Bipolar Pacing Research Articles

Epicardial Lead Performance Trends in Pediatric and Congenital Heart Disease.

Background: Epicardial pacing systems, rather than transvenous systems, are utilized in pediatric patients who are too small to undergo transvenous access and/or have complex congenital heart disease (CHD) anatomically precluding a transvenous system. Longitudinal performance studies indicate that epicardial leads have higher failure rates when compared with transvenous leads but there are limited data on lead measurement changes in the acute phase after implantation. The objective of this study was to assess epicardial lead performance in the acute postimplant period and at one-year follow-up. Methods: This is a retrospective single center study of children and adult patients with CHD undergoing epicardial bipolar pacing lead and generator implantation between January 2012 and June 2022. We empirically selected 2 V as a critical lead threshold. Results: There were 256 leads implanted in 127 patients (mean age 6.1 ± 9.8 years), including 201/256 (79%) leads in patients with CHD. At the time of implant, 47/256 leads (18%) had a lead threshold of ≥2 V. Of those, 42 of 47 (89%) had recorded threshold values on postoperative day 1 (POD1) and 37 of 42 (88%) had decreased to a more acceptable threshold that was <2 V. For patients with an implant threshold of ≥2 V; impedance >1000 ohms, presence of CHD, perioperative or acute postop status, and location of the lead (atrial vs ventricular) did not significantly impact the odds of having a persistently high threshold (≥2 V) on POD1. Conclusion: Epicardial pacing lead thresholds generally improve in the immediate postop period and in our experience most leads with a high implant threshold improved to <2 V by POD1.

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

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

Evaluating lesion integrity with diamond temp system

Abstract Background Pulmonary vein (PV) isolation by temperature-controlled (TC) radiofrequency ablation (RFA) is regaining popularity due to tissue-temperature feedback from thermocouples attached at the distal tip. The Diamond Temp (DT) ablation catheter system is uniquely able to monitor real time tissue temp during RFAs. The DT catheter tip has a 1.1 mm split tip electrode, allowing precise bipolar pacing during RFA. Loss of capture (LOC) with High output pacing (HOP) has been considered a surrogate to assess lesion transmurality [1]. This study evaluated the utility of DT catheter distal pacing to achieve durable lesions. Standard guidelines for TC ablation recommend achieving target tissue-temperature of 60ºC to produce durable lesions. The purpose of this study was to assess whether LOC is achieved at target tissue-temperature of 60ºC. Objective Pacing during ablation from distal tip micro electrode of the DT catheter and observing the time it takes for LOC at different segments around pulmonary veins. First pass isolation (FPI) percentage was also collected. Methods While target enrollment for this prospective study is 50 patients, these preliminary findings are based on analysis of the first 15 patients enrolled, all of whom had symptomatic, drug-refractory paroxysmal AF. Point-by-point RF lesions were delivered around ipsilateral PVs, divided into 4 segments: superior, inferior, anterior, and posterior. Ablation was performed in a TC mode with max temp setting of 60°C and max power of 50 watts. HOP was performed prior to start of ablation and discontinued once LOC was observed. Time taken to LOC around all 4 segments of PVs were recorded. Intracardiac echocardiography (ICE) was used to guide contact and monitor lesion formation. Results Overall mean time to LOC was 3.32 sec. Anterior sites exceeded this mean. Inferior, superior, and posterior sites generally had shorter times. 92.53% of locations achieved LOC within 2-5 sec of ablation. The right anterior PV had the longest time at 3.73 sec, exceeding the overall mean of 3.32 sec. All patient achieved FPI. Conclusion Reaching target therapeutic temp of 60°C alone may not be sufficient to achieve LOC around PVs. Ablation duration of 4 sec led to LOC in 92.53% of lesions. Certain anatomical regions like anterior locations required prolonged ablation time. Tissue thickness on ICE correlated directly with time required to LOC. This analysis shows that TC ablation with DT is effective; however, a therapeutic stable temperature of 60°C for at least 4 sec may be needed to achieve durable lesions around PVs. Tissue thickness on ICE and stability of temperature appear to be independent variables affecting duration prior to LOC.

Six transition patterns and seven capture types in different left bundle branch bipolar pacing configurations.

This study aims to explore the different transition patterns and capture types during two bipolar pacing tests based on the selective left bundle branch (LBB) capture determined by the continuous pacing and recording technique. In total, 67 patients completed two unipolar and two bipolar pacing tests based on selective LBB capture during screwing-in for left bundle branch pacing (LBBP) using the continuous pacing and recording technique. The electrophysiological characteristics and potential mechanisms of different pacing configurations were further evaluated in this study. We found six transition patterns and derived seven capture types in two bipolar pacing tests according to the analysis of continuous electrocardiogram and electrogram changes. Compared with the conventional configuration of "Tip-Ring+" bipolar pacing, "Ring-Tip+" testing had a lower threshold for simultaneous capture of the LBB and the left and right ventricular septum myocardium (1.57 vs. 2.84 V at 0.5 ms) and was the only configuration to yield the peculiar "LBBP + right ventricular septum pacing (RVSP)" capture type. In this study, we observed for the first time that "Ring-Tip+" bipolar pacing allows for a lower clinically applicable pacing threshold for simultaneous capture of the LBB and left and right ventricular septum myocardium, and the peculiar "LBBP + RVSP" capture type. This may be a more advantageous physiological pacing configuration, warranting further investigation and application in the future. Based on the specific selective LBB capture, we first found six transition patterns and derived seven capture types in two bipolar pacing tests due to the different thresholds of the LBB, left ventricular septal myocardial, and right ventricular septal myocardial. Compared with the conventional configuration of "Tip-Ring+" bipolar pacing, "Ring-Tip+" testing had a lower threshold for simultaneous capture of the LBB and the left and right ventricular septum myocardium (1.57 vs. 2.84 V at 0.5 ms) and was the only configuration to yield the peculiar "LBBP + RVSP" capture type. More pacing strategies should be released and investigated to achieve the best physiological pacing according to the individualized electrophysiological characteristics of patients.

Evaluation of Unipolar and Bipolar Left Bundle Branch Area Pacing

Evaluation of Unipolar and Bipolar Left Bundle Branch Area Pacing

Atrial fibrillation is perpetuated by human heart secretome in ex-vivo langendorff-perfused hearts

Abstract Introduction Atrial fibrillation (AF) confers high morbidity and mortality, yet parts of the underlying pathophysiology remain elusive. Left atrial (LA) pressure is altered by the presence of AF and vice-versa. The cardiac secretome might be influenced by LA pressure and potentially alters the susceptibility of the atria to AF. We investigated the effect of the human cardiac secretome on atrial electrophysiology in a translational ex-vivo setting. Methods We obtained venous (coronary sinus) serum samples during AF and in sinus rhythm (SR) in patients hospitalized for pulmonary vein isolation (PVI). Moreover, LA tissue was collected from patients undergoing cardiac surgery and coronary sinus serum samples were collected before (CTRL) and after intraoperative volume challenge (VC). Single cardiomyocytes were isolated from human LA tissue and Ca2+ dependent excitation-contraction coupling (ECC) was studied using confocal line-scan imaging with CTRL or VC. Moreover, a modified Langendorff-Setup with the ability to monitor and control intra-cardiac pressure was utilized to perfuse mouse hearts with AF and SR serum. A multielectrode array (MEA) was placed on the epicardial aspect of the left atrium to measure electrical signals in a spatiotemporal fashion. External bipolar burst pacing protocols were applied to test AF inducibility. Results Ca2+ dependent ECC (i.e. Ca2+ amplitude and release) in human cardiomyocytes was unaltered with exposure to VC serum. Upon introducing a modified version of the Langendorff setup with the ability of linear pressure adjustment, a burst pacing protocol to test for AF inducibility was successfully implemented in mice atria. Atria perfused with human AF serum showed significantly increased AF inducibility as compared to SR serum. Moreover, both, total AF duration as well as number of AF episodes (i.e. AF burden) were increased in AF vs. SR serum upon several different pacing protocols. Conclusion Cardiac secretome during increased LA pressure had no significant effect on Ca2+ dependent ECC in human cardiomyocytes. However, secretome during AF conferred pro-arrhythmogenic properties as compared to SR, further strengthening the concept of "AF begets AF". Ongoing experiments test the hypothesis of potential differences in the multi-level omics profile of AF serum as the underlying mechanism.

In a porcine model of implantable pacemakers for pediatric unilateral diaphragm paralysis, the phrenic nerve is the best target

BackgroundA frequent complication of Fontan operations is unilateral diaphragmatic paresis, which leads to hemodynamic deterioration of the Fontan circulation. A potential new therapeutic option is the unilateral diaphragmatic pacemaker. In this study, we investigated the most effective stimulation location for a potential fully implantable system in a porcine model.MethodsFive pigs (20.8 ± 0.95 kg) underwent implantation of a customized cuff electrode placed around the right phrenic nerve. A bipolar myocardial pacing electrode was sutured adjacent to the motor point and peripherally at the costophrenic angle (peripheral diaphragmatic muscle). The electrodes were stimulated 30 times per minute with a pulse duration of 200 µs and a stimulation time of 300 ms. Current intensity was the only variable changed during the experiment.ResultsEffective stimulation occurred at 0.26 ± 0.024 mA at the phrenic nerve and 7 ± 1.22 mA at the motor point, a significant difference in amperage (p = 0.005). Even with a maximum stimulation of 10 mA at the peripheral diaphragm muscle, however, no effective stimulation was observed.ConclusionThe phrenic nerve seems to be the best location for direct stimulation by a unilateral thoracic diaphragm pacemaker in terms of the required amperage level in a porcine model.

Accurate detection of lead malfunction from ECG-derived bipolar pacing stimulus amplitude

BackgroundOne common mode of lead failure is insulation breach, which may result in myopotential noise and device malfunction. “Pseudo-unipolarization” of bipolar pacing stimuli, as observed from a routine 12-lead electrocardiogram (ECG) due to stimulus current leak, has been observed with insulation breaches. ObjectiveWe sought to characterize this electrocardiographic finding to detect this type of lead malfunction. MethodsA total of 138 transvenous leads were analyzed, including 88 with known malfunction and 50 normal leads. The amplitude of a bipolar pacing stimulus on the ECG was recorded and compared with a control data set of newly implanted leads with bipolar stimuli normalized for output. ResultsThe malfunction group consisted of 61% right atrium and 39% right ventricle leads with mean pacing output of 2.74 V at 0.5 ms. There was a significant difference in ECG bipolar stimulus amplitudes at time of identification of failure (7.89 ± 7.56 mm/V; P < .001) compared with those of normal leads (0.86 ± 0.41 mm/V). Receiver operating characteristic curve for the prediction of lead malfunction based on absolute ECG amplitude displayed an area under the curve of 0.93 (95% CI, 0.891–0.969). When normalized for programmed stimulus output, a cutoff of 5 mm/V demonstrated a sensitivity of 91% and a specificity of 92% (area under the curve, 0.967; 95% CI, 0.938–0.996). ConclusionThe maximum amplitude of a bipolar pacing stimulus on the ECG is significantly lower in normal functioning leads compared with those with known malfunction. This simply derived variable demonstrated good accuracy at identifying lead failure due to insulation breach.

Twenty-four hour continuous transvenous temporary right ventricular pacing in healthy horses.

The ability to perform transvenous temporary cardiac pacing (TV-TP) is critical to stabilize horses with symptomatic bradyarrhythmias. Reports of successful TV-TP in horses are limited, and only briefly describe short-term pacing. To describe temporary, medium-term (24 h) transvenous right ventricular pacing in awake horses using a bipolar torque-directed pacing catheter. Six healthy adult institutional teaching horses. Prospective experimental study with 2 immediately successive TV-TP lead placements in each horse with a target location of the RV apex. One placement was performed primarily with echocardiographic guidance and 1 primarily with fluoroscopic guidance. In all placements, corresponding images were obtained with both imaging modalities. Horses were then paced for 24 h, unrestricted in a stall with continuous telemetric ECG monitoring. Echocardiographically determined lead position, episodes of pacing failure in the preceding 6 h, and pacing thresholds were recorded every 6 h. Pacing failure was defined as a period of loss of capture longer than 20 s. Pacing leads were placed with both guidance methods and maintained for 24 h with no complications. Two horses with leads angled caudally in the right ventricular apex had no pacing failure, the remaining 4 horses had varying degrees of loss of capture. Leads located in the right ventricular apex had longer time to pacing failure and lower capture thresholds P < 0.05. Medium-term TV-TP is feasible and has potential for stabilization of horses with symptomatic bradyarrhythmias. Lead position in the right ventricular apex appears optimal. Continuous ECG monitoring is recommended to detect pacing failure.

A novel pacing strategy for heart block in bilateral septal pacing: A case report

We present the case of a patient referred for conduction system pacemaker implantation after a complete block associated with transcatheter aortic valve replacement and reduced left ventricular function. In this case, we achieved bilateral septal pacing through the anodal capture of the right ventricular septum during bipolar pacing. This approach generated superior ventricular mechanical synchrony compared to left ventricular septum pacing (LVSP).

A novel method for septal reduction therapy by three-dimensional guided transvenous intraseptal pulsed-field ablation

BackgroundPulsed-field ablation (PFA) is a nonthermal method for achieving selective cell death with little inflammation response. However, there are no reports of PFA for septal reduction therapy (SRT). ObjectiveThe purpose of this study was to investigate the effectiveness and safety of PFA for SRT. MethodsA novel transvenous intraseptal PFA method with 3-dimensional (3D) guidance was introduced in Yorkshire pigs. Electrocardiographic parameters, transthoracic echocardiography, and histopathology were used to evaluated. ResultsThe maximum injury diameter of intramyocardial PFA increased with electric field intensity. After PFA, bipolar electrogram amplitude and pacing threshold measured by the PFA electrodes significantly decreased (F = 6.945, P = .007) or increased (F = 5.842, P = .024), respectively. In the ablated septal region, motion amplitude and systolic wall thickening rate significantly decreased and remained at low levels (motion amplitude: F = 20.793, P = .000; systolic wall thickening rate: F = 14.343, P = .000); however, septal thickness did not significantly change after PFA (F = 1.503, P = .248). Histologic examination showed specific cardiomyocyte death with gradually increased hyperchromatic cytoplasm and nuclear pyknosis, without obvious inflammatory cell infiltration in acute phase. TUNEL stain for fragmented DNA showed extensively positive in the ablation region 24 hours after PFA. During PFA, no sustained ventricular arrhythmia or atrioventricular conduction block occurred. ConclusionA novel intraseptal PFA method with 3D guidance was described. Intraseptal PFA resulted in effective myocardial injury and local hypokinesis without significant acute edema. Histologic examination showed widely programmed cardiomyocyte death with little inflammatory cell infiltration.

Slittable sheath supported right ventricular pacing lead implantation in persistent left superior vena cava with absent right superior vena cava: a case report

BackgroundPersistent left superior vena cava (PLSVC) is the most common variant of systemic venous drainage. In the absence of the right superior vena cava (RSVC), implantation of a right ventricular pacing lead may be challenging. Therefore specific implantation techniques and experiences in PLSVC are worth reporting.Case presentationWe present a case report of a 90-year-old Caucasian female patient with PLSVC during single chamber pacemaker implantation due to the third-degree atrioventricular block. With common implantation techniques, we did not even reach the right ventricle. Therefore slittable CPS Direct ™ Universal sheath was employed to overcome the acute angle from PLSVC to tricuspid valve and ensure more fixation stability for longer 100-cm right ventricular lead placement.ConclusionThis case demonstrates safe implantation of 100-cm long right ventricular bipolar active fixation pacing lead using common slittable CPS Direct ™ Universal sheath after failed attempts with „C“ and „J“ stylet shaped electrode. This sheath provides different angle towards tricuspid valve and more fixation stability in patient with PLSVC and absent connection to right atrium.

Autocapture algorithm behaviour in left bundle branch pacing

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Autocapture algorithms allow remote monitoring of patients, reducing the need for face-to-face hospital consultations and increasing patient safety. These algorithms are widely validated in patients with conventional pacing and are not recommended in His bundle pacing, but there is no information on its behaviour in left bundle branch pacing (LBBP). Purpose The objective was to analyse the autocapture algorithm behaviour in LBBP and its differences with conventional pacing and manual thresholds during device first programming (acute phase), after 1-7 days (subacute phase) and 1-3 months later (chronic phase). Methods Prospective non-randomised single-centre comparative study. Consecutive patients with an indication for cardiac pacing were included. The implant was performed in the left bundle branch area or in the right ventricle endocardium (outflow tract or apex) at the discretion of the operator. LBBP was considered according to published criteria. Autocapture algorithm was activated in both groups whenever allowed by the device. The thresholds manual measurement was performed with the intracavitary electrogram and the surface electrocardiogram. Results Sixty patients were included, 40 with LBBP and 20 with conventional pacing. Baseline characteristics of patients are shown in Figure 1. The feasibility of the autocapture algorithm was more frequent in late phases, with a favourable trend toward bipolar pacing (Figure 2A). The failures in the activation of the algorithm were mainly due to the absence of adequate safety margins (90.9% in conventional pacing and 86.6% in LBBP), the rest were attributable to atrial tachyarrhythmias (9.1 and 6.7%, respectively) and electrical noise (remaining 6.7% in LBBP). In LBBP group, there were not statistically significant differences between manual and automatic thresholds except in subacute phase (unipolar) (Figure 2B), and both remained stable during follow-up (average increase of 0.46V). Conclusions Autocapture algorithm is feasible in LBBP, with a favourable trend toward bipolar pacing. Automatic thresholds are similar to manual in patients with LBBP, and they remain stable during follow-up.

Single center experience with subcutaneous ICD in combination with previously implanted endocardial or epicardial antibradycardia or cardiac resynchronization devices

Abstract Funding Acknowledgements Type of funding sources: None. Background Subcutaneous ICD (S-ICD) is an established therapy for prevention of sudden cardiac death due to ventricular arrhythmias (VA). One major drawback of the S-ICD is the lack of antibradycardia pacing. Theroretically the S-ICD can be used in combination with endocardial or epicardial pacemaker (PM), or even cardiac resinchronization (CRT) devices, but recently there are only few case reports available on this topic. Purpose To evaluate the feasibility and safety of concomitant use of endocardial or epicardial PM or CRT devices and S-ICD in a single center patient cohort. Methods Fifty-seven patients underwent S-ICD implantation in our center between 2017 and 2022. Based on individualized decision making-process, six out of these patients underwent the S-ICD implantation without explantation of previuosly implanted transvenous devices, or after epicardial PM or CRT implantation (group 1). The procedural and follow-up data of these patients were compared with data of the other 51 patients (group 2). All patients underwent successful S-ICD screening before implantation. Patients with previously implanted devices were screened either in bipolar pacing mode and either during intrinsic rhythm, if present. S-ICD implantations were performed under general anaesthesia (33 %) or under deep sedation with ultrasound guided regional nerve blocks (66 %) using intermuscular generator placement and two incision technique. Defibrillation threshold test was performed successfully in all the 57 patients. Results All S-ICD implantations were performed successfully without any procedural complications. There were no significant difference between group 1 and group 2 in terms of age (52,3±20 yrs vs. 37,7±18,5 yrs, p=0,75), ejection fraction (49,2±25,6 % vs. 46,5±21 %, p=0,77), procedure duration (57±9,7 min. vs. 52,2±15,5 min., p=0,46), and the mean follow-up duration (20,5±23,6 months vs. 25±18,8 months, p=0,59). During follow-up, one patient in group 1 (17%), and 10 patients in group 2 (19,6 %) experienced adequate ICD therapies due to VA. There were no inadequate ICD therapy in group 1, but eight patients (15,6 %) in group 2 suffered from inadequate ICD shocks caused by T wave oversensing (3/8), atrial fibrillation (2/8) myopotential oversensing (2/8,) and S-ICD lead fracture (1/8). In group 1, no interferences occured between the implanted devices, and no missed S-ICD therapy were observed during induced or spontaeous VA due to pacing artefact oversensing by the S-ICD caused by undersensing of the VA by the pacemakers. Non of the patients in group 2 experienced symptomatic bradycardia required antibradycardia pacing during follow up. Conclusion Based on our observations, S-ICD implantation after previously implanted endocardial or epicardial pacemaker or CRT systems seems feasible and safe. After individualized decision-making, with careful screening and device programming the potential interference between the implanted devices can be prevented.

Capture threshold of bipolar and unipolar pacing of left ventricle via coronary sinus branch: longitudinal study.

The aim of this paper is to first monitor the changes in the capture threshold of endovascularly placed leads for left ventricle pacing, second to compare the pacing configurations, and third to verify the effect of Steroid elution for endovascular leads. The study included 202 consecutive single centre patients implanted with the Quartet™ lead (St. Jude Medical). The capture threshold and related lead parameters were tested during implantation, on the day of the patient's discharge, and 3, 9, and 15 months after implantation. The electrical energy corresponding to the threshold values for inducing ventricular contraction was recorded for subgroups of patients with bipolar and pseudo-unipolar pacing vectors and electrodes equipped with and without a slow-eluting steroids. The best setting for the resynchronization effect was generally chosen. Capture threshold was taken as a selection criterion only if there were multiple options with (expected) similar resynchronization effect. The measurements showed that the ratio of threshold energies of UNI vs. BI was 5× higher (p < 0.001) at implantation. At the end of the follow-up, it dropped to 2.6 (p = 0.012). The steroid effect in BI vectors was caused by a double capture threshold in the NSE group compared to the SE group (p < 0.001), increased by approximately 2.5 times (p < 0.001). The study concludes that after a larger initial increase in the capture threshold, the leads showed a gradual increase in the entire set. As a result, the bipolar threshold energies increase, and the pseudo-unipolar energies decrease. Since bipolar vectors require a significantly lower pacing energy, battery life of the implanted device would improve. When evaluating the steroid elution of bipolar vectors, we observe a significant positive effect of a gradual increase of the threshold energy.

PO-04-080 AN UNUSUAL CASE OF LEFT BUNDLE BRANCH AREA PACING LEAD MALFUNCTION

Left Bundle Branch Area Pacing (LBBAP) is being used for conduction system/physiological pacing. It is important to be aware of manifestations and causes of LBBAP lead malfunction. Identify set screw and connector block damage as a cause of LBBAP lead malfunction with varying pacing parameters. N/A 78 years old lady with dual chamber permanent pacemaker for sick sinus syndrome developed progressive rate related left bundle branch block with left ventricular (LV) systolic dysfunction. She underwent upgrade to a cardiac resynchronization therapy-pacemaker device with addition of LBBAP lead (SelectSecure 3830 Medtronic lead) with confirmation of lead position by typical LBBAP parameters and demonstration of optimal septal penetration on contrast administration (Figure). Unipolar and bipolar lead tip impedance was found to be extremely elevated at follow-up interrogation with elevated LBBAP threshold. Over the next few weeks, LBBAP lead impedance varied between 1000 to >3000 Ohms with variable capture threshold 1.2 to >5 Volt at 0.4 milliseconds (ms) (Figure). Bipolar pacing at capture threshold was septal morphology with only variable typical LBBAP pattern, consistent with anodal capture. LBBAP lead position appeared stable on chest X-ray and transthoracic echocardiogram without clear lead discontinuity. Available near-field electrogram (EGM) on device interrogation showed no noise with provocative maneuvers. Patient underwent elective lead revision. Trans esophageal echocardiogram (TEE) prior to pocket access confirmed stable lead position with adequate septal penetration without protrusion into LV (Figure). On opening the pocket, the 3830 lead was found to be minimally retracted in the header and was easily pulled out manually. Lead parameters including sensing, impedance and capture threshold were normal with selective LBBAP and local LBB potential (Figure). The lead remained loose within the header after set screw deployment. These findings were reproduced with right ventricular (model 5076) lead indicating set screw failure. A new pacemaker generator was implanted with consistently stable LBBAP parameters on follow-up. The explanted generator analysis showed LV setscrew socket and connector block damage (Figure). Set screw failure is a rare cause of pacemaker lead failure. LBBAP lead set screw failure may manifest in an atypical manner without lead noise and should be suspected in acute lead malfunction.

CE-454611-1 ISOLATED HIGH SHOCK IMPEDANCE DUE TO CALCIFIED POCKET AND THE MANAGEMENT

Impedance is the ratio of voltage to current in an electrical circuit. The most common causes of high shock impedance are lead conductor fracture and lead calcification often associated with lead malfunction. We present the first two cases of isolated high shock impedance from pocket calcification in which the lead function is normal. Case 1: A 73-year-old male with ICM, EF 10%, LBBB, sever COPD and Boston biventricular (BiV) ICD in 2013 that normalized EF. Shock impedance slowly rose from 70 Ω to 122 Ω in 2019 and 189 Ω in 2021. Lead extraction with a new system was considered at the time for generator exchange; however, the patient declined. The pocket was severely calcified, with normal defibrillator lead pacing parameters (pace impedance 796 Ω, pace threshold 0.8 V @ 0.4 msec). The calcium shell was removed (Figure 1A), and the shock impedance dropped to 146 Ω, and remained 137 Ω in one year follow up. Case 2: A 65-year-old female with NICM, EF 20%, LBBB, and Boston BiV ICD in 2013 that normalized QRS (Figure 1B). Shock impedance slowly rose from 65 Ω to 138 Ω (2019) and 165 Ω (2022). At the time of generator exchange, the pocket was heavily calcified. Defibrillator lead pacing parameters were normal (pace impedance 868 Ω, pace threshold 0.6 V @ 0.4 msec). After pocket decalcification, shock impedance reduced to 128 Ω. At one month follow up, shock impedance was stable at 130 Ω. N/A High shock impedance is a result of increased impedance in the circuit which includes the can. Lead fracture or calcification will alter lead function as well as shock impedance. This is managed by extraction. In contrast, pocket calcification, which only increases shock impedance, and can be easily managed by pocket decalcification. In both cases, patients benefited greatly from keeping their functional device and avoiding lead exchange. Lead fracture often results in abrupt increase in shock impedance. Calcification at the lead tip or at the pocket causes slow impedance rise. Unipolar and bipolar pacing impedance can also be used to localize the area of calcification. Normal bipolar pacing impedance and slow isolated high shock impedance should raise the suspicion of pocket calcification. Our cases highlight the importance of recognizing pocket calcification in the context of high shock impedance. Calcium removal at the pocket significantly reduces shock impedance. This management strategy can help to avoid lead extraction, a potentially high-risk operation.

PO-01-025 EPICARDIAL LEAD PERFORMANCE TRENDS IN PEDIATRICS AND CONGENITAL HEART DISEASE: WHAT STARTS UP, MUST COME DOWN

Small children and certain types of congenital heart disease (CHD) require epicardial CIED systems when pacing is indicated. Lead performance at implant is potentially affected by patient clinical status, as many of these systems are placed during other operation for CHD or in the post-operative period. Anatomical alterations and scarring from prior procedures may result in limited options and higher lead performance measurements are often accepted at implant. To assess evolution of epicardial lead performance in the acute post-implant period at mid-term follow-up. Retrospective single center study of children and adult congenital heart disease patients undergoing epicardial bipolar pacing lead and generator implantation between 1/2012-6/2022. Patients were censored in follow-up at the time of lead removal, patient death, or pacing polarity change to unipolar. There were 256 leads implanted in 128 pts (mean age 6.1 ± 9.8 years), including 201 (79%) leads implanted in patients with CHD and 138 (54%) implanted in the perioperative or immediate post-operative period (within 30 days). Implant sites were: 76 right atrial, 71 right ventricle, 39 left atrial and 70 left ventricle. Threshold for measurements were available at 6 weeks and 1 year for 160 (63%) and 138 (54%) respectively. The mean threshold at time of implant was 1.3 (range 0.1-6) V. Mean threshold change from implant to post op day 1 (POD1), 6 weeks and 1 year was: –0.34±0.78V (p=0.0001), –0.23 ±0.85V (p=0.003), and –0.2±0.9V (p=0.0026), respectively. At implant, 47 leads (18%) had a threshold ≥ 2 V, of which 42/47 (90%) decreased to <2 by POD1. Leads with higher threshold at implant had a mean decrease in threshold by POD1 of -1.33 V vs. -0.44 V for leads with an implant threshold of <2V (p<0.0001). For patients with an implant threshold of ≥2V, impedance >1000 ohms, CHD, perioperative or acute post-op status, and location of the lead did not significantly impact the odds of having a persistently higher threshold (≥2 V) on POD1. Epicardial pacing lead thresholds improve significantly in the immediate post-op period, even when initial measures could be considered unacceptably high and remain stable at one year post implant. Most leads with high implant thresholds improved to <2 by POD1. No factors effecting the likelihood of improvement were identified. While striving for low threshold at implant remains important, these data support a high likelihood that thresholds will optimize by POD 1.

Bipolar anodal septal pacing with direct LBB capture preserves physiological ventricular activation better than unipolar left bundle branch pacing.

Left bundle branch pacing (LBBP) produces delayed, unphysiological activation of the right ventricle. Using ultra-high-frequency electrocardiography (UHF-ECG), we explored how bipolar anodal septal pacing with direct LBB capture (aLBBP) affects the resultant ventricular depolarization pattern. In patients with bradycardia, His bundle pacing (HBP), unipolar nonselective LBBP (nsLBBP), aLBBP, and right ventricular septal pacing (RVSP) were performed. Timing of local ventricular activation, in leads V1-V8, was displayed using UHF-ECG, and electrical dyssynchrony (e-DYS) was calculated as the difference between the first and last activation. Durations of local depolarizations were determined as the width of the UHF-QRS complex at 50% of its amplitude. aLBBP was feasible in 63 of 75 consecutive patients with successful nsLBBP. aLBBP significantly improved ventricular dyssynchrony (mean -9 ms; 95% CI (-12;-6) vs. -24 ms (-27;-21), ), p < 0.001) and shortened local depolarization durations in V1-V4 (mean differences -7 ms to -5 ms (-11;-1), p < 0.05) compared to nsLBBP. aLBBP resulted in e-DYS -9 ms (-12; -6) vs. e-DYS 10 ms (7;14), p < 0.001 during HBP. Local depolarization durations in V1-V2 during aLBBP were longer than HBP (differences 5-9 ms (1;14), p < 0.05, with local depolarization duration in V1 during aLBBP being the same as during RVSP (difference 2 ms (-2;6), p = 0.52). Although aLBBP improved ventricular synchrony and depolarization duration of the septum and RV compared to unipolar nsLBBP, the resultant ventricular depolarization was still less physiological than during HBP.

The electrophysiological characteristics and meanings in left bundle branch pacing based on unipolar and bipolar pacing

Left bundle branch pacing (LBBP) is considered as an innovative physiologic pacing form because of lower thresholds compared with His bundle pacing and can partially resolve distal bundle disease (1). Our group had reported a novel LBBP lead implantation procedure guided by electrocardiogram (ECG) and electrogram (EGM) morphology under beat-to-beat monitoring, and found the isoelectric interval was a safe and precise endpoint for implantation, and was feasible in 87.8% (2). Few studies described the ECG and EGM characteristics of bipolar pacing due to the inaccuracy of selective left bundle branch pacing (SLBBP). This is the first case to report the electrophysiological characteristics of four unipolar or bipolar pacing modes and try to analyze the potential mechanism of different ECG and EGM morphology.