Biomedical Engineering Reference
In-Depth Information
Ta b l e 8 . 1
Cardiac activation
time in the heart
Location in the heart
Cardiac activation time (ms)
SA node (A)
0..10
Left atria muscle fibres (C)
70..90
AV node (B)
50..70
Bundle of His (D)
125..160
Right bundle branch (E)
145..180
Left bundle branch (F)
145..180
Right Purkinje fibres (G)
150..210
Left Purkinje fibres (H)
150..230
Ta b l e 8 . 2
Cardiac activation
velocity in the heart
Location in the heart
Conduction velocity (cm/sec)
A
→
B
30..50
A
→
C
30..50
B
→
D
100..200
→
D
E
100..200
D
→
F
100..200
E
→
G
300..400
F
→
H
300..400
of the conduction network in the heart system. The bundles branch into the Purkinje
fibres that diverge across the inner sides of the ventricular walls (see Fig.
8.5
(e)). On
reaching the end of the Purkinje fibres, the electrical impulse is transmitted through
the ventricular muscle mass by the ventricular muscle fibres themselves. Propaga-
tion along the conduction system takes place at a relatively high speed once it is
within the ventricular region, but prior to this (through the AV node), the velocity is
extremely slow [
24
,
30
].
The electrical system provides a synchronised system from atria to ventricles,
which aids the contraction of the heart muscle and optimises the haemodynamics.
Changed time intervals or conducting speeds between landmarks (see Fig.
8.4
(b)
and Fig.
8.6
) are a major cause of abnormalities in the heart system. Abnormal-
ities in electrical signals in the heart can generate various kinds of arrhythmias.
A slow conduction speed generates bradycardia and a fast conduction speed gen-
erates tachycardia. In this model, we consider the ranges of all possible values for
conduction speeds and conduction times for each landmark node and conduction
path. This model represents the morphological structure of the ECG signal through
the conduction network (see Fig.
8.6
).
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