Conduction System Pacing for Patients with Congenital Heart Disease

For patients with congenital heart disease (CHD), chronic ventricular pacing may lead to progressive cardiomyopathy owing to electromechanical dyssynchrony. Cardiac conduction system pacing (CSP) has been proposed as a physiologic pacing strategy-directly engaging the His-Purkinje system and preserving electromechanical synchrony. CSP may be indicated for a wide variety of children and adults with CHD and has emerged as an important tool in the armamentarium for cardiac implantable electronic device operators. This review provides the rationale, background, and supportive evidence for CSP in patients with CHD and discusses implant strategies and outcomes in the context of dominant ventricular morphologic categories.

Pacing of Specialized Conduction System

Right ventricular pacing for bradycardia remains the mainstay of pacing therapy. Chronic right ventricular pacing may lead to pacing-induced cardiomyopathy. We focus on the anatomy of the conduction system and the clinical feasibility of pacing the His bundle and/or left bundle conduction system. We review the hemodynamics of conduction system pacing, the techniques to capture the conduction system and the electrocardiogram and pacing definitions of conduction system capture. Clinical studies of conduction system pacing in the setting of atrioventricular block and after AV junction ablation are reviewed and the evolving role of conduction system pacing is compared with biventricular pacing.

Defining the distance between the His bundle and first septal perforator: implications for left bundle branch pacing

BACKGROUND

Left bundle branch pacing (LBBP) is a developing method of native conduction pacing, but cases of injury to the septal perforator arteries during implantation have been reported. Knowing the distance between the His bundle and the first septal perforator artery can help operators implant LBBP leads more safely.

METHODS

Using previously performed coronary CT angiography (CCTA) studies, the distance between the His bundle and the first septal perforator was measured.

RESULTS

A total of 50 CCTA studies were included. The mean distance from the His bundle to the first septal perforator (His-SP) along the line connecting the His bundle to the RV apex (His-RV apex) was 27.17 ± 7.7 mm with a range of 13.0 to 44.7 mm. The distance was greater than 2.0 cm in 84% of patients. To standardize this distance among patients with varying cardiac structures, the ratio between the His-SP distance and the His-RV Apex distance was also measured. The mean His-SP:His-RV Apex was 0.302 and the median was 0.298. Eighty-six percent of patients had a ratio of greater than 0.20.

CONCLUSION

Using this information, operators can aim to implant LBBP leads within 2.0 cm of the His bundle or 20% of the distance between the His bundle and the RV apex with minimal risk of causing vascular injury.

Physiology of Left Ventricular Septal Pacing and Left Bundle Branch Pacing

Following the recognition of the adverse effects of right ventricular pacing, alternative permanent pacing strategies aiming to maintain a synchronous ventricular contraction have been sought. The quest for the optimal pacing site has recently led to several promising and rapidly emerging new pacing strategies, such as left ventricular septal pacing and left bundle branch pacing. In both animal and human studies, these pacing strategies seem to maintain electrical and mechanical activation of the left ventricle to a (near)physiologic level. However, more studies on the long-term effects of both strategies are needed.

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.

Conduction System Pacing for Cardiac Resynchronization Therapy

Although conventional biventricular pacing has been shown to benefit patients with heart failure and conduction system disease, there are limitations to its therapeutic success, resulting in widely variable clinical response. Limitations of conventional biventricular pacing evolve around myocardial scar, fibrosis, and inability to effectively stimulate diseased tissue. Several observational and acute hemodynamic studies have demonstrated improved electrical resynchronization and echocardiographic response with conduction system pacing. This article provides a systematic review of conduction system pacing as a physiologic alternative to conventional CRT, which is currently undergoing rigorous investigation.

Generating Evidence to Support the Physiologic Promise of Conduction System Pacing: Status and Update on Conduction System Pacing Trials

Conduction system pacing avoids the potential deleterious effects of right ventricular pacing in patients with bradycardia and provides an alternative approach to cardiac resynchronization therapy. We focus on the available observational and randomized evidence and review studies supporting the safety, feasibility, and physiologic promise of conduction system approaches. We evaluate the randomized data generated from the available clinical trials of conduction system pacing, which have led to the recent inclusion of CSP in international guidelines. The scope for future randomized trials will building on the physiologic promise of conduction system approaches and offering information on clinical end points is explored.

Left Bundle Branch Area Pacing in Patients with Atrioventricular Conduction Disease: A Prospective Multicenter Study

BACKGROUND

The reported success rate of His bundle pacing (HBP) in patients with infranodal atrioventricular (AV) conduction disease is only 52-76%. The success rate of left bundle branch area pacing (LBBAP) in this cohort is not well studied.

OBJECTIVE

To evaluate the feasibility, safety, and electrophysiological characteristics of LBBAP in patients with AV conduction disease.

METHODS

Patients with AV conduction disease referred for pacemaker implantation at two centers between 02/2019 and 6/2021 were considered for LBBAP. Baseline demographic characteristics, procedural success rates, electrophysiological parameters and complications were assessed.

RESULTS

LBBAP was successful in 340/364 (93%) patients. Mean age was 72±13 years and mean follow-up was 331±244 days. Pacing indications were Mobitz I in 27 patients (7%), Mobitz II or 2:1 AV block or high-grade AV block in 94 patients (26%), complete heart block in 199 patients (55%) and sick sinus syndrome with isolated bundle branch block in 44 patients (12%). LBBB and RBBB were present in 57 patients (16%) and 140 patients (38%) respectively. Procedural success rates did not differ between indications (92.6%, 93.6%, 92.9% and 95% respectively) or between patients with narrow (<120ms) versus wide QRS (≥120ms). Mean LBBAP threshold was 0.77±0.34V at 0.4ms at implant and remained stable during follow-up. There were 4 (1.2%) acute LBBAP lead dislodgements.

CONCLUSIONS

LBBAP is safe and feasible with high success rates for patients with AV conduction disease. Contrary to HBP, LBBAP success rates remain high over the entire spectrum of AV conduction disease and lead parameters remain stable during follow-up.

Initial experience, feasibility and safety of permanent left bundle branch pacing: results from a prospective single-centre study

Background

Left bundle branch (LBB) pacing is a novel pacing technique which may serve as an alternative to both right ventricular pacing for symptomatic bradycardia and cardiac resynchronisation therapy (CRT). A substantial amount of data is reported by relatively few, highly experienced centres. This study describes the first experience of LBB pacing in a high-volume device centre.

Methods

Success rates (i.e. the ability to achieve LBB pacing), electrophysiological parameters and complications at implant and up to 6 months of follow-up were prospectively assessed in 100 consecutive patients referred for various pacing indications.

Results

The mean age was 71 ± 11 years and 65% were male. Primary pacing indication was atrioventricular (AV) block in 40%, CRT in 42%, and sinus node dysfunction or refractory atrial fibrillation prior to AV node ablation in 9% each. Baseline left ventricular ejection fraction was < 50% in 57% of patients, mean baseline QRS duration 145 ± 34 ms. Overall LBB pacing was successful in 83 of 100 (83%) patients but tended to be lower in patients with CRT pacing indication (69%, p = ns). Mean left ventricular activation time (LVAT) during LBB pacing was 81 ms and paced QRS duration was 120 ± 19 ms. LBB capture threshold and R‑wave sense at implant was 0.74 ± 0.4 mV at 0.4 ms and 11.9 ± 5.9 V and remained stable at 6‑month follow-up. No complications occurred during implant or follow-up.

Conclusion

LBB pacing for bradycardia pacing and resynchronisation therapy can be easily adopted by experienced implanters, with favourable success rates and safety profile.

Pacing of Specialized Conduction System

Right ventricular pacing for bradycardia remains the mainstay of pacing therapy. Chronic right ventricular pacing may lead to pacing-induced cardiomyopathy. We focus on the anatomy of the conduction system and the clinical feasibility of pacing the His bundle and/or left bundle conduction system. We review the hemodynamics of conduction system pacing, the techniques to capture the conduction system and the electrocardiogram and pacing definitions of conduction system capture. Clinical studies of conduction system pacing in the setting of atrioventricular block and after AV junction ablation are reviewed and the evolving role of conduction system pacing is compared with biventricular pacing.

Safety and efficacy of His-bundle pacing/left bundle branch area pacing versus right ventricular pacing: a systematic review and meta-analysis

BACKGROUND

Recent studies have demonstrated that right ventricular pacing (RVP) has deleterious effects on non-synchronized ventricular contraction, while His-bundle pacing (HBP) or left bundle branch area pacing (LBBaP) contribute to improvements in patients' mid- and long-term outcomes. This meta-analysis aimed to compare the safety and efficacy of physiologic pacing (HBP/LBBaP) versus those of RVP.

METHODS

A systematic search of PubMed, Cochrane Library, and Embase was conducted for studies that compared the effects of physiologic pacing and RVP. All eligible studies were published before January 1, 2021 and were conducted in humans. STATA software version 15.0 was used for all the data analyses.

RESULTS

Twenty articles (n = 2787 patients) were included in this meta-analysis. Compared to RVP, physiologic pacing was associated with a significantly shorter QRS duration and better cardiac function. Physiologic pacing was also correlated with lower rates of mitral regurgitation, pacing-induced cardiomyopathy, death, heart failure hospitalization, and atrial fibrillation, although the above results were not statistically significant. In addition, RVP led to the achievement of higher success rates than physiologic pacing, a shorter fluoroscopic time and mean procedure duration, a lower pacing threshold: the results were statistically significant. Compared with HBP, LBBaP appeared to have some advantages in R wave amplitudes, pacing threshold, fluoroscopic time, procedure time, and success rate, with statistically significant differences. Whereas HBP was associated with fewer surgical complications and shorter QRS duration, the results were not statistically significant.

CONCLUSION

Physiologic pacing (HBP/LBBaP) might be a better strategy than RVP and improve long-term clinical outcomes like cardiac function. Although LBBaP appears to have some advantages over HBP, the long-term benefits are still controversial. More large-scale randomized clinical trials are needed for further verification.

Permanent HIS bundle Pacing Feasibility in Routine Clinical Practice: Experience from an Indian Center

There is a paucity of experience regarding His bundle pacing (HBP) at laboratories initially attempting the procedure, especially in the Indian scenario. Patient who underwent HBP were selected for pacing therapy or in lieu of cardiac resynchronization therapy (CRT) at a single center. Among 22 patients attempted, 19 patients underwent successful implant, achieving selective HBP in 14 patients. There was a significant improvement in left ventricular ejection fraction (LVEF) (49.3 ± 9.3 vs. 36.7 ± 9.2) in the LV dysfunction subgroup (n = 6). Over a follow-up of 15 ± 6.5 months, thresholds were stable in all except one patient, and there was no requirement of lead revision. In summary, we found that HBP is a feasible option for achieving physiological pacing.

His Bundle Pacing: Getting on the Learning Curve

Permanent His bundle pacing prevents ventricular dyssynchrony in patients who depend on ventricular pacing and can provide an alternative means to implementing cardiac resynchronization therapy in patients with bundle branch disease and congestive heart failure. Adoption of His bundle pacing, however, has lagged in part due to perceived and real challenges in performing the procedure well and durably. This article focuses on what is required to get on the learning curve and developing technical competence.