Electrocardiogram ECG: Purpose and Types

What Is An Electrocardiogram (ECG)?

An electrocardiogram (ECG) is an associated medical exam that involves the assessment of the electrical activity of the heart that, in turn, allows to establish the presence of probable arrhythmias and other irregularities in the functioning of the heart. It is valuable in all sorts of cardiopathies starting from arrhythmia to acute myocardial infarction, as it reveals exhaustive data concerning the electrical activity of the heart.

Historical Background – Willem Einthoven

The ECG has its roots in its utilization in the early twentieth century, with Willem Einthoven who played the major role. Increasing the desynchronization of electricity in the heart he developed the first practical ECG machine in 1903 and was awarded the Nobel Prize in Medicine in 1924. Einthoven formulated the principles that paved the way for the development of modern cardiological practice and alterations within the management of heart diseases.

Objective Of ECG

• Diagnose Cardiac Conditions: Diagnose the different heart conditions such as arrhythmias, and myocardial infarction otherwise known as heart attack and heart failure.

• Monitor Heart Health: Evaluate the ability of the heart’s electrical signal over time to check the state of changes in the heart and assess treatment efficacy.

• Evaluate Heart Rhythm: Detects some forms of arrhythmia of the heart including atrial fibrillation of the atria or ventricular tachycardia of the ventricles.

• Assess Heart Function: Identify or define the location of the heart’s electrical conduction pathways and the defects if any that may be present in the conduction pathways.

• Pre-surgical Assessment: Determine if it is wise to subject the heart to surgeries or procedures that may harm it before carrying out the procedures.

• Aid in Risk Stratification: Assist in determining future risks of new cardiac events because of the patterns and abnormalities found in the ECG tracings.

How ECG Works – Basic Principle

The following describes how an ECG works:

• An ECG measures the electrical activity of the heart with leads positioned on the patient’s chest, arms and legs;

• It produces a shape of waves relating to the various phases of the cardiac action.

• Electrodes which are usually attached to the skin can pick up any electrical changes and convert them into graphs.

• Leads are then arranged on certain parts of the body where one gets to record electrical firing in that particular orientation.

• This setup helps formulate an inclusive picture of the electrical counterpart of the heart as well as locate any irregularities.

Components Of An ECG Waveform

The components of an ECG are discussed:

P Wave (Atrial Depolarisation)

The P wave depicts the electrical event that is related to the atrial depolarisation resulting in atrial contraction. This wave signifies the beginning of the cardiac cycle and determines the correct filling of the ventricles.

QRS Complex (Ventricular Depolarisation)

The QRS complex is due to the depolarisation of the ventricles and represents the actual contraction and the discharge of blood from the whole heart.

• Q Wave: The first one is downward whereas the second one represents the beginning of ventricular depolarization. This is often small or missing in some leads.

• R Wave: The large upward deflection is the peak of the R wave – this is rapid depolarization of the ventricles. It is the largest deflection in the QRS complex.

• S Wave: The further down slope after the R wave is indicative of the last part of ventricular depolarization, thus providing the shape of the QRS complex.

T Wave (Ventricular Repolarisation)

The T wave represents the phase of ventricular repolarisation, a time when the myocardium of the ventricles comes back to the state when it is going to contract again.

U Wave (if present)

The T wave is followed by the U wave and this wave is not always observed. It might express the repolarisation of the Purkinje fibres or some other phase of ventricular repolarization. That is, it may be either more apparent or less apparent to allow for additional diagnostic data.

Normal ECG Values (Standard Measurements)

The working of a normal ECG is shown below:

P Wave Normal Duration & Amplitude

It ranges from 0 to 30 seconds long depending on the extent of its influence on the AHP’s effectiveness and overall company performance 0.08 to 0.12 seconds and amplitude reaches 0. 25 millivolts. It is known as a small rounded and pointed wave which usually shows atrial depolarization.

QRS Complex Duration & Amplitude

Typically ranging from 0 to 3 months or even several years, it largely depends on the pathology grade and general health state of the patient and has a relatively greater amplitude than that of the P wave. The QRS complex refers to ventricular depolarization and the outlines of the complex consist of a downward stroke, a Q wave, an upward stroke, an R wave, and the final downward stroke, an S wave.

T Wave

Lasts between 0.10 to 0.25 seconds, with an amplitude of up to 0. 5 millivolts. It is normally smooth and tends to upward movement signifying the ventricular repolarization phase.

Normal Heart Rate (60-100 bpm)

Heart rate usually does not exceed sixty to hundred beats per minute (bpm) during the state of rest. It shows the normal range of rhythm and rate of the heart.

Interpretation Of A Normal ECG

The interpretation of a normal ECG is:

Identify the P Wave: Three of its attributes affecting periodically should be examined, the regularity of shape and duration.

Measure the QRS Complex: Check that its value reflects the average by comparing it with the normal range of the given period and its variation.

Assess the T Wave: Ensure it comes after the QRS complex and the size and shape are proportional.

Evaluate the Heart Rate: Determine the rate through the division of the number of R-R intervals with 60 and compare it with the normal range.

Check the Rhythm: Make sure that while interpreting the waves of the ECG, P waves, QRS complexes and T waves should be of the same pattern.

Example Of A normal ECG Strip

The strip would demonstrate a normal rhythm presented as a series of P waves, QRS complexes, and T waves where the PR interval and the QT interval would fall in the normal range. Pulse rate, 60-100 bpm falling under the sinus rate and rhythm.

Electrocardiogram NEET MCQs (With Answers & Explanations)

Types of questions asked from this topic are:

• Components of an ECG waveform

• Normal ECG values

Practice Questions for NEET

Q1. A machine used to obtain an ECG of a human's heart is

1. Electrocardiogram

2. Digital grapher

3. Electrocardiograph

4. Either 1 or 3

Correct answer: 3) Electrocardiograph

Explanation:

A graph that shows the electric current generated by the heart muscles being excited is called an electrocardiogram (ECG).
An electrocardiograph is a device used to record an electrocardiogram.
Einthoven is credited as the father of electrocardiography for creating the electrocardiograph.

A machine used to obtain an electrocardiogram (ECG) of a human’s heart.

Hence, the correct answer is option 3) Electrocardiograph.

Q2. Depolarisation atria is represented by

1. P wave

2. Q wave

3. T wave

4. QRS complex

Correct answer: 1) P wave

Explanation:

P wave is a small upward wave that indicates the depolarisation of the atria leading to contraction of both atria. It is caused by the activation of the SA node.

Hence, the correct answer is option 1) P wave.

Q3. If heart sound recording and ECG are superimposed the first heart sound would occur

1. At P wave

2. Just after P wave

3. Just before QRS complex

4. Just after QRS complex

Correct answer: 4) Just after QRS complex

Explanation:

QRS wave

• It begins after a fraction of a second of the P wave

• It begins as a small downward deflection (Q) and continues as a large upright (R) and triangular wave, ending as a downward wave (S) at its base

• QRS wave indicates depolarization of ventricles

• It is caused by the impulses of the contraction from the AV node through the Bundle of His and Purkinje fibers and the contraction of ventricular muscles

• In this wave there is a spread of electrical impulses through ventricles

• The normal duration of the QRS complex is <0.10 seconds

If heart sound recording and ECG are superimposed the first heart sound would occur just after the QRS complex, As the ventricular cells contract, intraventricular pressures increase above those in the atria, and the atrioventricular valves abruptly close. Closure of the atrioventricular valves results in the first heart sound, S1.

Hence, the correct answer is option 4) Just after the QRS complex.

Also Read-

• MCQs on Electrocardiogram

• Body Fluids and Circulation

• Components of Blood

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