ECG Flashcards
What is an ECG?
An Electrocardiogram is a test used to measure the electrical changes of the heart muscle
What happens during the P wave?
Atrial depolarisation
What happens during the QRS complex?
Ventricular depolarisation
(atrial repolarisation)
What happens during the T wave?
Ventricular repolarisation
What happens during the U wave?
Unknown (repolarisation of Purkinje fibres?) – rarely seen
What does 1 small square represent on ECG paper?
0.04s / 40ms
What does 1 large square represent on ECG paper?
0.2s / 200ms
How do you calculate HR?
300 / No. of large squares
How long is a normal PR interval?
120-220ms
Describe the PR interval
- Beginning of P wave to the beginning of QRS complex
- The time taken for the signal to travel from the SAN to the ventricular muscle
How long is a normal QRS complex?
120ms
Describe the QRS complex
How long it takes for the signal to spread through the ventricles
Describe the QT interval
- Beginning of the QRS to the end of the T wave
- Time taken for ventricular depolarisation and repolarisation to occur
Describe the ST segment
- End of the S wave to the beginning of the T wave
- The period between ventricular depolarisation and repolarisation
What leads make up the 12 lead ECG and how many electrodes?
Made up of 6 limb leads (4 electrodes) and 6 chest leads (6 electrodes)
What plane do the limb leads look at the heart in?
Vertical
What plane do the chest leads look at the heart in?
Horizontal
Which limb leads look at the left lateral surface of the heart?
I, II, and VL
Which limb leads look at the inferior surface of the heart?
III and VF
Which limb lead looks at the right atrium?
VR
Which chest leads look at the right ventricle?
V1 and V2
Which chest leads look at the septum, and anterior wall of the left ventricle?
V3 and V4
Which chest leads look at the anterior and lateral walls of the left ventricle?
V5 and V6
What do limb leads I, II and VL look at?
left lateral surface
What do limb leads III, and VF look at?
inferior surface
What does the limb lead VR look at?
right atrium
What do chest leads V1 and V2 look at?
right ventricle
What do chest leads V3 and V4 look at?
septum and anterior wall of the left ventricle
What do chest leads V5 and V6 look at?
anterior and lateral walls of the left ventricle
What is the rhythm strip?
will usually be taken from lead II, and it is a 10s reading from ONLY this lead
What is a deflection?
A deflection is a move from baseline voltage (upwards or downwards)
What does the deflection look like if a signal is moving towards an electrode?
the bigger deflection is positive
What does the deflection look like if a signal is moving away from electrode?
the bigger deflection is negative
What does the deflection look like if a signal is moving at right angles to an electrode?
the positive and negative deflections are the same
How does the electricity normally flow?
- normally goes from 11 o’clock to 5 o’clock, (VR to II)
- Lead II will therefore usually show the clearest image of electrical conduction
What happens to the axis if the right/left ventricle becomes hypertrophied?
the axis will swing to the side with the abnormality
What will right axis deviation show up on ECG as?
Lead I with negative deflection
What will left axis deviation show up on ECG as?
Lead III with negative deflection
What area of the heart does left coronary artery supply?
Anterolateral
Which ECG leads correspond to the left coronary artery?
I, aVL, V3-6
What area of the heart does left anterior descending supply?
Anterior
Which ECG leads correspond to the left anterior descending?
V1-4
What area of the heart does the circumflex supply?
Lateral
Which ECG leads correspond to the circumflex?
I, aVL, V5-6
What area of the heart does the right coronary artery supply?
Inferior
Which ECG leads correspond to the right coronary artery?
II, III, aVF
