ECG Recording Setup (Block Diagram and Waveform)

Contents

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Key learnings:

ECG Recording Setup Definition: The ECG recording setup is defined as a system to measure the electrical activity of the heart using various components and circuits to produce a clear ECG waveform.
ECG Block Diagram: The block diagram of an ECG recording setup includes essential components like the defibrillator protection circuit, lead selection logic, calibration circuit, pre-amplifier, power amplifier, feedback network, and output display unit.
Depolarisation and Repolarisation: Depolarisation is the contraction of heart muscle fibers, while repolarisation is the relaxation of these muscles, both crucial for heart function.
ECG Waveform Components: Key parts of the ECG waveform include the P wave, QRS complex, and T wave, each representing different phases of heart activity.
Output Display Unit: The output display unit, such as a CRO or pen chart recorder, is used to visualize the ECG waveform.

ECG Waveform

This is what an ECG waveform looks like:

Depolarisation

When electrical activity occurs, heart muscle fibers contract, producing movement. This condition is referred to as depolarisation. When blood is pumped around the body, the heart chambers contract, called systolic pressure.

Repolarisation

The realxation of heart muscles are called electrical repolarisation. Relaxed heart chambers are called diastolic.

Wave	Origin	Amplitude (mV)	Duration (seconds)
P wave	Due to depolarization of atria	0.25	0.12 to 0.22 (PR interval)
R wave (QRS Complex)	Due to repolarization of atria and ventricle contraction	1.60	0.07 to 0.1
T wave	Due to relaxation of myocardium	0.1 to 0.5	0.05 to 0.15 ST interval
S T interval	Contraction of ventricles	–	–
U wave	Due to slow expansion of purkinje fibers	< 0.1	0.2 (T – U interval)

ECG Recording Setup Block Diagram

Defibrillator Protection Circuit

One end of the electrode leads connects to the patient’s RA, LA, chest, and LL. The other end passes through the defibrillator protection circuit, which includes a buffer amplifier and overload voltage protection.

Lead Selection Logic

This block helps to select the type of electrode lead system. We can choose either bipolar or augmented electrode system.

Calibration Circuit

Calibration is a process that helps eliminate errors in the system. Changes in the lead selection circuit can cause artifacts in the ECG output. The calibration unit helps the technician correct these errors.

Pre Amplifier

An instrumentation amplifier and a differential amplifier with high gain and high CMRR are used as pre-amplifiers.

Power Amplifier

The output unit is driven by a power amplifier. After the signal is amplified by the pre-amplifier, it goes to the power amplifier. The output unit is attached to a pen motor, requiring high electrical power for recording. Therefore, high power gain amplifiers are used.