Heart Block

Question 1

What are the different types of heart block?

Answer 1

1) Prolonged conduction from A to V. PR>200ms
2) Mobitz I = progressive prolonged conduction from A to V and a missed ventricular contraction every now and again
Mobitz II= no progressive prolonged conduction from A to V but there is intermittent failure of conduction from A to V. Therefore there is an intermittent missed contraction of ventricles
3) Complete heart block= complete dissociation between atria and ventricles. There is no relationship between P and QRS on ECG.

Question 2

Why does ventricular contraction/depolarisation still occur in 3rd degree heart block even though there is no conduction through the AVN?

Answer 2

Because there are individual pacemaker cells in the ventricles that are activated as a backup when the AVN is not conducting properly.

Question 3

What are the ecg results in each of the heart blocks?

Answer 3

1) PR>200ms
2) Mobitz I= progressively prolonged PR interval. one non-conducted P wave and the following heart beat has a shorter PR interval. Then the following beats have progressively prolonged PR intervals» carries on like a cycle
3) MobitzII= Constant PR but intermittent missed P waves
4) 2:1 Block= 2 P waves per QRS. Normal consistent PR intervals
5) Complete Heart block= Completely dissociated P and QRS. Abnormally shaped QRS

Question 4

Aetiology? (3)

Answer 4

Lev’s disease» progressive fibrosis of heart» cannot conduct properly
Ischaemic heart disease» death of myocardial cells means that the pacemaker cells cannot function
Infective endocarditis

Question 5

Presenting symptoms? for all types?

Answer 5

1) Asymptomatic
2) Mobitz1= asymptomatic
3) Mobitz2 and 3rd= syncope (stokes adams attack due to reduced ventricular systole so less blood reaches brain)

Question 6

App Ix (4)

Answer 6

ECG= gold standard
Serum troponin» test for ischaemia which is a cause of heart block
CXR= Look at mediastinal enlargement because of enlarged heart
Echo= look at walls and valves at each heart beat

Question 7

Mx? for each type of heart block for chronic and acute

Answer 7

CHRONIC
1st degree= just monitor as it is asymptomatic
Mobitz1, 2 and 3rd= pacemaker to regulate the conduction

ACUTE
IV atropine (anti muscarinic so it stops the PNS innervation to the heart and increases the heart rate>> makes sure enough blood reaches body tissues)

Temporary External pacemaker

Question 8

Complications?

Answer 8

Asystole
Cardiac arrest
Heart failure
Pacemaker complications» infection etc

Question 9

Which types of heart block has a serious underlying pathology?

Answer 9

3rd degree heart block and mobitz II

These have worst prognosis compared to other 2