Image Processing Reference
In-Depth Information
Arrhythmias.
Pericarditis.
Generalized suffering affecting heart and blood pressure.
Cardiac medicine effects, especially digital and quinidine.
Electrolytic transformations.
In spite of the special value, the ECG is considered only a laboratory test. It is not an
absolute truth concerning the cardiac pathologies diagnosis. There are examples of patients
presenting string heart diseases which present a normal ECG, and also perfectly normal
patients getting an abnormal ECG (Goldschlager, 1989). Therefore, an ECG must always be
interpreted with the patient clinical information.
2. Electrocardiographic signal
According to (Proakis & Manolakis, 2007) a signal can be analyzed and processed in two
domains, time and frequency. ECG signal is one of the human body signals which can be
analyzed and worked in these two domains.
2.1 Time domain of an ECG signal
P, Q, R, S, T and U are specific wave forms identified in the time domain of an ECG signal.
The QRS complex, formed by Q, R and S waves, represents a relevant wave form because
the heart rate can be identified locating two successive QRS complex. Figure 2 presents
typical waves in an ECG signal.
Fig. 2. Typical wave forms of an ECG signal record
2.2 Frequency domain of an ECG signal
Frequency values of an ECG signal vary from 0 Hz to 100 Hz (Cuesta, 2001; Vidal & Pavesi,
2004; Vidal et al., 2008; Vidal & Gatica, 2010) whereas the associated amplitude values vary
from 0.02 mV to 5 mV. Table 1 describes the frequency and amplitude values of ECG, EMG
(electromiogram), and EEG (electroencephalogram) signals.
Signal Amplitude (mV) Frequency range (Hz)
ECG 0.02 - 5.0 0.05 - 100
EEG 0.0002 - 0.3 DC - 150
EMG 0.1 - 5.0 DC - 10000
Table 1. Amplitude and Frequency Range of Basic Bioelectrical Signals of the Human Being
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