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

Question 1

Define heart block

Answer 1

1st Degree AV Block : prolonged conduction through the AV node

2nd 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 ten begins again.

Mobitz Type II: intermittent or regular failure of conduction through the AV node. Also defined by the number of normal conductions per failed or abnormal
one (e.g. 2:1 or 3:1)

3rd Degree (Complete) AV Block: no relationship between atrial and ventricular contraction. Failure of conduction through the AV node leads to ventricular
contraction generated by a focus of depolarisation
within the ventricle

Question 2

Explain the aetiology/risk factors of heart block

Answer 2

MI or ischaemic heart disease (MOST COMMON)
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

Summarise the epidemiology of heart block

Answer 3

250,000 pacemakers are implanted every year and they are mostly for heart block

Question 4

Recognise the presenting symptoms of heart block

Answer 4

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 5

Recognise the signs of heart block on physical examination

Answer 5

Often NORMAL
Check for signs of a potential cause of heart block

Complete Heart Block - Slow large volume pulse, 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

Mobitz Type II and 3rd Degree Heart Block - Signs of reduced cardiac output (e.g. hypotension, heart failure)

Question 6

Identify appropriate investigations for heart block

Answer 6

ECG- GOLD STANDARD

CXR - Cardiac enlargement, Pulmonary oedema

TFTs
Digoxin level
Cardiac enzymes
Troponin

Echocardiogram - Wall motion abnormalities, Aortic valve disease, Vegetations

Question 7

ECG findings in hearth block?

Answer 7

First Degree- fixed prolonged PR interval (> 0.2 s)

Mobitz Type I (Wenckebach) - progressively prolonged PR interval, culminating in a P wave that is NOT followed by a QRS complex. The pattern then begins again.

Mobitz Type II - intermittently a P wave is NOT followed by a QRS. There may be a regular pattern of P waves not followed by QRS (e.g. 2:1 or 3:1)

Complete Heart Block - no relationship between P waves and QRS complexes. If QRS is initiated in the: Bundle of His - narrow complex
More distally - wide complex and slow rate (~ 30 bpm)

Question 8

Generate a management plan for heart block

Answer 8

Chronic Block
Permanent pacemaker is recommended in:
Complete heart block
Advanced Mobitz Type II
Symptomatic Mobitz Type I

Acute Block
If associated with clinical deterioration use IV atropine
Consider temporary (external) pacemaker

Question 9

Identify the possible complications of heart block

Answer 9

Asystole
Cardiac arrest
Heart failure
Complications of any pacemaker inserted

Question 10

Summarise the prognosis for patients with heart block

Answer 10

Mobitz Type II and 3rd degree block usually indicate serious underlying cardiac disease