ECG 1 Flashcards
Describe the components of a 12 ECG.
A 12 ECG includes three standard limb leads (I, II, III), augmented leads (aVR, aVL, aVF), six chest leads (V1-V6), and a rhythm strip.
Define the purpose of a rhythm strip in an ECG.
The rhythm strip is a longer continuous recording of standard limb lead II, providing a detailed view of the heart’s electrical activity over time.
Define the purpose of standard limb leads in an ECG.
Standard limb leads in an ECG focus on electrical events in the heart across the vertical or frontal plane, providing valuable information about the heart’s activity.
Describe the standard limb lead II in an ECG.
It is considered the most normal ECG lead and resembles the stereotypical trace, with the recording electrode in the left leg relative to the electrode in the right arm.
How does a wave of depolarisation affect the ECG trace when it spreads towards the left leg electrode?
It makes the left leg electrode positive relative to the right arm electrode, resulting in a positive going blip on the ECG trace.
Define the PR interval in an ECG.
It is the time from the start of the P wave to the start of the QRS complex, representing the duration from atrial depolarisation to ventricular depolarisation.
What does the QRS complex represent in an ECG?
It represents ventricular depolarisation.
How is ventricular repolarisation depicted on an ECG trace?
It is shown by the T wave, indicating the recovery phase of the ventricles.
Describe the significance of the u wave in an ECG.
The u wave’s significance is unclear, as its representation and role in cardiac activity remain uncertain.
What is the direction of the wave of depolarisation that causes a negative going blip on the ECG trace?
It is moving away from the electrode in the left leg towards the electrode in the right arm, making the left leg electrode negative relative to the right arm electrode.
How does a wave of repolarisation towards the left leg affect the ECG trace?
It makes the left leg electrode negative relative to the right arm electrode, resulting in a negative going blip on the ECG trace.
Define the T wave in an ECG.
It represents ventricular repolarisation, indicating the recovery phase of the ventricles after depolarisation.
Describe the time taken for the QRS complex in an ECG
The time taken for the cells in the ventricle to start depolarising to the last cells in the ventricle depolarising, usually about 0.08 s.
Define the QT interval in an ECG
The time taken from the ventricles depolarising to repolarising again, which varies with heart rate but is approximately 0.42 s at a resting heart rate of 60 bpm.
How does the size of the atria and ventricles affect ECG readings?
Atrial repolarisation is not visible on ECG because it coincides with ventricular depolarisation, which produces a larger signal due to the ventricles being much larger.
Do different parts of the ventricle depolarise at the same time?
No, different parts depolarise at different times and in different directions, leading to the complexity of the QRS complex.
Describe the depolarisation direction of the interventricular septum in an ECG
The interventricular septum depolarises from left to right, resulting in a negative Q wave when recorded from standard limb lead II.
Explain the reason behind the positive T wave in an ECG
The T wave is positive-going because the wave of repolarisation moves away from the electrode in the left leg, making it more positive relative to the electrode in the right arm.
Describe the difference in R wave size between standard limb lead II, I, and III in an ECG.
The R wave is bigger in standard limb lead II compared to standard limb lead I and III due to the alignment of the wave of depolarization with the axis of lead II.
Define augmented limb leads in an ECG.
Augmented limb leads are derived from one limb lead and recorded with respect to the other two limb leads, providing additional perspectives on the electrical events in the heart.
How are augmented limb leads aVR, aVL, and aVF recorded in an ECG?
aVR is recorded from the right arm relative to the left arm and left leg, aVL from the left arm relative to the right arm and left leg, and aVF from the left leg relative to the right arm and left arm.
Describe the information provided by augmented limb leads in an ECG.
Augmented limb leads, along with standard limb leads, offer six different views of the electrical events in the heart, enhancing the understanding of frontal or vertical plane electrical activity.
Do augmented limb leads aVR, aVL, and aVF show different R wave characteristics in an ECG?
Yes, the R wave characteristics differ in augmented limb leads - aVR typically shows a negative R wave, aVL may have a unique R wave appearance due to its perpendicular axis, and aVF usually displays a positive and reasonably large R wave.
How does the alignment of the depolarization wave affect the R wave appearance in augmented limb leads?
The alignment of the depolarization wave with the axis of the lead influences the appearance of the R wave - positive in the direction of the axis, negative when moving away, and potentially ambiguous when perpendicular to the axis.
