Biomedical Engineering Reference
In-Depth Information
Tabl e 6. 8.
Approximate depolarization instants in the heart wall (ms). The myocardium depo-
larization takes
50-100 ms after reaching the junction between the Purkinje fibers and the
subendocardial layer of the myocardium.
∼
Atria
5
→
85
AVN
50 (impulse arrival)
125 (activation departure)
His bundle
130
His branches
145
Purkinje fibers
150
Endocardial myofibers
→∼
190
Epicardial myofibers
→∼
250
Tabl e 6. 9.
Left ventri
cle activation timing (ms; Source: [
336
]; LV, RV: left
, right venticle).
Mid-left part of ventricular septum
0-10
Inner part of LV wall (septum, apex)
10-20
Ventricular septum, RV and LV inner apex
20-30
Heart apex, external RV, LV lateral walls
30-45
RV and LV bases
45-80
Atrioventricular delays can be assessed by the sum of intervals between atrial
and nodal cell firing and between nodal and ventricular cell firing. The conductance
time across the atrioventricular node is equal to about 10 ms (conduction velocity
∼
160 mm/s) [
594
]. The conduction barrier is located between the atrium and the
atrioventricular node.
6.2.5.6
His Bundle
The action potential runs in the
His bundle
, or atrioventricular bundle, beneath the
endocardium in the interventricular septum. The His bundle divides after a short
distance into 2 branches - the right and left bundle branches - that descend along
respective sides of the interventricular septum.
6.2.5.7
Purkinje Fibers
His bundle gives birth to the
Purkinje fibers
that remain subendocardial. Although
they localize just beneath the endocardium to end on cardiomyocytes, they can
penetrate into the myocardium. Cardiac Purkinje cells allow a very rapid and
almost simultaneous impulse distribution to activate the bulk of the ventricular
myocardium.
The action potential propagates through the ventricular myocardium at 0.3 to
0.5 m/s. Ventricular depolarization duration is equal to about 80 ms (Table
6.9
).
Excitation begins in the subendocardial layer in the interventricular septum.
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