ECG

Question 1

What formula can be used to calculate rate?

Answer 1

300 divided by number of large squares between adjacent R waves

Question 2

What is the duration of the QRS complex?

Answer 2

Less than 120ms (0.12seconds/3 squares)

Greater than 0.12 seconds suggests bundle branch block

Question 3

How long is the PR interval and what does a prolonged PR interval show?

Answer 3

Normal range 120-200ms (012.-0.2 seconds/3-5 small squares)

Prolonged PR interval shows 1st degree heart block (delayed AV conduction)

Question 4

What is the ST segment and what do changes in it show?

Answer 4

Isoelectric (flat line)

• Elevation = infarction
• Depression = ischaemia

Question 5

What is the QT interval and the consequences of it being prolonged?

Answer 5

Measures from the start of the QRS to end of T wave
Normal: 0.38-0.42 seconds
Prolonged QT interval can lead to VT (ventricular tachycardia) and sudden death

Question 6

What are pathological Q waves and what do they show?

Answer 6

Considered pathological if:

• > 40ms (1 square/1mm) wide
• > 2mm deep

Occur within a few hours of MI. May be there due to previous MI

Question 7

Criteria to diagnose STEMI?

Answer 7

• New LBBB

- ≥ 1mm ST elevation in leads II and III

Question 8

What is heart block and explain 1st degree HB?

Answer 8

HB = Disrupted passage of electrical impulse through the AV node

1st-degree HB: The PR interval is prolonged and unchanging; NO missed beats

Question 9

What is 2nd degree HB and its other names?

Answer 9

Mobitz I (Wenkebach)
- The PR interval becomes longer and longer until a QRS is missed, the pattern then resets. This is Wenckebach phenomenon

Mobitz II
- RSs are regularly missed. eg P - QRS - P - - P - QRS - P - this would be Mobitz II with 2:1 block (2P:1QRS). This is a dangerous rhythm as it may progress to complete heart block

Question 10

What is 3rd degree HB/complete HB?

Answer 10

No impulses are passed from atria to ventricles so P waves and QRSS appear independently of each other

• As tissue distal to the AVN paces slowly, the patient becomes very bradycardic, and may develop haemo- dynamic compromise
• Urgent treatment is required

Causes: IHD, inferior MI and more…

Question 11

Causes of ST elevation?

Answer 11

Acute MI - STEMI
Prinzmetal’s angina
Acute pericarditis (saddle-shaped)
Left ventricular aneurysm

Question 12

Causes of ST depression?

Answer 12

Digoxin toxicity (downward sloping)
NSTEMI
Acute posterior MI (ST depression in V1–V3)

Question 13

How does hyperkalaemia present on an ECG?

Answer 13

Tall, tented T wave, widened QRS, absent P waves, ‘sine wave’ appearance

Question 14

What does LBBB look like on an ECG?

Answer 14

• Wide QRS complexes (160 ms)
• M pattern in the QRS complexes, best seen in leads I, VL, V5 and V6
• W pattern in V1-3
• Inverted T waves in leads I, II, VL

‘WiLLiaM’
Cause: IHD, HTN, cardiomyopathy, STEMI

Question 15

What does RBBB look like on an ECG?

Answer 15

• Wide QRS complexes (160 ms)
• RSR1 pattern in lead V1 and deep
• Wide S waves in lead V6
• Inverted T waves in V1-V3/4
• Normal ST segments and T waves
• M pattern in V1
• W pattern in V5

‘MaRRoW’
Cause: PE, cor pulmonale