Electrocardiogram & arrythmias

Question 1

Outline the normal rate of the SA node, AV node and ventricular cells

Answer 1

SA Node; 60-100bpm

AV Node; 40-60bpm

Ventricular cells; 20-45bpm

Question 2

Outline ECG rhythm analysis

Answer 2

1. Rate
   
   • R waves in 3 seconds (15 large squares) x 20
2. Regularity
   
   • R-R distance constant?
3. P wave assessment
   
   • Exist?
   • Regular?
   • PR interval constant?
4. PR interval
   
   • 0.12-0.2 seconds is normal (3-5boxes)
5. QRS duration
   
   • 1-3 boxes

Question 3

Outline physiological sinus arrythmia

Answer 3

• Heart rate speeds up on inspiration, slows on expirations.
• Vagus has an inhibitory effect on SA node. When inspiring, vagus is inhibited, and so it cannot inhibit the SA node.
• EWen exhaling the vagus is stimulated, so it can inhibit the SA node.

Question 4

Outline sinus tachycardia

Answer 4

• Commonly seen in exercise, fever, thyrotoxicosis etc
• >100bpm
• SA node depolarising at a greater rate

Question 5

Outline sinus bradycardia

Answer 5

• Athletes, hypothyroidism, cold…
• <60bpm
• SA node depolaring at a slower rate than normal

Question 6

Outline supraventricular tachycardia