ECG interpretation Flashcards
P wave represents
represents the wave of depolarisation that spreads from the SA node throughout the atria
What does the isoelectric period after the P wace represent?
the time in which the impulse is travelling within the AV node
How long should a normal P wave last?
- 0.08-0.1 seconds
- 80-100 milliseconds
P-R interval
time from the onset of the P wave to the beginning of the QRS complex
represents the time between onset of atrial depolarisation and onset of ventricular depolarisation
Normal P-R interval usually lasts?
- 0.12-0.20 seconds
- 3-5 little squares
QRS complex
represents ventricular depolarisation
QRS complex normal time
upto 3 little squares
no more than 120 ms
ST segment
- isoelectric period following QRS
- represents the period in which the entire ventricle is depolarised and roughly corresponds to the plateau phase of ventricular action potential
T wave
represents ventricular repolarisation
longer in duration than depolarisation
U wave
a small ppositive U wave may follow the T wave which represents the last remnants of repolarisation
Q-T interval
represents the time for both ventricular depolarisation and repolarisation to occur, therefore roughly estimates the duration of a ventricular action potential
Normal Q-T duration
0.2-0.4 seconds depending on heart rate
at high heart rates Q-T segment will
shorten
ventricular action potentials shorten in duration
Names of 12 lead ECG
- 1,2,3, aVR, aVL, aVF, (frontal plane)
V1,V2,V3,V4,V5,V6 (horizontal plane)
Normal PQRST waves label
insert diagram
may not always see all waves in QRS
degree of heart standards ecg leads
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chest lead positions
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vertical and horizontal calibration markers
- vertical: 10 mV
- generally, 1 small = 1mV, 1 big =
5 squares
- generally, 1 small = 1mV, 1 big =
- horizontal: 1 small = 40ms, 5 small squares = 200 seconds, 5 big sqaures = 1 second
initial analysis of ecg
- check calibration is 2 high 1 wide
- rate
- QRS axis
- rhythm
calculation of heart rate from an ECg:
- count the squares between complexes:
- 5 large = 60bpm
- 4 large = 75 bpm
- 3 large = 100 bpm
- 2 = 150 bpm
- 6 = 50bpm
- for an irregular rhythm:
- count number of complexes in 30 large squares and multiply by 10
- 30 large squares = 6 seconds (in uk)
How to calculate the (mean frontal) QRS axis?
- overall direction of the electrical signal in the FRONTAL plane (not V leads)
- find the most isoelectric complex (goes up as much as it goes down) from leads: 1,2,3,aVF,aVR,aVL
- axis is 90 degrees from this
- normal QRS axis is between -30 and +120 degrees
- going toward which side?
Insert mean frontal QRS axis question
insert
- lead II is most isoelectric
- 90 degrees either side is +150 or -30
- look at AVL and lead I both have QRS waves upwards
- lead three has QRS downwards
- hence must be -30
Cardiac Rhythm (sinus)
- sinus rhythm = norm = atria contract before ventricles
- 1 p wave infront of every QRS complex
- resting generally between 60-90bpm
Tachycarda (3 common)
- fast heart
- atrial fibrillation
- supraventricular tachycardia
- ventriculary tachycardia
