Biomedical Engineering Reference
In-Depth Information
4.1 Introduction
As for the skeletal muscles, the contraction of the heart is induced by an electrical
stimulation. The electrocardiogram (ECG) is a noninvasive recording of this electri-
cal activity. It is obtained from a standard set of skin electrodes (Fig. 4.1, left) and
presented to the physician as the
12-lead ECG
, which is made of 12 graphs of the
recorded voltage
vs.
time (Fig. 4.1, right). As explained for instance in [42], there is
a direct connection between the ECG deflections and the electric state of the heart
muscle: the first deflection, called the P-wave (see lead I in Fig. 4.1, right), cor-
responds to the depolarization of the atria; the group made of the second, third and
fourth deflections, called the QRS-complex, corresponds to the depolarization of the
ventricles; the last deflection, called the T-wave, corresponds to the repolarization
of the ventricles.
The ECG is the most widely used clinical tool for the diagnosis of a broad range
of cardiac conditions (see, e.g., [1, 27]). From the modelling standpoint, although the
greatest challenge is the computation of the electrical activity of the heart, there are
many reasons to try and compute the corresponding ECG: it can be seen as a way
to assess the simulation since it can be easily submitted to the critical evaluation
of a medical doctor; computer based simulations of ECGs can be a valuable tool
for improving the understanding of some clinical signals; an ECG simulator can be
useful in building a virtual database of pathological conditions, in order to test and
Fig. 4.1.
Left
: ECG electrodes location (black dots).
Right
: reproduction of a normal 12-lead ECG:
standard leads (I, II, III), augmented leads (aVR, aVL, aVF) and chest leads (V1, V2,
V6). For
example, lead I corresponds to the difference of potential between L and R, lead II to the difference
between F and R, leads III to the difference between F and L (the other definitions can be found,
e.g., in [7])
...,
