Search

The spinal afferent innervation of the heart helps to regulate cardiac functions by sending sensory information through the dorsal root ganglia (DRG) to the brain. However, the distribution and morphology of spinal afferents in the heart are not well characterized due to tracer selections, the surgical access to upper thoracic DRGs, and the thickness of the heart tissues. In this study, we injected tracer dextran biotin (DB) into the left DRGs (C8-T3) of male Sprague-Dawley rats (3-5 months). After 16 days, flat-mounts of the whole left and right atria were prepared and diaminobenzidine stained. Then, the DB-labeled axons in the tissues were imaged, traced, and digitized using the Neurolucida system. Our results showed that the DB-labeled axons from left DRGs entered the left precaval vein and projected to the left and right atria, with predominant projection in the left atrial wall. DB-labeled varicose axons were observed in different layers, mostly in the epicardium and myocardium, but much less in the endocardium. In those layers, these spinal afferent axons branched out into simple to complex terminal arborizations, forming close appositions with cardiac muscles, intrinsic cardiac ganglia, blood vessels, and fat tissue. This work, for the first time, characterized cardiac spinal afferent distribution of the rat atria using anterograde tracing, which will provide the foundation for future studies of topographical cardiac spinal afferent innervation and remodeling in heart disease models., (© 2024 Wiley Periodicals LLC.)

Aims: Atrial fibrosis and autonomic remodelling are proposed pathophysiological mechanisms in atrial fibrillation (AF). Their impact on conduction velocity (CV) dynamics and wavefront propagation was evaluated., Methods and Results: Local activation times (LATs), voltage, and geometry data were obtained from patients undergoing ablation for persistent AF. LATs were obtained at three pacing intervals (PIs) in sinus rhythm (SR). LATs were used to determine CV dynamics and their relationship to local voltage amplitude. The impact of autonomic modulation- pharmacologically and with ganglionated plexi (GP) stimulation, on CV dynamics, wavefront propagation, and pivot points (change in wavefront propagation of ≥90°) was determined in SR. Fifty-four patients were included. Voltage impacted CV dynamics whereby at non-low voltage zones (LVZs) (≥0.5 mV) the CV restitution curves are steeper [0.03 ± 0.03 m/s ΔCV PI 600-400 ms (PI1), 0.54 ± 0.09 m/s ΔCV PI 400-250 ms (PI2)], broader at LVZ (0.2-0.49 mV) (0.17 ± 0.09 m/s ΔCV PI1, 0.25 ± 0.11 m/s ΔCV PI2), and flat at very LVZ (<0.2 mV) (0.03 ± 0.01 m/s ΔCV PI1, 0.04 ± 0.02 m/s ΔCV PI2). Atropine did not change CV dynamics, while isoprenaline and GP stimulation resulted in greater CV slowing with rate. Isoprenaline (2.7 ± 1.1 increase/patient) and GP stimulation (2.8 ± 1.3 increase/patient) promoted CV heterogeneity, i.e. rate-dependent CV (RDCV) slowing sites. Most pivot points co-located to RDCV slowing sites (80.2%). Isoprenaline (1.3 ± 1.1 pivot increase/patient) and GP stimulation (1.5 ± 1.1 increase/patient) also enhanced the number of pivot points identified., Conclusion: Atrial CV dynamics is affected by fibrosis burden and influenced by autonomic modulation which enhances CV heterogeneity and distribution of pivot points. This study provides further insight into the impact of autonomic remodelling in AF., Competing Interests: Conflict of interest: R.J.H. has received research grants, educational grants, and speaker’s fees from Biosense Webster, Medtronic, and Abbott. P.D.L. receives speaker fees and research grants from Medtronic, Abbott, and Boston Scientific. S.H. has received speaker’s fee from Abbott. S.H. and R.J.H. are shareholders in Rhythm AI Ltd. S.H. is a British Heart Foundation Clinical Intermediate Fellow and receives a grant from the British Heart Foundation., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Cardiology.)