Heart Block

Question 1

Define heart block

Answer 1

Impaired (Delayed or absent) conduction of electrical impulses from atria to ventricles

First Degree, second degree type I (Wenckebach/Mobitz I), second degree type II (Mobitz II), third degree/complete heart block

Question 2

Aetiology of first and second degree heart block

Answer 2

Normal variant 
High vagal tone (tonic elevation in athletes, transient vagotonia)
Sick sinus syndrome 
Acute myocarditis 
Drugs (beta blockers, CCBs, sodium channel blockers, adenosine )
Cardiomyopathy 
Post-catheter ablation for arrhythmia 
Severe electrolyte disturbance

Question 3

Aetiology of third degree heart block

Answer 3

IHD (especially inferior MI)
Idiopathic (Fibrosis of conduction system)
Congenital
Aortic valve calcification
Cardiac surgery/trauma
Digoxin toxicity 
Infiltration

Question 4

Symptoms of heart block

Answer 4

Syncope ± pre-syncope 
Fatigue 
Chest pain
Palpitations
Cause or vomiting

Question 5

Signs of heart block

Answer 5

Bradycardia (<40)
Hypertension
Wide pulse pressure
Cannon A wave in JVP 
Hypoxaemia

Question 6

Investigations for heart block

Answer 6

ECG

VBG (acid base balance)
Troponin (rule out ischaemia)
Serum potassium and calcium (hyper may be cause)
Serum digitalis (digoxin toxicity)

CXR (cause exclusion e.g, sarcoidosis - hilarious lymphadenopathy)
Echo (ventricular dysfunction or hypertrophy etc.)

Implantable loop recording (evidence of AV block)
Tilt-table testing (? neurocardiogenic syncope)
Cardiac stress testing(? ischaemia)

Question 7

Findings on ECG for heart block

Answer 7

First degree: PR prolongation

Second degree Mobitz I: Progressive PR prolongation until QRS is skipped

Second degree Mobitz II: No PR prolongation, random QRS skipped

Complete: Complete dissociation between P and QRS waves

Question 8

Management for first degree heart block

Answer 8

Monitor for symptoms + ECG

Symptomatic -> CCB and beta blockers STOPPED

Question 9

Management for second degree heart block

Answer 9

Treatment of reversible causes

Symptomatic: permanent pacemaker (PPM) or cardiac resynchronisation therapy ± ICD placement

Question 10

Management of complete heart block

Answer 10

1. Atropine 500mcg IV
2. Transcutaneous pacing

Dual-chamber pacemaker insertion
PPM or cardiac resynchronisation therapy ± ICD placement

Question 11

What is the management for heart block caused by beta blocker, CCB or digoxin toxicity

Answer 11

Beta blocker toxicity: glucagon
Calcium channel blocker toxicity: Calcium
Digitalis toxicity: digoxin Ab

Question 12

Complications of Heart block

Answer 12

Higher degree of heart block
Risk of MI, stroke and death
Pacemaker (risks 2-3%): bleeding, infection, vascular trauma, pneumothorax, pulse generator or lead malfunction, lead infection

Question 13

Prognosis of heart block

Answer 13

Related to degree of AV block + associated symptoms severity
Mortality high in those with acute MI that leads to AV block
Permanent pacing improves survival in 3rd degree block with excellent prognosis