Abstract
Localization of the components of the cardiac conduction system (CCS) is essential for many therapeutic procedures in cardiac surgery and interventional cardiology. While histological studies provided fundamental insights into CCS localization, this information is incomplete and difficult to translate to aid in intraprocedural localization. To advance our understanding of CCS localization, we set out to establish a framework for quantifying nodal region morphology. Using this framework, we quantitatively analyzed the sinoatrial node (SAN) and atrioventricular node (AVN) in ovine with postmenstrual age ranging from 4.4 to 58.3 months. In particular, we studied the SAN and AVN in relation to the epicardial and endocardial surfaces, respectively. Using anatomical landmarks, we excised the nodes and adjacent tissues, sectioned those at a thickness of 4 μm at 100 μm intervals, and applied Masson’s trichrome stain to the sections. These sections were then imaged, segmented to identify nodal tissue, and analyzed to quantify nodal depth and superficial tissue composition. The minimal SAN depth ranged between 20 and 926 μm. AVN minimal depth ranged between 59 and 1192 μm in the AVN extension region, 49 and 980 μm for the compact node, and 148 and 888 μm for the transition to His Bundle region. Using a logarithmic regression model, we found that minimal depth increased logarithmically with age for the AVN (R2 = 0.818, P = 0.002). Also, the myocardial overlay of the AVN was heterogeneous within different regions and decreased with increasing age. Age associated alterations of SAN minimal depth were insignificant. Our study presents examples of characteristic tissue patterns superficial to the AVN and within the SAN. We suggest that the presented framework provides quantitative information for CCS localization. Our studies indicate that procedural methods and localization approaches in regions near the AVN should account for the age of patients in cardiac surgery and interventional cardiology.
Highlights
In the mammalian heart, the cardiac conduction system (CCS) is responsible for initiation and propagation of electrical signals that trigger and synchronize mechanical function [1, 2]
We suggest that the presented framework provides quantitative information for CCS localization
Our studies indicate that procedural methods and localization approaches in regions near the atrioventricular node (AVN) should account for the age of patients in cardiac surgery and interventional cardiology
Summary
The cardiac conduction system (CCS) is responsible for initiation and propagation of electrical signals that trigger and synchronize mechanical function [1, 2]. Dysfunction of the CCS is associated with high morbidity and mortality [3,4,5,6,7] and has been linked to myocardial ischemia and infarction, cardiotoxicity of drugs, and complications due to surgical and interventional procedures [8,9,10,11,12,13,14]. Various surgical and interventional procedures can lead to CCS dysfunction including reconstructive surgeries for repair of critical congenital heart defects, ablation procedures in the right atrium (RA), and valve replacement [15, 16]. Beyond the importance of accurate localization of the CCS in surgical procedures, insights into the arrangement of the CCS are of high clinical relevance for other cardiac procedures such as His bundle ablation for treatment of supraventricular arrhythmia and His bundle pacing [23, 24]. Success rate of the pacing approach is highly dependent on exact lead placement, which is, in-turn dependent on accurate identification of His bundle location
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