Complete Heart Block

Question 1

What anatomical structure is affected in complete heart block?

Answer 1

The atrio-ventricular node

Question 2

What is the usual role of the AV node?

Answer 2

Transmission of electrical depolarisation wave from the atria to the ventricles

Question 3

Why does the AV node induce a short delay in transmission?

Answer 3

To allow the atria to contract before the ventricles contract

This prevents them from contracting together as this would not allow the AV nodes to open

Question 4

What structural abnormalities are present in complete heart block?

Answer 4

Fibrosis of the AV node

Necrosis/infarction of the AV node

Question 5

What happens in fibrosis of the AV node?

Answer 5

some of the normal cells are replaced with fibrous tissue due to cell death due to age

Question 6

What happens in necrosis/infarction of the AV node?

Answer 6

death of all/most of the cells in the AV node as a result of coronary artery disease

Question 7

What happens to the AV node in complete heart block?

Answer 7

There is complete failure of the AV node to transmit electrical impulses from the atria to the ventricles

Question 8

How does contraction of the atria and ventricles change in a patient with complete heart block?

Answer 8

The atria have their own electrical activity and contract independently of the ventricles

The ventricles develop their own pacemaker activity, which is usually at a much slower rate

Question 9

What prior events usually occur which result in complete heart block?

Answer 9

Usually occurs in elderly patients who have had a previous myocardial infarction, be taking beta blockers or other rate lowering drugs which act to block the AV node

Question 10

How can complete heart block present itself?

Answer 10

Chronic - Gradually and in isolation

Acute - Suddenly with other symptoms

Question 11

What symptoms are usually experienced in chronic complete heart block?

Answer 11

Tiredness and breathlessness with exercise

Question 12

What symptoms are usually experienced in acute complete heart block?

Answer 12

Light-headedness or collapse with loss of consciousness

Question 13

What symptoms are usually experienced if complete heart block is caused by coronary artery disease?

Answer 13

chest pain as well as light-headedness/collapse

Question 14

What clinical signs are seen in patients with complete heart block?

Answer 14

Slow pulse/heart rate which is much lower than 60 bpm

low blood pressure

cardiac syncope

Question 15

What is cardiac syncope?

Answer 15

Patient suddenly loses consciousness for a few seconds

Question 16

What abnormal test results are seen in a patient with complete heart block?

Answer 16

ECG

P waves may be buried within the QRS complex

Question 17

What medical/surgical interventions are used to treat complete heart block?

Answer 17

Paramedic staff may administer atropine

A temporary pacemaker may be introduced on arrival in hospital

Question 18

What does atropine do?

Answer 18

It blocks the vagus nerve and acetylcholine

This allows the heart rate to rise

Question 19

How is a temporary pacemaker introduced and what does it do?

Answer 19

A wire is introduced into a vein and then into the right ventricle

It allows a small electrical impulse to stimulate the heart

Question 20

What is the long-term treatment for complete heart block?

Answer 20

A permanent pacemaker

Question 21

What conditions are needed to fit a permanent pacemaker?

Answer 21

Complete heart block persists after recovering from an associated MI and after stopping heart rate lowering drugs