24 Questions
What is the significance of the J point in an ECG?
It is used to determine if the ST segment is isoelectric or elevated.
What does a widening of the QRS interval indicate?
Ventricles are delaying depolarisation.
What is the significance of a change in the height or amplitude of an ECG wave?
It indicates a pathological issue has arisen.
What is the purpose of chest leads in an ECG?
To provide 6 tracings/views of the heart in the horizontal plane.
What does the QT interval represent in an ECG?
The entire depolarisation and repolarisation of ventricles.
What is the significance of the PR interval in an ECG?
It represents the conduction of the AV node.
Which of the following electrodes acts as a ground electrode in tracings/views?
Right leg (RL) electrode
What is the relationship between Lead I, Lead II, and Lead III?
Lead I + Lead III = Lead II
Which of the following leads covers the high lateral wall of the left ventricle?
Lead I
What is the area of the heart covered by the precordial chest lead V1-V2?
Right ventricle
What is the characteristic of the R wave in the ECG waves from V1-V6?
Increase in size from V1-V6
What is the characteristic of the S wave in the ECG waves from V1-V6?
Decrease in size from V1-V6
Which of the following leads is opposite to lead I, II, and III?
aVR
What is the placement of the precordial chest lead V3?
Between V2 and V4
Which of the following leads cover the inferior wall of the heart?
aVF
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
What is the primary function of the cardiac cycle?
To generate a depolarising wave that spreads across the myocardium
Which of the following statements is true regarding the P wave?
It is formed by atrial depolarisation
What is the purpose of the electrodes in an ECG?
To record the movement of ions in the heart
What is the significance of the P-R segment in an ECG?
It represents the delay in conduction in the AV node
What is the sequence of depolarisation in the cardiac conduction system?
SA node, atria, AV node, ventricles
What is the purpose of Lead II in an ECG?
To produce a sinus rhythm tracing
What is the significance of the S-T segment in an ECG?
It represents the entire ventricular myocardium being depolarised and not repolarised yet
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
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
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.
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