P6015Histological pattern of penetrating His bundle division: implications for atrioventricular conduction damage during and following transcatheter aortic valve implantation

Background

Severe damage to the atrioventricular conduction system is one of the most common complications of transcatheter aortic valve implantation (TAVI) and can be linked to important comorbidity, increased healthcare expense, need for long-term monitoring and pacemaker implantation.

Purpose

To provide a detailed description of the His bundle (HB) arrangement within the left ventricular outflow tract.

Methods

We examined by dissection techniques and histological sections the course of the AV conduction axis (penetrating, non-branching and branching HB) in relation with the membranous and muscular interventricular septum in 57 structurally normal human heart specimens (48 males, 77±7 years)

Results

The AV conduction axis is located along the inferior edge of the membranous septum (MS). The MS is divided into AV and interventricular components and is located at the base of the interleaflet triangle between the right and non-coronary leaflets of the aortic valve. The conduction axis enters the AV component of the MS and is encircled by the fibrous tissue of the central fibrous body to reach the left ventricular outflow tract. The MS showed in cadaveric hearts variable dimensions in length (4.6±1.5 mm) with a range bewteen 1 to 9mm. In 17.5% of specimens the MS length was ≤2 mm. After penetrating the AV membranous septum it has a non-branching component that in 85.5% of cases runs only for a short distance (1–3 mm) along the septal crest before giving rise to the fascicles of the left bundle (LB) on the septal surface (Type A). The most anterior fibers of the LB originate at the end of the branching portion located underneath the inferior edge of the MS. In 5 hearts (9%) the HB division was found before it reached the interventricular MS (Type B) and in 3 cases (5.5%)2–3.5 mm distal to the crest (Type C). 22 hearts (49%) were shown to have a relatively left-sided deviation of the AV bundle with the anterior part of the bundle closely related to the nadir of attachment of the right coronary leaflet of the aortic valve. In the remaining 51% of hearts, the bundle coursed centrally or with a right-sided deviation. The HB measures were (mm, mean±SD (range)): length: 3±0.6 (2–4.5), width: 3.7±1.4 (2.5–5.6), thickness: 1.4±0.5 (0.5–2.2), HB to endocardium: 0.7±0.3 (0.2–1.5).

His bundle position types

Conclusions

A shorter membranous septum length, the variable HB dimensions and the left-sided deviation of the AV conduction axis are extremely relevant anatomic features that are linked to the frequent injury to the HB branch or complete AV block following TAVI.

P2275Left-sided deviation and fibrous-fatty infiltration of the right bundle branch in the elderly: implication for transcatheter aortic valve implantation (TAVI) procedure

Introduction

Permanent and irreversible damage to the conduction tissue is one of the most common complications of TAVI. Detailed knowledge of the anatomy of the atrioventricular (AV) bundle is crucial to minimize the potential for injury to the His bundle branch block or complete AV block.

Purpose

Preexisting anatomic location and damage of the right bundle branch (RBB) may have important unrecognized clinical implications.

Methods

The myocardial arrangement and the presence of fibrous and fatty tissue infiltration of the AV conduction axis and right bundle branch were examined by dissection techniques and histological sections in 57 structurally normal human heart specimens (48 males, 77±7 years).

Results

The AV conduction axis enters the AV component of the membranous septum and is encircled by the fibrous tissue of the central fibrous body. The AV bundle is divided in a non-branching portion and a branching portion. After a short distance of the non-branching component along the septal crest, the RBB arises at the end of the branching portion of the conduction axis and is located superficially in the muscular ventricular septum. The RBB takes off from the bundle at the level of origin of the superior fascicle of the left bundle, passing then through the thickness of the ventricular septum to emerge beneath the medial papillary muscle of the tricuspid valve. In 22 hearts (49%) in which we found to have a relatively left-sided deviation of the AV bundle in relation to the interventricular membranous septum the RBB runs intramyocardial along the muscular interventricular septum. In the remaining 51% of the hearts the RBB runs subendocardially in the crest of the interventricular muscular septum. We found connective tissue and fatty infiltration along the right bundle branch in 23 hearts (40%) from its origin to its distal part. A significant correlation was found between age and the presence of RBB fibrosis (85% of hearts from individuals with age >80 years). These 2 conditions may make the RBB very vulnerable to self-expanding aortic valves during or after TAVI (figure).

RBB and its critical region

Conclusions

The presence of an intramyocardial location of the RBB with a lef-sided deviation and the fibro-fatty infiltration found in the mayority of senescent hearts are relevant anatomic determinants that may increase the risk of complete AV block following a TAVI procedure.