ECG Reading

Question 1

How to read an ECG

Answer 1

• Check the patient
• Check the basics
• Rate
• Rhythm
• QRS axis
• P wave
• PR interval
• QRS complex
• ST segment
• T wave
• U wave
• QT interval
• Hypertrophy
• Ischemic changes
• Metabolic changes

Question 2

Check the basics

Answer 2

• ECG of the correctpatient
• ECG settings correct
  
  • Speed 25mm/ sec
  • Calibration 1cm/mV
  • AC filter 50Hz
  • Frequency 0.05-150 Hz
• ECG leads correctly placed (P wave in lead I upright, in lead aVR inverted)
• Sufficient quality

Question 3

Rate

Answer 3

• 300 150 100 75 60 50 43 38 33 30
• Atrial rate = ventricular rate
• Bradycardia < 60 b/min
• Tachycardia > 100 b/min

Question 4

Rhythm

Answer 4

• P wave for every QRS
• Atrial rate - ventricular rate
• PAC, PJC, or PVC

Question 5

QRS axis

Answer 5

Normal if Lead I and aVF both positive

Question 6

P wave

Answer 6

Especially lead II and V1

• Present
• Followed by QRS
• Normal size and shape

Question 7

PR interval

Answer 7

• Normal 0.12 - 0.20 seconds (3 - 5 small blocks)
• AV block present?

Question 8

QRS complex

Answer 8

• Normal qidth (< 0.12 seconds/ 3 small blocks)
• Equal height (no electrical alternans)
• No bundle branch block
• No pathological Q wave (> 0.04 seconds wide, > 1/4 R deep)
• Other waves (delta, Osborn, pacing)
• Small complexes

Question 9

Small QRS - differential diagnosis

Answer 9

• Tamponade
• Hypothyroidism
• COPD
• Obesity
• Myocarditis

Question 10

ST segment

Answer 10

• Elevation < 1mm
• Depression < 0.5mm
• Normal shape

Question 11

T wave

Answer 11

• Normal height (< 5mm in limb leads, < 10mm in precordial leads)
• No inversion

Question 12

Tall T wave

Answer 12

• Narrow base, symmetrical peak
  
  • Hyperkalemia
  • Hypermagnesemia
• Broad base, asymmetrical
  
  • Ischemia

Question 13

U wave

Answer 13

If present, not larger than T wave

Question 14

QT interval

Answer 14

Less than half the RR distance

Question 15

Hypertrophy

Answer 15

• Left atrium
  
  • Broad P wave (> 0.12s)
  • Notched P wave in lead II
  • Biphasic P wave in V1
• Right atrium
  
  • P wave tall and peaked in lead II and V1 (> 2.5mm)
• Left Ventricle
  
  • Left axis deviation
  • Sokolow Lyon > 35mm
  • R in aVL > 12mm
• Right Ventricle
  
  • Right axis deviation
  • Tall R in V1 and aVR

Question 16

Strain Patterns

Answer 16

• Asymmterical ST depression
• T wave inversion
• Left ventricle: lead I, aVL, V4-6
• Right ventricle: lead II, III, aVF, V1-3

Question 17

Ischemia

Answer 17

• ST segment elevation/ depression in contiguous leads (NB - frequency response range appropriate)
• Pathological Q waves
• Dynamic T wave inversion, hyperacute T waves
• Left axis deviation and divergence of mean QRS and T wave axis
• New BBB
• RV infarct: aVR and V4R
• Posterior infarct: tall R in V1

Question 18

Metabolic Changes

Answer 18

• Hyperkalemia
  
  • Tall, peaked T wave with narrow base
  • T wave > R wave in 2 or more leads
  • Flattened P wave
  • Widened QRS
• Hypermagnesemia
  
  • Peaked T wave
• Hypercalcemia
  
  • Short QT interval
• Hypokalemia
  
  • Big U wave
• Hypomagnesemia
  
  • Long QT
• Hypocalcemia
  
  • Long QT

Question 19

Contiguous Leads

Answer 19

• Inferior - II, III, aVF
• Septal - V1, V2
• Anterior - V3, V4
• Lateral - I,aVL, V5, V6
• Posterior wall - V1, V2, (V7, V8, V9)
• Right ventricle: aVR, V4R, inferior leads