Heart blocks

Question 1

What does the ECG look like in first degree AV block? (5)

Answer 1

• Rate variable
• Regular narrow QRS
• P waves present
• P:QRS 1:1
• PR interval more than 200ms

Question 2

What is first degree AV block? (2)

Answer 2

• Block at level of His bundle

- Every beat goes through to ventricles but just takes longer

Question 3

What are the 2 types of second degree AV block?

Answer 3

• Mobitz type I

- Mobitiz type II

Question 4

What is a Mobitz type I second degree AV block? (3)

Answer 4

• Gradual prolongation of PR interval over a few heart cycles
• Until atrial impulse completely blocked = P-wave not followed by QRS complex
• Cycle repeats itself over and over again: each ends in blocked P wave

Question 5

Explain the pathology of Mobitz type I second degree AV block? (7)

Answer 5

• Successful conduction of atrial impulse (either with normal or abnormal PR interval).
• AV node is dysfunctional - can’t repolarise adequately by the time the next impulse arrives
• Slower conduction than previously
• PR interval = prolonged
• AV node more and more exhausted (i.e more and more refractory) each time
• Until completely refractory: blocks the atrial impulse
• AV node then recovers, cycle starts again

Question 6

What does Mobitz type I second degree AV block look like on an ECG? (3)

Answer 6

• Rate less than 60bpm
• Irregular narrow QRS
• P:QRS not 1:1
• Increasing PR interval for 3 beats
• Dropped for 4th beat

Question 7

How can Mobitz type I second degree AV block be physiological?

Answer 7

High vagal tone

Question 8

What does Mobitz type II second degree AV block look like on an ECG? (4)

Answer 8

• Rate less than 60bpm
• Irregular narrow QRS
• P:QRS not 1:1
• Normal PR interval with intermittent dropped beats

Question 9

What is the difference between a Mobitz type I and type II heart block?

Answer 9

• 1=heart skips beats in regular pattern vs type 2=irregular
• 1=can compensate, few symptoms. 2=can’t compensate, many symptoms
  2
  1=AV node, 2=His-Purkinje system

Question 10

Which type of Mobtiz heart block definitely needs a pacemaker?

Answer 10

Type II

Question 11

What is third degree AV block? (5)

Answer 11

• Complete heart block
• P waves completely dissociated from QRS complex
• Normal atrial contraction
• No beats conducted to ventricles
• Ventricles still excited by own internal ‘ectopic pacemaker’ system

Question 12

Why is a 3rd degree heart block serious? (3)

Answer 12

• Some patients=death
• Others= automaticity from ventricular myocytes to compensate, so still sending beats despite no relay of signal
• Urgent pacemaker needed in case this changes

Question 13

What are the ECG signs of hyperkalaemia? (2)

Answer 13

• Tented T waves

- Reduced P wave amplitude

Question 14

What are the ECG signs of hypokalaemia? (3)

Answer 14

• Reduced T waves
• ST depression
• Prolonged PR interval