AV blocks

Question 1

Name the ECG features of a 1st degree AV heart block

Answer 1

Elongated PR interval where it is more than 0.20s long, rhythm can be otherwise normal sinus / sinus brady etc

Question 2

Name the ECG features of 2nd degree AV heart block Mobitz type 1

Answer 2

Progressive prolongation of the PR interval leading to a dropped QRS complex (non-conducted P wave), can be regularly irregular or irregularly irregular

Question 3

Name the ECG features of 2nd degree AV heart block Mobitz type 2

Answer 3

Intermittent dropped QRS complexes (non-conducted P waves) without progressive prolongation of the PR interval, can be regularly irregular or irregularly irregular

Question 4

Name the ECG features of 3rd degree AV heart block - complete block

Answer 4

Severe bradycardia due to absence of AV conduction, complete AV dissociation, with independent atrial and ventricular rates, The P-P interval is regular and the R-R interval is regular but they do not align with one another

Question 5

What can cause 1st degree AV heart block?

Answer 5

• Increased vagal tone
• Athletic training
• Inferior MI
• Mitral valve surgery
• Myocarditis (e.g. Lyme disease)
• Electrolyte disturbances (e.g. Hyperkalaemia)
• AV nodal blocking drugs: beta-blockers, calcium channel blockers, digoxin, amiodarone
• May be a normal variant

Question 6

What can cause 2nd degree AV heart block Mobitz type 1?

Answer 6

Usually a reversible conduction block at the level of the AV node, malfunctioning AV nodal cells fatigue over time until they fail to conduct an impulse
- Drugs: beta-blockers, calcium channel blockers, digoxin, amiodarone
- Inferior MI
- Myocarditis
- Cardiac surgery

Question 7

Which of the 2nd degree heart blocks is most commonly associated with haemodynamic compromise?

Answer 7

Mobitz type 2

Question 8

What can cause 2nd degree AV heart block Mobitz type 2?

Answer 8

• Anterior Mi with septal infarction
• Idiopathic fibrosis of the heart’s conduction system
• Cardiac surgery
• Inflammatory or autoimmune conditions
• Hyperkalaemia
• Drugs: beta-blockers, calcium channel blockers, digoxin, amiodarone
  etc

Question 9

What can cause a complete 3rd degree AV block?

Answer 9

• End point / progression of a second degree heart block
• Progressive fatigue of AV nodal cells
• Increased vagal tone in acute phase of inferior MI
• Sudden onset of complete conduction failure in His-Purkinje system, can be secondary to septal infarction in acute anterior MI