Heart Blocks

Question 1

What causes AV block?

Answer 1

When conduction is delayed for too long at AVN or bundle of His

Question 2

The normal PR interval should be?

Answer 2

200ms or less (5 small boxes)

Question 3

Describe 1st degree AV block

Answer 3

Prolonged PR interval.

1st degree AV block usually asymptomatic - doesn’t require treatment

Question 4

2nd degree AV block includes Mobitz 1 and Mobitz 2. Describe each one

Answer 4

Mobitz 1 - PR interval gets progressively longer until heart drops a beat. Typically benign and no treatment required.

Mobitz 2 - some normal PR intervals followed by a dropped beat. Can be dangerous - requires treatment with a pacemaker

Question 5

Mobitz 2 can progress into 3rd degree AV block (aka complete heart block). Describe 3rd degree AV block

Answer 5

No impulses conducted to automaticity causes Ventricular escape rhythm.

End result is that there is AV dissociation - reduced CO –> leading to syncope or sudden cardiac death

ECG: P waves and QRS complexes appear at their own rates

Question 6

How are 3rd degree AV blocks treated?

Answer 6

Give them a pacemaker asap

Question 7

What are the causes of AV block

Answer 7

1. MI - esp in RCA as RCA supplies AVN
2. Electrolyte disturbances (e.g. hyperkalaemia)
3. Lyme disease
4. Medication (e.g. Bbs, CCBs, adenosine, amiodarone, digoxin)

Question 8

In an ECG, what signs would show RCA MI?

Answer 8

Inferior wall MI - i.e. ST elevation in leads 2, 3, avF

Question 9

What is a normal QRS complex duration

Answer 9

Less than 120ms or 3 small boxes

Question 10

Generally speaking, all BBBs have which feature regarding QRS complexes?

Answer 10

Wide QRS

Question 11

In RBBB, what configuration do the right sided chest leads (i.e. V1, V2, V3) show?

Answer 11

RSR configuration - pronounced R wave, followed by deep S wave, then another R wave. Looks like the capital letter M

Question 12

What are causes of RBBB

Answer 12

RVH
RHF
PE

Question 13

In LBBB, what configuration is present and in which chest leads?

Answer 13

Lead 1, aVL, V5, V6 = tall R waves

In V1, tall S waves

May also find ST Depression and T wave inversion

Question 14

What are the causes of LBBB?

Answer 14

LBBB never occurs in normal hearts ! (whereas RBBB can)

Hypertension
Ischaemia
Dilated cardiomyopathy
Aortic stenosis

Question 15

A new LBBB in a person with chest pain may be a sign of?

Answer 15

MI

Question 16

How to treat Lyme disease?

Answer 16

IV antibiotics