Heart Block

Question 1

Heart block in either AV node or His bundle=
Heart block lower in the conduction system=

Answer 1

Heart block in either AV node or His bundle= AV block
Heart block lower in the conduction system= bundle branch block

Question 2

Definiton of
1st degree heart block:
2nd degree heart block (both types):
3rd degree heart block:

Answer 2

1st degree heart block: prolongation of PR interval to >0.2s (normally 0.12-0.2s)

2nd degree heart block (both types): AV node fails to conduct every episode of depolarisation, so not all P waves are associated with QRS complexes
Mobitz Type 1: progressive lengthening of PR interval till 1 QRS complex is dropped
Mobitz Type 2: PR interval is constant but 2 or 3 P waves per QRS complex

3rd degree heart block: AV node fails to conduct ANY depolarisation from SA node and an alternative pacemaker is estabished elsewhere in the heart –> P waves and QRS complexes are not associated with each other

Question 3

Sx and Signs of heart blocks

Answer 3

1st degree: no Sx

2nd degree Type 1: light-headedness, dizziness, syncope

2nd degree Type 2: SoB, postural hypotension, chest pain, risk of complete HB

3rd degree: dizziness, fatigue, lightheadedness, syncope, bradycardia

Question 4

Tx for heartblocks

Answer 4

1st degree: none

2nd degree: Mobitz Type 2 requires pacemaker to avoid complete heartblock

3rd degree: Pacemaker, IV atropine

Question 5

Causes of different types of heartblocks?

Answer 5

1st degree: HypoK, myocarditis inferior MI, AVN blocking drugs like BBlockers and CCB

2nd degre: acute MI, AVN blocking drugs

3rd degree: structural heart disease, ischaemic heart disease, hypertension, endocarditis, Lyme disease

Question 6

Pathophysiology of RBBB and LBBB

Answer 6

RBBB: RBB doesnt conduct impulse –> both ventricles dont receive impulse simultaneously –> impulse spreads to LV and then RV –> causing ‘M’ shape of QRS complex in V1 and ‘W’ shape in V6

reverse is true for LBBB

Question 7

Which BBB may require pacemaker?

Answer 7

LBBB