**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.


Table 1. Amplitude and Frequency Range of Basic Bioelectrical Signals of the Human Being

154 Applications of Digital Signal Processing

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

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

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

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

**Signal Amplitude (mV) Frequency range (Hz)** 

Table 1. Amplitude and Frequency Range of Basic Bioelectrical Signals of the Human Being

ECG 0.02 - 5.0 0.05 - 100 EEG 0.0002 - 0.3 DC - 150 EMG 0.1 - 5.0 DC - 10000

x Generalized suffering affecting heart and blood pressure. x Cardiac medicine effects, especially digital and quinidine.

x Arrhythmias. x Pericarditis.

x Electrolytic transformations.

**2. Electrocardiographic signal** 

**2.1 Time domain of an ECG signal** 

typical waves in an ECG signal.

interpreted with the patient clinical information.

analyzed and worked in these two domains.

Fig. 2. Typical wave forms of an ECG signal record

(electromiogram), and EEG (electroencephalogram) signals.

**2.2 Frequency domain of an ECG signal** 

As it is appreciated, the amplitude values of human body bioelectrical signals are measured in micro volts (mV). Furthermore, the amplitude values of these signals are small voltage values and are being caught using traditional electronic devices. This is an important characteristic which must be considered to implement an electronic device in order to obtain bioelectrical signals.

There are different sources of noise at the moment of getting a human body signal. The frequency domain helps us to know of how additional sources affect the important signal in the time domain.

Figure 3 shows frequency range of QRS complex of an ECG signal next to the frequency range of common noise sources.

Fig. 3. Frequency range of QRS complex on an ECG signal next to noise sources (Vidal et al., 2008)
