11. 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
12. 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
13. 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
14. 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
15.
16.
17.
18.
19. 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
20.
21. 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
22. 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.
29. 1. True septal wall:
flap valve of OF (1.5-2.4
cm2)
2 . Limbus: pronounced
superiorly & laterally
Fusion of septum primum
and secundum
3. Folds, interposed between
the chamber: no the true
septal wall
33. 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
34. 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
41. Blood supply and Risk of Nodal Artery
and AV Conduction Tissue Injury
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
45. 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
47. 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.
We will start by discussing normal impulse formation and then move into common conduction disturbances.
Initiation of the cardiac cycle normally begins with initiation of the impulse at the SA (sinoatrial) node.
After the SA node fires, the resulting depolarization wave passes through the right and left atria, which produces the P-wave on the surface EKG and stimulates atrial contraction.
Following activation of the atria, the impulse proceeds to the atrioventricular (AV) node, which is the only normal conduction pathway between the atria and the ventricles. The AV node slows impulse conduction, which allows time for the atria to contract and for blood to be pumped from the atria to the ventricles prior to ventricular contraction. Conduction time through the AV node accounts for most of the duration of the PR interval. Just below the AV node, the impulse passes through the bundle of His. A small portion of the last part of the PR interval is represented by the conduction time through the bundle of His.
After the impulse passes through the bundle of His, it proceeds through the left and right bundle branches. A small portion of the last part of the PR interval is represented by the conduction time through the bundle branches.
Next the impulse passes through the Purkinje fibers (interlacing fibers of modified cardiac muscle). Conduction time through the Purkinje system is represented by a small portion of the last part of the PR interval.
The impulse passes quickly through the bundle of His, the left and right bundle branches, and the Purkinje fibers, leading to depolarization and contraction of the ventricles. The QRS complex on the EKG represents the depolarization of the ventricular muscle mass.
Koch triangle is an important anatomic area for cardiac arrhythmias. Radiofrequency energy was frequently applied in this area to ablate AVNRT, paraseptal accessory pathways and some atrial tachycardia. The line of tricuspid leaflet attachment forms the anterior border, the tendon of todaro is the posterior border and the apex lies the central fibrous body. The AV node and its posterior extension is shown here. In addition, the short dot line indicates the septal isthmus and long dot line indicates the cavo-tricuspid isthmus.
We should also understand the course of right coronary artery and the nodal artery in this region. The mean distance between nodal area and endocardial surface is 3.5 mm. In addition, the compact AV node is possible to locate in close vicinity of tricuspid annulus. Therefore, we should be careful to deliver energy within Koch triangle.