Impact of Physiologic Pacing Versus Right Ventricular Pacing Among Patients With Left Ventricular Ejection Fraction Greater Than 35%: A Systematic Review for the 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society

Ablate and pace strategy for atrial fibrillation: pacing modalities, ablation approaches and impact on patient outcomes

INTRODUCTION

In patients with symptomatic, refractory atrial fibrillation the ablate and pace (A&P) strategy (pacemaker implantation followed by atrio-ventricular junction ablation (AVJA)) is superior to medical therapy in improving quality of life and prognosis. Despite its well-proven benefits, this invasive therapeutic option is still underutilized in clinical practice. The choice of pacing modality (right ventricular pacing, biventricular pacing, BVP, or conduction system pacing, CSP) is crucial and can have significant clinical implications. In particular, in recent years CSP is emerging as an alternative to BVP, showing a good effectiveness and safety profile. Other important aspects are the timing of ablation, the approach used for AVJA, and the correct device programming after AVJA.

AREAS COVERED

This article reviews the currently available evidence on this therapeutic strategy with a particular focus on its impact on patient outcome, recognized indications, technical considerations, and future perspectives.

EXPERT OPINION

With the availability of more robust evidence confirming the better effectiveness and safety profile of CSP compared to conventional pacing modalities, in the next few years CSP will become the standard pacing modality in candidates for A&P. The routine adoption of this pacing modality could lead to a wider use of A&P in clinical practice.

Takotsubo syndrome induced by de novo left bundle branch area pacing: a case report

Background

Takotsubo syndrome (TS), traditionally associated with emotional or physical stressors, manifests as transient left ventricular (LV) abnormalities mimicking acute coronary syndrome. Surgical procedures, such as pacemaker implantation, have emerged as potential TS triggers. Conduction system pacing (CSP), including His bundle pacing and left bundle branch area pacing (LBBAP), is a novel technique utilizing the heart's intrinsic conduction system. Despite documented cases of TS post-pacemaker implantation, the literature exploring the association between CSP and TS remains sparse.

Case summary

In a case involving a 62-year-old woman with 2:1 atrioventricular block, an uncomplicated de novo LBBAP procedure was followed by post-procedural dizziness and dyspnoea. An initial transthoracic echocardiography revealed moderate-severe LV dysfunction, accompanied by elevated troponin levels. Coronary angiography showed unobstructed coronary arteries, while left ventriculography exhibited a classic apical ballooning. The patient had a favourable recovery, with LV function improvement noted before discharge.

Discussion

Takotsubo syndrome may be triggered by other non-traditional physical stressors including traditional RV pacing and LBBAP. Clinicians should be aware of this potential, albeit rare, complication of LBBAP to ensure timely recognition and management. Increased awareness is vital for optimizing patient care during CSP procedures.

His Bundle Pacing and Left Bundle Branch Pacing in Patients with Heart Failure

BACKGROUND

His bundle pacing (HBP) and left bundle branch pacing (LBBP) are emerging therapies for patients with heart failure and conduction disorders, offering potential advantages over traditional pacing methods. These approaches aim to restore physiological conduction and improve cardiac function more effectively.

OBJECTIVE

This study aims to evaluate the efficacy and safety of HBP and LBBP in patients with heart failure and conduction disturbances, comparing these techniques to conventional pacing.

METHODS

A comprehensive review of recent studies and clinical trials was conducted, focusing on the performance of HBP and LBBP in improving cardiac function, reducing QRS duration, and enhancing overall patient outcomes. The analysis includes data on clinical efficacy, procedural safety, and long-term benefits associated with these pacing modalities.

RESULTS

Both HBP and LBBP have demonstrated significant improvements in cardiac function and clinical outcomes compared to conventional pacing. HBP effectively restores physiological conduction with improved synchronization and a reduction in QRS duration. LBBP has shown enhanced left ventricular activation, leading to better overall cardiac performance. Both techniques have been associated with a lower incidence of complications and a higher success rate in achieving optimal pacing thresholds.

CONCLUSIONS

HBP and LBBP offer promising alternatives to traditional pacing for patients with heart failure and conduction disorders. These advanced pacing strategies provide superior clinical outcomes and improved cardiac function with reduced risk of complications. Further research and clinical trials are needed to fully establish the long-term benefits and safety profiles of these techniques in diverse patient populations.

Review of Atrioventricular Node Ablation Combined with Permanent His-Purkinje Conduction System Pacing in Patients with Atrial Fibrillation with Heart Failure

With the advancement of pacing technologies, His-Purkinje conduction system pacing (HPCSP) has been increasingly recognized as superior to conventional right ventricular pacing (RVP) and biventricular pacing (BVP). This method is characterized by a series of strategies that either strengthen the native cardiac conduction system or fully preserve physical atrioventricular activation, ensuring optimal clinical outcomes. Treatment with HPCSP is divided into two pacing categories, His bundle pacing (HBP) and left bundle branch pacing (LBBP), and when combined with atrioventricular node ablation (AVNA), can significantly improve left ventricular (LV) function. It effectively prevents tachycardia and regulates ventricular rates, demonstrating its efficacy and safety across different QRS wave complex durations. Therefore, HPCSP combined with AVNA can alleviate symptoms and improve the quality of life in patients with persistent atrial fibrillation (AF) who are unresponsive to multiple radiofrequency ablation, particularly those with concomitant heart failure (HF) who are at risk of further deterioration. As a result, this "pace and ablate" strategy could become a first-line treatment for refractory AF. As a pacing modality, HBP faces challenges in achieving precise localization and tends to increase the pacing threshold. Thus, LBBP has emerged as a novel approach within HPCSP, offering lower thresholds, higher sensing amplitudes, and improved success rates, potentially making it a preferable alternative to HBP. Future large-scale, prospective, and randomized controlled studies are needed to evaluate patient selection and implantation technology, aiming to clarify the differential clinical outcomes between pacing modalities.

Feasibility, safety and outcomes of conduction system pacing for bradycardia amongst the very elderly

The impact of age (≥ 85 vs < 85 years) on clinical outcomes and pacemaker performance of conduction system pacing (CSP) compared to right ventricular pacing (RVP) were examined. Consecutive patients from a prospective, observational, multicenter study with pacemakers implanted for bradycardia were studied. The primary endpoint was a composite of heart failure (HF)-hospitalizations, pacing-induced cardiomyopathy requiring cardiac resynchronization therapy or all-cause mortality. Secondary endpoints were acutely successful CSP, absence of pacing-complications, optimal pacemaker performance defined as pacing thresholds < 2.5 V, R-wave amplitude ≥ 5 V and absence of complications, threshold stability (no increases of > 1 V) and persistence of His-Purkinje capture on follow-up. Among 984 patients (age 74.1 ± 11.2 years, 41% CSP, 16% ≥ 85 years), CSP was independently associated with reduced hazard of the primary endpoint compared to RVP, regardless of age-group (< 85 years: adjusted hazard ratio [AHR] 0.63, 95% confidence interval [CI] 0.40-0.98; ≥ 85 years: AHR 0.40, 95% CI 0.17-0.94). Among patients with CSP, age did not significantly impact the secondary endpoints of acute CSP success (86% vs 88%), pacing complications (19% vs 11%), optimal pacemaker performance (64% vs 69%), threshold stability (96% vs 96%) and persistent His-Purkinje capture (86% vs 91%) on follow-up (all p > 0.05). CSP improves clinical outcomes in all age-groups, without compromising procedural safety or pacemaker performance in the very elderly.

Case Report: Left bundle branch pacing in an amyloid light-chain cardiac amyloidosis patient with atrioventricular block

Introduction

Amyloid light-chain cardiac amyloidosis is a progressive infiltrative disease characterized by the deposition of amyloid fibrils in the cardiac tissue, which can cause serious atrioventricular block requiring pacemaker implantation. Left bundle branch pacing has emerged as an alternative method for delivering physiological pacing to achieve electrical synchrony of the left ventricle. However, left bundle branch pacing in patients with amyloid light-chain cardiac amyloidosis has not been studied in detail. Therefore, in this study, we present a case of left bundle branch pacing in a patient with amyloid light-chain cardiac amyloidosis.

Case summary

A 66-year-old male patient with amyloid light-chain cardiac amyloidosis presented with syncope for 1 month. Holter monitoring revealed intermittent third-degree atrioventricular block. Left bundle branch pacing was performed successfully. During the 1-year follow-up, it was observed that the left bundle branch capture threshold remained stable without any pacemaker-related complications or left ventricle systolic dysfunction, and there was no recurrence of syncope.

Conclusion

Left bundle branch pacing appears to be a safe and feasible option for patients with amyloid light-chain cardiac amyloidosis experiencing atrioventricular block.

2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines

AIM

The "2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation" provides recommendations to guide clinicians in the treatment of patients with atrial fibrillation.

METHODS

A comprehensive literature search was conducted from May 12, 2022, to November 3, 2022, encompassing studies, reviews, and other evidence conducted on human subjects that were published in English from PubMed, EMBASE, the Cochrane Library, the Agency for Healthcare Research and Quality, and other selected databases relevant to this guideline. Additional relevant studies, published through November 2022, during the guideline writing process, were also considered by the writing committee and added to the evidence tables, where appropriate.

STRUCTURE

Atrial fibrillation is the most sustained common arrhythmia, and its incidence and prevalence are increasing in the United States and globally. Recommendations from the "2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation" and the "2019 AHA/ACC/HRS Focused Update of the 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation" have been updated with new evidence to guide clinicians. In addition, new recommendations addressing atrial fibrillation and thromboembolic risk assessment, anticoagulation, left atrial appendage occlusion, atrial fibrillation catheter or surgical ablation, and risk factor modification and atrial fibrillation prevention have been developed.

2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines

AIM

The "2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Patients With Atrial Fibrillation" provides recommendations to guide clinicians in the treatment of patients with atrial fibrillation.

METHODS

A comprehensive literature search was conducted from May 12, 2022, to November 3, 2022, encompassing studies, reviews, and other evidence conducted on human subjects that were published in English from PubMed, EMBASE, the Cochrane Library, the Agency for Healthcare Research and Quality, and other selected databases relevant to this guideline. Additional relevant studies, published through November 2022, during the guideline writing process, were also considered by the writing committee and added to the evidence tables, where appropriate.

STRUCTURE

Atrial fibrillation is the most sustained common arrhythmia, and its incidence and prevalence are increasing in the United States and globally. Recommendations from the "2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation" and the "2019 AHA/ACC/HRS Focused Update of the 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation" have been updated with new evidence to guide clinicians. In addition, new recommendations addressing atrial fibrillation and thromboembolic risk assessment, anticoagulation, left atrial appendage occlusion, atrial fibrillation catheter or surgical ablation, and risk factor modification and atrial fibrillation prevention have been developed.

Clinical Outcomes in Conduction System Pacing Compared to Right Ventricular Pacing in Bradycardia

BACKGROUND

Conduction system pacing (CSP) provides more physiological ventricular activation than right ventricular pacing (RVP).

OBJECTIVES

This study evaluated the differences in clinical outcomes in patients receiving CSP and RVP.

METHODS

Consecutive patients with pacemakers implanted for bradycardia from 2016 to 2021 in 2 centers were prospectively followed for the primary composite outcome of heart failure (HF) hospitalizations, upgrade to biventricular pacing, or all-cause mortality, stratified by ventricular pacing burden (Vp) .

RESULTS

Among 860 patients (mean age 74 ± 11 years, 48% female, 48% atrioventricular block), 628 received RVP and 231 received CSP (95 His-bundle pacing, 136 left bundle branch pacing). The primary outcome occurred in 217 (25%) patients, more commonly in patients with RVP than CSP (30% vs 13%, P < 0.001). In multivariable analyses, CSP was independently associated with 47% reduction of the primary outcome (adjusted hazard ratio [AHR]: 0.53; 95% CI: 0.29-0.97; P = 0.04) and HF hospitalization alone (AHR: 0.40; 95% CI: 0.17-0.95; P = 0.04), among only patients with Vp >20%. The incidence of the primary outcome was highest among RVP with Vp >20% and lowest in CSP with Vp >20% (35% vs 10%, P < 0.001). Compared with RVP with Vp >20%, both CSP with Vp >20% (AHR: 0.51; 95% CI: 0.28-0.91; P = 0.02) and all patients with Vp ≤20% (AHR: 0.73; 95% CI: 0.54-0.99; P = 0.04) were independently associated with reduced primary outcome, driven primarily by reductions in HF hospitalizations (P < 0.05). Event-free survival was similar between CSP with Vp >20% and those needing ≤20% Vp.

CONCLUSIONS

CSP significantly reduced adverse clinical outcomes for bradycardic patients requiring ventricular pacing and should be the preferred pacing modality of choice.

Case report: What course to follow when left bundle branch pacing encounters acute myocardial infarction?

Compared with traditional right ventricular apical pacing, His-bundle pacing (HBP) provides more physiologic pacing by activating the normal conduction system. However, HBP has some limitations including higher pacing thresholds. In addition, disease in the distal His-Purkinje system may prevent the correction of abnormal conduction. Left bundle branch pacing (LBBP) may overcome these disadvantages by providing lower pacing thresholds and relatively narrow QRS duration that improve cardiac function. Here, we describe a rare case of a transient loss of ventricular capture due to acute anterior wall myocardial infarction in an LBB-paced patient. With the improvement of the ischemia, the function of the pacemaker partly recovered. We review the adaptations, advantages, and limitations, and long-term safety of LBBP.

Risk factors of pacing dependence and cardiac dysfunction in patients with permanent pacemaker implantation

AIMS

Right ventricular pacing (RVP) dependence could impair left ventricular ejection fraction (LVEF). This study aimed to illuminate the relationship between RVP proportion and LVEF, as well as disclosing independent predictors of RVP dependence.

METHODS AND RESULTS

Patients indicated for permanent pacemaker implantation were included (2016-2020). The ventricular pacing lead was placed in right ventricular apex or septum. Pacing mode programming followed universal standard. Electrocardiographic, echocardiographic, and serological parameters were collected. RVP dependence was defined according to its influence on LVEF. This study was of case-control design. Included patients were matched by potentially confounding factors through propensity score matching. A total of 1183 patients were included, and the mean duration of follow-up was 24 months. Percentage of RVP < 80% hardly influenced LVEF; however, LVEF tended to decrease with higher RVP proportion. High degree/complete atrioventricular block (AVB) [odds ratio (OR) = 5.71, 95% confidence interval (CI): 3.66-8.85], atrial fibrillation (AF) (OR = 2.04, 95% CI: 1.47-2.82), percutaneous coronary intervention (PCI) (OR = 2.89, 95% CI: 1.24-6.76), maximum heart rate (HR_max ) < 110 b.p.m. (OR = 2.74, 95% CI: 1.58-4.76), QRS duration > 120 ms (OR = 2.46, 95% CI: 1.42-4.27), QTc interval > 470 ms (OR = 2.01, 95% CI: 1.33-3.05), and pulmonary artery systolic pressure (PASP) > 40 mmHg (OR = 1.93, 95% CI: 1.46-2.56) were proved to predict RVP dependence.

CONCLUSIONS

High RVP percentage (>80%) indicating RVP dependence significantly correlates with poor prognosis of cardiac function. High degree/complete AVB, AF, ischaemic aetiology, PCI history, HR_max  < 110 b.p.m., QRS duration > 120 ms, QTc interval > 470 ms, and PASP > 40 mmHg were verified as independent risk factors of RVP dependence.

Clinical Outcomes Associated With His-Purkinje System Pacing vs. Biventricular Pacing, in Cardiac Resynchronization Therapy: A Meta-Analysis

Aims

His-Purkinje system pacing has recently emerged as an alternative to biventricular pacing (BIVP) in cardiac resynchronization therapy (CRT). The aim of this study was to conduct a meta-analysis comparing the clinical outcomes associated with His-Purkinje system pacing (HPSP) vs. BIVP in patients with heart failure. There is also a comparison of clinical outcomes of His-bundle pacing (HBP) and left bundle branch pacing (LBBP) in the His-Purkinje system.

Methods

We searched the Cochrane Library, Embase, and PubMed, for studies published between January 2010 and October 2021 that compared the clinical outcomes associated with HPSP vs. BIVP and HBP vs. LBBP in HPSP in patients who underwent CRT. The pacing threshold, R-wave amplitudes, QRS duration, New York Heart Association functional (NYHA), left ventricular ejection fraction (LVEF), and LV end-diastolic diameter (LVEDD) of heart failure, at follow-up, were extracted and summarized for meta-analysis.

Results

A total of 18 studies and 1517 patients were included in our analysis. After a follow-up period of 9.3 ± 5.4 months, the HPSP was found to be associated with shorter QRS duration in the CRT population compared to that in the BIVP (SMD, −1.17; 95% CI, −1.56 to −0.78; P &lt; 0.00001; I2 = 74%). No statistical difference was verified between HBP and LBBP on QRS duration (SMD, 0.04; 95% CI, −0.32 to 0.40; P = 0.82; I2 = 84%). In the comparison of HPSP and BIVP, the LBBP subgroup showed improved LVEF (SMD, 0.67; 95% CI, 0.42–0.91; P &lt; 0.00001; I2 = 0%), shorter LVEDD (SMD, 0.59; 95% CI, 0.93–0.26; P = 0.0005; I2 = 0%), and higher New York Heart Association functional class (SMD, −0.65; 95% CI, −0.86 to −0.43; P &lt; 0.00001; I2 = 45%). In terms of pacing threshold and R-wave amplitude clinical outcomes, LBBP has a lower pacing threshold (SMD, 1.25; 95% CI, 1.12–1.39; P &lt; 0.00001; I2 = 47%) and higher R-wave amplitude (MD, −7.88; 95% CI, −8.46 to −7.31; P &lt; 0.00001; I2 = 8%) performance compared to HBP.

Conclusion

Our meta-analysis showed that the HPSP produced higher LVEF, shorter QRS duration, and higher NYHA functional class in the CRT population than the BIVP as observed on follow-up. LBBP has a lower pacing threshold and higher R-wave amplitude. HPSP may be a new and promising alternative to BIVP in the future.

Emerging Implantable Device Technology for Patients at the Intersection of Electrophysiology and Heart Failure Interdisciplinary Care

Cardiac implantable electronic devices (CIEDs), including implantable cardioverter-defibrillators (ICDs) and cardiac resynchronization therapy (CRT), are part of guideline- indicated treatment for a subset of patients with heart failure with reduced ejection fraction (HFrEF). Current technological advancements in CIEDs have allowed the detection of specific patient physiologic parameters used for forecasting clinical decompensation through algorithmic, multiparameter remote monitoring. Other recent emerging technologies, including cardiac contractility modulation (CCM) and baroreflex activation therapy (BAT), may provide symptomatic or physiologic benefit in patients without an indication for CRT. Our goal in this state-of-the-art review is to describe the commercially available new technologies, purported mechanisms of action, evidence surrounding their clinical role, limitations, and future directions. Finally, we underline the need for standardized workflow and close interdisciplinary management of this population to ensure the delivery of high-quality care.

Impact of physiological pacing on functional mitral regurgitation in systolic dysfunction: Initial echocardiographic remodeling findings after His bundle pacing

BACKGROUND

Although His bundle pacing (HBP) has been shown to improve left ventricular ejection fraction (LVEF), its impact on mitral regurgitation (MR) remains uncertain.

OBJECTIVES

The aim of this study was to evaluate change in functional MR after HBP in patients with left ventricular (LV) systolic dysfunction.

METHODS

Paired echocardiograms were retrospectively assessed in patients with reduced LVEF (<50%) undergoing HBP for pacing or resynchronization. The primary outcomes assessed were change in MR, LVEF, LV volumes, and valve geometry pre- and post-HBP. MR reduction was characterized as a decline in ≥1 MR grade post-HBP in patients with ≥grade 3 MR at baseline.

RESULTS

Thirty patients were analyzed: age 68 ± 15 years, 73% male, LVEF 32% ± 10%, 38% coronary artery disease, 33% history of atrial fibrillation. Baseline QRS was 162 ± 31 ms: 33% left bundle branch block, 37% right bundle branch block, 17% paced, and 13% narrow QRS. Significant reductions in LV end-systolic volume (122 mL [73-152 mL] to 89 mL [71-122 mL], P = .006) and increase in LV ejection fraction (31% [25%-37%] to 39% [30%-49%], P < .001) were observed after HBP. Ten patients had grade 3 or 4 MR at baseline, with reduction in MR observed in 7. In patients with at least grade 3 MR at baseline, reduction in LV volumes, improved mitral valve geometry, and greater LV contractility were associated with MR reduction. Greater reduction in paced QRS width was present in MR responders compared to non-MR responders (-40% vs -25%, P = .04).

CONCLUSIONS

In this initial detailed echocardiographic analysis in patients with LV systolic dysfunction, HBP reduced functional MR through favorable ventricular remodeling.

Three-year outcome after transcatheter aortic valve implantation: Comparison of a restrictive versus a liberal strategy for pacemaker implantation

BACKGROUND

Conduction disturbances after transcatheter aortic valve implantation (TAVI) are common, heterogeneous, and frequently result in permanent pacemaker implantation (PPI). Pacemaker therapy with a high rate of right ventricular pacing is associated with heart failure, hospitalizations, and reduced quality of life.

OBJECTIVE

The purpose of this study was to compare medium-term outcomes between PPI implantation strategies, as choosing the right indication for PPI is still an area of uncertainty and information on outcomes of PPI regimens beyond 1 year is rare.

METHODS

We compared outcomes after 3 years between a restrictive PPI strategy, in which the lowest threshold for PPI was left bundle branch block (LBBB) (QRS >120 ms) with the presence of new atrioventricular block (PQ >200 ms), and a liberal PPI regimen, in which PPI already was performed in patients with new-onset LBBB.

RESULTS

Between January 2014 and December 2016, TAVI was performed in 884 patients at our center. Of these, 383 consecutive, pacemaker-naive patients underwent TAVI with the liberal PPI strategy and subsequently 384 with the restrictive strategy. The restrictive strategy significantly reduced the percentage of patients undergoing PPI before discharge (17.2% vs 38.1%; P <.001). The incidence of the primary endpoint (all-cause-mortality and hospitalization for heart failure) after 3 years was similar in both groups (30.7% vs 35.2%; P = .242), as was all-cause-mortality (26.6% vs 29.2%; P = .718). Overall, patients who required PPI post-TAVI had significantly more hospitalizations due to heart failure (14.8% vs 7.8%; P = .004).

CONCLUSION

A restrictive PPI strategy after TAVI reduces PPI significantly and is safe in medium-term follow-up over 3 years.

Left Bundle Branch Pacing: Current Knowledge and Future Prospects

Cardiac pacing is an effective therapy for treating patients with bradycardia due to sinus node dysfunction or atrioventricular block. However, traditional right ventricular apical pacing (RVAP) causes electric and mechanical dyssynchrony, which is associated with increased risk for atrial arrhythmias and heart failure. Therefore, there is a need to develop a physiological pacing approach that activates the normal cardiac conduction and provides synchronized contraction of ventricles. Although His bundle pacing (HBP) has been widely used as a physiological pacing modality, it is limited by challenging implantation technique, unsatisfactory success rate in patients with wide QRS wave, high pacing capture threshold, and early battery depletion. Recently, the left bundle branch pacing (LBBP), defined as the capture of left bundle branch (LBB) via transventricular septal approach, has emerged as a newly physiological pacing modality. Results from early clinical studies have demonstrated LBBP's feasibility and safety, with rare complications and high success rate. Overall, this approach has been found to provide physiological pacing that guarantees electrical synchrony of the left ventricle with low pacing threshold. This was previously specifically characterized by narrow paced QRS duration, large R waves, fast synchronized left ventricular activation, and correction of left bundle branch block. Therefore, LBBP may be a potential alternative pacing modality for both RVAP and cardiac resynchronization therapy with HBP or biventricular pacing (BVP). However, the technique's widespread adaptation needs further validation to ascertain its safety and efficacy in randomized clinical trials. In this review, we discuss the current knowledge of LBBP.

Optimizing single-chamber pacing in dogs Part 1: Rate determinations, rate interventions and hysteresis

Determining ideal pacing rates to meet physiological needs and optimizing programming to prevent unnecessary right ventricular pacing in dogs requires an understanding of heart rate profiles and applicable pacing technology. The heart rate and rhythm of the dog is complex necessitating investigation of rate requirements of activity and circadian influences. Overlaying this information are a multiplicity of other factors such as age, breed, temperament, cardiovascular disease and underlining rhythm disorders that contribute to the difficulty in making general conclusions. However, all such information permits better implementation of programming options with the goal of better outcomes. In this review (Part 1 of a two-part review) instantaneous heart rate, rolling average heart rate, simple average heart rate, heart rate tachograms, RR interval tachograms (2D, 3D and dynamic), and Poincaré plots (2D, 3D and dynamic) are discussed as they apply to decisions in the determination and examination of pacing rates for dogs programmed in the VVI pacing mode (Ventricular paced, Ventricular sensed, Inhibited pacing). The applicable pacing operations available for three pacemaker companies are reviewed (Abbott, Biotronik/Dextronix, and Medtronic). The programmable options considered include: slowest pacing rate without additional features to extend the pacing interval, sleep/rest rate preferences, hysteresis to lengthen pacing interval following intrinsic beats, and intermittent increases in pacing following abrupt loss of intrinsic rhythm. Recommendations are suggested for follow-up of individual dogs with examination of pacing statistics and Holter monitoring.

Optimizing single-chamber pacing in dogs. Part 2: Rate adaptive pacing

Proper programming of pacemakers for dogs in the rate adaptive mode requires an understanding of the rate requirements for each individual and the interplay of programmable features. The specific advantages and disadvantages of the rate adaptive mode should be considered on a case by case basis. Fundamentally, two components are linked in the implementation of rate adaptive pacing: (1) sensing the need for a change in rate and (2) responding with the appropriate alteration in pacing rate. The programming interaction of these two components are interdependent and affected by the rates programmed. These features may be adjusted manually or automatically. In this review (Part 2 of a two-part review) the considerations required to program each aspect that optimizes the pacing rate profile are reviewed. These include the lower rate, upper sensor rate, activities of daily life rate, sensor threshold, acceleration and deceleration, slope, activities of daily life zone, exertion zone, automatic versus manual adjustments and closed loop stimulation. The programming features of pacemakers manufactured by three companies are summarized (Abbott, formerly St. Jude; Biotronik/Dextronix; Medtronic). Means of assessing the success of pacemaker programing is examined through examples of pacemaker data, Holter analysis, Poincaré plots and tachograms. Finally, the questions and considerations for rate adaptive pacing in dogs that demand investigation are proposed.

Effects of long-term right ventricular apex pacing on left ventricular dyssynchrony, morphology and systolic function

BACKGROUND

Right ventricular apex (RVA) is still the most common implanted site in the world. There are a large number of RVA pacing population who have been carrying dual-chamber permanent pacemaker (PPM) over decades. Comparison of left ventricular dyssynchrony, morphology and systolic function between RVA pacing population and healthy population is unknown.

METHOD

This case-control study enrolled 61 patients suffered from complete atrioventricular block (III°AVB) for replacement of dual-chamber PPM. Then, 61 healthy controls matched with PPM patients in gender, age, follow-up duration and complications were included. The lead impedance, pacing threshold and sensing were compared between at implantation and long-term follow-up. Left ventricular (LV) dyssynchrony, morphology and systolic function were compared between RVA pacing population (RVA group) and healthy population (healthy group) at implantation (baseline) and follow-up. And clarify the predictors of LV systolic function in RVA group at follow-up.

RESULTS

After 112.44 ± 34.94 months of follow-up, comparing with parameters at implantation, atrial lead impedance decreased significantly (690 ± 2397 Ω vs 613 ± 2257 Ω， p = 0.048); atrial pacing threshold has a increased trend and P-wave amplitude has a decreased trend, but there was no statistical differences; while, RVA ventricular lead threshold increased significantly (0.50 ± 0.23 V vs 0.91 ± 0.47 V， p < 0.001), impedance (902 ± 397 Ω vs 680 ± 257 Ω，p < 0.001) and R-wave amplitude (11.71 ± 9.40mv vs 7.00 ± 6.91 mv， p < 0.001) decreased significantly. Compared with healthy group, long-term RVA pacing significantly increased ventricular dyssynchrony (mean QRS duration, 156.21 ± 29.80 ms vs 97.08 ± 15.70 ms， p < 0.001), left atrium diameter (LAD, 40.61 ± 6.15 mm vs 37.49 ± 4.80 mm，p = 0.002), left ventricular end-diastolic diameter (LVEDD, 49.15 ± 5.93 mm vs 46.41 ± 3.80 mm，p = 0.003), left ventricular hypertrophy (LVMI, 121.86 ± 41.52 g/m2 vs 98.41 ± 25.29 g/m2，p < 0.001), significantly deteriorated degree of tricuspid regurgitation (p < 0.001), and significantly decreased left ventricular ejection fraction (LVEF, 61.38 ± 8.10% vs 64.64 ± 5.85%, p = 0.012), but after long-term RVA pacing, the mean LVEF was still more than 50%. Long-term RVA group LVEF was negatively correlated with preimplantation LVMI (B = -0.055，t = -2.244，p = 0.029), LVMI at follow-up (B = -0.081，t = -3.864，p = 0.000) and tricuspid regurgitation at follow-up (B = -3.797，t = -3.599，p = 0.001).

CONCLUSION

In conclusion, although long-term RVA pacing has significantly effects on left ventricular dyssynchrony, morphology and systolic function in III°AVB patients, the mean LVEF is still >50%. High preimplantation LVMI can predict the decline of LVEF.

Development of New-Onset or Progressive Atrial Fibrillation in Patients With Permanent HIS Bundle Pacing Versus Right Ventricular Pacing: Results From the RUSH HBP Registry

Background

Conventional right ventricular pacing (RVP) has been associated with an increased incidence of atrial fibrillation (AF). We sought to compare the occurrence of new‐onset AF and assessed AF disease progression during long‐term follow‐up between His bundle pacing (HBP) and RVP.

Methods and Results

We included patients undergoing initial dual‐chamber pacemaker implants at Rush University Medical Center between January 1, 2016, and June 30, 2019. A total of 360 patients were evaluated, and 225 patients (HBP, n=105; RVP, n=120) were included in the study. Among the 148 patients (HBP, n=72; RVP, n=76) with no history of AF, HBP demonstrated a lower risk of new‐onset AF (adjusted hazard ratio [HR], 0.53; 95% CI, 0.28–0.99; P=0.046) compared with traditional RVP. This benefit was observed with His or RVP burden exceeding 20% (HR, 0.29; 95% CI, 0.13–0.64; P=0.002), ≥40% (HR, 0.31; P=0.007), ≥60% (HR, 0.35; P=0.015), and ≥80% (HR, 0.40; P=0.038). There was no difference with His or RV pacing burden <20% (HR, 0.613; 95% CI, 0.213–1.864; P=0.404). In patients with a prior history of AF, there was no difference in AF progression (P=0.715); however, in a subgroup of patients with a pacing burden ≥40%, HBP demonstrated a trend toward a lower risk of AF progression (HR, 0.19; 95% CI, 0.03–1.16; P=0.072).

Conclusions

HBP demonstrated a lower risk of new‐onset AF compared with RVP, which was primarily observed at a higher pacing burden.