Physiology: A first look at the ECG Flashcards
What are the Standard Limb Leads?
Look at electrical activity in the vertical and frontal plains of the heart The 3 leads include: SLL I SLL II SLL III
Where are the electrodes placed in SLL I?
Left arm with respect to right arm
Where are the electrodes placed in SLL II?
Left leg with respect to right arm
Where are the electrodes placed in SLL III
Left leg with respect to left arm
Why is SLL II important?
As it is in the same plain as the wave of depolarisation of the heart
What does a wave of depolarisation towards the left leg produce at SLL II?
Produce a positive wave relative to the Right arm
What does a wave of depolarisation away from the left leg produce at SLL II?
Produces a negative wave relative to the right arm
What does a wave of repolarisation towards the left leg produce at SLL II?
Produce a negative wave relative to the right arm
What does a wave of repolarisation away from the left leg produce at SLL II?
Produces a positive wave relative to the right arm
What does a normal ECG look like?
What does ECG stand for?
Electrocardiogram
What does the p-wave represent in an ECG?
Atrial Depolarisation
What does the QRS complex represent in an ECG?
Ventricular Depolarisation
What does a T-wave represent in an ECG?
Ventricular Repolarisation
What does the PR interval represent in an ECG?
Time between atrial depolarisation to ventricular depolarisation (ie through the AV node)
What does the QT interval on an ECG represent?
Time between ventricular depolarisation to the end of ventricular repolarisation
Why is atrial repolarisation not observed on an ECG?
Atrial repolarisation occurs at the same time as ventricular depolarisation and due to the fact ventricular depolarisation involves more tissues and occurs faster the electrical signal swamps the repolarisation
What does the Q in the QRS complex represent on an ECG?
The interventricular septum depolarising from the left to the right
What does the R section in the QRS complex represent on an ECG?
bulk of the ventricle depolarising from the inner tissue (endocardial) to the outer tissue (epicardial)
What does the S section of the QRS complex represent on an ECG?
Upper part of the interventricular septum depolarising
Why is the T-wave a positive wave?
Action potentials are longer in endocardial cell compared to epicardial cells and therefore repolarisation occurs from outside to in, in the opposite direction of depolarisation
What are the augmented limb leads?
Allow alternative perspectives on the electrical events that occur in the heart. This allows allows 6 perspectives on the frontal plane
Where are the precordial (chest) leads and what event do the they record?
They are arranged at the front of the heart and it records events of the heart in the transverse plane
What is progression in an ECG?
Occurs in the precordial leads
A change in size in R wave from V1 to V6 causing a change from negative to positive occuring around V3 and V4
