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

Question 1

Define 1st degree AV block

Answer 1

prolonged conduction through the AV node

Question 2

Define 2nd degree AV block - Mobitz type I

Answer 2

progressive prolongation of AV node conduction culminating in 1 atrial impulse failing to be conducted through AV node, then cycle begins again

Question 3

Define 2nd degree AV block - Mobitz type II

Answer 3

intermittent or regular failure of conduction through the AV node (also defined by no. of normal conductions per failed/abnormal one e.g. 2:1)

Question 4

Define 3rd degree (complete) AV block

Answer 4

no relationship between atrial & ventricular contraction - failure of conduction through AV node leads to ventricular contraction generated by focus of depolarisation within the ventricle

Question 5

Aetiology of heart block

6

Answer 5

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 conducting system

Question 6

Epidemiology of heart block

prevalence

Answer 6

250,000 pacemakers implanted every year & mostly for heart block

Question 7

Presenting symptoms of heart block

1 1st, 1 2nd, 2 mob2/3rd

Answer 7

1st degree
Asymptomatic

2nd degree
Usually asymptomatic

Mobitz type II & 3rd degree
May cause Strokes-Adams attacks
May also cause dizziness, palpitations, chest pain & heart failure

Question 8

Define Strokes-Adams attack

Answer 8

syncope caused by ventricular asystole

Question 9

Signs of heart block on physical examination

2 general + mob2/3rd + 2 3rd

Answer 9

Often NORMAL
Check for signs of a potential cause

Mobitz type II & 3rd degree
Signs of reduced cardiac output (e.g. hypotension, heart failure)

Complete heart block
Slow large volume pulse
JVP may show cannon A waves

Question 10

Investigations for heart block

4 types

Answer 10

ECG - gold standard
CXR
Bloods
Echocardiogram

Question 11

Investigations for heart block - ECG

1st, 2 mob1, 2 mob2, 2 3rd

Answer 11

1st degree
Fixed prolonged PR interval (> 0.2 secs)

Mobitz type I
Progressively prolonged PR interval, culminating in P wave that is NOT followed by QRS
Pattern then begins again

Mobitz type II
Intermittently P wave is NOT followed by QRS
May be a regular pattern of P waves not followed by QRS (e.g. 2:1, 3:1)

Complete heart block
No relationship between P waves & QRS complexes
If QRS is initiated in the:
bundle of His = narrow complex
more distally = wide complex & slow rate (30 bpm)

Question 12

Investigations for heart block - CXR

2

Answer 12

Cardiac enlargement

Pulmonary oedema

Question 13

Investigations for heart block - bloods

4

Answer 13

TFTs
Digoxin level
Cardiac enzymes
Troponin

Question 14

Investigations for heart block - echocardiogram

3

Answer 14

Wall motion abnormalities
Aortic valve disease
Vegetations

Question 15

Management of chronic heart block

1.3

Answer 15

Permanent pacemaker recommended in:

• complete heart block
• advanced Mobitz type II
• symptomatic Mobitz type I

Question 16

Management of acute heart block

2

Answer 16

If associated w/ clinical deterioration us IV atropine
Consider temporary (external) pacemaker

Question 17

Complications of heart block

4

Answer 17

Asystole
Cardiac arrest
Heart failure
Complication of any pacemaker inserted

Question 18

Prognosis of heart block

Answer 18

Mobitz type II & 3rd degree block usually indicate serious underling cardiac disease

Question 19

Define cannon A waves

Answer 19

seen occasionally on jugular vein of people w/ certain cardiac arrhythmias
Occurs when atria & ventricles contract simultaneously