How to Interpret the ECG Flashcards
What do you check first when checking an ECG?
Demographics and Calibration
What do you look for in Demographics?
Patient Name, DoB, Any Symptoms
ECG date and Time
What is the correct calibration of an ECG trace?
Paper speed 25mm/s
1 mV calibration deflection (Start of Trace) = 2 large squares in height
How many seconds in one small square?
0.04s
How many in one big square?
0.2s (5 x Small Squares)
What do you analyse next?
Rate and Rhythm - Use the Rhythm Strip
How do you calculate rate?
300/ no. of big squares between R peaks
OR
If irregular - total R waves on ECG x 6 (ECG STRIP USUALLY 10 SECONDS LONG)
How do you work out the rhythm regularity?
Mark 4 R waves on a piece of paper and move along trace to confirm
How do you figure out if it is a sinus rhythm?
look for a normal P wave before each QRS
What is the normal rate?
60-100 bpm
What are causes of sinus bradycardia?
<60 bpm
Physical fitness, hypothermia, hypothyroidism, SA node disease, beta-blockers
What are the causes of sinus tachycardia?
> 100 bpm
exercise, pain, anxiety, thyrotoxicosis, pregnancy, anaemia, PE, hypovolaemia, fever
What can cause irregularity (missing P waves)
AF, ectopics, 2nd degree AV block
What can cause loss of sinus rhythm?
No P waves, irregular QRS - AF
Sawtooth Baseline - Atrial Flutter
Broad complex tachy with no P waves - VF or VT
Narrow complex tachycardia with abnormal/no P waves - SVT
What leads to you look at for cardiac axis?
Leads I and II
What should the QRS complexes be in normal axis?
Predominantly positive
What happens in Left Axis Deviation
R waves point away from each other - QRS positive in lead I and negative in lead II
https://lifeinthefastlane.com/wp-content/uploads/2011/02/Left-Axis-Deviation-LAD-ECG-Labelled.jpeg
(Legs apart)
What happens in Right Axis deviation?
R waves point towards each other. QRS negative in Lead I and positive in lead II and Lead III.
https://lifeinthefastlane.com/wp-content/uploads/2011/02/Right-Axis-Deviation-RAD-ECG-Labelled.jpeg
(Legs together)
What causes left axis deviation?
LV hypertrophy strain, left anterior hemiblock, inferior MI, WPW, VT
What causes right axis deviation?
Tall & thin, RV hypertrophy/strain e.g. in PE, left posterior hemiblock, lateral MI, WPW
What do you look at next?
P wave in rhythm strip
What’s the height of P wave?
2 or less small squares
What causes a bifid P wave?
LA hypertrophy caused by mitral stenosis
P mitrale wave
What causes a peaked P wave?
RA hypertrophy
P pulmonale wave
What should we look at next friends?
PR Interval in da rhythm strip
What is the correct length of the PR interval?
3-5 small squares
What is the PR interval?
Start of P (atrial depolarization) to the start of the QRS complex (ventricular depolarization)
What causes a decreased PR interval?
Accessory conduction pathway
What causes an increased PR interval?
1st degree AV block, 2nd degree AV block, 3rd degree (complete) heart block
1st degree - PR >5 small squares and regular
What do you look at next?
QRS complex
What do you look at first with QRS?
R waves progression in chest leads (V1-V6)
Dominant S in V1 to dominant R in V6, transition point V3/V4
What are some abnormalities in R wave progression?
Dominant R wave in V1 and V2 - RV hypertrophy, posterior MI
clockwise rotation i.e. transition point after V4 - RV enlargement (chronic lung disease)
What’s the correct length of the QRS complex?
<3 small squares
Where do you look for the QRS complex length?
Rhythm strip
What do you look for in RBBB?
RSR1 pattern (M pattern) in V1 and W pattern in V6 (Remember: MaRRoW)
What do you look for LBBB?
W pattern in QRS in V1 and M (RSR1) pattern in V6
Remember: WiLLiaM
Where do you look for the height of the QRS?
Leads V1 and V5/V6
What is the correct height of the QRS complex?
<4 big squares
What is a dominant R wave in V1 signify?
RV hypertophy
Which leads have small Q waves?
I, aVL and V6 (LV leads)
What is a pathological Q wave?
> 40ms in width, >2mm in depth, seen in leads V1 to V3. They indicate prior or current full thickness MI.
Where do you look at the ST segments?
Check in all leads
What is ST elevation?
The ST segment is isoelectric. ST elevation is an elevation greater than 1 small square that occurs in infarct.
What is ST depression?
A depression in the ST segment deeper than 1 square or more. Sign of ischaemia.
What are different morphological abnormalities of the ST segment and what do they signify?
Saddled - Pericarditis Upperward sloping - normal variant Downward sloping (reverse tick) - digoxin toxicity
What leads show an inferior MI and which vessel is occluded?
Lead II, III, aVF
Right coronary artery
What leads show an anteroseptal MI and which vessel is occluded?
V1-V4
LAD
What leads show an anterolateral MI and which vessel is occluded?
V4-V5, I, aVL
LAD or left circumflex
What leads show a lateral MI and which vessel is occluded?
V5-V6, I, aVL
Left circumflex
What leads show a posterior MI and which vessel is occluded?
Dominant R wave in V1-V2, ST depression
Left circumflex or right coronary
Where do you check the T wave?
All leads
Where is the T wave NORMALLY inverted?
III, aVR, V1 (right leads)
