Electrocardiogram Flashcards
What information does an ECG provide? What information does it not provide?
Tells you about: . Timing and direction of depolarisation . Disturbances in rate and rhythm . AV conduction time . Mass of active myocardium and ischaemic areas
. Doesn’t tell you anything about mechanical force
. Can’t see atrial repolarisation because it’s quite a small electrical event and is obscured by ventricular depolarisation, however it happens at the same time as ventricular depolarisation
What does an ECG show you about timing and direction of depolarisation?
Shows atrial depolarisation, ventricular depolarisation, and ventricular repolarisation (atrial repolarisation is too small an electrical event to be detected but happens at the same time as ventricular depolarisation)
What can an ECG show about heart rate and rhythm?
If there’s tachy/bradycardia, sinus rhythm (normal rhythm), or arrhythmias
What could a downward deflection represent?
. Depolarisation moving away from a positive electrode or towards a negative electrode
. Repolarisation towards a positive electrode or away from a negative electrode
What does an upward deflection show?
. Depolarisation moving towards a positive electrode or away from a negative electrode
. Repolarisation away from a positive electrode or towards a negative electrode
What does a deflection with minimal amplitude tell us?
. Minimal amplitude shows depolarisation is perpendicular to electrode (neither moving towards or away)
What would depolarisation away from a negative electrode show on an ECG trace?
Upward deflection
What would depolarisation towards a positive electrode show on an ECG trace?
Upward deflection
What would depolarisation away from a positive electrode show?
Downward deflection
What would depolarisation towards a negative electrode show?
Downward deflection
Negative electrode sees the same thing as …
A diametrically opposite positive electrode
Why do deflections always return back to the base line?
Because there’s maximal depolarisation resulting in no more movement
When viewing limb lead 2, what does the first upward deflection show?
Atrial depolarisation
When viewing limb lead 2, what does the first small downwards deflection show?
Septal depolarisation
When viewing limb lead 2, what does the large upward deflection show?
Ventricular depolarisation
When viewing limb lead 2, what does the last upward deflection show?
Ventricular repolarisation
Where are the unipolar leads placed?
. Limb leads- Left shoulder, right shoulder, groin area
. Chest leads- V1, V2 (right side of heart), V3 (apex), V4, V5, V6 (left side of heart)
What is the first wave called?
P wave
What is the final wave called?
T wave (unless U waves are present)
What is any negative wave after a P wave but before an R wave called?
Q wave
What is the first positive wave after a Q wave called?
R wave
What is any negative wave after an R wave called?
S wave
What is any positive wave after an S wave called?
R’ wave
Draw and label a classical ECG trace.
Check slide 21 in ECG lecture!
Draw and label an ECG taken from the positive electrode at the right shoulder.
Check slide 21 in ECG lecture!
What does the P wave show?
Atrial depolarisation
What does the QRS complex show?
Ventricular depolarisation
What does the T wave show?
Ventricular repolarisation
What is axis deviation and what is it caused by?
When the cardiac axis is skewed (average direction of depolarisation is skewed), which is caused by extreme hypertension or valvular heart disease
