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