ECG made easy Flashcards
Why is it best to electrically consider the heart to be just two chambers?
As the atria contract together and the ventricles contract together
What is the normal electrical conduction path in the heart?
Depolarisation begins in the sinoatrial node –> atrioventricular node (which slows conduction) –> bundle of his –> right/left bundle branch –> purkinje fibres
What is normal/sinus rhythm?
60-100bpm
What does the P wave represent?
Atrial contraction
What does the QRS complex represent?
Ventricular contraction
Why is the p wave smaller than the QRS complex?
As there is more ventricular muscle mass
What does the t wave represent?
Ventricular repolarisation
What is a u wave? Who might have one?
Repolarisation of papillary muscles
Only present in some individuals
If preceded by normal T wave –> physiological
If preceded by flattened t wave –> pathological
What is the standard rate that ECGs run at?
25mm/s
How much time does 1 large square represent?
0.2s
How much time does 1 small square represent?
0.04s
How many large boxes are equal to 1 minute?
300
How many large squares represent 1 second?
5
How can you calculate HR from an ECG?
300/no. of large boxes between the R-R interval
What is the PR interval?
Time between start of p wave and start of QRS complex
What is a normal PR time?
120-200ms (3-5 small squares)
What can a short PR interval mean?
Depolarisation occurring too close to AV node/abnormally fast conduction from atria to ventricles
What does the QRS duration represent?
How long ventricular contraction takes
What is the normal QRS duration?
120ms (3 small squares) or less
What things may cause a prolonged QT interval?
Electrolyte abnormalities
Drugs
What can a prolonged QT lead to?
Ventricular tachycardia
Define a prolonged QT interval
Greater than 450ms
What surface of the heart do leads I, II and VL look at?
Left lateral surface
What surface of the heart do leads III and VF look at?
Inferior surface
What lead looks at the right atrium?
VR
What plane do the chest leads look at the heart in?
Horizontal plane
What part of the heart do leads V1 and V2 look at?
Right ventricle
What part of the heart do leads V3 and V4 look at?
Interventricular septum
What part of the heart do leads V5 and V6 look at?
Anterior and lateral walls of left ventricle
When the ECG machine detects a wave of depolarisation towards it does it cause an upwards or downwards deflection on the ecg?
Upwards
When the ECG machine detects a wave of depolarisation away from it does it cause an upwards or downwards deflection on the ecg?
Downwards
What does it mean if the QRS is mainly upwards?
The depolarisation is moving towards that lead
What does it mean if the QRS is mainly downwards?
The depolarisation is moving away from that lead
What pattern of QRS do you see when the wave of depolarisation is moving at right angles to the lead?
R and S wave are of equal size
Which two leads look at the heart from opposite directions?
II and VR
