Electroanatomical mapping of the atrioventricular septum: novel insights into the anatomy, physiology, and pacing of the conduction system
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BACKGROUND: His bundle pacing (HBP) is a relatively new treatment modality for patients experiencing issues with the cardiac conduction system. The treatment is thought to be an advantageous therapy compared with the standard treatment because it uses the native conduction pathway instead of introducing a non-physiological correction pathway which has been documented to increase the risk of heart failure. First carried out in humans in 2000 (Deshmukh, Casavant, Romanyshyn, & Anderson, 2000), HBP has been shown to be superior to right ventricular pacing and equivalent to cardiac resynchronization therapy. Because of the relative recency of the application of this technique in humans, there is a need for more studies to understand the long-term effectiveness and to guide training for new clinicians. OBJECTIVES: The objectives of this study were to (1) define the utility of three-dimensional mapping as a guiding tool for lead placement in HBP, (2) investigate the electroanatomical imaging of the atrioventricular (AV) septum, bundle of His, and other areas of the conduction system, (3) apply these observations to guide optimal pacing lead placement in the clinical setting, and (4) describe the correction of right and left bundle branch blocks by HBP. METHODS: Patients with pacemaker indication due to diseased conduction system were identified and recommended to undergo His bundle lead implantation. The lead was navigated into the heart by fluoroscopy and progressing the catheter through the axillary, subclavian, and cephalic veins. During the procedure, electroanatomical mapping was conducted by a quadripolar catheter to guide lead placement. His cloud, non-selective capture, and selective capture areas were marked and used to generate a 3D model layering the patient conduction system onto the physical anatomy. Pacemapping was then utilized to identify the most suitable area for disease correction. Results: HBP mapping data were available in 24 patients. Several different responses to pacemapping were observed in the area of the AV septum including selective HBP (S-HBP), non-selective HBP (NS-HBP) (with upper, lower, and common variants), and right bundle branch (RBB) capture. Capture areas were superimposed onto the 3D model in real time and used to guide lead implantation for purposes of correcting various forms of conduction disease. The use of electroanatomical mapping (EAM) reduced the need for fluoroscopic guidance compared with the non-EAM-assisted procedure. Four common patterns were observed while mapping: (1) pattern 1, selective capture surrounded by upper and lower non-selective regions of capture; (2) pattern 2, selective capture surrounded by a common non-selective region of capture; (3) pattern 3, two separate non-selective capture areas with no selective capture; (4) pattern 4, common non-selective capture area with no selective capture. There was no correlation between capture threshold voltage and location of non-selective capture. Also, no correlation was found between capture threshold voltage and presence of common non-selective versus upper and lower non-selective capture areas. Patients with left bundle branch block (LBBB) and RBBB had similar His capture anatomy and were correctable by NS-HBP. CONCLUSIONS: HBP guided by electroanatomical mapping should be considered as a standard approach during pacemaker implantation. Because the underlying conduction anatomy is variable among patients, the use of EAM can direct lead positioning at a more physiologic location. In addition, EAM-guided implantation can reduce the need for fluoroscopy.