**1. Introduction**

152 Applications of Digital Signal Processing

Yang, C. T., Chang, C. L., Hung C.C. & Wu F. (2001). Using a Beowulf cluster for a remote

Singapore, Nov. 5ޤ9, 2001.

sensing application, *Proceedings of 22nd Asian Conference on Remote Sensing*,

An electrocardiogram (ECG) is a graphical record of bioelectrical signal generated by the human body during cardiac cycle (Goldschlager, 1989). ECG graphically gives useful information that relates to the heart functioning (Dubis, 1976) by means of a base line and waves representing the heart voltage changes during a period of time, usually a short period (Cuesta, 2001).

Putting leads on specific part of the human body, it is possible to get changes of the bioelectrical heart signal (Goldschlager, 1989) where one of the most basic forms of organizing them is known as Einthoven lead system which is shown in Figure 1 (Vidal & Pavesi, 2004; Vidal et al., 2008).

Fig. 1. Einthoven lead system

### **1.1 ECG usefulness**


A DSP Practical Application: Working on ECG Signal 155

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

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

Figure 3 shows frequency range of QRS complex of an ECG signal next to the frequency

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

Building a device to get and process the ECG signal must consider the signal characteristics. According to (Cuesta, 2001; Vidal & Pavesi, 2004), facing individually each part of the global

Figure 4 presents each part or block of a basic digital ECG according to reviewed literature

problems is a technique applicable in order to get good practical results.

Fig. 4. Blocks Diagram of a Basic Digital ECG.

bioelectrical signals.

the time domain.

2008)

**3. Digital ECG** 

range of common noise sources.


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.
