Application to biomedical signals - Practical Biomedical Signal Analysis Using MATLAB - page 177

FIGURE 4.30: (SEE COLOR INSERT) Body surface maps of QRST integral:
A) healthy volunteer, B) patient after myocardial infarction (MI) with documented
episode of ventricular tachycardia (VT). From [Fereniec et al., 2008].
The pioneer of body surface potential mapping (BSPM) is B. Taccardi [Taccardi,
1962, Taccardi, 1963] who recorded the ECG from 200 electrodes. He described the
time-varying potential distribution on the thorax with the aim of relating its evolu-
tion to the propagation of the activity in the heart muscle. At present the technique
is used in many laboratories. The construction of maps involves triangulation of the
body surface and interpolation, usually by means of biharmonic splines [Sandwell,
1987]. The BSPM technique was used for quantification of different phenomena oc-
curring during the heart cycle, e.g., the spatial distribution of the late atrial poten-
tials [Jokiniemi et al., 2003] and the distribution of electric field during the phase of
repolarization [Khaddoumi et al., 2006]. In the above work the quantification of the
electric field shape dispersion was proposed.
Diagnostic application of BSPM includes, e.g., detection of myocardial infarction,
[De Ambroggi et al., 1988] , left ventricular hypertrophy [Corlan and De Ambroggi,
2000], and myocardial ischemia [Hanninen et al., 2001]. At present even portable
devices for high resolution ECG mapping are available [Rosik et al., 2001].
Vectorcardiography is a method of recording the magnitude and direction of the
electrical forces that are generated by the heart by means of a continuous series of
vectors that form curving lines around a central point. In vectorcardiography the
trajectory of the heart vector in 3D space is traced ( Figure 4.27) . The strength and
direction of electric currents passing through the heart are represented as vector loops
and the information about the directional evolution of the heart vector in time is
found. This technique enables observation of the depolarization and repolarization
in particular fragments of the cardiac muscle during its evolution which means that
it permits detection of even small changes in electric activity of individual fragments
of the cardiac muscle caused for example by ischemia or applied treatment. Usually
evolution of electrical activity connected with QRS complex, P-wave, or ST complex
is followed. High resolution vectorcardiography reveals changes related either to an