Anatomical Considerations for His Bundle Pacing

Conduction system pacing: how far are we from the "electrical" bypass?

Conduction system pacing is an alternative practice to conventional right ventricular apical pacing. It is a method that maintains physiologic ventricular activation, based on a correct pathophysiological basis, in which the pacing lead bypasses the lesion of the electrical fibers and the electrical impulse transmits through the intact adjacent conduction system. For this reason, it might be reasonably characterized by the term "electrical bypass" compared to the coronary artery bypass in revascularization therapy. In this review, reference is made to the sequence of events in which conventional right ventricular pacing may cause adverse outcomes. Furthermore, there is a reference to alternative strategies and pacing sites. Interest focuses on the modalities for which there are data from the literature, namely for the right ventricular (RV) septal pacing, the His bundle pacing (HBP), and the left bundle branch pacing (LBBP). A more extensive reference is about the HBP, for which there are the most updated data. We analyze the considerations that limit HBP-wide application in three axes, and we also present the data for the implantation and follow-up of these patients. The indications with their most important studies to date are then described in detail, not only in their undoubtedly positive findings but also in their weak aspects, because of which this pacing mode has not yet received a strong recommendation for implementation. Finally, there is a report on LBBP, focusing mainly on its points of differentiation from HBP.

Conduction system pacing: overview, definitions, and nomenclature

Pacing from the right ventricle is associated with an increased risk of development of congestive heart failure, increases in total and cardiac mortality, and a worsened quality of life. Conduction system pacing has become increasingly realized as an alternative to right ventricular apical pacing. Conduction system pacing from the His bundle and left bundle branch area has been shown to provide physiologic activation of the ventricle and may be an alternative to coronary sinus pacing. Conduction system pacing has been studied as an alternative for both bradycardia pacing and for heart failure pacing. In this review, we summarize the clinical results of conduction system pacing under a variety of different clinical settings. The anatomic targets of conduction system pacing are illustrated, and electrocardiographic correlates of pacing from different sites in the conduction system are defined. Ultimately, clinical trials comparing conduction system pacing with standard right ventricular apical pacing and cardiac resynchronization therapy pacing will help define its benefit and risks compared with existing techniques.

Cardiac Resynchronisation with Conduction System Pacing

To date, biventricular pacing (BiVP) has been the standard pacing modality for cardiac resynchronisation therapy. However, it is non-physiological, with the activation spreading between the left ventricular epicardium and right ventricular endocardium. Up to one-third of patients with heart failure who are eligible for cardiac resynchronisation therapy do not derive benefit from BiVP. Conduction system pacing (CSP), which includes His bundle pacing and left bundle branch area pacing, has emerged as an alternative to BiVP for cardiac resynchronisation. There is mounting evidence supporting the benefits of CSP in achieving synchronous ventricular activation and repolarisation. The aim of this review is to summarise the current options and outcomes of CSP when used for cardiac resynchronisation in patients with heart failure.

Preoperative planning for transaortic septal myectomy using cardiac computed tomography in patients with subaortic septal hypertrophy associated with aortic stenosis: case series

Background

Electrocardiogram-gated cardiac computed tomography (CT) imaging enables a more accurate understanding of the patient's cardiac anatomy. Preoperative planning for transaortic septal myectomy (TASM), based on cardiac CT, may be useful in patients with subaortic septal hypertrophy associated with severe aortic stenosis (AS).

Case summary

Two elderly patients (age >80 years) with subaortic septal hypertrophy associated with AS underwent surgical aortic valve replacement (SAVR) and concomitant TASM after preoperative planning based on cardiac CT. Both patients showed subaortic septal hypertrophy with blood flow acceleration, left ventricular (LV) hypercontractility, and a short distance from the coaptation point of the mitral valve to the septum, resulting in possible dynamic LV outflow tract (LVOT) obstruction after resolution of AS. Optimal mid-diastolic images, selected from the 70-80% phase, were used for preoperative TASM planning. Planned sizes for myectomy based on multi-planar reconstruction were 10 × 26 × 9 mm (width × length × depth) and 10 × 25 × 9 mm for patient 1 and 2, respectively, while resected tissue size was 10 × 24 × 8 mm and 9 × 24 × 8 mm in patient 1 and 2, respectively. After TASM procedure, SAVR was performed with bioprosthetic valve. Postoperative course of both patients was uneventful with no evidence of complete atrioventricular block, septal perforation, or blood flow acceleration at the LVOT.

Discussion

Preoperative planning based on cardiac CT images is safe and useful for guiding adequate myectomy and preventing associated complications in patients with subaortic septal hypertrophy associated with AS.

Improved Outcomes of Conduction System Pacing in Heart Failure with Reduced Ejection Fraction - A Systematic Review and Meta-analysis

Conduction system pacing (CSP) - His bundle pacing (HBP) and Left bundle branch area pacing (LBBAP) - are emerging alternatives to biventricular pacing (BVP) for cardiac resynchronization therapy (CRT) in heart failure. However, evidence is largely limited to small and observational studies. We conducted a meta-analysis including a total of 15 randomized control trials (RCTs) and non-RCTs that compare CSP (HBP & LBBAP) with BVP in patients with CRT indications. We assessed the mean differences in QRS duration (QRSd), pacing threshold, left ventricular ejection fraction (LVEF), and New York Heart Association (NYHA) class score. CSP resulted in a pooled mean QRSd improvement of -20.3 ms (95% CI -26.1 - -14.5, p<0.05, I²=87.1%) versus BVP. For LVEF, a weighted mean increase of 5.2% (95% CI 3.5-6.9, p<0.05, I²=55.6) was observed following CSP versus BVP. The mean NYHA score was reduced by -0.40 (95% CI -0.6 - -0.2, p<0.05, I²=61.7) post-CSP versus BVP. Subgroup analysis of outcomes by LBBAP and HBP demonstrated statistically significant weighted mean improvements from both CSP modalities for QRSd and LVEF compared to BVP. LBBAP resulted in NYHA improvement compared to BVP without differences between CSP subgroups. LBBAP is associated with a significantly lowered mean pacing threshold of -0.51V (95% CI -0.68 - -0.38) whilst HBP had increased the mean threshold (0.62V, 95% CI -0.03 - 1.26) compared to BVP, however, this was associated with significant heterogeneity. Overall, both CSP techniques are feasible and effective CRT alternatives for heart failure. Further RCTs are needed to establish long-term efficacy and safety.

Case report: Challenges and implications of conduction system pacing in pediatrics: Case series

Cardiac electrical stimulation in children usually is needed in the setting of complete congenital atrioventricular block, atrioventricular block after heart surgery, and bradycardia associated with some specific channelopathies. In cases of atrioventricular block, the high percentage of ventricular stimulation raises concern on the deleterious effects of chronic stimulation of the right ventricle. In recent years, physiologic stimulation has developed as a valid approach for adult patients and a great interest has risen in offering conduction system pacing also to the pediatric population. We present three pediatric cases of stimulation of the conduction system (His bundle or left bundle branch), in order to show the intrinsic particularities and challenges implied in these new techniques.

Diagnosis of cardiac sarcoidosis in patients presenting with cardiac arrest or life-threatening arrhythmias

OBJECTIVE

Cardiac sarcoidosis (CS) may present with cardiac arrest or life-threatening arrhythmias. There are limited data on this subgroup of patients with CS. Advanced imaging including cardiovascular magnetic resonance (CMR) and cardiac 18-fluorodeoxyglucose (FDG) positron emission tomography (PET) are used for diagnosis. This study aimed to describe advanced imaging patterns suggestive of CS among patients presenting with cardiac arrest or life-threatening arrhythmias.

METHODS

An imaging database of a CS referral centre (Royal Brompton Hospital, London) was screened for patients presenting with cardiac arrest or life-threatening arrhythmias and having imaging features of suspected CS. Patients diagnosed with definite or probable/possible CS were included.

RESULTS

Study population included 60 patients (median age 49 years) with male predominance (76.7%). The left ventricle was usually non-dilated with mildly reduced ejection fraction (53.4±14.8%). CMR studies showed extensive late gadolinium enhancement (LGE) with 5 (4-8) myocardial segments per patient affected; the right ventricular (RV) side of the septum (28/45) and basal anteroseptum (28/45) were most frequently involved. Myocardial inflammation by FDG-PET was detected in 45 out of 58 patients vs 11 out of 33 patients with oedema imaging available on CMR. When PET was treated as reference to detect myocardial inflammation, CMR oedema imaging was 33.3% sensitive and 77% specific.

CONCLUSIONS

In patients with CS presenting with cardiac arrest or life-threatening arrhythmias, LGE was located in areas where the cardiac conduction system travels (basal anteroseptal wall and RV side of the septum). While CMR was the imaging technique that raised possibility of cardiac scarring, oedema imaging had low sensitivity to detect myocardial inflammation compared with FDG-PET.

Ventricular Septal Defect Exposure by Tricuspid Valve Chordal Detachment-A Retrospective Matched Study

Background: Transatrial approach is the standard method in repairing ventricular septal defects (VSD) in the pediatric population. However, the tricuspid valve (TV) apparatus might obscure the inferior border of the VSD risking the adequacy of repair by leaving residual VSD or heart block. Detachment of the TV chordae has been described as an alternative technique to TV leaflet detachment. The aim of this study is to investigate the safety of such a technique. Methods: Retrospective review of patients who underwent VSD repair between 2015 and 2018. Group A (n = 25) had VSD repair with TV chordae detachment were matched for age and weight to group B (n = 25) without tricuspid chordal or leaflet detachment. Electrocardiogram (ECG) and echocardiogram at discharge and at 3 years of follow-up were reviewed to identify new ECG changes, residual VSD, and TV regurgitation. Results: Median ages in groups A and B were 6.13 (IQR 4.33-7.91) and 6.33 (4.77-7.2) months. New onset right bundle branch block (RBBB) was diagnosed at discharge in 28% (n = 7) of group A versus 56% (n = 14) in group B (P = .044), while the incidence dropped to 16% (n = 4) in group A versus 40% (n = 10) in group B (P = .059) in the 3 years follow-up ECG. Echocardiogram at discharge showed moderate tricuspid regurgitation in 16% (n = 4) in group A and 12% (n = 3) in group B (P = .867). Three years of follow-up echocardiography revealed no moderate or severe tricuspid regurgitation and no significant residual VSD in either group. Conclusion: No significant difference in operative time was observed between the two techniques. TV chordal detachment technique reduces the incidence of postoperative RBBB without increasing the incidence of TV regurgitation at discharge.

Adverse effects of right ventricular pacing on cardiac function: prevalence, prevention and treatment with physiologic pacing

Right ventricular (RV) pacing is the main treatment modality for patients with advanced atrioventricular (AV) block. Chronic RV pacing can cause cardiac systolic dysfunction and heart failure (HF). In this review, we discuss studies that have shown deleterious effects of chronic RV pacing on systolic cardiac function causing pacing-induced cardiomyopathy (PiCM), heart failure (HF), HF hospitalization, atrial fibrillation (AF) and cardiac mortality. RV apical pacing is the most widely used and studied. Adverse effects of RV pacing appear to be directly related to pacing burden and are worse in patients with pre-existing left ventricular (LV) dysfunction. Chronic RV pacing is also associated with heart failure with preserved ejection fraction (HFpEF). Mechanisms, risk factors, clinical and echocardiographic features, and strategies to minimize RV pacing-induced cardiac dysfunction are discussed in light of the latest data. Studies on biventricular (Bi-V) pacing upgrade in patients who develop RV PiCM, use of alternate RV pacing sites, de novo Bi-V pacing, and physiologic pacing using HIS bundle pacing (HBP) and left bundle area (LBBA) pacing in patients with an anticipated high RV pacing burden are discussed.

Conduction system pacing in pediatric and congenital heart disease

Conduction system pacing (CSP) has evolved rapidly to become the pacing method of choice for many adults with structurally normal hearts. Studies in this population have repeatedly demonstrated superior hemodynamics and outcomes compared to conventional pacing with the recruitment of the native conduction system. Children and patients with congenital heart disease (CHD) are also likely to benefit from CSP but were excluded from original trials. However, very recent studies have begun to demonstrate the feasibility and efficacy of CSP in these patients, with growing evidence that some outcomes may be superior in comparison to conventional pacing techniques. Concerns regarding the technical challenges and long-term lead parameters of His Bundle Pacing (HBP) have been overcome to many extents with the development of Left Bundle Branch Area Pacing (LBBAP), and both techniques are likely to play an important role in pediatric and CHD pacing in the future. This review aims to assimilate the latest developments in CSP and its application in children and CHD patients.

Fascicular ventricular tachycardia arising from the left side His and its adjacent region: a subset of upper septal idiopathic left ventricular tachycardia

AIMS

Fascicular ventricle tachycardia (FVT) arising from the proximal aspect of left His-Purkinje system (HPS) has not been specially addressed. Current study was to investigate its clinical, electrocardiographic, and electrophysiological characteristics.

METHODS AND RESULTS

Eighteen patients who were identified as this rare FVT were consecutively enrolled, and their scalar electrocardiogram and electrophysiological data were collected and analysed. The ventricular tachycardia (VT) morphology was similar to sinus rhythm (SR) in eight patients, left bundle branch block type in one patient, right bundle branch block type in seven patients, and both narrow and wide QRS type in two patients. During VT, right-sided His potential preceded the QRS with His-ventricle (H-V) interval of 36.3 ± 12.4 ms, which was shorter than that during SR (-51.4 ± 8.6 ms) (P = 0.002). The earliest Purkinje potentials (PPs) were recorded within 7 ± 3 mm of left-side His and preceded the QRS by 49.1 ± 14.0 ms. Mapping along the left anterior fascicle and left posterior fascicle revealed an antegrade activation sequence in all with no P1 potentials recorded. In the two patients with two VT morphologies, the earliest PP was documented at the same site, and the activation sequence of HPS remained antegrade. Ablation at the earliest PP successfully eliminated the tachycardia, except one patient who developed complete atrial-ventricular block and two patients who abandoned ablations. After at least 12 months follow-up, 15 patients were free from any recurrences.

CONCLUSIONS

Fascicular ventricle tachycardia arising from the proximal aspect of left HPS was featured by recording slightly shorter H-V interval and absence of P1 potentials. Termination of VT requires ablation at the left-sided His or its adjacent region.

The Impact of Cardiac Chamber Volumes on Permanent His Bundle Pacing Procedural Outcomes-A Single Center Experience

His bundle pacing (HBP) has several pitfalls, such as the inability to identify the His bundle and lack of capture at acceptable thresholds. The majority of data regarding HBP were obtained using a dedicated non-deflectable delivery system. This study aimed to evaluate the impact of cardiac chamber dimensions on permanent HBP procedural outcomes when using this type of fixed-curve catheter. Seventy-two patients subjected to HBP from the 1st of January to the 31st of December 2021 at our institution were retrospectively reviewed. The baseline clinical characteristics and echocardiographic measurements of all the cardiac chambers were recorded, as well as procedural outcomes (HB electrogram identification and overall procedural success). During the procedure, the HB electrogram was recorded in 59 patients (81.9%) and successful permanent HBP was achieved in 33 patients, representing 45.8% of all the studied patients. Left atrial (LA) and right atrial (RA) volumes were significantly higher in patients without HB electrogram identification. Only LA and RA volumes were statistically associated with HB electrogram localization, while there was no significant association between the echocardiographic parameters and procedural success. LA volumes above 93 mL and RA volumes above 60 mL had an 8.81 times higher chance of failure to localize the HB electrogram compared with patients with lower volumes (p < 0.001). When considering non-deflectable delivery catheters for HBP, careful preprocedural echocardiographic analysis of the atrial volumes could help in the proper selection of implanting tools, thus optimizing the procedural outcomes and costs.

The basic heart anatomy and physiology from the cardiologist's perspective: Toward a better understanding of left ventricular mechanics, systolic, and diastolic function

A comprehensive understanding of the cardiac structure-function relationship is essential for proper clinical cardiac imaging. This review summarizes the basic heart anatomy and physiology from the perspective of a heart imager focused on myocardial mechanics. The main issues analyzed are the left ventricular (LV) architecture, the LV myocardial deformation through the cardiac cycle, the LV diastolic function basic parameters and the basic parameters of the LV deformation used in clinical practice for the LV function assessment.

Anatomy for right ventricular lead implantation

To understand the position of a pacing lead in the right ventricle and to correctly interpret fluoroscopy and intracardiac signals, good anatomical knowledge is required. The right ventricle can be separated into an inlet, an outlet, and an apical compartment. The inlet and outlet are separated by the septomarginal trabeculae, while the apex is situated below the moderator band. A lead position in the right ventricular apex is less desirable, last but not least due to the thin myocardial wall. Many leads supposed to be implanted in the apex are in fact fixed rather within the trabeculae in the inlet, which are sometimes difficult to pass. In the right ventricular outflow tract (RVOT), the free wall is easier to reach than the septal due to the fact that the RVOT wraps around the septum. A mid-septal position close to the moderator band is relatively simple to achieve and due to the vicinity of the right bundle branch may produce a narrower paced QRS complex. Special and detailed knowledge is necessary for His bundle and left bundle branch pacing.

His Bundle Pacing: My Experience, Tricks, and Tips

His Bundle Pacing (HBP) is a form of physiologic pacing achieved through implantation of a pacing electrode into the His bundle. HBP began 20 years ago without any dedicated tools. As specific tools became available HBP quickly spread and proved to be a viable alternative to traditional right ventricle pacing. HBP is reliable and effective in preserving the physiologic ventricular synchrony with clinical benefits particularly evident when a high percentage of pacing is required. Unipolar signals from the lead tip guide the implant. 3D electroanatomical mapping could further assist the procedure.

Comparative effects of left bundle branch area pacing, His bundle pacing, biventricular pacing in patients requiring cardiac resynchronization therapy: A network meta-analysis

Background

The comparative effects of different types of cardiac resynchronization therapy (CRT) delivered by biventricular pacing (BVP), His bundle pacing (HBP), and left bundle branch area pacing (LBBAP) remain inconclusive.

Hypothesis

HBP and LBBAP may be advantageous over BVP for CRT.

Methods

PubMed, Embase, Web of Science, and the Cochrane Library were systematically searched for studies that reported the effects after BVP, HBP, and LBBAP for CRT. The effects between groups were compared by a frequentist random‐effects network meta‐analysis (NMA), by which the mean differences (MDs) and 95% confidence intervals (CIs) were calculated.

Results

Six articles involving 389 patients remained for the final meta‐analysis. The mean follow‐up of these studies was 8.03 ± 3.15 months. LBBAP resulted in a greater improvement in LVEF% (MD = 7.17, 95% CI = 4.31 to 10.04), followed by HBP (MD = 4.06, 95% CI = 1.09 to 7.03) compared with BVP. HBP resulted in a narrower QRS duration (MD = 31.58 ms, 95% CI = 12.75 to 50.40), followed by LBBAP (MD = 27.40 ms, 95% CI = 10.81 to 43.99) compared with BVP. No significant differences of changes in LVEF improvement and QRS narrowing were observed between LBBAP and HBP. The pacing threshold of LBBAP was significantly lower than those of BVP and HBP.

Conclusion

The NMA first found that LBBAP and HBP resulted in a greater LVEF improvement and a narrower QRS duration compared with BVP. Additionally, LBBAP resulted in similar clinical outcomes but with lower pacing thresholds, and may therefore offer advantages than does HBP for CRT.

High-resolution parahisian mapping and ablation using microelectrode embedded ablation catheters

BACKGROUND

Accurate mapping of the compact atrioventricular (AV) node is critical during ablation of a range of arrhythmias.

OBJECTIVE

The purpose of this multicenter prospective study was to test the hypothesis that microelectrode (ME)-embedded catheters more accurately define the near-field compact AV node compared to conventional catheters.

METHODS

For the mapping phase, detailed AV junction maps were created in 47 patients using an ME-embedded catheter. His electrograms (EGMs) detected by conventional electrodes (His_c) and by ME (His_μ) were annotated. For the ablation phase, AV nodal ablation (Qmode 50 W) was performed in 10 patients after pacemaker implantation, with initial His_c-only ablation in group 1 (n = 6) and initial His_μ ablation in group 2 (n = 4). For the clinical phase, a prospective registry of parahisian tachycardia using QDOT was obtained.

RESULTS

In the mapping phase, 7.0 ± 5.4 His_c and 8.0 ± 5.6 His_μ points were acquired per map (n = 47). His_μ cloud was smaller and more proximally located than His_c cloud: (99.4 ± 74.7 mm² vs 197.6 ± 110.6 mm²; P = .0008). His_μ EGMs had larger amplitudes than His_c EGMs (0.40 ± 0.38 mV vs 0.16 ± 0.1 mV; P = .0002). In the ablation phase, for group 1: His_c-only ablation never resulted in AV block, whereas His_μ ablation resulted in AV block after limited ablation in all patients (after 13.3 ± 9.2 s); and for group 2: His_μ ablation always resulted in AV block after 1 application (after 14.3 ± 10.3 s). In the clinical phase, a His_μ-avoidance strategy could avoid AV block in a prospective registry of 11 patients.

CONCLUSION

ME more accurately defines the region of the compact node, and ablation in this region is associated with a high risk for AV block. ME-based mapping has the potential to significantly enhance ablation safety and efficacy.

Left bundle branch pacing: An evolving site for physiological pacing

For patients with symptomatic bradyarrhythmia, cardiac pacing is the only appropriate treatment option. Electrical and mechanical dyssynchrony caused by traditional right ventricular apical pacing leads to left ventricular dysfunction and atrial arrhythmias. Physiological pacing stimulates natural cardiac conduction, resulting in synchronized ventricular contraction. Even if His bundle pacing (HBP) is an ideal physiological pacing modality, it is technically not always feasible because of high capture thresholds, disease in the distal His bundle, and follow-up troubleshooting issues. Left bundle branch pacing (LBBP) has been proposed as a viable alternative to HBP since it provides lead stability, a low and stable pacing threshold, and correction of distal conduction system disease.

The relationship between anatomy and electrical parameters in His bundle pacing: A transthoracic echocardiography evaluation

PURPOSE

The implantation site of the His bundle (HB) lead may influence pacing parameters. Our aim was to characterize the anatomical location of the HB lead tip and its relationship with acute electrical parameters.

METHODS

Consecutive patients who underwent HB lead implantation, guided by standard fluoroscopy and electrophysiology, were prospectively enrolled. The relationship between HB lead tip and tricuspid valve plane (TVP) was assessed with post-procedure transthoracic echocardiography.

RESULTS

Twenty-five patients were studied. In 11 patients (44%), the HB lead tip did not cross the TVP (A group): in 7 cases it was screwed in the right atrium at a mean distance of -6.1 mm from the TVP and, in 4 cases, at the level of the tricuspid annulus. In the remaining 14 patients (56%), the lead tip crossed the TVP (V group): it was screwed in the right ventricle at a mean distance of 9.3 mm from the TVP. A and V groups had comparable HB capture thresholds (1.6 ± 1 V vs 1.7 ± 0.7 V, 1 ms pulse-width; p = 0.66); selective HB capture was significantly more represented in the A group (91% vs 21%; p = 0.001). Significantly higher R-wave amplitudes were seen in the V group (6.7 ± 3 vs 2.5 ± 1.7 mV; p = 0.0004), and they positively correlated with the distance from the TVP (p = 0.0038). Atrial oversensing was never observed.

CONCLUSION

In a consecutive cohort of HB pacing recipients, the rate of patients who had an effective HB capture in the atrium was substantial and was characterized by different electrophysiological properties than in the ventricle.

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.

Comparison of electrical characteristics and pacing parameters of pacing different parts of the His-Purkinje system in bradycardia patients

PURPOSE

We aimed to evaluate the electrical characteristics and pacing parameters at different locations of His-Purkinje system pacing.

METHODS

Patients who successfully underwent His-Purkinje system pacing with bradycardia indications from April 2018 to August 2019 were retrospectively analyzed according to the lead location confirmed by visualization of the tricuspid value annulus, postoperative echocardiography, and pacing electrocardiogram. The electrical characteristics and pacing parameters were compared among these patients.

RESULTS

A total of 135 patients were retrospectively analyzed. Among them, 30 patients received atrial side HBP (aHBP group), 52 received ventricular side HBP (vHBP group), and 53 received left bundle branch pacing (LBBP group). The proportion of non-selective pacing was significantly lower in aHBP group (30.0%) than in vHBP (75.0%) and LBBP group (90.6%). LBBP had significantly shorter procedural and fluoroscopic duration than aHBP and vHBP. The capture threshold was significantly higher (1.07 ± 0.26 V/1.0 ms vs. 0.89 ± 0.22 V/1.0 ms vs. 0.77 ± 0.18 V/0.4 ms, P < 0.01, respectively), and the R-wave amplitude was significantly lower (3.71 ± 1.72 mV vs. 5.81 ± 2.37 mV vs. 10.27 ± 4.71 mV, P < 0.05 respectively) in aHBP group than those in the other two groups at implantation and during 3-month follow-up. No significant differences were observed in complications among groups during 3-month follow-up.

CONCLUSION

VHBP and LBBP had better pacing performances than aHBP and might be more ideal pacing methods for bradycardia patients.

High-intensity ultrasound catheter ablation achieves deep mid-myocardial lesions in vivo

BACKGROUND

Radiofrequency ablation of epicardial and mid-myocardial ventricular arrhythmias is limited by lesion depth.

OBJECTIVE

The purpose of this study was to generate deep mid-interventricular septal (IVS) lesions using high-intensity ultrasound (US) from an endocardial catheter-based approach.

METHODS

Irrigated US catheters (12 F) were fabricated with 3 × 5 mm transducers of 5.0, 6.5, and 8.0 MHz frequencies and compared in an ex vivo perfused myocardial ablation model. In vivo septal ablation in swine (n = 12) was performed via femoral venous access to the right ventricle. Lesions were characterized by echocardiography, cardiac magnetic resonance imaging, and electroanatomic voltage mapping pre- and post-ablation, and at 30 days. Four animals were euthanized immediately post-ablation to compare acute and chronic lesion histology and gross pathology.

RESULTS

In ex vivo models, maximal lesion depth and volume was achieved by 6.5 MHz catheters, which were used in vivo. Lesion depth by gross pathology was similar post-ablation (10.8 mm; 95% confidence interval [CI] 9.9-12.4 mm) and at 30 days (11.2 mm; 95% CI 10.6-12.4 mm) (P = .56). Lesion volume decreased post-ablation to 30 days (from 255 [95% CI 198-440] to 162 [95% CI 133-234] mm³; P = .05), yet transmurality increased from 58% (95% CI 50%-76%) to 81% (95% CI 74%-93%), attributable to a reduction in IVS thickness (from 16.0 ± 1.7 to 10.6 ± 2.4 mm; P = .007). Magnetic resonance imaging confirmed dense septal ablation by delayed enhancement, with increased T1 time post-ablation and at 30 days and increased T2 time only post-ablation. Voltage mapping of both sides of IVS demonstrated reduced unipolar (but not bipolar) voltage along the IVS.

CONCLUSION

High-intensity US catheter ablation may be an effective treatment of mid-myocardial or epicardial ventricular arrhythmias from an endocardial approach.

His bundle pacing insights from electroanatomical mapping: Topography and pacing targets

OBJECTIVES

To characterize 3D electroanatomical mapping (EAM) of the His bundle (HB) region.

BACKGROUND

Visualization of selective (S) and nonselective (NS) HB capture areas by EAM has not been described and may help guide HB pacing (HBP).

METHODS

EAM was performed via NavX system in 17 patients (pts) undergoing HBP. HB cloud, S-HB, NS-HB, and right bundle (RB) capture areas were mapped.

RESULTS

S-HBP areas were identified in 11, NS-HBP in 14, and RB in 11 pts. Two NS-HBP areas (upper and lower) either separated by S-HBP (8 pts) or almost contiguous (5 pts) were observed. S-HBP area measured: 1.1 ± 0.9 cm² , NS upper: -1.2 ± 0.9 cm² , NS lower: -1.2 ± 0.9 cm² , RB: -1.7 ± 1.3 cm² , total His cloud: -4.1 ± 2.7 cm² . Electrocardiogram (ECG) pacemaps were different between upper and lower NS-HBP areas in 13/14 pts (p = .006). ECG differences between NS clouds were present in inferior leads in 9 pts (more negative QRS complex from lower NS area) and in precordial leads in 5 pts. There was no correlation between HBP lead location and capture threshold. R-wave amplitude was higher at more distal locations on HB cloud (p = .02).

CONCLUSION

(1) Pacemapping identifies distinct regions that may correspond to HB anatomy. (2) A linear S-HBP area is typically surrounded by two separate NS areas. (3) Pace-map ECGs from upper and lower NS-HBP areas have different morphologies. (4) These EAM features and pace-mapping may be helpful to the implanter.

[Anatomic pitfalls and challenges of His bundle pacing]

Long-term right ventricular apical pacing is known to be deleterious for left ventricular function leading to the clinical picture of heart failure with all the possibly associated complications, ranging up to death of the affected patient. This led to the ambition to find alternative pacing sites such as pacing at the right ventricular outflow tract or septal pacing. An attractive alternative is selective His bundle pacing with the goal to use the physiologic His-Purkinje system in order to enable intrinsic conduction and physiologic myocardial contraction. To find and identify the His bundle poses a challenge for operators. For exact endocardial mapping, knowledge of the anatomic landmarks is as important as the ability to evaluate local electrocardiograms. The goal of this review is to characterize the anatomic landmarks to help physicians to identify these precise targets for His bundle pacing.