Heart block

Question 1

What is heart block?

Answer 1

When the electrical signal passing through the AV node - which controls heart rate - is partially or completely blocked

Question 2

1st degree heart block
1) What happens in a first degree heart block?
2) What is the ECG finding in a first degree heart block?

Answer 2

1) Electrical impulse still reaches the ventricles but moves slower than normal through the AV node
2) Longer PR interval

Question 3

2nd degree type I heart block/Mobitz type I/Wenckebach’s AV block
1) What happens in a 2nd degree type I heart block?
2) What is the classic ECG finding of this type of heart block?

Answer 3

1). Electrical signals get gradually weaker until it doesn’t pass through the AV node – therefore failing to stimulate a ventricular contraction. After this happens the atrial impulse returns to being strong and the cycle repeats
2) Increasing PR interval until the P wave no longer conducts to the ventricle – resulting in an absent QRS complex after a P wave

Question 4

2nd degree type II heart block/Mobitz type II
1) What happens in a second degree type II heart block?
2) What effect does this have on an ECG?
3) In this type of heart block, what does a 3:1 ratio mean?

Answer 4

1) Most of the atrial signals reach the ventricles but occasionally some don’t
2) When the atrial signal doesn’t pass to the ventricles there’s a missing QRS complex.
3) There is usually a set ratio of P waves to QRS complexes, for example 3 P waves to each QRS complex would be referred to as a 3:1 block

Question 5

2:1 block
1) What is a 2:1 block?
2) What can cause it?

Answer 5

1) 2 P waves for each QRS complex – every second P wave isn’t strong enough to stimulate a QRS complex
2) Mobitz type I or II

Question 6

3rd degree heart block
1) What happens in a third degree heart block?
2) What are the ECG findings?

Answer 6

1) Electrical signals from the atria to the ventricles is completely blocked. To compensate the ventricle beats on its own but this rate is slower and more irregular
2) No relationship between P waves and QRS complexes

Question 7

1) What is it called when a baby is born with a heart block
2) Name a scenario where babies are more likely to have a congenital heart block
3) More commonly heart block develops later in life – acquired heart block. Name 2 causes of acquired heart block
4) What is the commonest cause of heart block?
5) Name 3 medications that can cause heart block

Answer 7

1) Congenital heart block
2) If they’re born with a heart defect, mother has an autoimmune condition i.e. lupus
3) Coronary artery disease with or without heart attack, cardiomyopathies, heart valve disease, damage to the heart during heart surgery, electrolyte abnormalities – especially high potassium, side effect of medications
4) Coronary artery disease
5) Beta blockers, digoxin, CCBs, antihypertensives, antiarrhythmics, muscle relaxers and sedatives, antidepressants and antipsychotics, diuretics and lithium

Question 8

Name a symptom someone with heart block may present with

Answer 8

Fainting, dizziness, chest pain, tiredness, palpitations, shortness of breath

Question 9

How is it diagnosed?

Answer 9

ECG

Question 10

Name a complication of heart block

Answer 10

• Heart failure
• Arrhythmias
• Heart attack
• Sudden cardiac arrest

Question 11

1) What is almost always the treatment for 3rd degree heart block, and sometimes the treatment for 2nd degree heart block?
2) If the heart block is unstable or there’s a risk of asystole, what is the 1st line medication?

Answer 11

1) Pacemaker
2) Atropine