Condition- Heart Block (1st, 2nd, 3rd degree)

Question 1

What is heart block? How many types are there?

Answer 1

Impaired conduction of electrical impulses from the atria to the ventricles

• 1st Degree
• 2nd Degree
  
  • Mobitz Type I
  • Mobitz Type II
• 3rd Degree

Question 2

What is the most common cause of heart block? (+ list some other causes of it)

Answer 2

• MI/ IHD
• Infection (e.g. rheumatic fever, infective endocarditis)
• Drugs (e.g. digoxin)
• Metabolic (e.g. hyperkalaemia)
• Infiltration of conducting system (e.g. sarcoidosis)
• Degeneration of the conducting system

Question 3

What symptom do some classes of heart block cause?

Answer 3

STOKES-ADAMS ATTACK

Question 4

What is a stokes-adams attack?

Answer 4

Vasovagal syncope caused by ventricular asystole

Question 5

In which grades of heart block are stokes-adams attacks seen?

Answer 5

Mobitz Type II and 3rd Degree

Question 6

List some symptoms that may be experienced by people with the different classes of heart block

Answer 6

• 1st Degree - asymptomatic
• 2nd Degree - usually asymptomatic
• Mobitz Type II and 3rd Degree - may cause Stokes-Adams Attacks (syncope caused by ventricular asystole)
  
  • May also cause dizziness, palpitations, chest pain and heart failure

Question 7

List two key signs of 3rd degree heart block

Answer 7

• Slow large volume pulse- wide pulse pressure
• JVP may show cannon a waves
  
  • Cannon A Waves: waves seen occasionally in the jugular vein of humans with certain cardiac arrhythmias. This occurs when the atria and ventricles contract simultaneously

Plus may see signs of reduced cardiac output (e.g. hypotension, HF)

Question 8

Which type of heart block is this and why?

Answer 8

FIRST DEGREE HEART BLOCK

• Prolonged P-R interval (>3-5 small squares = >0.2s)

Question 9

Which type of heart block is this and why?

Answer 9

2nd Degree Mobitz Type I (Wenckebach)

• PR interval gets progressively longer
• Ends in P wave followed by dropped QRS complex

Question 10

Which type of heart block is this and why?

Answer 10

2nd Degree Mobitz Type II

• Intermittent random dropped QRS complexes
• Or fixed ratio of dropped QRS complexes

Question 11

Which type of heart block is this and explain why…

Answer 11

Complete Heart Block

• No relation between p waves and QRS complexes
• Atrial pacemaker cells have a rate of 60 bpm so p waves occur more frequently
• Ventricular pace maker cells have a rate of 30bpm so QRS complexes are much slower
• QRS is much wider because impulse initiated more distally instead of bundles of His

Question 12

What is a ventricular escape beat?

Answer 12

A beat caused by ventricular pacemaker cells after prolonged inactivity if AVN fails to activate ventricular cells due to heart block

Question 13

List four blood tests to order for someone with heart block

Answer 13

• TFTs
• Troponin
• Cardiac Enzymes
• Digoxin levels

Question 14

What is the first line treatment for someone with acute onset heart block? And what would you do if this fails?

Answer 14

1. IV atropine (to increase SAN activity + conduction to AVN)
2. Cessation of AV nodal blocking medication/ counteracting its toxicity
3. Temporary pacemaker

Question 15

How is first degree heart block and asymptomatic Mobitz Type I heart block managed?

Answer 15

Monitoring (+ regular ECGs)

Question 16

For which types of heart block is a permanent pacemaker recommended?

Answer 16

• Complete heart block
• Advanced Mobitz Type II
• Symptomatic Mobitz Type I

Question 17

List some AV-nodal blocking drugs that could lead to the development of Heart Block and list some medications which could be given to counteract each of their toxicity

Answer 17

• Digitalis => Digoxin Immune Fab
• Beta blockers => Glucagon
• CCBs => Calcium Chloride