Principle Parts and Types of ECG Recorders

Building Blocks of an ECG System

In Electrocardiography (ECG) recorder five leads from the patient are connected to the ECG recorder through a selector switch to obtain 12 lead configurations as illustrated below:

A standard voltage of 1 mV is used to calibrate the recorder. The output from the lead selector switch is amplified using a differential amplifier with a high common mode rejection ratio. It is called a preamplifier. The output of the preamplifier goes to a DC amplifier which is called the pen amplifier as it provides the power to drive the pen motor that records the ECG trace.

ECG recorder employs heat sensitive paper as the recording paper. The pen is actually an electrically heated stylus which is called recording stylus. The recorder also has a marking stylus to mark a code indication of the standard lead configuration on the trace. The paper speed is kept at 25 m/s or 50 m/s.

Related: Electrocardiogram (ECG)

Types of ECG Recorders

The common types of ECG recorder are discussed as follows:

Single Channel Recorder

This is the most frequently used type of ECG recorder and it is portable. As the name suggests, the output of one out of 12 standard lead configurations is traced at a time. Twelve traces are therefore recorded on a paper of length 3 to 6 feet. Hence it is inconvenient to read and store.

Three-channel Recorder

The recorder records the output of three leads simultaneously. It can also switch automatically to the next group of three leads to carry out the recording. The time required for recording 12 traces is considerably reduced.

Vector Electrocardiograph

This recorder presents an image of both the magnitude and the spatial orientation of the heart vector.

ECG for Computer Processing

This method requires that the ECG signals from the standard leads be transmitted sequentially to the computer using some appropriate means together with all the information regarding the patient.

Continuous ECG Recording (Holter recording)

Typically ECG represents a brief recording of the cardiac activity. However, arrhythmia may occur under certain conditions at any unspecified time. Hence, continuous recording that was introduced by physician Holter to capture ECG at the time of arrhythmia. In this case, a small device like magnetic tape recorder which can be worn in a shirt pocket is used and it allows the recording of the ECG continuously for 24 hrs. The recorded tape is analyzed using a special scanning device.

You can also read: Biomedical Signals Acquisition Instruments