Lecture 6.1 - Basics of ECG

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Questions and Answers

What is the significance of the J point in an ECG?

It is the point where the ST segment becomes elevated in normal individuals.

It is used to determine if the ST segment is isoelectric or elevated. (correct)

It is the point where the T wave starts.

It is the point where the QRS interval begins.

What does a widening of the QRS interval indicate?

Delayed repolarization of the ventricles.

Abnormal depolarization of the atria.

Ventricles are delaying depolarisation. (correct)

Conduction delay in the AV node.

What is the significance of a change in the height or amplitude of an ECG wave?

It is a sign of cardiac conduction delay.

It is a normal variation in ECG waveform.

It indicates a pathological issue has arisen. (correct)

It is a normal response to exercise.

What is the purpose of chest leads in an ECG?

To provide 6 tracings/views of the heart in the horizontal plane. Signup and view all the answers

What does the QT interval represent in an ECG?

The entire depolarisation and repolarisation of ventricles. Signup and view all the answers

What is the significance of the PR interval in an ECG?

It represents the conduction of the AV node. Signup and view all the answers

Which of the following electrodes acts as a ground electrode in tracings/views?

Right leg (RL) electrode Signup and view all the answers

What is the relationship between Lead I, Lead II, and Lead III?

Lead I + Lead III = Lead II Signup and view all the answers

Which of the following leads covers the high lateral wall of the left ventricle?

Lead I Signup and view all the answers

What is the area of the heart covered by the precordial chest lead V1-V2?

Right ventricle Signup and view all the answers

What is the characteristic of the R wave in the ECG waves from V1-V6?

Increase in size from V1-V6 Signup and view all the answers

What is the characteristic of the S wave in the ECG waves from V1-V6?

Decrease in size from V1-V6 Signup and view all the answers

Which of the following leads is opposite to lead I, II, and III?

aVR Signup and view all the answers

What is the placement of the precordial chest lead V3?

Between V2 and V4 Signup and view all the answers

Which of the following leads cover the inferior wall of the heart?

aVF Signup and view all the answers

What is the relationship between the bipolar limb leads and Einthoven's triangle?

The bipolar limb leads can be represented schematically in terms of Einthoven's triangle Signup and view all the answers

What is the primary function of the cardiac cycle?

To generate a depolarising wave that spreads across the myocardium Signup and view all the answers

Which of the following statements is true regarding the P wave?

It is formed by atrial depolarisation Signup and view all the answers

What is the purpose of the electrodes in an ECG?

To record the movement of ions in the heart Signup and view all the answers

What is the significance of the P-R segment in an ECG?

It represents the delay in conduction in the AV node Signup and view all the answers

What is the sequence of depolarisation in the cardiac conduction system?

SA node, atria, AV node, ventricles Signup and view all the answers

What is the purpose of Lead II in an ECG?

To produce a sinus rhythm tracing Signup and view all the answers

What is the significance of the S-T segment in an ECG?

It represents the entire ventricular myocardium being depolarised and not repolarised yet Signup and view all the answers

What is the relationship between the direction of the current and the deflection on an ECG?

+ve current moving towards the +ve electrode gives a +ve deflection Signup and view all the answers

Study Notes

ECG Waves

T wave: ventricular repolarization, with action potential durations shorter in the anterobasal region
Negative charge moving towards the negative electrode gives a positive deflection after a short period of time
U wave may be present due to delayed repolarization of papillary muscles and chordinae tendinae

ECG Waves and Cardiac Cycle

PR interval: conduction of AV node
Conduction delay/block elongated: links to PR interval
Widening of QRS interval: ventricles are delaying depolarization
ST segment: should always be isoelectric (conditions like MI could stop the straight line showing)
J point: used to determine if the ST segment is isoelectric or elevated
QT interval: indicates the entire depolarization and repolarization of ventricles

ECG and Electrodes

ECG can be recorded by limb electrodes or including chest electrodes
12 lead ECG: 12 views of the heart
Chest leads: 6 electrodes giving 6 tracings/views (horizontal plane)
Unipolar leads: only have positive electrodes
Limb leads: 4 electrodes giving 4 tracings/views (frontal plane)

Impulse Conducting System of the Heart

Cardiac cycle relies on wave of excitation spreading across the myocardium in a sequential process
Depolarizing (+ve) current is generated in SA node
Spreads to atrium and then to the AV node
From the AV node, the +ve current moves to bundle branches depolarizing the interventricular septum
The +ve current then moves to the purkinje fibres depolarizing the ventricles

ECG Graphical Representation

Captures the electrical activity of the heart (movement of currents)
Graphical representation of electrical activity of the heart
The electrodes placed in the body capture movement of ions and record it
+ve current moving towards +ve electrode will give a +ve deflection
+ve current moving away from +ve electrode will give a -ve deflection
+ve current moving perpendicular to the electrodes will give isoelectric line

Normal ECG

Lead II: most commonly used to produce the sinus rhythm tracing (rhythm strip)
P wave: formed by atrial depolarization
P-R segment: 0.1s delay in conduction in AV node leading to P-R segment
Q wave: septal depolarization
R wave: ventricular (apex) depolarization
S wave: ventricular wall depolarization
QRS complex: ventricular depolarization
S-T segment: entire ventricular myocardium is depolarized and is not repolarized yet

Limb Leads

Three bipolar limb leads: Lead I, Lead II, and Lead III
Lead I: LA (+) to RA (-)
Lead II: LL (+) to RA (-)
Lead III: LL (+) to LA (-)
Leads I, II, and III can be represented schematically in terms of a triangle, called Einthoven's triangle
The area of heart covered by the leads:
- Lead I: high lateral wall of left ventricle
- Lead II and III: inferior portion of right and left ventricle

Unipolar Limb Leads

The abbreviation 'a' refers to augmented; V to voltage/vector; and R, L, and F to right arm, left arm, and left foot (leg) respectively
The area of heart covered by:
- aVR: right ventricle and basal septum
- aVL: high lateral wall of left ventricle
- aVF: inferior wall of the heart

Precordial Chest Leads

In horizontal/transverse plane
Placement: V1 to V6
The area of heart covered by:
- V1-V2: right ventricle
- V2-V3: basal septum
- V2-V4: anterior wall of the heart
- V5-V6: lateral wall of the heart
The ECG waves:
- R wave increases in size from V1-V6
- S wave decreases in size from V1-V6

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Description

This quiz covers the different waves and intervals in an electrocardiogram (ECG), including the T wave, PR interval, and QRS interval, and their relation to the cardiac cycle.