lecture 10 - electrocardiogram/ECG Flashcards
At resting membrane potential, is the charge inside the heart negative or positive compared to the outside?
Negative
What does the gap between the P wave and Q wave on ECG represent in terms of electrical activity of the heart?
The pause created by the AV node to create time for distinct atrial and ventricular contractions.
On an ECG, the what does the polarity of voltage change at an electrode depend on?
The direction in which the wave of potential change is moving
What kind of directions of depolarisation causes a positive potential (upwards line) on an ECG trace?
Depolarisation towards a positive electrode/repolarisation away from a positive electrode
What kind of direction of depolarisation causes a negative potential (downwards line) on an ECG trace?
Depolarisation away from a positive electrode
What are the locations of the standard limb leads (I,II,III)?
Left arm, right arm, left leg (plus an earth on right leg)
What is the purpose of the ‘Einthoven Triangle’?
Orients the frontal plane of the body, forming a triangle with the heart in the middle and a standardised lead position
Why is it that both repolarisation and depolarisation will appear as an upwards line on ECG?
Upwards potentials are marked by the direction of the depolarisation/repolarisation - a depolarisation and repolarsiation in opposite directions will appear the same. As the heart repolarises in the opposite direction to the way it depolarises, the T wave appears the same as the P wave.
What is the difference between a segment and interval on ECG?
Segments are the distance between the end of one wave and the beginning of the next, while intervals include both the waves and segments and the distance between them.
What is happening in the conduction pathways of the heart during the PR interval of an ECG?
Excitation is spread through the atria, paused at AV node and spread to bundle of His
What is happening in the conduction pathways of the heart during the QS interval of an ECG?
Excitation is spreading through the ventricles.
What is the name for a combination of 2 electrodes, where an ECG recording is made between?
Bipolar lead
What are the augmented limb leads?
3 leads (aVR, aVL, aVF) using the same electrodes as those for the standard limb leads, but used the augmented voltage measured with the electrodes.
How many chest leads are used in ECG?
6: V1, V2,V3…..
What are the leads of a 12 lead ECG?
- 3 standard limb leads: I, II, III
- 3 augment leads: aVR, aVL, aVF
- 6 chest leads: V1, V2, V3, V4, V5, V6
