Application to biomedical signals - Practical Biomedical Signal Analysis Using MATLAB - page 171

FIGURE 4.27: The 3-D Frank's electrode system. Black dots—the heart vector
trajectory projections on sagittal, frontal, and transverse planes are marked. From
[Malmivuo and Plonsey, 1995].
The heart pacemakers are influenced by the sympathetic and parasympathetic por-
tions of the autonomic nervous system. The sympathetic system acts quickly to in-
crease heart rate, blood pressure, and respiration; the parasympathetic system acts
to decrease heart rate and slow down respiration and blood flow (e.g., during falling
asleep).
The disturbances in the generation or propagation of electrical activity of the heart
are reflected in the ECG, hence it is a widely used clinical test for heart diseases.
However, this doesn't mean that all abnormal features of electrical heart activity will
be observed in ECG, since according to the Helmholtz law, already mentioned in