Interpretation fo ECGs Flashcards
Electrical conduction of the heart
SAN -> AVN -> Bundle of His -> L & R bundle branches -> Purkinje fibres
Where does the left bundle branch conduct to?
Left posterior fascicle
Septal fascicle
Left anterior fascicle
What does the P wave represent?
atrial depolarisation
What does the QRS complex represent?
ventricular depolarisation
What does the T wave represent?
ventricular repolarisation
What should you look at first when you look at an ECG?
Check it is the right person - name, DOB, hospital number
What should you do second when you look at an ECG?
Assess calibration
- paper speed = 25mm/sec
- calibration = 1mV=10mm
Position of 6 chest leads
V1 = 4th ICS RHS V2 = 4th ICS LHF V3 = 5th rib LHS V4 = 5th ICS LHS, mid clavicular line, apex beat V5 = between 4 and 6 V6 = mix axillary line
Which leads should be positive?
Lead II
avF
> Lead III
Which leads should be negative?
avR
What are your 6 standard leads?
avR,L,F
leads 1,2,3
How much does 1 small square represent?
40msec
How much does 1 big square represent?
200 msec
How long is the PR interval?
3-5 small sq
120-200 msec
How long is the QRS duration?
<3 small sq
<120 msec
How long is the QT interval?
<440 msec
dependent on HR so sometimes corrected
How to read an ECG?
- confirm patient
- confirm calibration
- comment of rhythm
- rate
- axis
- P waves
- PR interval/heart block
- QRS morphology/ST segments/T waves
- QT interval
What to do if there is no electrical activity?
- check patient is well
- are leads connected
- check for interference (phones/chargers)
- check calibration is correct
How to assess rhythm/
- are QRS complexes regular?
- is there a P wave before every QRS = sinus rhythm
What is the definition of sinus rhythm?
Presence of P wave before every QRS
What is a rhythm strip?
Normally in lead II or I as good to look at QRS
10 second strip on 1 lead
Who gets sinus arrhythmia?
Young
Good vagal tone
Athletes
Deep slow respirations
What are ectopics?
When heart throws off extra beats
- above AVN = supra-ventricular ectopics
- below AVN = ventricular ectopics
How can you differentiate between ectopics?
- supraventricular = narrow QRS complex = above AVN
- ventricular = broad QRS complex = below AVN
How to comment on HR?
- normal is 50-100
- count number of big squares between QRS complexes
- divide 300 by no. of big squares
- not to use if irregular rhythm
What is the axis of the heart?
The electrical vector of the heart
Direction of depolarisation
What is the general normal direction of depolarisation?
From aVR -> II
From top of right shoulder diagonally down to left
What is the normal axis?
-30 to +120
What is L axis deviation?
Axis more negative than -30
Anticlockwise
What is R axis deviation?
Axis > +120
Clockwise
When is the axis abnormal and when is there deviation?
Lead II negative = abnormal
Lead III negative = LAD
Lead I negative = RAD
Causes of RAD?
Children Tall thin adults RVH PE/chronic lung disease L. posterior hemiblock ASD/VSD Wolff Parkinson White Syndrome (L. accessory pathway)
Causes of LAD?
LVH
LBBB of L. anterior hemiblock
Q waves of inferior MI
Wolff Parkinson White Syndrome (R. sided accessory pathway)
How to assess P wave morphology?
- lead II or I
- P mitrale = looks like an M = due to L atrial hypertrophy
- P pulmonale = tall and thin = R atrial hypertrophy
What is the PR interval?
Delay from SAN to AVN conduction
Normal PR interval
120-200msec
3-5 small sq
Types of heart block
1st degree
2nd degree (Mobits type 1 and 2)
Complete heart block
Bundle branch block
PR normal
QRS >120 msec
Delay in ventricular repolarisation
L or R
2nd degree heart block Mobitz type 1 (wenkebach)
Progressive increase in PR interval
Followed by non-conducted QRS
2nd degree heart block Mobitz type 2
Non conducted QRS after every 2nd P wave
Broad QRS complex
Complete heart block
P waves unrelated to QRS
A-V dissociation/loss of conduction
Wolf Parkinson White Syndrome
Short PR interval
Wide QRS
Delta wave
Pointy QRS
Pre-excitation through accessory pathway
Supra-ventricular tachycardia
Regular
Narrow complex tachycardia
No P waves or atrial activity
Caused by an eddie
LBBB
WiLLiaM morphology W pattern around V1,2 M pattern around V5,6 QRS >120/3 small sq LAD
RBBB
QRS >120 MaRRoW morphology M around V1,2 W around V5,6 RAD
LVH
- large QRS voltages!
- may have ST depression and T wave inversion
What leads look at the lateral wall?
V5,6
lead I
aVL
What leads look at the anterior wall?
V2,3,4
What leads look at the inferior wall?
Leads 2,3
aVF
ECG changes associated with MI
- MINUTES = peaked T waves
- MINS TO HOURS = ST elevation (if STEMI) or depression (NSTEMI)
- HOURS = Q waves, inverted T waves
Old infarction
T wave inversion
Antero-lateral Q waves
Wellens Syndrome
Very deep T wave inversion
LAD syndrome
Probable antero-lateral NSTEMI
High risk patient
AF
No P waves
Irregularly irregular ventricular rhythm
Atrial Flutter
Re-entrant circuit in RA Flutter rate = 300bpm HR = 150bpm Regularly irregular Flutter wave = give saw tooth pattern on ECG
Atrial tachycardia
- abnormal focus of atrial depol
- abnormal P wave morphology
- unexplained tachycardia
AVNRT
Atrio-ventricular node re-entrant tachycardia
Accessory pathway in AVN
Leads to SVT
Eddie current
Depol and Repol same tissue again and again
Broad complex tachycardias
VT (emergency)
SVT (with abnormal conduction)
WPW via accessory pathway
ALLWAYS CONSIDERED VT UNTIL PROVEN OTHERWISE
Ventricular Fibrillation
Abnormal QRS waves
Patient in arrest not conscious
Need defib
Regular tachy rhythms
Sinus
SVT
Flutter
VT
Regular brady rhythms
Sinus
CHB
Irregular tachy rhythms
AF
Sinus with multiple ectopics
Irregular brady rhythms
AF overuse beta blockers
Exaggerated sinus
Narrow QRS complex rhythms
Sinus
AF
Flutter
SVT
Broad QRS complex rhythms
VT
SVT with BBB
CHB
