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
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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
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- 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
Atrial fibrillation on ECg
no p waves
irregular
multiple short circuits in atria hence very irregular to AV node
Supraventiruclar tachycardia on ECG
regular, narrow complexes
short circuuit that runs regularly in atria
fairly bengin
Ventricular tachycardia
regular, broad complexes
short circuit that runs regularlry in ventricle
very dangerous
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atrial fibrillation
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supraventricular tachycardia
150bpm
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ventricular tachycardia
broad regular complexes
Bradycardia (2)
slow heart rate
- problems at AV node = heart block, doesnt get to ventricle
- sinus node dysfunction
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complete heart block (AV node problem)
30bpm
Heart Block ECG features
number of QRS complexes, ten square gap, 30 bpm,
lots of p waves at normal rate
not getting through AV node
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sinus node dysfunction
intermittent p waves
Sinus node dysfunction ecg features
- no p waves on first because no sinus beat
- second and third have p waves
- 30 bpm
Tall complexes on ecg show signify
ventriculr hypertrophy
broad complexes on ecg signify
bundle branch block
more than 3 squares wide QRS
ST elevation on ecg signify
MI or pericarditis
ST depression/ T wave inversion signifies
many causes
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left ventricular hypertrophy (complexes go off the page or run into each other)
T waves may also be inverted when complexes are big
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left bundle branch block
broad complexes
V1 lead generally will go downwards
eight squares between p and QRS
still attached tho so first degree heart block
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triphasic large downwards qrs
V1 and V2 mostly above baseline
right bundle branch block
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st segment elevated above baseline
on standard leads st segment elevated
v leads st segment is depressed, reciprocal change
sixth complex is an ectopic beat
acute inferior ST segment elevation myocardial infarc (acute inferior STEMI)
Q wave MI
deeply inverted Q waves
virtually no R waves
T waves may be inverted
- extensive damage to myocardium
