ECG Flashcards
What does ECG stand for?
Electrocardiogram
What is an ECG?
Recording of electrical activity around the heart from body surface
What does an ECG check? (7)
- Heart rhythm
- Electrical activity
- Heart rate
- Myocardium thickness
- Size and position of heat chambers
- Conduction system integrity
- Drug effects on heart
How does an ECG create measurements?
Sensors attached to the skin detect electrical signals produced by the heart each time it beats
What two parts of a depolarisation wave does an ECG measure? (2)
- Amplitude
- Direction
What is an ECG representative of?
Electrical events of the cardiac cycle
How are the electrical events of the cardiac cycle represented on the ECG cycle?
Characteristic waveform recorded graphically against time
What are the 3 lead systems in a 12 lead ECG? (3)
- Limb leads
- Precordial/chest leads
- Augmented limb leads
What are the limb leads in an ECG? (3)
- Lead I
- Lead II
- Lead III
What are the chest/percordial leads? (6)
- VI
- V2
- V3
- V4
- V5
- V6
What are the augmented limb leads? (3)
- avL
- avF
- avR
What is a lead in an ECG? (2)
- Potential difference of electrical activity between two electrodes
(Virtual) - Shows heart electrical activity from particular angle
What 3 limbs are used in an ECG? (3)
- Right arm
- Left arm
- Left leg
What colour is a right arm electrode typically?
Red
What colour is a left arm electrode typically?
Yellow
What colour is a left leg electrode typically?
Black
What limbs is lead I made up of? And which one is the positive/negative electrode?
- Left arm (positive)
- Right arm (negative)
What do the limb leads represent on an ECG?
Potential difference between 2 limbs at a time
Are limb leads bipolar/unipolar?
Bipolar
What does a bipolar lead mean?
Electrodes registering voltage between 2 electrodes
What does a unipolar lead mean? (2)
- Activity in heart directed towards/below electrode
- Potential difference between heart activity (positive recording electrode) and indifferent negative electrode
What is the purpose of the lead connected to the right leg?
Reference electrode for recording purposes to complete electric circuit
Plays no role in ECG itself
What is the purpose of the limb ECG leads?
Gives information on general heart activity and direction
What is the purpose of the chest ECG leads?
Gives information on activity relative to area within the heart myocardium
What limbs is lead II made up of? And which one is the positive/negative electrode?
- Right arm (negative)
- Left leg (positive)
What limbs is lead III made up of? And which one is the positive/negative electrode?
- Left arm (negative)
- Left leg (positive)
What triangle do the 3 limb leads form?
Equilateral eithoven’s triangle
What lead is usually used to form the rhythm strip?
Lead II
Why is lead II used to form the rhythm strip?
P waves clearest here
What is a positive deflection?
Depolarisation towards the positive electrode, above isolectric line
What is a negative deflection?
Depolarisation away the positive electrode, below isoelectric line
What is the purpose of the augmented chest leads?
Give additional means of info to identify directionality of waveform propagation across the heart
Where is lead V1 placed?
Right hand side of sternum
Where is lead V2 placed?
Left hand side of sternum
Where is lead V3 placed?
3
Where is lead V4 placed?
4
Where is lead V5 placed?
5
Where is lead V6 placed?
6
What indicates the direction of electricity in the heart?
Towards the lead with the most positive deflection
What is seen on an ECG when depolarisation is going towards a lead?
Positive deflection
R wave bigger than S (and Q) wave
What is seen on an ECG when electricity is going away from a lead?
Negative deflection
R wave smaller than S (and Q) wave
What is normal cardiac axis? (2)
- Between -30degrees and +90degrees
What lead sees the most positive deflection in normal cardiac axis and why?
Lead II as this is at 5 oclock
Draw the normal cardiac axis diagram
See notes
Why direction does depolarisation normally happen in and why?
11 oclock to 5oclock
Apex is at that angle
What lead sees the most negative deflection in normal cardiac axis and why?
aVR - opposite direction to lead II
What deflections are seen in which leads in normal cardiac axis? (3)
- Positive lead I
- Positive avF
- Lead II most positive compared to I and III
What deflections are seen in which leads in right axis deviation?
- Negative lead I
- Positive avF
What deflections are seen in which leads in left axis deviation?
- Positive lead I
- Negative avF
- Extreme: positive lead II
Give examples of conditions with right axis deviation
- Dextracardia (depolarisa
Right ventricular hypertrophy
What causes left axis deviation?
Conduction defects and not by increased mass of the left ventricle.
What height/amplitude is shown by a small square on an ECG? mm and mv
0.1mv=1mm
What height/amplitude is shown by a large square on an ECG? mm and mv
0.5mv=5mm
What time is shown by a small square on an ECG?
0.04 seconds
What time is shown by a large square on an ECG?
0.2 seconds
What is a normal value for PR interval? Seconds + squares
120 (0.12)-200ms (0.2secs)
3-5 small sqs
What is a normal value for QRS interval/width? Seconds + squares
80-120ms (0.12secs)
3 small sqs
What is a normal value for QT interval?
360-440ms
What is QTc?
QT interval corrected for rate
= QT/R-R interval
How is heart rate calculated using squares?
300 /Large squares R-R interval
What is the normal level of variation in rhythm?
Less than 10% R-R interval
Normal bpm?
60-100
Calculating rate from an ECG if irregular rhythm?
Number of complexes on rhythm strip by 6
How long is each rhythm strip?
10 seconds
Order of reading ECG?
- Patient details
- ECG date and time
- HR
- Heart rhythm
- Cardiac axis
- P waves (present, each followed by QRS, duration, direction, shape)
- P-R interval (heart block)
- QRS (Width/height)
- ST segment
- T waves (height? Inverted?)
How to check heart rhythm (2)
- Mark out consecutive R-R intervals on a piece of paper
- Move them along the rhythm strip to check if the subsequent intervals are the same
Normal QRS/T wave height? (2)
- 5mm limb leads
- 10mm chest lead
What is checked for in P waves?
- Present
- Each followed by QRS
- Duration
- Direction
- Shape
Normal P wave duration?
120-200ms
