Heart block

Question 1

Define

Answer 1

Impairment of the atrioventricular (AV) node impulse conduction, as represented by the interval between P wave and QRS complex

First-degree AV block
Prolonged conduction through the AV node

Second-degree AV block
Mobitz type I (Wenckebach) → Progressive prolongation of AV node conduction culminating in one atrial impulse failing to be conducted through the AV node
The cycle then begins again

Mobitz type II → Intermittent or regular failure of conduction through AV node
Defined by the number of normal conductions per failed or abnormal one (e.g. 2:1 or 3:1)

Third-degree (complete) AV block
No relationship between atrial and ventricular contraction
Failure of conduction through the AV node leads to a ventricular contraction generated by a focus of depolarization within the ventricle (ventricular escape)

Question 2

Causes

Answer 2

• MI or ischemic heart disease (most common cause)
• Infection (rheumatic fever, infective endocarditis)
• Drugs (digoxin, β blockers ,Ca2+ channel antagonists)
• Metabolic (↑K+, cholestatic jaundice, hypothermia)
• Infiltration of conducting system (sarcoidosis,
  amyloidosis)
• Degeneration of conducting system

Question 3

Symptoms

Answer 3

First degree: Asymptomatic
􏰀 Wenckebach: Usually asymptomatic
Laura Tan CARDIO 16

􏰀 Mobitz type II and third-degree block:
May cause Stokes–Adams attacks (syncope caused by ventricular asystole)
Also: dizziness, palpitations, chest pain and heart failure

Question 4

Signs

Answer 4

Examination often normal
Mobitz type II: signs of ↓CO (hypotension, heart failure)
Third degree (complete): slow large volume pulse, cannon waves in JVP

Question 5

Investigations

Answer 5

ECG
CHEST XRAY
BLOODS
ECHO

Question 6

Management

Answer 6

Chronic block -> pacemaker

acute -> iv atropine + external pacemaker

Question 7

Complications

Answer 7

asystole, arrest, HF

Question 8

Prognosis

Answer 8

MOBITZ - serious

Question 9

Epidemiology

Answer 9

Majority of the 250 000 pacemakers implanted annually are for heart block.