His-Purkinje System Research Articles

Research progress on His-Purkinje Conduction System Pacing in patients with heart failure and left bundle branch block

左束支传导阻滞（LBBB）可导致心室电传导延迟、收缩不同步，是加重心力衰竭（心衰）的重要因素，亦是心衰治疗的重要靶点。传统双心室起搏可纠正LBBB、改善心功能，但其受到技术及解剖的限制，仍有部分患者难以从中获益。随着对希氏-浦肯野系统认识的深入、导线置入工具的改进及技术的发展，希氏-浦肯野系统起搏作为一种生理性起搏方式，成为当前研究的热点。希氏-浦肯野系统起搏可纠正LBBB、恢复电机械同步性，有望作为传统双心室起搏的替代疗法用于心衰伴LBBB患者。该文对希氏-浦肯野系统起搏在心衰伴LBBB患者中应用的理论及临床进展进行了综述。.

The success rate of His-Purkinje system pacing in patients with various sites of atrioventricular block

Objective: To evaluate the success rate of His-Purkinje system pacing (HPSP) in patients with various sites of atrioventricular block (AVB) and provide clinical evidence for the selection of HPSP in patients with AVB. Methods: This is a retrospective case analysis. 637 patients with AVB who underwent permanent cardiac pacemaker implantation and requiring high proportion of ventricular pacing from March 2016 to September 2021 in the Department of Cardiology, General Hospital of Northern Theater Command were enrolled. The site of AVB was determined by electrophysiological examination. His bundle pacing (HBP) was performed in the first 130 patients (20.4%) who were classified as the HBP group and HPSP included HBP and/or left bundle branch pacing (LBBP) was performed in later 507 patients (79.6%) and these patients were classified as the HPSP group. The basic clinical information such as age and sex of the two groups was compared, and the success rates of HBP or HPSP in patients with different sites of AVB and QRS intervals were analyzed. Results: The age of HBP group was (66.4±15.9) years with 75 males (57.7%). The age of HPSP group was (66.8±13.6) years with 288 (56.8%) males. Among 637 patients, 63.0% (401/637) had atrioventricular node block; 22.9% (146/637) had intra-His block; 14.1% (90/637) had distal or inferior His bundle block. Totally, the success rate of HPSP was higher than that of HBP [93.9% (476/507) vs. 86.9% (113/130), P<0.05]. In each group of patients with various AVB sites, the success rate of HPSP was higher than that of HBP respectively and both success rates of HBP and HPSP showed a declining trend with the distant AVB site. The success rate of HBP in patients with atrioventricular node block and intra-His block was higher than that in patients with distal or inferior His bundle block [95.2% (79/83) vs. 47.1% (8/17), P<0.001; 86.7% (26/30) vs. 47.1% (8/17), P=0.010]. The success rate of HPSP was higher than that of HBP in patients with distal or inferior His bundle block [87.7% (64/73) vs 47.1% (8/17), P=0.001]. In patients with QRS<120 ms, 94.9% (520/548) of AVB sites were in atrioventricular node or intra-His, and HBP had a similar high success rate with HPSP [95.6% (109/114) vs. 96.3% (418/434), P=0.943] in these patients. In patients with QRS ≥ 120 ms, 69.7% (62/89) of AVB sites were at distal or inferior His bundle, and the success rate of HBP was only 25.0% (4/16), while the success rate of HPSP was as high as 79.5% (58/73), P<0.001. Conclusions: In patients with QRS<120 ms and atrioventricular node block or intra-His block, success rates of HBP and HPSP are similarly high and HBP might be considered as the first choice. In patients with QRS ≥ 120 ms and AVB site at distal or inferior His bundle, the success rate of HPSP is higher than that of HBP, suggesting LBBP should be considered as the first-line treatment option.

Premature Complexes and Blocked P Wave.

Premature Complexes and Blocked P Wave.

Conduction system pacing vs. biventricular pacing in patients with ventricular dysfunction and AV block.

It is unknown whether His-Purkinje conduction system pacing (HPCSP), as either His bundle or left bundle branch pacing, could be an alternative to cardiac resynchronization therapy (BiVCRT) for patients with left ventricular dysfunction needing ventricular pacing due to atrioventricular block. The aim of the study is to compare the echocardiographic response and clinical improvement between HPCSP and BiVCRT. Consecutive patients who successfully received HPCSP were compared with a historical cohort of BiVCRT patients. Patients were 1:1 matched by age, LVEF, atrial fibrillation, renal function and cardiomyopathy type. Responders were defined as patients who survived, did not require heart transplantation and increased LVEF ≥5 points at 6-month follow-up. HPCSP was successfully achieved in 92.5% (25/27) of patients. During follow-up, 8% (2/25) of HPCSP patients died and 4% (1/25) received a heart transplant, whereas 4% (1/25) of those in the BiVCRT cohort died. LVEF improvement was 10% ± 8% HPCSP versus 7% ± 5% BiVCRT (p=.24), and the percentage of responders was 76% (19/25) HPCSP versus 64% (16/25) BiVCRT (p=.33). Among survivors, the percentage of patients who improved from baseline II-IV mitral regurgitation (MR) to 0-I MR was 9/11 (82%) versus 2/8 (25%) (p=.02). Compared to those with BiVCRT, patients with HPCSP achieved better NYHA improvement: 1 point versus 0.5 (OR 0.34; p=.02). HPCSP in patients with LVEF ≤45% and atrioventricular block improved the LVEF and induced a response similar to that of BiVCRT. HPCSP significantly improved MR and NYHA functional class. HPCSP may be an alternative to BiVCRT in these patients. (Figure1. Central Illustration). [Figure: see text].

His-Optimized and Left Bundle Branch-Optimized Cardiac Resynchronization Therapy: In Control of Fusion Pacing.

Fusion pacing, which exploits conduction via the intrinsic His-Purkinje system, forms the basis of recent cardiac resynchronization therapy (CRT) optimization algorithms. However, settings need to be constantly adjusted to accommodate for changes in AV conduction, and the algorithms are not always available (eg, depending on the device, in case of AV block or with atrial fibrillation). His-optimized cardiac resynchronization therapy (HOT-CRT), and left-bundle branch optimized cardiac resynchronization therapy (LOT-CRT) which combines conduction system pacing with ventricular fusion pacing, provide constant fusion with ventricular activation (irrespective of intrinsic AV conduction). These modalities provide promising treatment strategies for patients with heart failure, especially in those with chronic atrial fibrillation who require CRT (in whom the atrial port is usually plugged and can be used to connect the conduction system pacing lead).

Electrophysiological differences of deep sedation with dexmedetomidine versus propofol

Abstract Funding Acknowledgements Type of funding sources: None. Background Dexmedetomidine and propofol are commonly used drugs for deep sedation during cardiovascular interventions. Patients undergoing these interventions often have impaired sinus node function or atrioventricular (AV) conduction disease. Anesthetics used for deep sedation may further compromise sinus node function and AV nodal conduction, and thereby interfere with the intervention. Purpose To compare the electrophysiological effects of dexmedetomidine and propofol on the function of the sinus node and AV conduction. Methods We randomized patients undergoing first atrial fibrilation ablation 1:1 to deep sedation by dexmedetomidine (DEX group) versus propofol (PRO group), according to a standardized protocol. At the end of the ablation procedure with the patients still deeply sedated and hemodynamically stable, we conducted a standard electrophysiological study and assessed sinus node function, properties of AV conduction and atrial refractoriness. Results Of 160 patients (65±11 years old; 32% female) included into the study, 80 patients were randomized to the DEX and PRO group each. Procedure duration (128±59 minutes) and sedation depth, as assessed by the "Modified Observer’s Assessment of Alertness/Sedation" score (median 3; interquartile range 2, 3), was not different among groups. DEX group patients received a mean of 231±111 mcg of dexmedetomidine and PRO group patients a mean of 657±356 mg of propofol. The table shows the results of the electrophysiological study. DEX group patients had lower sinus rate and longer unadjusted sinus node recovery time (SNRT) at pacing cycle lengths of 600, 500 and 400 ms. However, both corrected (SNRT-RR) and normalized (SNRT/RR) SNRT did not differ among groups. Compared to PRO group patients, AV nodal conduction was slower in DEX group patients as evidenced by longer PR and AH intervals, and a higher Wenckebach cycle length and AV node effective refractory period (ERP) was observed. Conduction properties in the His-Purkinje system were not different among groups, as QRS width and HV interval were similar. An arrhythmia, mainly atrial fibrillation, was induced in 33 patients (21%) during the electrophysiological study, without differences among groups. Conclusions Sinus rate and AV conduction are slower during deep sedation with dexmedetomidine compared to propofol. These differences in electrophysiological effects need to be taken into account when using these anesthetics during cardiovascular interventions.

Permanent his bundle pacing in suprahisian versus infrahisian atrioventricular block . A single center experience

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Permanent His bundle pacing is currently considered the most physiological form of cardiac pacing. The main benefit of the procedure, compared to right ventricular pacing, is encountered in atrioventricular block, where a high burden of ventricular pacing is expected. One of the limits of His bundle pacing is a distal conduction abnormality in the His-Purkinje system. Nevertheless, there is published data that shows the possibility of conduction system capture even in these patients. This retrospective study evaluated the feasibility of permanent His bundle pacing in patients with second or third degree AV block, taking into account the level of block : suprahisian vs. infrahisian. Material and methods 45 patients with second or third degree AV block with an attempt at permanent His bundle pacing and an available intraprocedural hisian electrogram for review were included. The procedure went as follows: a lead delivery system including a preformed 3D shaped sheath and a lumenless lead with a fixed exposed helix was placed at the septal atrioventricular junction. Careful mapping was performed until a His bundle signal was recorded. At that site, the pacing response was evaluated at variable pacing outputs. The procedural criteria for success was conduction system capture (selective or non-selective) with an amplitude of less than 2,5V/1ms. If the criteria was met, the lead was fixed, an atrial lead was placed and both connected to a dual-chamber pacemaker. The periprocedural characteristics and those at the three-months follow-up were noted. Results 28 patients (62,2%) were diagnosed with suprahisian block, with a procedural success rate of 89 % and 17 (37,8%) with infrahisian block, with a procedural success rate of 59%. QRS duration was 96,4±21,6 ms in those with suprahisian block vs. 119,4±23,8 ms in those with infrahisian block (p=0,0027). There was no significant statistical difference regarding acute His bundle pacing thresholds (1,13±0,63 V/1ms vs. 1,25±0,76 V/1ms, p= 0,66), ventricular sensing (3,46±1,5 mV vs. 3,21±1,6 mV, p= 0,68) and fluoroscopy time (12,75±8,3 min vs. 10,78±9,5 min, p= 0,57) between suprahisian and infrahisian block. Also, the paced QRS duration was similar between the two groups (86,9±13,4 ms vs. 82±14,7 ms, p= 0,38) and narrower than the baseline complex. The three-months follow-up showed stable pacing and sensing parameters, without other procedural or lead related complications. Conclusions In atrioventricular block, permanent His bundle pacing achieves atrioventricular resynchronization, while maintaining rapid and synchronous biventricular depolarization. As expected, in suprahisian blocks the success rate is superior to infrahisian blocks. Nevertheless, in a significant proportion of the latter cases, His bundle pacing can recrute the intrinsic conduction system.

Short QRS Duration After His-Purkinje Conduction System Pacing Predicts Left Ventricular Complete Reverse Remodeling in Patients With True Left Bundle Branch Block and Heart Failure.

ObjectiveThis study aimed to explore the outcomes of His-Purkinje conduction system pacing (HPCSP) and to screen the predictors of left ventricular (LV) complete reverse remodeling in patients with true left bundle branch block (LBBB) and heart failure with reduced ejection fraction (HFrEF).MethodsPatients who underwent HPCSP for true LBBB and HFrEF from April 2018 to August 2020 were consecutively enrolled. All participants were followed up for at least 1 year. Thrombosis, infection, lead dislodgement, perforation, and other complications were observed after HPCSP. Clinical data, including echocardiographic parameters, electrocardiogram measurements, and cardiac function, were assessed before and after the procedure.ResultsA total of 46 patients were enrolled. HPCSP was successfully deployed in 42 cases (91.30%), which included 37 cases with His bundle pacing (HBP) and 5 cases with left bundle branch pacing (LBBP). The QRS duration decreased significantly (169.88 ± 19.17 ms vs. 113.67 ± 20.68 ms, P < 0.001). Left ventricular end-systolic volume (LVESV) (167.67 ± 73.20 ml vs. 85.97 ± 62.24 ml, P < 0.001), left ventricular end-diastolic diameter (LVEDD) (63.57 ± 8.19 mm vs. 55.46 ± 9.63 mm, P = 0.003) and left ventricular ejection fraction (LVEF) (26.52 ± 5.60% vs. 41.86 ± 11.56%, P < 0.001) improved dramatically. Complete reverse remodeling of the LV with normalized LVEF and LVEDD was found in nearly half of the patients (45.24%). A short QRS duration after HPCSP was a strong predictor of normalized LVEF and LVEDD (P < 0.001). The thresholds increased markedly in two patients approximately 6 months after HBP. No patients died during the total follow-up period of 20.07 ± 6.45 months.ConclusionComplete reverse remodeling of the LV could be found in nearly half of the patients with HFrEF and true LBBB after HPCSP, and the short QRS duration after HPCSP was a strong predictor.

Evaluation of electrophysiological characteristics and ventricular synchrony: An intrapatient-controlled study during His-Purkinje conduction system pacingversus right ventricular pacing.

Objectives to BackgroundTo compare electromechanical ventricular synchrony when pacing from different sites, including right ventricular apex pacing (RVAP), right ventricular septum pacing (RVSP), His bundle pacing (HBP), left bundle branch pacing (LBBP), and RVSP during unipolar pacing from the ring electrode of LBBP lead (RVSPring) in each patient and evaluate the correlations between electrophysiological characteristics and ventricular synchrony.MethodsTwenty patients with complete atrioventricular block indicated for dual‐chamber pacemaker implantation were included in the study. Unipolar pacing at different sites, including RVAP, RVSP, HBP, LBBP, and RVSPring, was successively performed in each patient. The pacing characteristics and echocardiogram parameters were collected and compared among intrinsic rhythm and pacing at different sites.ResultsSimilar to HBP (114.84 ± 18.67 ms), narrower paced QRSd was found in LBBP (116.15 ± 11.60 ms) as compared to RVSPring (135.11 ± 13.68 ms), RVSP (141.65 ± 14.26 ms), and RVAP (160.15 ± 19.35 ms) (p < .001). LBBP showed comparable pacing parameters to RVAP or RVSP and was significantly better than HBP, with maintained cardiac function. TS‐12‐SD was significantly improved in LBBP (41.80 ± 20.97 ms) than RVAP (69.70 ± 32.42 ms, p = .003) and RVSP (63.30.56 ± 32.53 ms, p = .018) but similar to HBP (51.50 ± 25.67 ms, p = .283) or RVSPring (57.80 ± 25.65 ms, p = .198). Among these pacing strategies, negative values of interventricular mechanical delay (IVMD) were only identified in LBBP (−19.25 ± 18.43 ms), significantly different from RVAP (35.00 ± 30.72 ms), RVSP (22.85 ± 22.05 ms), HBP (5.20 ± 18.64 ms), and RVSPring (16.00 ± 26.76 ms (all p < .05). Using Pearson's analysis, Sti‐LVAT was positively correlated with QRS duration, IVMD, TS‐12‐SD, LVEDV, and LVESV, while a negative relationship could be observed for left ventricular ejection fraction.ConclusionsHis‐Purkinje conduction system pacing (HPCSP) achieved better electrical and mechanical synchrony than conventional RV pacing. For interventricular synchrony, only LBBP initiated earlier LV activation than RV, in accordance with the right bundle branch block (RBBB) pattern of paced QRS during LBBP. Sti‐LVAT might be a good parameter correlating with LV systolic function and mechanical synchrony.

The Bradycardic Agent Ivabradine Acts as an Atypical Inhibitor of Voltage-Gated Sodium Channels.

Background and purpose: Ivabradine is clinically administered to lower the heart rate, proposedly by inhibiting hyperpolarization-activated cyclic nucleotide-gated cation channels in the sinoatrial node. Recent evidence suggests that voltage-gated sodium channels (VGSC) are inhibited within the same concentration range. VGSCs are expressed within the sinoatrial node and throughout the conduction system of the heart. A block of these channels thus likely contributes to the established and newly raised clinical indications of ivabradine. We, therefore, investigated the pharmacological action of ivabradine on VGSCs in sufficient detail in order to gain a better understanding of the pro- and anti-arrhythmic effects associated with the administration of this drug. Experimental Approach: Ivabradine was tested on VGSCs in native cardiomyocytes isolated from mouse ventricles and the His-Purkinje system and on human Nav1.5 in a heterologous expression system. We investigated the mechanism of channel inhibition by determining its voltage-, frequency-, state-, and temperature-dependence, complemented by a molecular drug docking to the recent Nav1.5 cryoEM structure. Automated patch-clamp experiments were used to investigate ivabradine-mediated changes in Nav1.5 inactivation parameters and inhibition of different VGSC isoforms. Key results: Ivabradine inhibited VGSCs in a voltage- and frequency-dependent manner, but did not alter voltage-dependence of activation and fast inactivation, nor recovery from fast inactivation. Cardiac (Nav1.5), neuronal (Nav1.2), and skeletal muscle (Nav1.4) VGSC isoforms were inhibited by ivabradine within the same concentration range, as were sodium currents in native cardiomyocytes isolated from the ventricles and the His-Purkinje system. Molecular drug docking suggested an interaction of ivabradine with the classical local anesthetic binding site. Conclusion and Implications: Ivabradine acts as an atypical inhibitor of VGSCs. Inhibition of VGSCs likely contributes to the heart rate lowering effect of ivabradine, in particular at higher stimulation frequencies and depolarized membrane potentials, and to the observed slowing of intra-cardiac conduction. Inhibition of VGSCs in native cardiomyocytes and across channel isoforms may provide a potential basis for the anti-arrhythmic potential as observed upon administration of ivabradine.

PC-577-01 FASCICULAR ECTOPY FROM THE RIGHT CORONARY SINUS OF VALSALVA

Fascicular ectopic complexes (FEC) can cause symptoms and pseudo atrio-ventricular block (AVB). Ablation is a viable option but carries a risk of AVB. Successful far-field ablation of left anterior fascicular beats from right aortic sinus of Valsalva (RASoV) has been reported. We present a case of FEC with earliest HPS signal and successful ablation from the RASoV. N/A A 60-year-old woman had palpitations and blocked P waves. ECG revealed frequent FEC and occasional blocked P waves (fig. 1a). We postulated this to be due to concealed FEC (pseudo AVB). She failed flecainide and presented for ablation. A decapolar catheter was placed across the right His-Purkinje system (HPS). She had frequent FECs with early activation of the HPS. We observed FECs with complete antegrade block within the HPS but retrograde penetration into the atrium proving this as the mechanism for pseudo AVB (fig. 1b). Activation mapping of the right and left (retroaortic) HPS was performed with the earliest HPS potential on the decapolar catheter as the fiducial reference. Activation progressed retrograde to the proximal His and antegrade to the RBB, both being later than the distal His. Similarly, the left bundle branch and both fascicles were late. Mapping in the RASoV identified a His-like signal in sinus rhythm that was the earliest site in FEC, 7 ms ahead of reference (fig 1c & d). Focal radiofrequency ablation immediately abolished FECs. Monitoring overnight revealed no further FECs or blocked P waves, and patient reported relief of symptoms. Mapping of FEC should include the RASoV. The anatomic basis for such fascicular potential in the RASoV may be the dead-end tract of the conduction axis reported by Kurosawa and Becker.

PO-643-06 EVALUATION OF ELECTROCARDIOGRAPHIC AND INTRACARDIAC ELECTROGRAM CHARACTERISTICS FOR RESPONSE TO HIS-PURKINJE CONDUCTION SYSTEM PACING IN PATIENTS WITH LEFT BUNDLE BRANCH BLOCK CORRECTED BY HIS BUNDLE PACING

His-Purkinje conduction system pacing (HPCSP) has been proved to improve clinical outcomes in patients with left bundle branch block (LBBB) and heart failure. However, some patients still remain non-responsive to HPCSP.

CI-569-04 SEPTAL FLASH CORRECTION WITH HIS-PURKINJE PACING PREDICTS ECHOCARDIOGRAPHIC RESPONSE IN RESYNCHRONIZATION THERAPY

His-Purkinje conduction system pacing (HPCSP) has been proposed as an alternative to cardiac resynchronization therapy (CRT); however, no predictors of echocardiographic response have been described. Septal flash (SF) is a marker of intraventricular dyssynchrony. The study aimed to analyze whether HPCSP corrects SF in patients with CRT indication, and if correction of SF predicts echocardiographic response. Prospective observational study (n=30). Left ventricular ejection fraction (LVEF) was measured with echocardiography at baseline and at 6-month follow-up. Echocardiographic response was defined as increase in 5 points LVEF. ECG Imaging was performed (CardioInsight Mapping Vest-Medtronic) in 2 patients to validate ventricular activation shortening and to study the basal and HPCSP activation pattern. HPCSP shortened QRS duration by 48±21ms and SF was significantly decreased (baseline 3.6±2.2mm vs HPCSP 1.5±1.5mm p<0.0001). At 6-months, mean LVEF improvement was 8.6% ± 8.7% and 64% of patients were responders. There was a significant correlation between SF correction and increased LVEF (r=0.61, p=0.004). A correction of ≥1.5mm had 81% sensitivity and 80% specificity to predict echocardiographic response (area under curve 0.86, p=0.019). HPCSP improves intraventricular dyssynchrony and results in 64% echocardiographic responders at 6-month follow-up. Dyssynchrony improvement with SF correction may predict echocardiographic response at 6-month follow-up (Fig.1.).

PO-648-06 FEASIBILITY AND CLINICAL BENEFITS OF REIMPLANTATION OF HIS-PURKINJE CONDUCTION SYSTEM PACING LEAD

His-Purkinje conduction system pacing (HPCSP) proves to be safe and feasible over the long-term follow-up. However, lead-related complications such as increasing of his capture threshold, dislodgement, infection, hematoma etc. may require lead extraction and reimplantation.

Conduction system pacing in prosthetic heart valves.

There has been increasing interest in physiologic pacing techniques that directly activate the specialized conduction system. We aimed to assess outcomes of conduction system pacing (CSP) in patients with prosthetic heart valves. This systematic review was performed according to PRISMA guidelines. Freeman-Tukey double arcsine transformation with the random-effect model was used to summarize the data. Outcomes studied were 1) implant success (defined as ability to recruit the His-Purkinje system or the distal Purkinje system); (2) lead parameters at implant and follow-up; and (3) procedure-related complications. This systematic review of 7 studies included 267 unique patients in whom CSP was attempted with either HBP or LBBAP for pacing indications after a prosthetic valve. HBP was attempted in 38% (n = 108), while LBBAP in 62% (n = 175) patients. The overall success rate of CSP was 87%, while in patients post-TAVR, the overall success rate was 83.2%. In the subgroup analysis, LBBAP had a significant higher overall success rate compared to HBP (94.3% vs. 76.5%, p interaction = 0.02) and post-TAVR patients (94.3 vs. 66.9%, p interaction < 0.01), respectively. The LBBAP thresholds were significantly lower compared to HBP both at implant (0.67 ± 0.4 @ 0.44ms vs. 1.35 ± 1 @ 0.85ms, p interaction < 0.01) and at a mean follow-up of 12.4 ± 8months (0.73 ± 0.1 @ 0.44ms vs. 1.39 ± 1 @ 0.85ms, p interaction < 0.01), respectively. CSP is safe and feasible in patients with a prosthetic valve, with a significantly higher success rate and superior lead parameters with LBBAP than HBP, especially in patients post-TAVR.

3rd-Degree Atrioventricular Block.

3rd-Degree Atrioventricular Block.

Rate dependence of early afterdepolarizations in the His-Purkinje system: A simulation study

Background and ObjectiveEarly afterdepolarizations (EADs) are associated with a variety of arrhythmias and have the property of rate dependence. EADs can occur in Purkinje cells while the effect of rate dependence of EADs in the His-Purkinje system has not been fully investigated. In order to reveal the rate dependence of EADs in the His-Purkinje system and its effect on ventricular electrical activities, the simulation research was carried out in this manuscript. MethodsThis manuscript first studied the relationship between the occurrence of EADs and stimulation cycle length on the DiFranNoble cell model. Then, the relationship between the rate dependence of EADs and the conduction block of the His-Purkinje system at slow heart rates was studied on the rabbit whole ventricular model including the His-Purkinje system, and its mechanism was analyzed from multiple angles. Results① The rate dependence of EADs is related to the inconsistency of EADs occurrence in the His-Purkinje system. When the stimulation cycle length is long or short enough, EADs either occur or not occur stably in the His-Purkinje system, while in a certain stimulation cycle length window, the chaotic state of EADs will be observed. ② The key subcellular factors x-gate is an important mechanism involved to the rate dependence of EADs in the His-Purkinje system. ③ The discrete distribution of x-gate values and the “source-sink” mechanism lead to the inconsistency of EADs in the His-Purkinje system. The prolonged action potential duration caused by EADs can lead to conduction block at slow heart rates. ConclusionThe rate dependence of EADs in Purkinje system can lead to disordered ventricular electrical activity.

Septal flash correction with His-Purkinje pacing predicts echocardiographic response in resynchronization therapy.

BackgroundHis‐Purkinje conduction system pacing (HPCSP) has been proposed as an alternative to Cardiac Resynchronization Therapy (CRT); however, predictors of echocardiographic response have not been described in this population. Septal flash (SF), a fast contraction and relaxation of the septum, is a marker of intraventricular dyssynchrony.MethodsThe study aimed to analyze whether HPCSP corrects SF in patients with CRT indication, and if correction of SF predicts echocardiographic response. This retrospective analysis of prospectively collected data included 30 patients. Left ventricular ejection fraction (LVEF) was measured with echocardiography at baseline and at 6‐month follow‐up. Echocardiographic response was defined as increase in five points in LVEF.ResultsHPCSP shortened QRS duration by 48 ± 21 ms and SF was significantly decreased (baseline 3.6 ± 2.2 mm vs. HPCSP 1.5 ± 1.5 mm p < .0001). At 6‐month follow‐up, mean LVEF improvement was 8.6% ± 8.7% and 64% of patients were responders. There was a significant correlation between SF correction and increased LVEF (r = .61, p = .004). A correction of ≥1.5 mm (baseline SF – paced SF) had a sensitivity of 81% and 80% specificity to predict echocardiographic response (area under the curve 0.856, p = .019).ConclusionHPCSP improves intraventricular dyssynchrony and results in 64% echocardiographic responders at 6‐month follow‐up. Dyssynchrony improvement with SF correction may predict echocardiographic response at 6‐month follow‐up.

Modeling the His-Purkinje Effect in Non-invasive Estimation of Endocardial and Epicardial Ventricular Activation

Inverse electrocardiography (iECG) estimates epi- and endocardial electrical activity from body surface potentials maps (BSPM). In individuals at risk for cardiomyopathy, non-invasive estimation of normal ventricular activation may provide valuable information to aid risk stratification to prevent sudden cardiac death. However, multiple simultaneous activation wavefronts initiated by the His-Purkinje system, severely complicate iECG. To improve the estimation of normal ventricular activation, the iECG method should accurately mimic the effect of the His-Purkinje system, which is not taken into account in the previously published multi-focal iECG. Therefore, we introduce the novel multi-wave iECG method and report on its performance. Multi-wave iECG and multi-focal iECG were tested in four patients undergoing invasive electro-anatomical mapping during normal ventricular activation. In each subject, 67-electrode BSPM were recorded and used as input for both iECG methods. The iECG and invasive local activation timing (LAT) maps were compared. Median epicardial inter-map correlation coefficient (CC) between invasive LAT maps and estimated multi-wave iECG versus multi-focal iECG was 0.61 versus 0.31. Endocardial inter-map CC was 0.54 respectively 0.22. Modeling the His-Purkinje system resulted in a physiologically realistic and robust non-invasive estimation of normal ventricular activation, which might enable the early detection of cardiac disease during normal sinus rhythm.

His-Purkinje Conduction System Pacing inAtrioventricular Block: New Insights Into Site of Conduction Block.

This study aims to assess the safety and feasibility of achieving His-Purkinje conduction system pacing (HPCSP) in consecutive patients with atrioventricular block (AVB) and to describe the site of conduction block in patients with infranodal AVB. HPCSP has evolved as the preferred form of physiologic pacing. Left bundle branch area pacing (LBBAP) has emerged as an effective alternative to His bundle pacing (HBP). Consecutive patients with AVB referred for pacemaker implantation were included in the study. HBP or LBBAP was attempted in all patients. Site of conduction block was identified as nodal or infranodal (intra-Hisian or infra-Hisian) AVB. HPCSP was attempted in 333 consecutive patients with AVB and was successful in 322 (97%) patients. HBP was achieved in 140 patients, LBBAP in 179 patients, and both in 3 patients. Site of conduction block was nodal in 55% and infranodal in 45% (intra-Hisian 89%; infra-Hisian 4%; indeterminate 7%). QRS duration at baseline was 111 ± 27 versus 129 ± 31 (P< 0.001) compared to 126 ± 24 vs 125 ± 21 milliseconds (P=0.75) during HBP and LBBAP, respectively. HBP thresholds at implant were higher compared to LBBAP (1.2 ± 0.7V at 0.9 milliseconds vs 0.6 ± 0.3V at 0.5 milliseconds; P< 0.001) but remained stable during follow-up. Lead revision was required in 3% and 2% of patients with HBP and LBBAP, respectively. HPCSP pacing was successfully performed in 97% of unselected patients with AVB irrespective of the site of conduction block. True infra-Hisian block (distal His-Purkinje conduction disease) is rare. HBP and LBBAP were complementary in achieving stable and low capture thresholds.