Anatomy Relevant to Conduction System Pacing and Identifying the Level and Extent of Block

Raja Selvaraj
Professor of Cardiology
JIPMER

Overview

Anatomy relevant to conduction system pacing
Level and extent of block in LBBB

Late 19th Century - Kent vs His

His W, Jr. Die Thätigkeit des embryonalen Herzens und deren Be-

deutung für die Lehre von der Herzbewegung beim Erwachsenen. Arb aus d med Klinik zu Leipzig 1893; 1:14–49.

Kent AFS. Researches on the structure and function of the mam-

malian heart. J Physiol 1893; 14:233–254.

AV conduction axis

Triangle of Koch

Variable location of compact AVN

Cabrera J-Á, Anderson RH, Macías Y, et al. Variable Arrangement of the Atrioventricular Conduction Axis Within the Triangle of Koch: Implications for Permanent His Bundle Pacing. JACC Clin Electrophysiol. 2020;6(4):362-377.

Penetrating bundle - TV septal leaflet

F I G U R E 6 The Variable Location of the Penetrating Bundle in Relation to the Septal leaflet of the Tricuspid Valve The different relationships of the site of penetration of the conduction axis and the insertion of the STV relative to the membranous septum in 3 different hearts are shown. (A,A1) In the first heart, the conduction axis is distant from the insertion of the septal leaflet, located on the right side of the ACMS. (B,B1) In the second heart, the site of penetration is at the level of insertion of the STV and is within the atrioventricular component of the membranous septum. (C,C1) In the third heart, the site of penetration is again within the atrioventricular component of the membranous septum. (C1) The axis becomes insulated within the IVMS, and hence the bundle of His is sited below the hinge of the STV. Abbreviations as i

Longitudinal dissociation

Fine Structure of the His Bundle By THOMAS N. JAMES, M.D., AND LIBi SHEiw, M.D. Cifculation, Volume XLIV, July 1971

Branching bundle

Left bundle branch and fascicles

LBB - variability

Demoulin JC, Kulbertus HE. Histopathological examination of concept of left hemiblock. Br Heart J. (1972) 34:807–14

LBBB - Level and extent

"Incomplete LBBB"

How complete is LBBB ?

Barrett PA, Yamaguchi I. Jordan JL, et al. Electrophysiologicalfactors of left bundle-branch block. Br Heart J 1981;45:594-60 I

Level of block

Upadhyay GA, Cherian T, Shatz DY .. Roderick Tung. Intracardiac Delineation of Septal Conduction in Left Bundle-Branch Block Patterns. Circulation 2019;139:1876-88

Level of block

Localized conduction block - 64%
- Within His bundle - 72%
- Proximal left bundle - 28%
Intraventricular conduction delay with intact purkinje activation - Others
Those with proximal CCB responded to HBP

Upadhyay GA, Cherian T, Shatz DY .. Roderick Tung. Intracardiac Delineation of Septal Conduction in Left Bundle-Branch Block Patterns. Circulation 2019;139:1876-88

Level of block determines correction with HBP

Identification with ECG

Activation after LBB transection

VENEROSE RS, SEIDENSTEIN M, STUCKEY JH, HOFFMAN BF. Activation of subendocardial Purkinje fibers and muscle fibers of the left septal surface before and after left bundle branch block. Am Heart J. 1962 Mar;63:346-61

Multilevel block - transseptal, endocardial, transmural

Characterization of Left Ventricular Activation in Patients With Heart Failure and Left Bundle-Branch Block. Angelo Auricchio et al. Circulation. 2004;109:1133–1139

Functional block due to wavefront propagation ?

Characterization of Left Ventricular Activation in Patients With Heart Failure and Left Bundle-Branch Block. Angelo Auricchio et al. Circulation. 2004;109:1133–1139

Practical Implications

Anatomy
- More important for HBP
Level of block
- Explains why HBP works
- LBP advantages over HBP
Distal block
- Proximal LBP may not correct in all
- Additional CS lead ?