise and device malfunction. "Pseudo-unipolarization" of bipolar pacing stimuli, as observed from a routine 12-lead ECG has been observed with insulation breaches. We sought to characterize this ECG finding to detect lead this type of lead malfunction. Methods138 transvenous leads were analyzed (88 with known malfunction and 50 normal leads). The highest amplitude (any of 12-leads on standard ECG, 10mm/mV, GE Marquette) of a bipolar pacing stimulus on ECG was recorded and compared to a control dataset of newly implanted leads. An ROC curve for maximum ECG bipolar pacing stimulus amplitude was generated for prediction of lead functional status (normal vs malfunction). ResultsThe cohort (49% females, 34% non-white) had an average age of 67 {+/-} 16 years at implant. The malfunction group consisted of 61% RA and 39% RV leads with mean pacing output 2.74V at 0.5ms. There was a significant difference in ECG bipolar stimulus amplitudes at time of identification of failure (15.06 {+/-} 13.533mm or 7.89 {+/-} 7.56mm per V, p<0.001) compared to those of normal leads (2.54 {+/-} 1.265mm or 0.86 {+/-} 0.41mm per V). An EKG stimulus amplitude cut-off at 3.5mm for the prediction of this type of lead malfunction demonstrated a sensitivity of 86.4% and a specificity of 76%. When normalized for programmed stimulus output, a cutoff of 5mm/V demonstrated a sensitivity of 91% and a specificity of 92% (AUC 0.967 95% CI 0.938-0.996). ConclusionFor a given output, the maximum amplitude of a bipolar pacing stimulus on ECG is significantly lower in normal functioning leads compared to those with known malfunction due to insulation breach. This simply-derived variable demonstrated good accuracy at identifying this lead failure due to insulation breach and exposed electrodes.

Background: Patients with Fontan circulation experience significant morbidity from supraventricular tachyarrhythmias (SVTs). However, the electrophysiological features of SVT and the efficacy and safety of catheter ablation in patients with Fontan circulation are poorly understood. This study aimed to elucidate the electrophysiological features of SVT and evaluate the efficacy and safety of catheter ablation in patients with Fontan circulation. Methods: Forty-nine patients (age, 29.2{+/-}10.0 years; 27 males) with functional single ventricle and Fontan circulation who had undergone electrophysiological study for SVT were retrospectively enrolled. Parameters analyzed included underlying congenital heart disease, Fontan type, conduit puncture technique, tachycardia mechanisms, tachycardia origin site, acute success rate, procedure-related complications, and recurrence. Results: Fifty-nine SVTs were induced, and 69 catheter ablations were performed. The Fontan types included atriopulmonary connection (APC, 18.4%), lateral tunnel (LT, 38.8%), and extracardiac conduit (ECC, 42.9%). Inducible tachycardias included intra-atrial reentrant tachycardia (IART, 39.0%), focal atrial tachycardia (AT, 28.8%), atrioventricular reentrant tachycardia (11.9%), atrioventricular nodal reentrant tachycardia (10.2%), and atrioventricular reciprocating tachycardia involving the twin atrioventricular nodes (10.2%). The right atrial (RA) lateral wall was the most common location of IART and focal AT. The acute success and complication rates were 73.5% and 4.1%, respectively. Recurrence rate was 34.7% during follow-up of 78.0{+/-}71.9 months. The cumulative recurrence rate was significantly lower in patients who underwent LT or ECC Fontan procedures than in those who underwent the APC Fontan procedure (P<0.001). Conclusions: Catheter ablation for SVT is effective and safe in patients who have undergone LT and ECC Fontan procedures.

BackgroundBipolar voltage (BV) electrograms for left atrial (LA) substrate characterization depend on catheter design and electrode configuration. The aim of the study was to investigate the relationship between the BV amplitude (BVA) using four different catheters and to identify their specific LA cutoffs for scar and healthy tissue. MethodsConsecutive high-resolution electroanatomic mapping was performed using a multipolar Orion catheter (Orion-map), a duo-decapolar variable circular mapping catheter (Lasso-Map) and an irrigated focal ablation catheter with minielectrodes (Mifi-map). Virtual remapping using the Mifi-map was performed with a 4.5 mm tip-size electrode configuration (Nav-map). BVAs were compared in voxels of 3x3x3 mm3. The equivalent BVA cutoff for every catheter was calculated for established reference cutoff values of 0.1 mV, 0.2 mV, 0.5 mV, 1.0 mV, and 1.5 mV. ResultsWe analyzed 25 patients (72% men, age 68{+/-}15 years). For scar tissue, a 0.5 mV cutoff using the Nav corresponds to a lower cutoff of 0.35 mV for the Orion and of 0.48 mV for the Lasso. Accordingly, a 0.2 mV cutoff corresponds to a cutoff of 0.09 mV for the Orion and of 0.14 mV for the Lasso. For a healthy tissue cutoff at 1.5 mV, a larger BVA cutoff for the small electrodes of the Orion and the Lasso was determined of 1.68 mV and 2.21 mV, respectively. ConclusionsWhen measuring LA BVA in scar and healthy tissue, relevant differences were seen between focal, multielectrode and mini-electrode catheters. Adapted cutoffs for scar and healthy tissue are required.

Despite significant advances in the prevention of cardiovascular diseases, sudden cardiac death (SCD) persists as a major public health problem. Among young and apparently healthy individuals, Long-QT syndrome (LQTS) represents a leading progenitor of SCD owing to fatal ventricular arrhythmia. Scientific understanding of this association has grown in recent years, and the mortality rate after LQTS diagnosis has significantly decreased. However, despite medical treatment advances, life-threatening ventricular arrhythmias still occur. Until now, no research has established the degree to which this inherited condition arises from an underlying arrhythmogenic electroanatomical substrate. Here, we present direct evidence showing that LQTS patients who survive spontaneous malignant arrhythmias harbor structural electrophysiological abnormalities localized in the epicardium of the right ventricle. We further show that the elimination of these abnormalities by means of catheter ablation successfully suppresses malignant arrhythmias, offering a new approach for the effective treatment of LQTS patients.

BackgroundHeart Rate Score (HRSc), the percent of all atrial paced and sensed event in the largest 10 bpm rate histogram bin of a pacemaker, predicts survival in patients with cardiac devices. No correlation between HRSc and development of atrial fibrillation (AF) has been reported. ObjectiveTo evaluate the relationship between pacemaker post-implantation HRSc and newly-developed AF incidence. MethodsPatients with dual-chamber pacemakers, implanted 2013-2017, with ALTITIUDE remote monitoring data with [&ge;]600,000 beats of histogram data collected at baseline were included (N=34,543). HRSc was determined from the post-implantation histogram data during the initial 3 months. Patients were excluded if they had AF, defined as atrial high-rate episodes >5 minutes or >1% of right atrial beats >170 bpm during the initial 3-months post-implantation. New AF, after the baseline period, was defined by each of the following: >1%, >10% or >25% of atrial beats >170 bpm or Atrial Tachycardia Response (ATR) events >24 hr. ResultsPatients were followed a median of 2.8 (1.0-4.0) years. Patients with initial HRSc[&ge;]70% were older, had higher %RA pacing, had lower %RV pacing and were more likely programmed with rate-response vs subjects with HRSc<70%. The incidence of AF increased in proportion to HRSc (Log-Rank P-value <0.001); results were insensitive to AF definition. Initial HRSc (HR:1.07, 95% CI:1.05-1.09; P<0.0001) independently predicted AF after adjusting for age, gender, % RV pacing and rate-response programming. The %RA pacing and initial HRSc correlated. ConclusionHRSc predicts subsequent AF independent of well-known risk factors in pacemaker patients.

BackgroundFlecainide and other class-Ic antiarrhythmic drugs (AADs) are widely used in Andersen-Tawil syndrome type 1 (ATS1) patients. However, class-Ic drugs might be proarrhythmic in some cases. We investigated the molecular mechanisms of class-I AADs proarrhythmia and whether they might increase the risk of death in ATS1 patients with structurally normal hearts. Methods and ResultsOf 53 ATS1 patients reviewed from the literature, 54% responded partially to flecainide, with ventricular arrhythmia (VA) reduction in only 23%. Of the latter patients, VA persisted in 20-50%. Flecainide was ineffective in 23%, and surprisingly, 13.5% suffered a non-fatal cardiac arrest. In five cardiac-specific ATS1 mouse models (Kir2.1{Delta}314-315, Kir2.1C122Y, Kir2.1G215D and Kir2.1R67W and Kir2.1S136F), flecainide or propafenone (40 mg/Kg i.p.) differentially prolonged the P wave, and the PR, QRS and QTc intervals compared to Kir2.1WT; Kir2.1S136F had milder effects. Flecainide increased VA inducibility in all mutant mice except Kir2.1S136F, which exhibited significant VA reduction. At baseline, Kir2.1G215D cardiomyocytes had the lowest inward rectifier K+ channel (IK1) reduction, followed by Kir2.1C122Y, Kir2.1R67W and Kir2.1S136F. Kir2.1C122Y cardiomyocytes had a significant decrease in sodium inward current (INa). Flecainide (10 {micro}M) slightly increased IK1 density in Kir2.1WT and Kir2.1S136F, while it decreased both IK1 and INa in Kir2.1C122Y and Kir2.1R67W, despite normal trafficking of mutant channels. Optical mapping in ATS1 patient-specific iPSC-CM monolayers expressing Kir2.1C122Y, Kir2.1G215D and Kir2.1R67W showed an increase in rotor incidence at baseline and under flecainide, confirming the dru[g]s proarrhythmic effect. Lastly, in-silico molecular docking predicts that the Kir2.1-Cys311 pharmacophore-binding site is altered in Kir2.1C122Y heterotetramers, reducing flecainide accessibility and leading to channel closure and arrhythmias. ConclusionsClass-Ic AADs are only partially effective and might be proarrhythmic in some ATS1 patients. Kir2.1 mutations impacting the resting membrane potential and cellular excitability create a substrate for life-threatening arrhythmias, raising significant concern about using these drugs in some ATS1 patients. CLINICAL PERSPECTIVE NOVELTY AND SIGNIFICANCEO_ST_ABSWhat is known?C_ST_ABSO_LIAndersen-Tawil syndrome type 1 (ATS1) is a rare autosomal dominant disease caused by loss-of-function mutations in the KCNJ2 gene, which encodes the Kir2.1 channel responsible for the repolarizing, strong inwardly rectifying current IK1. C_LIO_LIATS1 treatment is empirical and subject to clinical judgment. It includes the use of class-Ic antiarrhythmic drugs (AADs), mainly flecainide, alone or in combination with {beta}-adrenergic blocking drugs. However, pharmacological treatment is partial and might fail, leading to life-threatening ventricular arrhythmias (VA) and sudden cardiac death (SCD) in some ATS1 patients. C_LIO_LISome ATS1 mutations are known to disrupt the Kir2.1-Nav1.5 channelosome in mice and human iPSC-CMs, with consequent reductions in cardiac excitability and conduction velocity (CV), leading to VA, which may be exacerbated by flecainide. C_LI What new information does this article contribute?O_LIIn our analysis of 53 ATS1 patients, flecainide showed partial effectiveness. While a few patients experienced complete disappearance of VA, others had persistent arrhythmias and even suffered non-fatal cardiac arrest while on medication. C_LIO_LIIn murine models expressing five relevant ATS1 mutations, flecainide or propafenone produced differential alteration in the P wave, PR, QRS and QTc intervals, and increased VA inducibility compared with Kir2.1WT mice. Additionally, flecainide differentially affected IK1 and the Na+ inward current (INa) current densities despite normal trafficking of mutant channels. C_LIO_LIIn patient-specific induced pluripotent stem cell derived cardiomyocyte (iPSC-CM) monolayers flecainide reduced CV and increased rotor incidence, confirming the drug[s] proarrhythmic effect. C_LIO_LIIn-silico molecular docking studies predicted that the Cys311 pharmacophore binding site and flecainide accessibility are altered in mutated Kir2.1 channels, leading to premature channel closure and arrhythmias. C_LIO_LIWe conclude that class-Ic AADs are only partially effective and might be proarrhythmic in some ATS1 patients. C_LIO_LIThese findings raise concern about the use of class-Ic AADs in ATS1 patients and highlight the need for further studies to guide personalized therapy. C_LI

Background Substrate mapping using multielectrode catheters is increasingly used for post-myocardial infarction (MI) ventricular tachycardia (VT) avoiding repeated VT induction and mapping during VT. However, these catheters may mechanically induce ventricular arrhythmias with hemodynamic compromise. This study compares pro-arrhythmogenicity between single-tip and multi-spline catheters during functional substrate mapping. Methods Thirty post-MI patients (age 68{+/-}8 years, 97% male, LVEF 40% [IQR 33-46]) referred for VT ablation at two centers (2021-2024) underwent endocardial mapping during baseline rhythm in random order with both a multi-spline catheter (Octaray, n=4; Pentaray, n=26) and a single-tip QDOT catheter. The protocol was prematurely terminated if (i) two mechanically induced VTs required ECV, (ii) recurrent ATP-treated mechanical VTs caused hemodynamic compromise, or (iii) excessive mechanically induced ectopy impaired catheter contact. Mapping time, point density, and mechanically induced arrhythmias were assessed. Results Multi-spline catheters enabled faster mapping (26{+/-}9 vs 60{+/-}16 minutes, p<0.001) with more acquired points (p<0.001). VTs were more frequently mechanically induced with multi-spline catheters (median 2 [IQR 1-4] vs 0 [0-3], p<0.05) and these VTs were faster (304ms, IQR 292-320] vs 373ms, IQR [316-405], p=0.01) and degenerated more often into VF (3 vs. 0). Overall, 17 patients (57%) experienced at least one mechanically induced VT; seven (23%) required cardioversion, and mapping was prematurely terminated in eight (27%), all while using multi-spline catheters. Conclusion Multi-spline catheters allow rapid substrate mapping but with substantial risk of mechanically induced arrhythmias, requiring premature termination of substrate mapping because of safety concerns. Their use in post-MI VT ablation warrants careful risk?benefit assessment.

IntroductionChanges in tricuspid regurgitation (TR), mitral regurgitation (MR) and left ventricular ejection fraction (LVEF) are frequently noted after conventional pacemaker implantation but prior studies evaluating whether left bundle branch area (LBBA) or leadless pacemakers modify those observed changes are limited. This study aims to compare changes in TR, MR and LVEF after implantation of conventional right ventricular (RV), leadless, and LBBA pacemakers. MethodsInclusion criteria were first-time pacemaker implantation and pre- and post-implant echocardiography. Change in TR, MR and LVEF were analyzed using post-hoc adjusted Kruskal-Wallis and chi-squared testing, and multivariable ordinal logistic regression. ResultsAmong 400 consecutive patients (RV, n=228; LBBA, n=136; leadless, n=36), the change in TR grade differed between pacemaker types (median [interquartile range] grade change: LBBA 0[0,0], leadless 0[0,1], RV 0[0,1]; p<0.01). The prevalence of severe TR was similar between pacemaker groups before implant (p=0.93), but more frequent following implant of RV and leadless pacemakers compared to LBBA pacemakers (p=0.02). In multivariable ordinal logistic regression, leadless (OR 2.26, p=0.03) and RV pacemakers (OR 1.66, p=0.03) both predicted TR worsening compared to LBBA. The change in MR grade differed between pacemaker types (grade change: LBBA 0[-1,0], leadless 0[0,1], RV 0[0,0]; p<0.01). The change in LVEF differed between pacemaker types (LVEF change: LBBA 0[- 5,7]%, leadless -5[-14,1]%, RV -3[-9,2]%; p<0.01). ConclusionChange in TR, MR grade and LVEF following pacemaker implant varied by pacemaker type. Compared to leadless and RV, LBBA pacemaker implant was associated with more favorable changes in valvular and ventricular function. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=191 HEIGHT=200 SRC="FIGDIR/small/25327288v1_ufig1.gif" ALT="Figure 1"> View larger version (63K): org.highwire.dtl.DTLVardef@1995106org.highwire.dtl.DTLVardef@967746org.highwire.dtl.DTLVardef@70c52dorg.highwire.dtl.DTLVardef@1a142ec_HPS_FORMAT_FIGEXP M_FIG C_FIG