ECG interpretation

Question 1

In what order should you interpret an ECG?

Answer 1

1. General info
2. Rate
3. Rhythm
   a) P + QRS
   b) PR interval
   c) QRS
   d) Q waves
   e) R waves
   f) QT segment
   g) ST segment
4. Territory
5. Axis

Question 2

What general information should you obtain from an ECG?

Answer 2

-Patient ID
-Date and time, compare with previous
-Speed of rhythm strip (normal is 25mm/s, 10s long)

Question 3

How do you assess rate on an ECG?

Answer 3

-If regular, do 300 divided by the number of large squares between complexes
-If irregular, count number of complexes in a strip and multiply by 6
-1 small square = 40ms, 1 large square = 200ms

Question 4

How do you assess the P + QRS segments?

Answer 4

Ask: are there P waves for every QRS?
YES = sinus
NO = not in sinus (AF)

Question 5

How do you assess the PR interval?

Answer 5

Normal = <200ms
If prolonged –> heart block (AVN block)
1. First degree HB = PR interval is consistently prolonged, always followed by QRS
2. Mobitz I = PR interval is increasingly prolonged until there is a dropped beat
3. Mobitz II = PR interval is consistently prolonged but there are dropped beats, occurring in a pattern or randomly
4. 3rd degree / complete = no correlation between P and QRS

Question 6

How do you assess the QRS complex?

Answer 6

Normal = <120ms
If wide –> bundle branch block
Assess type by looking at V1 and V6
1. LBBB = W shaped QRS in V1, M shaped in V6 (WiLLiaM)
2. RBBB = M shaped QRS in V1, W shaped in V6 (MaRRoW)

Question 7

How do you assess the Q wave?

Answer 7

Should appear flat and then deflect negatively / downwards

Question 8

How do you assess the R wave?

Answer 8

Should gradually shift from negative to positive from V1-V6

Question 9

How do you assess the QT segment?

Answer 9

Normal QTc = <450ms (F), <430ms (M)
If prolonged, can be caused by:
-electrolyte disturbances
-drugs eg clarithromycin, anti-psychotics
-Can lead to torsades de pointes

Question 10

How do you assess the ST segment?

Answer 10

Compared to the baseline, is it a) flat? b) elevated? c) depressed?
-Elevated = 2 small sq in chest leads, 1 in limb leads
-Indicates ischaemia

Question 11

Which leads represent which anatomical areas of the heart (ie territory)?

Answer 11

SEPTAL = V1, V2
ANTERIOR = V3, V4
LATERAL = I, aVL, aVR, V5, V6
INFERIOR = II, III, aVF
(note: individual leads’ territory below
I = lateral view
II = inferior view (R)
III = inferior view (L)
aVR = lateral view
aVL = lateral view
aVF = inferior)

Question 12

How do you assess axis?

Answer 12

Check leads I + III for deviation
-If I is +ve and III is -ve = LAD (Leaving each other)
-If I is -ve and III is +ve = RAD (Reaching each other)

Question 13

What would you expect to see on an ECG with pericarditis?

Answer 13

-Global saddle ST elevation
-Down-sloping from T to P waves (Spodlick’s sign)
-PR depression

Question 14

What would you expect to see on an ECG with tamponade?

Answer 14

-Variable amplitude of R waves due to heart being moved by fluid in pericardial sac
-So distance from leads varies

Question 15

What would you expect to see on an ECG with atrial flutter?

Answer 15

-Saw-tooth appearance

Question 16

What would Hyperkalaemia look like on an ECG?

Answer 16

-Tall tented T waves
-Flattened P waves
-Prolonged PR
-Wide QRS

Question 17

What would hypokalaemia look like on an ECG?

Answer 17

-T wave inversion
-Prominent U waves
-Prolonged QT