The normal variants in the left bundle branch system

Difference of ventricular synchrony between LBBP, LBFP and LVSP: A speckle tracking echocardiographic study

PURPOSE

Left bundle branch area pacing (LBBAP) has emerged as a physiological and stable form of pacing. We aim to compare the mechanical ventricular synchrony of LBBP, LBFP, and LVSP.

METHODS

Proximal Left bundle branch pacing (LBBP), left bundle fascicular pacing (LBFP) and left ventricular septal pacing (LVSP) were identified in patients with bradycardia who successfully underwent LBBAP. Patients with left ventricular ejection fraction (LVEF) < 50% or QRS duration (QRSd) ≥ 120 ms were excluded. By using electrocardiograms, the left ventricular activation time (LVAT) and QRS duration (QRSd) were measured to examine electrophysiological synchrony. As indications of mechanical synchrony, global longitudinal strain (GLS), global circumferential strain (GCS), global radial strain (GRS), and peak strain dispersion (PSD) were evaluated by using 2-dimensional speckle tracking echocardiography (2D-STE).

RESULTS

In 56 patients, data were collected during LBBP (n = 18), LBFP (n = 16), and LVSP (n = 22). LVSP resulted in a longer LVAT (91.3 ± 14.9 ms) than LBBP (77.1 ± 10.8 ms, P < 0.05) and LBFP (72.1 ± 9.6 ms, P < 0.05), but all three groups had similar QRSd. There were no differences in GLS, GCS, GRS, or PSD between LBBP, LBFP, and LVSP.

CONCLUSIONS

In patients with normal cardiac function and narrow QRS, though LBBAP with LBB capture resulted in better electrophysiological synchrony than without, the mechanical synchrony of the three groups was comparable.

The clinical anatomy of the atrioventricular conduction axis

It is axiomatic that the chances of achieving accurate capture of the conduction axis and its fascicles will be optimized by equally accurate knowledge of the relationship of the components to the recognizable cardiac landmarks, and we find it surprising that acknowledged experts should continue to use drawings that fall short in terms of anatomical accuracy. The accuracy achieved by Sunao Tawara (1906) in showing the location of the atrioventricular conduction axis is little short of astounding. Our purpose in bringing this to current attention is to question the need of the experts to have produced such inaccurate representations, since the findings of Tawara have been extensively endorsed in very recent years. The recent studies do no more than point to the amazing accuracy of the initial account of Tawara. At the same time, we draw attention to the findings described in the middle of the 20th century by Ivan Mahaim (1947). These observations have tended to be ignored in recent accounts. They are, perhaps, of equal significance to those seeking specifically to pace the left fascicles of the branching atrioventricular bundle.

Tailored electrocardiographic-based criteria for different pacing locations within the left bundle branch

BACKGROUND

Electrocardiographic (ECG)-based criteria are used to confirm left bundle branch (LBB) pacing (LBBP), but current cutoff values have never been validated for different pacing locations.

OBJECTIVE

The purpose of this study was to describe diagnostic performance of V6-R wave peak time (RWPT), V6-V1 interpeak interval, and aVL-RWPT for different pacing sites within the LBB and to determine 100% specific values for each criterion at each pacing location.

METHODS

Consecutive patients with confirmed LBBP were selected. Population was divided into subgroups based on the site of pacing: left bundle trunk pacing (LBTP), left septal fascicular pacing (LSFP), left posterior fascicular pacing (LPFP), and left anterior fascicular pacing (LAFP).

RESULTS

A total of 147 patients with unequivocal LBB capture were analyzed. Left fascicular pacing was more frequently achieved (82.8%) than LBTP (17.2%). Diagnostic performance of V6-RWPT, V6-V1 interpeak interval, and aVL-RWPT for discrimination of LBBP was good in all subgroups. V6-RWPT cutoff values with 100% specificity (SP) for LBBP discrimination were 75 ms in LBTP, 68 ms in LPFP, 81 ms in LAFP, and 79.5 ms in LSFP. V6-V1 interpeak interval cutoff values with 100% SP for LBBP discrimination were 35.5 ms in LBTP, 53.5 ms in LPFP, 41 ms in LAFP, and 46 ms in LSFP. In LAFP, aVL-RWPT cutoff value with 100% SP for LBBP discrimination was 68 ms, but was 74 ms in LBTP, 74.5 ms in LSFP, and 73.5 ms in LPFP.

CONCLUSIONS

Tailored ECG-based criteria might be useful to confirm LBBP at different pacing locations within the LBB.

Outcomes of dual-chamber implantable cardioverter defibrillator for left bundle branch area pacing: A systematic review of literature

OBJECTIVE

This systematic review of literature aimed to evaluate the safety and efficacy of dual-chamber ICDs for LBBAP in patients with left bundle branch block (LBBB).

METHODS

Digital databases were searched systematically to identify studies reporting the left bundle branch area pacing (LBBAP) with implantable cardioverter defibrillator (ICD) placement in patients with LBBB. Detailed study and patient-level baseline characteristics including the type of study, sample size, follow-up, number of cases, age, gender, and baseline characteristics were abstracted.

RESULTS

In a total of three studies, 34 patients were included in this review. There was a significant improvement reported in QRS duration in all studies. The mean QRS duration at baseline was 170 ± 17.4 ms, whereas the follow-up QRS duration at follow-up was 121 ± 17.3 ms. Two studies reported a significant improvement of 50% in LVEF from baseline. No lead-related complications or arrhythmic events were recorded in any study. The findings of the systematic review suggest that dual-chamber ICD for LBBAP is a promising intervention for patients with heart conditions.

CONCLUSION

The procedure offers significant improvements in QRS duration and LVEF, and there were no lead-related complications or arrhythmic events recorded in any of the studies.

Cardiac ventricular false tendons: A meta-analysis

Ventricular false tendons are fibromuscular structures that travel across the ventricular cavity. Left ventricular false tendons (LVFTs) have been examined through gross dissection and echocardiography. This study aimed to comprehensively evaluate the prevalence, morphology, and clinical importance of ventricular false tendons using a systematic review. In multiple studies, these structures have had a wide reported prevalence ranging from less than 1% to 100% of cases. This meta-analysis found the overall pooled prevalence of LVFTs to be 30.2%. Subgroup analysis indicated the prevalence to be 55.1% in cadaveric studies and 24.5% in living patients predominantly studied by echocardiography. Morphologically, left and right ventricular false tendons have been classified into several types based on their location and attachments. Studies have demonstrated false tendons have important clinical implications involving innocent murmurs, premature ventricular contractions, early repolarization, and impairment of systolic and diastolic function. Despite these potential complications, there is evidence demonstrating that the presence of false tendons can lead to positive clinical outcomes.

Left Bundle Branch Pacing: A Paradigm Shift in Physiological Pacing for Patients With Atrioventricular Block and Preserved Left Ventricular Systolic Function, A Systematic Review and Meta-analysis

His-Purkinje conduction system pacing (HPCSP) via His bundle pacing (HBP) and Left Bundle Branch Pacing (LBBP) offer a physiological approach to pacing by restoring normal ventricular activation. This meta-analysis compares the feasibility, outcomes, and success rates of HBP and LBBP in patients with atrioventricular block (AVB) and preserved left ventricular function. A systematic search identified studies comparing LBBP with HBP in AVB patients with preserved systolic function. Primary outcomes included QRS duration, success rates, pacing threshold, and improvement in R-wave amplitudes. Secondary outcomes were procedure time and fluoroscopy time. Random-effects models calculated odds ratios (OR) and mean differences (MD) with 95% confidence intervals (CI). Methodological quality was assessed using the Newcastle-Ottawa scale. Among 382 screened articles, seven observational studies involving 1035 patients were analyzed. The mean age was 69.9 years, the mean LVEF was 59.3%, and the average follow-up duration was 8.7 months. LBBP showed higher R-wave amplitudes (MD 7.88, 95% CI 7.26 to 8.50, P < 0.0001) and lower pacing thresholds (MD -0.64, 95% CI -0.81 to -0.47, P < 0.0001) compared to HBP. LBBP had shorter procedure time (MD -17.81, 95% CI -30.44 to -5.18, P = 0.006) and reduced fluoroscopy time (MD -5.39, 95% CI -8.81 to -1.97, P = 0.002). No significant differences were observed in QRS duration or success rates. LBBP offers advantages over HBP, including improved electrical activation, lower pacing thresholds, and shorter procedure and fluoroscopy times. Success rates and QRS duration reductions were comparable between LBBP and HBP. These findings support LBBP as a feasible and effective alternative to HBP in AVB patients with preserved systolic function.

QRS axis and polarity in the inferior leads during left bundle branch pacing: Novel criteria in the search for better results

BACKGROUND

Left bundle branch pacing (LBBP) may be achieved in various anatomical sites within the interventricular septum (IVS), thus influencing paced QRS duration (QRSd).The purpose of this study was to determine whether paced QRS axis (QRSâ) and predominant polarity in inferior leads could be associated with a shorter paced QRSd.

METHODS

We analyzed paced QRSd, QRSâ, polarity in inferior leads, and IVS thickness in patients referred for LBBP. Three paced morphology patterns in the inferior leads were considered: All positive (P), all negative (N) and intermediate (combination of isoelectric, positive, and negative complexes, (I). Patients were divided into two groups according to a paced QRSd < 120 or ≥ 120 ms.

RESULTS

A total of 125 patients were included (age 76 ± 10 years, 46% female). Mean baseline QRSâ was 8 ± 37°. Paced QRSd was significantly shorter as compared to baseline (120 ± 10 vs. 127 ± 33 ms; p = .017) and significantly different according to paced QRS morphology pattern in the inferior leads (P 49%, 119 ± 9; N 30%, 126 ± 12; I 21%; 113 ± 10 ms; p < .001) or paced QRSâ (Normal 59%, 116 ± 1; Right 6%, 129 ± 1; Left 35%, 124 ± 11 ms; p < .001). On multivariate analysis, a QRSâ > -30°(OR 5.79 [2.40-13.93; 95% CI] p = .001), an Intermediate pattern in inferior leads (OR 3.00 [1.67-8.43; 95% CI] p = .037), and an IVS thickness ≤ 10 mm (OR 2.59 [1.10-6.10; 95% CI]; p = .029) were significantly associated with a paced QRSd < 120 ms.

CONCLUSIONS

During LBBP, a QRSâ > -30° and intermediate final polarity in inferior leads are associated with a shorter paced QRSd.

Conduction system pacing for ventricular pacing requirement is feasible and effective on patients with hypertrophic cardiomyopathy and cardiac dysfunction

Objective

We aimed to evaluate the feasibility and safety of his-bundle pacing (HBP) and left bundle branch pacing (LBBP) in patients with hypertrophic cardiomyopathy (HCM) and heart failure (HF).

Methods

Patients with HF and interventricular septal thickness (IVST) ≥ 13 mm resulted from HCM, who accepted conduction system pacing (CSP) with a percentage of ventricular pacing > 40% from May 2018 to April 2022 were consecutively enrolled in our center. LBBP was preferred and HBP was the alternative therapy unless IVST ≥ 16 mm or LBBP failed, whereas LBBP would be the alternative therapy if HBP failed in patients with IVST ≥ 16 mm. All patients were followed up for at least one year. Data including clinical, echocardiographic parameters and electrocardiogram measurements, were collected and evaluated in patients with and without left ventricular ejection fraction (LVEF) < 50%.

Results

A total of 27 patients (65.93 ± 9.09 years old) were enrolled and only 3 patients failed in CSP (11.11%) via LBBP (6/13) and HBP (18/21) procedures. LVEF (P = 0.521), left ventricular end-diastolic diameter (LVEDD) (P = 0.816), and QRS duration (P = 0.928) did not worsen after CSP, and left atrial diameter (LAD) (49.58 ± 8.99 mm vs.47.04 ± 9.82 mm, P = 0.045) tended to improve slightly after 19.19 ± 7.71 months follow-up. Of note, LVEF (39.22%±7.51% vs. 45.22%±9.59%, P = 0.015), LVEDD (52.11 ± 10.10 mm vs. 48.33 ± 9.07 mm, P = 0.037), LAD (50.33 ± 8.93 mm vs. 46.11 ± 5.97 mm, P = 0.013) and New York Heart Association (NYHA) grade (2.67 ± 0.5 vs. 1.38 ± 1.02, P = 0.029) improved in 9 patients with LVEF < 50%, whereas LVEF (P = 0.372), LVEDD (P = 0.665), LAD (P = 0.093) and NYHA grade (P = 0.452) did not deteriorate in patients with preserved ejection fraction.

Conclusion

CSP was safe and feasible in patients with HCM and cardiac dysfunction, and did not worsen cardiac performance especially in patients with LVEF < 50%. HBP might be an effective alternative to LBBP in patients with significantly thickened interventricular septum.

The Atrioventricular Conduction Axis Revisited for the 21st Century

Although first described in the final decade of the 19th century, the axis responsible for atrioventricular conduction has long been the source of multiple controversies. Some of these continue to reverberate. When first described by His, for example, many doubted the existence of the bundle we now name in his honour, while Kent suggested that multiple pathways crossed the atrioventricular junctions in the normal heart. It was Tawara who clarified the situation, although many of his key definitions have not universally been accepted. In key studies in the third decade of the 20th century, Mahaim then suggested the presence of ubiquitous connections that provided "paraspecific" pathways for atrioventricular conduction. In this review, we show the validity of these original investigations, based on our own experience with a large number of datasets from human hearts prepared by serial histological sectioning. Using our own reconstructions, we show how the atrioventricular conduction axis can be placed back within the heart. We emphasise that newly emerging techniques will be key in providing the resolution to map cellular detail to the gross evidence provided by the serial sections.

The QRS frontal plane axis changes during left bundle branch block after transcatheter aortic valve replacement

BACKGROUND AND AIMS

Left bundle branch block (LBBB) is common after transcatheter aortic valve replacement (TAVR) and associated with a left or normal QRS axis. We aim to assess the QRS frontal plane axis shift changes during LBBB after TAVR and determine if the risk of procedure-related high degree atrioventricular block (AVB) is affected by QRS axis shift changes.

METHODS AND RESULTS

In a retrospective single-center study of 720 consecutive patients who underwent TAVR, 141 (19.6%) with normal baseline QRS duration developed a new LBBB after TAVR and constituted the study group. Most patients (59.6%) were females and the mean age of the cohort was 81.2 ± 6 years.

RESULTS

As compared with the baseline QRS axis before TAVR, the occurrence of LBBB was associated with a leftward QRS axis shift (by 40 ± 28.3°) in 73% of the study patients and a rightward (by 18.6 ± 19.4°) or no change in QRS axis in 25.6% and 1.4% of the study patients, respectively. A left QRS axis (-30°) was observed in 14.9% and 38.3% of the study patients before and after TAVR, respectively. The group of patients exhibiting a rightward or no QRS axis shift had a greater incidence of high degree AVB than the group of patients exhibiting a leftward QRS axis shift (18.4% vs. 6.8%, p = .056).

CONCLUSION

Although post TAVR-LBBB is associated with a leftward QRS axis shift in most patients, a non-negligible proportion of patients (27%) exhibited a rightward or no QRS axis shift. The latter group tend to have a higher risk of developing high degree AVB.

Cardiac Conduction System Pacing: A Comprehensive Update

The field of cardiac pacing has changed rapidly in the last several years. Since the initial description of His bundle pacing targeting the conduction system, recent advances in pacing the left bundle branch and its fascicles have evolved. The field and investigators' knowledge of conduction system pacing including relevant anatomy and physiology has advanced significantly. The aim of this review is to provide a comprehensive update on recent advances in conduction system pacing.

Predictors of implantation failure in left bundle branch area pacing using a lumenless lead in patients with bradycardia

Background

Left bundle branch area pacing (LBBAP) is a novel conduction system pacing technique. In this multicenter study, we aimed to evaluate the procedural success, safety, and preoperative predictors of procedural failure of LBBAP.

Methods

LBBAP was attempted in 285 patients with pacemaker indications for bradyarrhythmia, which were mainly atrioventricular block (AVB) (68.1%) and sick sinus syndrome (26.7%). Procedural success and electrophysiological and echocardiographic parameters were evaluated.

Results

LBBAP was successful in 247 (86.7%) patients. Left bundle branch (LBB) capture was confirmed in 54.7% of the population. The primary reasons for procedural failure were the inability of the pacemaker lead to penetrate deep into the septum (76.3%) and failure to achieve shortening of stimulus to left ventricular (LV) activation time in lead V6 (18.4%). Thickened interventricular septum (odds ratio [OR], 2.48; 95% confidence interval [CI], 1.15-5.35), severe tricuspid regurgitation (OR, 8.84; 95% CI, 1.22-64.06), and intraventricular conduction delay (OR, 8.16; 95% CI, 2.32-28.75) were preoperative predictors of procedural failure. The capture threshold and ventricular amplitude remained stable, and no major complications occurred throughout the 2-year follow-up. In patients with ventricular pacing burden >40%, the LV ejection fraction remained high regardless of LBB capture.

Conclusions

Successful LBBAP was affected by abnormal cardiac anatomy and intraventricular conduction. LBBAP is feasible and safe as a primary strategy for patients with AVB, depending on ventricular pacing.

Pacemaker after Sutureless and Rapid-Deployment Prostheses: A Progress Report from the SURD-IR

OBJECTIVES

The aim of this study was to investigate the need for postoperative permanent pacemaker implantation (PPI) following sutureless and rapid-deployment aortic valve replacement (SuRD-AVR) in the context of a progress report from a large multicenter international registry (SURD-IR).

METHODS

We retrospectively analyzed 4,166 patients who underwent SuRD-AVR between 2008 and 2019. The primary outcome was the need for PPI before discharge. The study population was analyzed separately according to the implanted prostheses (Su cohort and RD cohort). Each cohort was divided into two groups based on the operation date: an early group ("EG" = 2008-2016) and a late group ("LG" = 2017-2019).

RESULTS

The rate of PPI decreased significantly in the Su cohort over time (EG = 10.8% vs LG = 6.3%, p < 0.001). In the Su cohort, a decrease in age, risk profile, and incidence of bicuspid aortic valve, increased use of anterior right thoracotomy, reduction of cardiopulmonary bypass time and of associated procedures, and more frequent use of smaller prostheses were observed over time. In the RD cohort, the rate of PPI was stable over time (EG = 8.8% vs LG = 9.3%, p = 0.8). In this cohort, a younger age, lower risk profile, and higher incidence of concomitant septal myectomy were observed over time.

CONCLUSION

Our analysis showed a significant decrease in the PPI rate in patients who underwent Su-AVR over time. Patient selection as well as surgical improvements and a more accurate sizing could be correlated with this phenomenon. The RD cohort revealed no significant differences either in patient's characteristics or in PPI rate between the two time periods.

Anatomy and Pathology of the Cardiac Conduction System

The cardiac conduction system is formed of histologically and electrophysiologically distinct specialized tissues uniquely located in the human heart. Understanding the anatomy and pathology of the cardiac conduction system is imperative to an interventional electrophysiologist to perform safe ablation and device therapy for the management of cardiac arrhythmias and heart failure. The current review summarizes the normal and developmental anatomy of the cardiac conduction system, its variation in the normal heart and congenital anomalies, and its pathology and discusses important clinical pearls for the proceduralist.

Left Bundle Branch Block: Characterization, Definitions, and Recent Insights into Conduction System Physiology

Left bundle branch block (LBBB) is not just a simple electrocardiogram alteration. The intricacies of this general terminology go beyond simple conduction block. This review puts together current knowledge on the historical concept of LBBB, clinical significance, and recent insights into the pathophysiology of human LBBB. LBBB is an entity that affects patient diagnosis (primary conduction disease, secondary to underlying pathology or iatrogenic), treatment (cardiac resynchronization therapy or conduction system pacing for heart failure), and prognosis. Recruiting the left bundle branch with conduction system pacing depends on the complex interaction between anatomy, site of pathophysiology, and delivery tools.

Transcatheter Aortic Valve Replacement Guided by Preprocedural Simulation of Fluoroscopic Location of the Membranous Septum

We show the virtual simulation of the fluoroscopic location of the membranous septum using preprocedural cardiac computed tomographic data sets. Recognizing the risk distance before the procedure can help individualize implantation strategy to reduce the risk of atrioventricular conduction axis damage during transcatheter aortic valve replacement. (Level of Difficulty: Advanced.).

Conduction system pacing improves the outcomes on patients with high percentage of ventricular pacing and heart failure with mildly reduced ejection fraction

Aims

This study aimed to investigate the efficacy and safety of CSP in patients with a high percentage of ventricular pacing and heart failure with HFmrEF.

Methods

Patients who underwent CSP for HFmrEF and ventricular pacing >40% were consecutively enrolled from January 2018 to May 2021. All participants were followed up at least 12 months. Clinical data including cardiac performance and lead outcomes were compared before and after the procedure. Left ventricular ejection fraction (LVEF) was measured using the biplane Simpson's method. HFmrEF was defined as heart failure with the LVEF ranging from 41%-49%.

Results

CSP was successfully performed in 64 cases (96.97%), which included 16 cases of left bundle branch pacing (LBBP) and 48 cases of His bundle pacing (HBP). After a mean of 23.12 ± 8.17 months follow-up, NYHA classification (P < 0.001), LVEF (42.45 ± 1.84% vs. 49.97 ± 3.57%, P < 0.001) and left ventricular end diastolic diameter (LVEDD) (55.59 ± 6.17 mm vs. 51.66 ± 3.48 mm, P < 0.001) improved significantly. During follow-up, more than half (39/64,60.9%) of patients returned to normal LVEF and LVEDD with complete reverse remodeling. The pacing threshold in LBBP was lower (0.90 ± 0.27 V@0.4 ms vs. 1.61 ± 0.71 V@0.4 ms, P < 0.001) than that in HBP. No perforation, electrode dislodging, thrombosis or infection was observed during follow-up.

Conclusions

CSP could improve the clinical outcomes in patients with HFmrEF and a high percentage of ventricular pacing. LBBP might be a better choice because of its feasibility and safety, especially in patients with infranodal atrioventricular block.

Approach to Left Bundle Branch Pacing

Cardiac pacing refers to the implantation tool serving as a treatment modality for various indications, the most common of which is symptomatic bradyarrhythmia. Left bundle branch pacing has been noted in the literature to be safer than biventricular pacing or His-bundle pacing in patients with left bundle branch block (LBBB) and heart failure, thereby becoming the focus of further research on cardiac pacing. A review of the literature was conducted using a combination of keywords, including "Left Bundle Branch Block," "Procedural techniques," "Left Bundle Capture," and "Complications." The following factors have been investigated as key criteria for direct capture: paced QRS morphology, peak left ventricular activation time, left bundle potential, nonselective and selective left bundle capture, and programmed deep septal stimulation protocol. In addition, complications of LBBP, inclusive of septal perforation, thromboembolism, right bundle branch injury, septal artery injury, lead dislodgement, lead fracture, and lead extraction, have also been elaborated on. Despite clinical implications based on clinical research comparing the use of LBBP with other forms such as right ventricular apex pacing, His-bundle pacing, biventricular pacing, and left ventricular septal pacing, a paucity in the literature on long-term effects and efficacy has been noted. LBBP can thus be considered to have a promising future in patients requiring cardiac pacing, assuming that additional research on clinical outcomes and the limitation of significant complications such as thromboembolism can be established.

The effectiveness and feasibility of using multi-lead ECG monitoring combined with a programmed intracavitary ECG to complete left bundle branch area pacing

BACKGROUND

Left bundle branch area pacing (LBBaP) as an alternative method for delivering physiological pacing, is difficult for many primary hospitals that lack the electrophysiological multichannel recorder to carry out. We hope to find a simple and feasible method that combines the multi-lead surface electrocardiogram (ECG) monitoring and the intracavity ECG of the pacing programmer to achieve LBBaP.

METHODS

A total of 50 patients with bradycardia indications who attempted permanent pacemaker implantation were included in this study. We referred to multi-lead surface ECG monitoring and pacing system analyzer (PSA), combined with the nine-zone pacing method of the LBBaP, to complete LBBaP. We assessed multiple parameters to verify whether the LBBaP was successfully achieved and used univariable analysis of variance for repeated measures to judge the feasibility and effectiveness of LBBaP without the electrophysiological multichannel recorder.

RESULTS

LBBaP was successfully archived without the electrophysiological multichannel recorder in 44 of 50 patients (88%). In the study, paced QRS duration and the stimulus to peak left ventricular activation time (Sti-LVAT) were 117.04 ± 10.34 ms and 71.10 ± 7.91 ms and had no significant changes in the 3-month follow-up. The unipolar pacing threshold and R-wave amplitudes were 0.85 ± 0.32 V and 10.36 ± 5.24 mV at baseline respectively, which also showed stability during the 1-month and 3-month follow-up. During the 3-month follow-up, no lead-related complication was recorded.

CONCLUSION

It is effective and feasible to achieve LBBaP combining the multi-lead ECG monitoring and the intracavitary ECG of PSA without the electrophysiological multichannel recorder, which could be an alternative to perform LBBaP.

Feasibility of leadless left ventricular septal pacing with the WiSE-CRT system to target the left bundle branch area: A porcine model and multicenter patient experience

BACKGROUND

The WiSE-CRT system delivers leadless endocardial left ventricular (LV) pacing to achieve cardiac resynchronization therapy. The electrode is conventionally placed on the lateral wall, but implanting on the LV septum may have advantages, including capture of the left bundle branch, and improved battery longevity owing to reduced distance from the transmitter.

OBJECTIVE

The purpose of this study was to assess the feasibility of leadless LV septal pacing via the WiSE-CRT system.

METHODS

Two pigs underwent electrode implantation on the LV septum with subsequent anatomical and histological examination. Eight patients underwent implantation of the WiSE-CRT system with deployment of the electrode on the LV septum via an interatrial transseptal approach.

RESULTS

Deployment of the electrode on the LV septum was successful in both animals. Histological examination demonstrated electrode tines in close proximity to Purkinje tissue. WiSE-CRT implantation with an LV septal electrode was successful in all patients. Biventricular capture was confirmed, with a significant reduction in QRS duration (187.1 ± 33.8 ms vs 149.5 ± 15.7 ms; P = .009). Temporary LV pacing achieved further QRS reduction (139.8 ± 12.4 ms), and in 4 patients the peak LV activation time in lead V5/V6 was <90 ms, suggesting left bundle branch capture. At early follow-up, the median LV pacing percentage was 98.5% and 5 patients (62.5%) improved symptomatically. The transmitter-to-electrode distance was lower than the distance to the lateral wall during acoustic window screening (8.8 ± 1.6 cm vs 11.9 ± 1.5 cm; P = .002).

CONCLUSION

Leadless LV septal pacing with the WiSE-CRT system to target the left bundle branch appears feasible. Further study is required to assess the efficacy and safety of this technique.

Speckle tracking imaging evaluation of left ventricular myocardial work comparing right ventricular septal pacing with His-Purkinje system area pacing

Aims

We sought to objectively assess left ventricular myocardial work (MW) parameters after right ventricular septal pacing (VSP) and His-Purkinje system area pacing (HPSAP) procedures.

Materials and methods

Patients undergoing double-chamber pacemaker implantation for III-degree atrioventricular block (III° AVB) were assessed 1 year after implantation. VSP and HPSAP groups (20 and 23 patients, respectively) were compared against 40 healthy age-matched volunteers. Two-dimensional ultrasound speckle tracking imaging was used to obtain the global myocardial work index (GWI), global myocardial work efficiency (GWE), global myocardial constructive work (GCW), global myocardial wasted work (GWW), left ventricular stratified strain, and peak strain dispersion (PSD).

Results

GWI, GWE, and GCW parameters were improved in HPSAP compared to VSP, while GWW was significantly larger in the VSP group compared to the HPSAP group (all p < 0.05). HPSAP outperformed the VSP group in comparisons of global left ventricular longitudinal strain and stratified strain. Compared to controls, the GCW of all segmental myocardium (17/17 segments) in the VSP group was significantly reduced, while 70.59% (12/17 segments) in the HPSAP group was lower than the control group. GCW in the left ventricular segment of the HPSAP group was bigger than the VSP group (29.41%; 5/17 segments) and mainly concentrated in the ventricular septum and inferior wall.

Conclusion

Our findings suggest that HPSAP performance outcomes are improved over VSP after 1 year, especially in left ventricular contractile synchrony, and HPSAP is beneficial to the effective myocardial work of the left ventricle.

Criteria for differentiating left bundle branch pacing and left ventricular septal pacing: A systematic review

Background

As a novel physiological pacing technique, left bundle branch pacing (LBBP) can preserve the left ventricular (LV) electrical and mechanical synchronization by directly capturing left bundle branch (LBB). Approximately 60-90% of LBBP were confirmed to have captured LBB during implantation, implying that up to one-third of LBBP is actually left ventricular septal pacing (LVSP). LBB capture is critical for distinguishing LBBP from LVSP.

Methods and results

A total of 15 articles were included in the analysis by searching PubMed, EMBASE, Web of Science, and the Cochrane Library database till August 2022. Comparisons of paced QRS duration between LVSP and LBBP have not been uniformly concluded, but the stimulus artifact to LV activation time in lead V5 or V6 (Stim-LVAT) was shorter in LBBP than LVSP in all studies. Stim-LVAT was used to determine LBB capture with a sensitivity of 76-95.2% and specificity of 78.8-100%, which varied across patient populations.

Conclusion

The output-dependent QRS transition from non-selective LBBP to selective LBBP or LVSP is direct evidence of LBB capture. LBB potential combined with short Stim-LVAT can predict LBB capture better. Personalized criteria rather than a fixed value of Stim-LVAT are necessary to confirm LBB capture in different populations, especially in patients with LBB block or heart failure.

Occurrence of ventricular septal perforation in patients with permanent left bundle branch pacing followed up using echocardiographic and computed tomography images

OBJECTIVE

To explore short-term changes after left bundle branch pacing (LBBP) using echocardiography and computed tomography (CT), especially for postoperative ventricular septal perforation.

METHODS

Between January and September 2019, 33 patients with atrioventricular block underwent LBBP at Beijing Anzhen Hospital. All the patients were evaluated using electrocardiography, pacing, parameters and echocardiographic measurements, including for major complications, during the 1, 3, 6, 12 and 24-month follow-up. Interval perforations were examined during a 1-month follow-up echocardiogram and CT.

RESULTS

Left bundle branch pacing was successfully performed in 100% (33/33) of patients. The mean seizure threshold was stable and unchanged postoperatively at the 1, 3, 6, 12 and 24-month follow-up. The paced QRS duration of the LBBP was 119.72 ± 2.53 ms and <130 ms in all patients. Unipolar impedance during the procedure was higher than 500 Ω (662.00 ± 181.50 Ω). No ventricular septal perforation occurred at the end of the procedure. At the 1-month follow-up, two patients reported transthoracic echocardiography, with CT revealing septal lead perforation. Through CT, two other patients were found to have septal lead perforation, and echocardiography indicated that the pacing lead had penetrated the interventricular septum and entered the left subendocardium. At the 1, 3, 6, 12 and 24-month follow-up, these four patients exhibited no significant increase in pacing threshold or impedance (p > .05). No ventricular thrombus or stroke was detected.

CONCLUSION

Permanent LBBP is safe and feasible in patients with bradycardia. Echocardiography and/or CT can more accurately evaluate changes in cardiac structure and function after LBBP.

Complete Atrioventricular Block Caused by Retrograde Transaortic Approach

A 61-year-old female was referred for catheter ablation of symptomatic and frequent premature ventricular complexes presented with right bundle branch block and a prominent inferior frontal plane QRS axis. A retrograde transaortic approach was routinely performed. A sustained complete atrioventricular block was repeatedly encountered while the ablation catheter was attempting to cross the aortic valve with different curves and manipulations. The procedure was abandoned. The mechanical atrioventricular block could only have been caused by the retrograde transaortic approach. We should be cautious when performing a retrograde transaortic catheter manipulation in some patients.

Atrioventricular conduction in PM recipients after transcatheter aortic valve implantation: Implications using Wenckebach point measurement

Background

Atrioventricular (AV) conduction disturbances requiring permanent pacemaker implantation (PPI) are a common complication after transcatheter aortic valve implantation (TAVI). However, a significant proportion of patients might recover AV conduction at follow-up.

Objectives

The aim of our study was to evaluate the recovery of AV conduction by determination through Wenckebach point in patients with PPI and therefore identify patients who could benefit from device reprogramming to avoid unnecessary RV pacing.

Methods

We enrolled 43 patients that underwent PM implantation after TAVI at our Department from January 2018 to January 2021. PM interrogation was performed at follow-up and patients with native spontaneous rhythm were further assessed for AV conduction through WP determination.

Results

A total of 43 patients requiring a PM represented the final study population, divided in patients with severely impaired AV conduction (no spontaneous valid rhythm or WP < 100; 26) and patients with valid AV conduction (WP ≥ 100; 17). In the first group patients had a significantly higher number of intraprocedural atrioventricular block (AVB) (20 vs. 1, p < 0.005), showed a significant higher implantation depth in LVOT (7.7 ± 2.2 vs. 4.4 ± 1.1, p < 0.05) and lower ΔMSID (−0.28 ± 3 vs. −3.94 ± 2, p < 0.05).

Conclusion

AV conduction may recover in a significant proportion of patients. In our study, valve implantation depth in the LVOT and intraprocedural AV block are associated with severely impaired AV conduction. Regular PM interrogation and reprogramming are required to avoid unnecessary permanent right ventricular stimulation in patients with AV conduction recovery.

[Anatomy of the left ventricle for endocardial ablation]

As with all cardiac interventions, performing left ventricular ablation requires profound knowledge of cardiac anatomy. The aim of this article is to provide an overview of left ventricular anatomy and to characterize complex and clinically relevant structures from an electrophysiologist-centered perspective. In addition to the different access routes, the trabecular network, the left ventricular outflow tract, and the left ventricular conduction system, complex anatomical structures such as the aortomitral continuity and the left ventricular summit are also explained. In addition, this article offers multiple clinical examples that combine ECG, anatomy, and electrophysiologic study.

Uncommon output-dependent paced QRS morphology transition during left bundle branch pacing

We report a patient who underwent left bundle branch pacing (LBBP) because of intermittent complete heart block. During unipolar pacing at a deep septal site, a transition in QRS morphology from nonselective to selective pacing (presence of a discrete component on the intracardiac electrogram) was observed, but this was accompanied by concomitant prolongation of the stimulus-to-left ventricular activation time from 96 to 116 ms. However, with several additional turns of the lead, a transition from nonselective to selective LBBP with a short and constant stimulus-to-left ventricular activation time of 78 ms was achieved. Our case suggests that a paced QRS morphology transition from nonselective to selective pacing does not always indicate LBBP. Assessment of high-output pacing is mandatory to achieve LBBP. This article is protected by copyright. All rights reserved.

DURABILITY OF LEFT BUNDLE BRANCH AREA PACING

BACKGROUND

Left bundle branch area pacing (LBBAP) is a form of conduction system pacing. Long term data on the safety and performance of LBBAP one year post device implantation has not been well described.

METHODS AND RESULTS

Sixty-five patients (49% females) who received LBBAP for bradycardia indications using the SelectSecure 3830 lead (Medtronic, Minneapolis, MN) were retrospectively evaluated. Clinical variables were examined. Lead parameters were obtained at implant and during regular follow-up. Mean age of patients was 75.7±10.1 years with left ventricular ejection fraction 59.8±10.4%. Indications for pacing were atrioventricular block 55%, sinus node dysfunction 19%, tachy-brady syndrome 15%, atrioventricular node ablation 8%, and bail out CRT 3%. Mean baseline QRS measured 120±38ms, paced QRS duration was 138±22ms. Paced QRS narrowed by 24ms in those with preexisting left bundle branch block (BBB), increased by 1ms in those with preexisting right BBB, and increased by 42ms in those with no BBB. LBBAP threshold at implant was 0.521±0.153V @0.4ms, and increased to 0.654±0.186V at 3 months (+26%), 0.707±0.186 V at 6 months (+36%), and 0.772±0.220V at 12 months (+48%). Patients with left BBB showed the maximum benefit with QRS narrowing 24ms. Pacing impedance remained unchanged with no procedure related complications.

CONCLUSION

LBBAP is a durable form of conduction system pacing with pacing thresholds remaining relatively stable over 12 months post device implantation. Patients with left BBB display the narrowest paced QRS. This article is protected by copyright. All rights reserved.

The Terminal End of Retro-aortic root branch ------An unrecognized Origin for " Proximal Left Anterior Fascicle" Premature Ventricular Complexes with narrow QRS duration

BACKGROUND

Premature ventricular complexes (PVCs) with narrow QRS duration, inferior frontal plane QRS axis and right bundle branch block(RBBB) pattern generally originate from the proximal segment of the left anterior fascicle(LAF).

OBJECTIVE

This study aimed to investigate the exact origin of this category of PVCs.

METHODS

22 patients with assumed proximal LAF-PVCs were enrolled in the present study. Detailed mapping of fascicular potentials (FPs) was performed during sinus rhythm (SR) and PVCs.

RESULTS

During SR, a cluster of FPs could be found at the most superior portion of the left ventricle (LV). These FPs represented the terminal end of a discrete branch of the left fascicular system which we named the "retro-aortic root branch"(RARB). The shortest distance between the proximal LAF and the terminal end of RARB was 13.5±4.2mm. The earliest activation site of PVCs in all patients were confirmed at the terminal end of RARB, where the FP-V interval was 35.1±4.3 ms during PVCs. The shortest distance from the RCC to the EAS was 5.3±3.5mm. PVCs could be eliminated by ablation from the RCC in 45.5%(10/22) cases, in the remaining cases, ablation at the EAS in the LV endocardium successfully abolished PVCs.

CONCLUSIONS

The terminal end of the retro-aortic root branch was the actual origin site for PVCs with inferior frontal plane axis, RBBB pattern and narrow QRS duration. Ablation in the right coronary cusp or at the earliest activation site in the LV could both eliminate PVCs safely with high efficacy.

Initial Experience with Left Bundle Branch Area Pacing with Conventional Stylet-Driven Extendable Screw-In Leads and New Pre-Shaped Delivery Sheaths

Until recently, left bundle branch area pacing (LBBAp) has mostly been performed using lumen-less fixed screw leads. There are limited data on LBBAp with conventional style-driven extendable screw-in (SDES) leads, particularly data performed by operators with no previous experience with LBBAp procedures. In total, 42 consecutive patients undergoing LBBAp using SDES leads and newly designed delivery sheaths (LBBAp group) were compared with those treated with conventional right ventricular pacing (RVp) for atrioventricular block (RVp group, n = 84) using propensity score matching (1:2 ratio). The LBBAp was successful in 83% (35/42) of patients, with satisfactory pacing thresholds (0.8 ± 0.2 V at 0.4 ms). In the LBBAp group, the mean paced-QRS duration obtained during RV apical pacing (173 ± 18 ms) was significantly reduced by LBBAp (116 ± 14 ms, p < 0.001). Compared with the RVp group, the LBBAp group showed more physiological pacing, suggested by a much narrower paced-QRS duration (116 ± 14 vs. 151 ± 21 ms, p < 0.001). The pacing threshold was comparable in both groups. The LBBAp group revealed stable pacing thresholds for 6.8 ± 4.8 months post-implant and no serious complications including lead dislodgement or septal perforation. The novel approach of LBBAp using SDES leads and the new dedicated pre-shaped delivery sheaths was effectively and safely performed, even by inexperienced operators with LBBAp procedures.

Computed tomography imaging-identified location and electrocardiographic characteristics of left bundle branch area pacing in bradycardia patients

INTRODUCTION

Left bundle branch area pacing (LBBAP) is a novel physiological pacing modality. The relationship between the pacing lead tip location and paced electrocardiographic (ECG) characteristics remains unclear. The objectives are to determine the lead tip location within the interventricular septum (IVS) and assess the location-based ECG QRS duration (QRSd) and left ventricular activation time (LVAT).

METHODS

This multi-center study enrolled 50 consecutive bradycardia patients who met pacemaker therapy guidelines and received LBBAP implantation via the trans-ventricular septal approach. After at least 3 months post implant, 12-lead ECGs and pacing parameters were obtained. Cardiac computed tomography (CT) imaging was performed to assess the LBBAP lead tip distance from the LV blood pool.

RESULTS

Among the 50 patients, analyzable CT images were obtained in 42. In 23 of the 42 patients, the lead tips were within 2 mm to the LV blood pool (the LV subendocardial (LVSE) group), 13 between 2 mm and 4 mm (the Near-LVSE group), and the remaining 6 beyond 4 mm (the mid-LV septal (Mid-LVS) group). No significant differences in paced QRSd were found among the 3 groups (LVSE, 107±15 ms; Near-LVSE, 106±13 ms; Mid-LVS, 104±15 ms; P=0.87). LVAT in the LVSE (64±7 ms) was significantly shorter than in the Mid-LVS (72±8 ms; P<0.05), but not significantly different from that in the Near-LVSE (69±8 ms; P>0.05).

CONCLUSION

In routine LBBAP practice, paced narrow QRSd and fast LVAT, indicative of physiological pacing, was consistently achieved for lead tip location in the LV subendocardial or near LV subendocardial region. This article is protected by copyright. All rights reserved.

A single-centre prospective evaluation of left bundle branch area pacemaker implantation characteristics

Background

Left bundle branch area pacing (LBBAP) has recently been introduced as a physiological pacing technique with synchronous left ventricular activation. It was our aim to evaluate the feasibility and learning curve of the technique, as well as the electrical characteristics of LBBAP.

Methods and results

LBBAP was attempted in 80 consecutive patients and electrocardiographic characteristics were evaluated during intrinsic rhythm, right ventricular septum pacing (RVSP) and LBBAP. Permanent lead implantation was successful in 77 of 80 patients (96%). LBBAP lead implantation time and fluoroscopy time shortened significantly from 33 ± 16 and 21 ± 13 min to 17 ± 5 and 12 ± 7 min, respectively, from the first 20 to the last 20 patients. Left bundle branch (LBB) capture was achieved in 54 of 80 patients (68%). In 36 of 45 patients (80%) with intact atrioventricular conduction and narrow QRS, an LBB potential (LBB_pot) was present with an LBB_pot to onset of QRS interval of 22 ± 6 ms. QRS duration increased significantly more during RVSP (141 ± 20 ms) than during LBBAP (125 ± 19 ms), compared to 130 ± 30 ms without pacing. An even clearer difference was observed for QRS area, which increased significantly more during RVSP (from 32 ± 16 µVs to 73 ± 20 µVs) than during LBBAP (41 ± 15 µVs). QRS area was significantly smaller in patients with LBB capture compared to patients without LBB capture (43 ± 18 µVs vs 54 ± 21 µVs, respectively). In patients with LBB capture (n = 54), the interval from the pacing stimulus to R‑wave peak time in lead V6 was significantly shorter than in patients without LBB capture (75 ± 14 vs 88 ± 9 ms, respectively).

Conclusion

LBBAP is a safe and feasible technique, with a clear learning curve that seems to flatten after 40–60 implantations. LBB capture is achieved in two-thirds of patients. Compared to RVSP, LBBAP largely maintains ventricular electrical synchrony at a level close to intrinsic (narrow QRS) rhythm.

Supplementary Information

The online version of this article (10.1007/s12471-022-01679-7) contains supplementary material, which is available to authorized users.

The Physiologic Mechanisms of Paced QRS Narrowing During Left Bundle Branch Pacing in Right Bundle Branch Block Patients

Left bundle branch pacing (LBBP) is a physiological pacing technique that captures the left bundle branch (LBB) directly, causing the left ventricle (LV) to be excited earlier than the right ventricle (RV), resulting in a “iatrogenic” right bundle branch block (RBBB) pacing pattern. Several studies have recently shown that permanent LBBP can completely or partially narrow the wide QRS duration of the intrinsic RBBB in most patients with bradycardia, although the mechanisms by which this occurs has not been thoroughly investigated. This article presents a review of the LBBP in patients with intrinsic RBBB mentioned in current case reports and clinical studies, discussing the technique, possible mechanisms, future clinical explorations, and the feasibility of eliminating the interventricular dyssynchronization accompanied with LBBP.

Membranous septum morphology and risk of conduction abnormalities after transcatheter aortic valve implantation

BACKGROUND

There are limited data on the association of membranous septum (MS) morphology and transcatheter heart valve (THV) implantation depth, and the development of new conduction abnormalities (CA) after transcatheter aortic valve implantation (TAVI).

AIMS

The aim of this study was to describe the morphology of the MS and predict the risk of new CA after TAVI based on the MS morphology and THV implantation depth.

METHODS

Based on preprocedural CT scans, the MS depth was measured for every 25% of the entire MS width in 272 TAVI patients without preprocedural bundle branch block (BBB) or pacemaker. Post-procedural CT scans for THV implantation depth assessment were available in 130 of these patients.

RESULTS

The MS depth was a median of 2.5 mm (IQR 1.4-3.8) deeper at the posterior edge when compared to the anterior edge of the MS. New CA developed in 7.1% of patients in whom the THV did not cross the lower MS border at its anterior edge (3.6% with new BBB and high degree CA, respectively), in 18.8% of patients (15.6% with new BBB and 3.1% with new high-degree CA) where the THV overlapped the lower MS border by <2.5 mm and in 47.1% of patients (24.3% with new BBB and 22.9% with new high-degree CA) with THV overlap of the lower MS border by ≥2.5 mm.

CONCLUSIONS

The difference of the MS depth and THV implantation depth measured at the anterior edge of the MS predicted new CA after TAVI.

Computerized tomography image correlation of His bundle/deep septal pacing location and outcomes: an analysis from the Canberra HIs bundle/deep septal Pacing Study (CHIPS)

Background

Localisation of the conduction system under fluoroscopy is not easy and the ideal location of the pacing leads in physiological pacing is still being debated.

Objective

The primary aim was to assess the lead locations using cardiac CT scan. Secondary aims were clinical outcomes including success and safety of the procedure and lead performance.

Methods

Of the 100 consecutive patients who received physiological pacing, 34 patients underwent follow-up cardiac CT scan. The four different types of pacing were identified as His bundle (HBP), para-Hisian, left bundle branch (LBBP), and deep septal pacing.

Results

Most patients had successful HBP via the right atrium (RA) (87.5%) as compared to the right ventricle (RV) (12.5%). Lower thresholds were observed when leads were placed within 2 mm of the junction of the membranous and muscular ventricular septum. Unlike HBP, LBBP was possible at a wide region of the septum and selective capture of individual fascicles was feasible. LBBP showed deeper penetration of leads into the septum, as compared to deep septal pacing (70% vs. 45%). Approximately, 80% of patients did not have an intra-ventricular portion of the membranous septum.

Conclusions

The anterior part of the atrio-ventricular (AV) septum at the junction between the membranous and muscular septum via RA appeared to be the best target to successfully pace His bundle. LBBP was possible at a wide region of the septum and selective capture of individual fascicle was feasible. Adequate depth of penetration of lead was very important to capture the left bundle.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10840-022-01133-z.

A Comparison of the Electrophysiological and Anatomic Characteristics of Pacing Different Branches of the Left Bundle Conduction System

Introduction: Left bundle branch pacing (LBBP) is a rapidly growing conduction system pacing technique. However, little is known regarding the electrophysiological characteristics of different types of LBBP. We aimed to evaluate the electrophysiological characteristics and anatomic lead location with pacing different branches of the left bundle branch.

Methods: Consecutive bradycardia patients with successful LBBP were enrolled and classified into groups according to the paced electrocardiogram and the lead location. Electrocardiogram, pacing properties, vectorcardiogram, and lead tip location were analyzed.

Results: Ninety-one patients were enrolled, including 48 with the left bundle trunk pacing (LBTP) and 43 with the left bundle fascicular pacing (LBFP). The paced QRS duration in the LBTP group was significantly shorter than that in the LBFP group (108.1 ± 9.9 vs. 112.9 ± 11.2 ms, p = 0.03), with a more rightward QRS transition zone (p = 0.01). The paced QRS area in the LBTP group was similar to that during intrinsic rhythm (35.1 ± 15.8 vs. 34.7 ± 16.6 μVs, p = 0.98), whereas in the LBFP group, the paced QRS area was significantly larger compared to intrinsic rhythm (43.4 ± 15.8 vs. 35.7 ± 18.0 μVs, p = 0.01). The lead tip site for LBTP was located in a small fan-shaped area with the tricuspid valve annulus summit as the origin, whereas fascicular pacing sites were more likely in a larger and more distal area.

Conclusions: Pacing the proximal left bundle main trunk produced better electrical synchrony compared with pacing the distal left bundle fascicles. A visualization technique can facilitate achieving LBTP.

A Case of Premature Ventricular Complexes from the Proximal Left Bundle Branch Successfully Ablated from the Right Coronary Cusp

Background: Premature ventricular complexes (PVCs) from the proximal left bundle branch (LBB) can be ablated inthe left ventricular outflow tract but can easily damage normal conduction bundles. Here, we report a case of successfulablation of PVCs from the proximal LBB within the right coronary cusp (RCC).Case presentation: Our patient was a 70-year-old woman with PVCs from the proximal LBB that were successfully ablated via the RCC through radiofrequency catheter ablation with a 3D mapping system; she had a complication of incomplete right bundle branch block (RBBB) and remained asymptomatic during follow-up.Conclusion: The RCC provides an alternative approach for ablating PVCs originating from the proximal LBB, owing to the close relationship between the RCC and proximal LBB.

The Atrioventricular Conduction Axis and its Implications for Permanent Pacing

Extensive knowledge of the anatomy of the atrioventricular conduction axis, and its branches, is key to the success of permanent physiological pacing, either by capturing the His bundle, the left bundle branch or the adjacent septal regions. The inter-individual variability of the axis plays an important role in underscoring the technical difficulties known to exist in achieving a stable position of the stimulating leads. In this review, the key anatomical features of the location of the axis relative to the triangle of Koch, the aortic root, the inferior pyramidal space and the inferoseptal recess are summarised. In keeping with the increasing number of implants aimed at targeting the environs of the left bundle branch, an extensive review of the known variability in the pattern of ramification of the left bundle branch from the axis is included. This permits the authors to summarise in a pragmatic fashion the most relevant aspects to be taken into account when seeking to successfully deploy a permanent pacing lead.

Understanding the Aortic Root Using Computed Tomographic Assessment: A Potential Pathway to Improved Customized Surgical Repair

There is continued interest in surgical repair of both the congenitally malformed aortic valve, and the valve with acquired dysfunction. Aortic valvar repair based on a geometric approach has demonstrated improved durability and outcomes. Such an approach requires a thorough comprehension of the complex 3-dimensional anatomy of both the normal and congenitally malformed aortic root. In this review, we provide an understanding of this anatomy based on the features that can accurately be revealed by contrast-enhanced computed tomographic imaging. We highlight the complimentary role that such imaging, with multiplanar reformatting and 3-dimensional reconstructions, can play in selection of patients, and subsequent presurgical planning for valvar repair. The technique compliments other established techniques for perioperative imaging, with echocardiography maintaining its central role in assessment, and enhances direct surgical evaluation. This additive morphological and functional information holds the potential for improving selection of patients, surgical planning, subsequent surgical repair, and hopefully the subsequent outcomes.

Block of branching portion of bundle of His from catheter shaft during ablation of left ventricular outflow tract ventricular premature complexes

Ventricular premature contractions are often located in the left ventricular outflow tract (LVOT). Components of the normal atrioventricular conduction apparatus are located just below the aortic valve in proximity to the membranous septum, between the noncoronary cusp and right coronary cusp. We present a case of injury to the bundle of His during an ablation of a ventricular premature contraction in the LVOT below the left coronary cusp, remote from the bundle of His, due to pressure from the proximal shaft of the catheter between the noncoronary cusp and the right coronary cusp.

Left Bundle Branch Block: Characterization, Definitions, and Recent Insights into Conduction System Physiology

Left bundle branch block (LBBB) is not just a simple electrocardiogram alteration. The intricacies of this general terminology go beyond simple conduction block. This review puts together current knowledge on the historical concept of LBBB, clinical significance, and recent insights into the pathophysiology of human LBBB. LBBB is an entity that affects patient diagnosis (primary conduction disease, secondary to underlying pathology or iatrogenic), treatment (cardiac resynchronization therapy or conduction system pacing for heart failure), and prognosis. Recruiting the left bundle branch with conduction system pacing depends on the complex interaction between anatomy, site of pathophysiology, and delivery tools.

Anatomy and Pathology of the Cardiac Conduction System

The cardiac conduction system is formed of histologically and electrophysiologically distinct specialized tissues uniquely located in the human heart. Understanding the anatomy and pathology of the cardiac conduction system is imperative to an interventional electrophysiologist to perform safe ablation and device therapy for the management of cardiac arrhythmias and heart failure. The current review summarizes the normal and developmental anatomy of the cardiac conduction system, its variation in the normal heart and congenital anomalies, and its pathology and discusses important clinical pearls for the proceduralist.

Left Ventricular Summit-Concept, Anatomical Structure and Clinical Significance

The left ventricular summit (LVS) is a triangular area located at the most superior portion of the left epicardial ventricular region, surrounded by the two branches of the left coronary artery: the left anterior interventricular artery and the left circumflex artery. The triangle is bounded by the apex, septal and mitral margins and base. This review aims to provide a systematic and comprehensive anatomical description and proper terminology in the LVS region that may facilitate exchanging information among anatomists and electrophysiologists, increasing knowledge of this cardiac region. We postulate that the most dominant septal perforator (not the first septal perforator) should characterize the LVS definition. Abundant epicardial adipose tissue overlying the LVS myocardium may affect arrhythmogenic processes and electrophysiological procedures within the LVS region. The LVS is divided into two clinically significant regions: accessible and inaccessible areas. Rich arterial and venous coronary vasculature and a relatively dense network of cardiac autonomic nerve fibers are present within the LVS boundaries. Although the approach to the LVS may be challenging, it can be executed indirectly using the surrounding structures. Delivery of the proper radiofrequency energy to the arrhythmia source, avoiding coronary artery damage at the same time, may be a challenge. Therefore, coronary angiography or cardiac computed tomography imaging is strongly recommended before any procedure within the LVS region. Further research on LVS morphology and physiology should increase the safety and effectiveness of invasive electrophysiological procedures performed within this region of the human heart.

Contrast-enhanced image-guided lead deployment for left bundle branch pacing

BACKGROUND

Left bundle branch pacing (LBBP) is a novel conduction system pacing modality, but pacing lead deployment remains challenging.

OBJECTIVES

This study aimed to evaluate the feasibility of visualization-enhanced lead deployment for LBBP implantation and to assess LBBP characteristics on the basis of lead tip location.

METHODS

Successful LBBP with a well-defined lead tip location by visualization of the tricuspid value annulus in 20 patients was retrospectively analyzed to develop an image-guided technique to identify the LBBP target site. This technique was then prospectively tested in 60 patients who were randomized into 2 groups, one using the standard approach (the standard group) and the other using the image-guided technique (the visualization group). The procedural details, electrophysiological characteristics, and short-term follow-up were compared between groups.

RESULTS

LBBP was successfully achieved in 28 patients in the standard group and in 29 in the visualization group. The procedural and fluoroscopic durations in the visualization group (66.76 ± 14.62 and 7.83 ± 2.05 minutes) were significantly shorter than those in the standard group (85.46 ± 20.19 and 11.11 ± 3.51 minutes) (P < .01). The number of lead deployment attempts in the visualization group was lower than that in the standard group (2.03 ± 1.18 vs 2.96 ± 1.17; P < .01), and the proportion of left bundle branch potential recorded was higher (79.3% vs 46.4%; P = .01).

CONCLUSION

Using a visualization technique, the procedural and fluoroscopic durations for LBBP implantation were significantly shortened with fewer lead repositioning attempts.