Foundations of Medical Imaging and Signal Recording - Biomedical Signal Analysis: Contemporary Methods and Applications - page 6

R

T

P

ST segment

QS

Figure 1.2
Typical waveform of an ECG. The P -wave denotes the atrial depolarization, and
the QRS -wave the ventricular depolarization. The T -wave describes the ventricular
recovery.

when the membrane becomes permeable, and repolarization is the re-
covery phase of the ion concentrations returning to normal.
The waveform of the typical ECG is displayed in figure 1.2 with
the typical deflections labeled P, QRS ,and T , corresponding to atrial
contraction (depolarization), ventricular depolarization, and ventricular
repolarization, respectively.
The interpretation of an ECG is based on (a) morphology of waves
and (b) timing of events and variations observed over many beats.
The diagnostic changes observed in the ECG are permanent or
transient occlusion of coronary arteries, heart enlargement, conduction
defects, rhythm, and ionic effects.

Electromyogram (EMG)
The electromyogram records the electrical activity of muscles and is used
in the clinical environment for the detection of diseases and conditions
such as muscular distrophy or disk herniation. There are two types of
EMG: intramuscular and surface EMG (sEMG). Intramuscular EMG is
performed by inserting a needle which serves as an electrode into the
muscle. The action potential represents a waveform of a certain size and
shape. Surface EMG (sEMG) is done by placing an electrode on the skin
over a muscle in order to detect electrical activity of this muscle.