Heart block (1st, 2nd, 3rd degree) - arrhythmias

Question 1

What is another name for heart block?

Answer 1

Atrioventricular (AV) block

Question 2

What is heart block?

Answer 2

Atrioventricular (AV) block is a cardiac electrical disorder defined as impaired (delayed or absent) conduction from the atria to the ventricles.

The severity of the conduction abnormality is described in degrees:

• first-degree;
• second-degree, type I (Wenckebach or Mobitz I) or type II (Mobitz II);
• third-degree (complete) AV block.

This classification scheme should be applied only during sinus rhythm & not during rapid atrial arrhythmias or to premature atrial beats

Question 3

What is

a) 1st degree heart block
b) 2nd degree - type I and type II - heart block
c) 3rd degree heart block

?

Answer 3

a) 1st degree = fixed prolongation of PR interval >0.2 s (or >200ms)

b)

2nd degree type I = progressive prolongation of the PR interval with eventual loss of AV conduction for 1 beat

2nd degree type II = Occasional loss of AV conduction for 1 beat (during sinus rhythm, excluding premature atrial beats) preceded and followed by fixed, unchanging PR intervals.

c) 3rd degree =

Question 4

What is the cause of heart block?

Answer 4

• fibrosis of conduction system
• calcification of conduction system,
• CAD (including patients with a chronic disease and/or an acute coronary syndrome),
• medication
  
  • e.g. AV-nodal blocking agents (i.e., beta-blockers, calcium-channel blockers, digitalis, adenosine),
  • anti-arrhythmic medications such as sodium-channel blockers, and some class III agents (i.e., sotalol and amiodarone)
  • some indigenous medicines.
• high vagal tone
• cardiomyopathy (e.g., hypertrophic, sarcoid, amyloid, haemochromatosis);
• calcification from adjacent valvular calcification;
• post catheter ablation for arrhythmias;
• post-surgical causes (i.e., valve repair or replacement myectomy, septal ethanol ablation);
• blunt cardiac injury
• Severe electrolyte disturbance
• Severe acidosis
• Severe hypoxaemia
• neuromuscular disorders
  
  • (myotonic dystrophy
  • Kearns-Sayre syndrome
  • Erb dystrophy
  • peroneal muscular atrophy)
• myocarditis
• infective endocarditis
• congenital

Question 5

What are the risk factors for heart block?

Answer 5

• increased vagal tone
• use of AV nodal blocking agents
• underlying cardiovascular disease (e.g., CAD or an acute coronary syndrome; HTN, CHF, LVH or cardiomyopathy)
• acid-base disturbance
• neuromuscular disorders
• recent cardiac surgery
• age: 50-60+
  *

Question 6

What are some weak risk factors for heart block?

Answer 6

• sarcoidosis
• myocarditis
• infective endocarditis
• hypoxemia
• blunt cardiac injury
• some indigenous medicines

Question 7

Summarise the epidemiology of heart block

Answer 7

• men > women
• age: 50-60+
• usually preceded by intraventricular block (although there is no causation)

Question 8

What are the presenting symptoms of 1st degree heart block?

Answer 8

• Patients with PR interval >0.30s (or >300 ms) may show dyspnoea.

Question 9

What are the presenting symptoms of 2nd degree (both type I and II) heart block?

Question 10

What are the presenting symptoms of 3rd degree heart block?