ECG interpretation Flashcards
- Rate
Count number of large squares in 1 R-R interval (n)
Divide 300 by n to calculate rate
Normal - 60 to100 bpm
Tachycardia - >100 bpm
Bradycardia - <60 bpm
- Rhythm
Is it regular or irregular?
Classify the irregularity - regularly irregular or irregularly irregular
- Cardiac axis
Healthy individual = spread from 11 o’clock to 5 o’clock
Look at leads I, II & III
Normal = +ve deflections in I, II & III (most +ve in 2)
RAD = lead III has most +ve deflection, lead I is -ve
LAD = lead I has most +ve deflection, leads II & III are -ve
TIP: think of it as in a RAD, the electrical activity wants to move away from the right and more towards the left. Lead III is the most left as it’s calculated by LL-LA. In a LAD the electrical activity wants to move away from the left and more towards the right. Although limb I may not be the only lead that has a right sided part, it is the one that has a right sided part closest to the heart (i.e., RA) so it’ll be the most positive
- P wave
Are they present?
Is each P wave followed by a QRS complex?
Do they look normal?
Are there any missing P waves?
- PR interval
Normal - 0.12-0.2 s (or 3-5 small squares)
Prolonged - >0.2 s (suggests presence of an AV block)
Shortened - < 0.12 s
What are the different types of AV block?
Type 1 = PR interval prolonged but at a constant level
Type 2 Mobitz type 1 = PR interval gets longer and longer, until the QRS complex completely drops off before starting again in the next cycle
Type 2 Mobitz type 3 = PR interval remains constant but the P wave isn’t always followed by a QRS complex
Type 2 Mobitz type 3 (complete heart block) = P wave is not followed by QRS complex at all
Name a cause of PR interval shortening
Wolff-Parkinson-White syndrome
Accessory pathway = shorter time for atrial impulse to reach ventricles
Can be associated with a delta wave
- QRS complex
a) Width
-Narrow (<0.12 or 3 small squares) = GOOD
-Broad (> 0.12 or 3 small squares) = BAD (abnormal depolarisation sequence)
b) Height
-Small (< 5 mm in limb leads or < 10 mm in chest leads)
-Tall = VENTRICULAR HYPETROPHY
c) Morphology
-Delta (ventricles being activated too early = WPW)
- Q waves (pathological - > 25% size of R wave that follows or >2 mm in height and >0.04 ms or 1 small square in width)
- R & S waves = transition from S > R to R > S should occur in lead V3 or V4 (poor progression i.e., S > R persisting to V5/V6 shows previous MI or poor positioning of leads)
-J point segment (where S meets ST segment) - can be elevated (“high-take off”)
- ST segment
Normal = Isoelectric (i.e., flat)
ST elevation > 1 mm (1 small square) in ≥ 2 contiguous limb leads or > 2mm in ≥ 2 chest leads = SIGNIFICANT (acute full-length thickness MI)
ST depression ≥ 0.5 mm in ≥ 2 contiguous leads = myocardial ischaemia
- T waves
Tall - >5mm in limb leads AND >10 mm in chest leads (causes = hyperkalaemia, hyperacute STEMI)
Inverted - normal in V1, normal variant in lead III
Biphasic (two peaks) - seen in hypokalaemia and ischaemia
Flattened - seen in electrolyte imbalance or ischaemia
Name causes of inverted T waves
Ischaemia
BBBs (V4-6 in LBBB and V1-3 in RBBB)
Pulmonary embolism
Left ventricular hypertrophy (in lateral leads)
Hypertrophic cardiomyopathy (widespread)
General illness
- U wave
Not common
> 0.5 mm deflection after the T wave (best seen in V2 or V3)
Slower bradycardia = larger U wave
Causes = electrolyte imbalances, hypothermia, secondary to antiarrhythmic therapy (e.g., digoxin, procainamide)
What is considered QT prolongation in men?
> 440 ms
What is considered QT prolongation in women?
> 470ms
Good diagram showing ECG interpretation
Good diagram showing pathological Q waves
