Evidence for concealed fasciculo-ventricular connections as revealed by His bundle pacing

Novel cardiac CT method for identifying the atrioventricular conduction axis by anatomic landmarks

BACKGROUND

Understanding the conduction axis location aids in avoiding iatrogenic damage and guiding targeted heart rhythm therapy.

OBJECTIVE

Cardiac structures visible with clinical imaging have been demonstrated to correlate with variability in the conduction system course. We aimed to standardize and assess the reproducibility of predicting the location of the atrioventricular conduction axis by cardiac computed tomography.

METHODS

We evaluated 477 patients with acquired aortic valve disease by cardiac computed tomography to assess variability in cardiac structures established to relate to the conduction system. We standardized 3 points (points A-C) to estimate the course from the atrioventricular node to the nonbranching bundle and left bundle branch origin and further compared this with measures of variability in the aortic root and membranous septum.

RESULTS

The mean distances between the aortic valve virtual basal ring and points A, B, and C were 9.5 ± 3.5 (0.3-20.1) mm, 5.0 ± 2.6 (-1.7 to 15.9) mm, and 2.9 ± 2.5 (-5.2 to 12.0) mm, respectively. The midpoint of the membranous septum deviated posteriorly a median of -4.4 (interquartile range, -12.4 to +3.0) degrees relative to the commissure between the right coronary and noncoronary leaflets. Intraclass coefficients for both intraobserver and interobserver variability for all measured points were excellent (≥0.78).

CONCLUSION

These findings further infer the intimate yet highly variable relationship between the conduction axis and aortic root. This reproducible and standardized approach needs validation in populations of patients requiring accurate identification of the atrioventricular components of the conduction axis, which may serve as a noninvasive means for estimating its location.

Outcomes with physiologic His bundle pacing in patients with narrow QRS complex

BACKGROUND

In patients with narrow QRS complex, both ventricular and biventricular pacing is associated with increased cardiac morbidity and mortality. This risk is not decreased by ventricular pacing avoidance algorithms, which cause nonphysiologic atrioventricular (AV) delays.

OBJECTIVE

This study aimed to report outcomes in patients with narrow QRS complex when the paced complex is in normal range and physiologic AV delays are programmed.

METHODS

In 196 patients with QRS duration of 92 ± 10 ms, permanent pacing was done at the site of the His bundle electrogram. The pacemakers were then programmed to maintain physiologic AV delays and to increase heart rates in response to exercise. Patients received usual care and were observed for 3 years.

RESULTS

The paced complex exhibited a delta wave, and the ventricular activation time, QRS axis, and lead I voltage remained in normal range. Physiologic programming resulted in His bundle pacing burden of 92%. In patients with decreased ejection fraction, there was significant improvement in left ventricular function, left ventricular dilation, and mitral regurgitation (P < .003). In patients with normal ejection fraction, left ventricular function remained normal without new valvular abnormalities. The 3-year all-cause mortality was 10%, and there was no increase in heart failure admissions.

CONCLUSION

In patients with narrow QRS complex, when paced QRS morphology is maintained in normal range and AV dyssynchrony is avoided, His bundle pacing is associated with low all-cause mortality and improvement in abnormal echocardiographic parameters. The paced QRS morphology and physiologic AV delays may be important factors to evaluate in future trials of conduction system pacing.

A new dimension in cardiac imaging: Three-dimensional exploration of the atrioventricular conduction axis with hierarchical phase-contrast tomography

Much of our understanding of the atrioventricular conduction axis has been derived from early 20th-century histologic investigations. These studies, although foundational, are constrained by their 2-dimensional representation of complex 3-dimensional anatomy. The variability in the course of the atrioventricular conduction axis, and its relationship to surrounding cardiac structures, necessitates a more advanced imaging approach. Using hierarchical phase-contrast tomography of an autopsied heart specimen with cellular resolution, this review provides a contemporary understanding of the atrioventricular conduction axis. By correlating these findings with 3-dimensional computed tomographic reconstructions in living patients, we offer clinicians the insights needed accurately to predict the location of the atrioventricular conduction axis. This novel approach overcomes the inherent limitations of 2-dimensional histology, enhancing our ability to understand and visualize the intricate relationships of the conduction axis within the heart.

Revisiting the Atrioventricular Conduction Axis for the 21st Century

In this review, we summarise the ongoing debate surrounding the anatomy of the atrioventricular conduction axis and its relevance to pacing. We highlight previous disagreements and emphasise the importance of understanding the anatomical location of the axis. We give credit and support to the initial descriptions by His and Tawara, in particular their attention to the relationship of the atrioventricular conduction axis with the membranous septum. We express our disagreements with recent diagrams that incorrectly, in our opinion, depict the left bundle and right bundle branches. We offer our own latest understanding of the location and relationships of the atrioventricular conduction axis, including details of its development, and differences between human and animal hearts. We also emphasise the importance of understanding the relationship between the inferior pyramidal space and the inferoseptal recess so as appropriately to place the axis within the heart. We conclude by emphasising the need to consider the heart in the context of the body, describing its component parts by using attitudinally appropriate nomenclature.

Multicenter Hemodynamic Assessment of the LOT-CRT Strategy: When Does Combining Left Bundle Branch Pacing and Coronary Venous Pacing Enhance Resynchronization?: Primary Results of the CSPOT Study

BACKGROUND

Left bundle branch area pacing (LBBAP) may be an alternative to biventricular pacing (BVP) for cardiac resynchronization therapy (CRT). We sought to compare the acute hemodynamic and ECG effects of LBBAP, BVP, and left bundle-optimized therapy CRT (LOT-CRT) in CRT candidates with advanced conduction disease.

METHODS

In this multicenter study, 48 patients with either nonspecific interventricular conduction delay (n=29) or left bundle branch block (n=19) underwent acute hemodynamic testing to determine the change in left ventricular pressure maximal first derivative (LV dP/dtmax) from baseline atrial pacing to BVP, LBBAP, or LOT-CRT.

RESULTS

Atrioventricular-optimized increases in LV dP/dtmax for LOT-CRT (mean, 25.8% [95% CI, 20.9%-30.7%]) and BVP (26.4% [95% CI, 20.2%-32.6%]) were greater than unipolar LBBAP (19.3% [95% CI, 15.0%-23.7%]) or bipolar LBBAP (16.4% [95% CI, 12.7%-20.0%]; P≤0.005). QRS shortening was greater in LOT-CRT (29.5 [95% CI, 23.4-35.6] ms) than unipolar LBBAP (11.9 [95% CI, 6.1-17.7] ms), bipolar LBBAP (11.7 ms [95% CI, 6.4-17.0]), or BVP (18.5 [95% CI, 11.0-25.9] ms), all P≤0.005. Compared with patients with left bundle branch block, patients with interventricular conduction delay experienced less QRS reduction (P=0.026) but similar improvements in LV dP/dtmax (P=0.29). Bipolar LBBAP caused anodal capture in 54% of patients and resulted in less LV dP/dtmax improvement than unipolar LBBAP (18.6% versus 23.7%; P<0.001). Subclassification of LBBAP capture (European Heart Rhythm Association criteria) indicated LBBAP or LV septal pacing in 27 patients (56%) and deep septal pacing in 21 patients (44%). The hemodynamic benefit of adding left ventricular coronary vein pacing to LBBAP depended on baseline QRS duration (P=0.031) and success of LBBAP (P<0.004): LOT-CRT provided 14.5% (5.0%-24.1%) greater LV dP/dtmax improvement and 20.8 (12.8-28.8) ms greater QRS shortening than LBBAP in subjects with QRS ≥171 ms and deep septal pacing capture type.

CONCLUSIONS

In a CRT cohort with advanced conduction disease, LOT-CRT and BVP provided greater acute hemodynamic benefit than LBBAP. Subjects with wider QRS or deep septal pacing are more likely to benefit from the addition of a left ventricular coronary vein lead to implement LOT-CRT.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04905290.

Narrow QRS ectopy with concealed connections from a para-Hisian origin to the proximal left fascicles

INTRODUCTION

Catheter ablation of ectopy originating from the vicinity of the His bundle can be challenging.

METHODS AND RESULTS

We report a case of a 33-year-old man with narrow QRS ectopy with preferential conduction from a para-Hisian origin to the proximal left fascicles, which was successfully eliminated by radiofrequency ablation in the right coronary cusp, guided by ultrahigh-resolution mapping of the His bundle, bundle branch, and fascicular electrograms.

CONCLUSION

Some narrow QRS ectopy may originate from the vicinity of the conduction system, instead of the "true" conduction system, and have concealed connections from its origin to the conduction system.

The Upper Common Pathway in Atrioventricular Nodal Reentrant Tachycardia: A Comprehensive Review of Evidence and Current Perspectives

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common form of paroxysmal supraventricular tachycardia, and its diagnostic and therapeutic approaches have been well-established. Traditionally, AVNRT is understood to be an intranodal reentry having two bystander pathways; the upper common pathway (UCP) which connects to the atrium and the lower common pathway which connects to the ventricle. However, the existence of the UCP remains a subject of ongoing debate. The assertion of the UCP's presence is supported by electrophysiological evidence suggesting that the atrium is not essential for the perpetuation of AVNRT. Nonetheless, numerous anatomical studies have failed to identify any structure that could be conclusively designated as the UCP. The histological and electrophysiological characteristics of the slow and fast pathways, which are the core components of AVNRT, suggest the inclusion of atrial myocardium in the reentry circuit. While clear interpretation of these discrepancies remains elusive, potential explanations may be derived from existing evidence and recent research findings concerning the actual AVNRT circuit.