Anatomy of Cardiac Conduction System

曹玄明 醫師陽明大學附設醫院

Normal Sinus Rhythm

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animation

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Impulse Formation In SA Node

Atrial Depolarization

Delay At AV Node

Conduction Through Bundle Branches

Conduction Through Purkinje Fibers

Ventricular Depolarization

Discovery of anatomic substrates for conduction

1852. Stanius: impulses were conducted across the atrioventricular junction through the myocardium in amphibian hearts

1893. His: the presence of a solitary muscle bundle crossing the fibrous plane of AV insulation

1893. Kent: found multiple muscular strands crossing the insulated AV planes

1906. Tawara: clarification of the existence of a specialized axis: atrioventricular node, continued as the bundle of His and terminated in the ventricular Purkinje cells

1907. Keith and Flack: confirm the existence of AV node and also discover the location of cardiac pacemaker: sinus node

Criterions for the histological definition

of cardiac conduction system

Histological discrete from the adjacent working myocardium

Serially traceable from section to section Insulated from the adjacent working

myocardium by a sheath of fibrous tissue

Sinus node

The sinus node is located at the junction of superior caval vein with the right atrium, spindle shape structure 10-20mm long, 2-3mm wide and thick

90% cases: it is positioned just inferior to the crest of the right atrial appendage

10% cases: it extended as a horseshoe across the crest, reaching into the interatrial groove

In human heart, an extensive area within the terminal crest adjacent to the node where nodal cells intermingled with working atrial myocytes

The paranodal area was separated by short zone of atrial myocardium from true node

This specialized myocytes is very likely to generate abnormal rhythm

Cells from the SA node region exhibit a wide variety of morphologies.

Only spindle and spider shaped cells exhibit a typical electrophysiological characteristics of pacemaker cell

Presence of hyperpolarization-activated current, If; and absence of inwardly rectifying K current, Ik1; and spontaneous beating under physiological conditions

Function of SA node

Sinus node cells function as electrically coupled oscillators that discharge synchronously because of mutual entrainment.

Faster discharging cells area slowed by the cells firing more slowly

The interaction depends on the degree of coupling and the EP characteristics of each sinus nodal cells.

Blood supply of SA node

55-60% from RCA40-45% from LCX

Internodal and intraatrial conduction

Three intraatrial pathways

1. anterior internodal pathway: SA nodeanterior interatrial band (Backmann bundle)

2. Middle internodal pathway: SA node crest of IAS AVN

3. posterior internodal tract: SA node crista terminalis eustachian ridge IAS above coronary sinus

Interatrial bundles

Septum primum

Foramen secundum

Foramen ovale

Septum secundum

1. True septal wall: flap valve of OF (1.5-2.4

cm2)2 . Limbus: pronounced

superiorly & laterally Fusion of septum primum

and secundum3. Folds, interposed between

the chamber: no the true septal wall

Europace 2007

The atrioventricular axis

The normal junction area:

(1) Transitional cell zone

(2) Atrioventricular node (compact node): located at the apex of koch triangle

(3) Bundle of His: distal part of compact AV node ,perforates central fibrous body and through the annulus fibrosis

AV conduction axis can be segregated into two connecting compartments based on immunohistological analyses

(1) Connexin45: compact node and transitional cell

(2) Coexpressing of connexin43 and connexin45: His bundle, lower nodal cells and posterior nodal extension

Ho Clin Anat 2009

KOCH Triangle

The mean distance from nodal artery to endocardium 3.5± 1.5mm

18% patients had compact node close to the hinge of TV

Sanchez Quintata JCE 2001

Blood supply and Risk of Nodal Artery and AV Conduction Tissue Injury

Dual AVN and AVNRT

Anderson JCE 1999 Ho Circulation 2008

Pre-excitation and AP mediated tachycardia

Bundle branches

These structures begin at the superior margin of interventricular septum

Left bundle branch onto the septum beneath the non-coronary cusp fascicular system (anterior and posterior)

Right bundle branch unbranched AV bundle down the right interventricular septum RV apex

Trifascicular bundle branch system

Terminal Purkinje fibers

These fibers connect with the ends of the bundle branches to form networks on the endocardial surface of both ventricles.

Less concentrated at the base of ventricles and at the papillary muscle

In human, they penetrate the inner 1/3 of the endocardium.

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