Revision - Heart Block

Question 1

Define a prolonged PR interval

Answer 1

> 0.2s

Question 2

Define 1st degree heart block

Answer 2

Consistent prolongation of PR interval due to delayed conduction via AV node

Question 3

What is the PR inverval on an ECG?

Answer 3

From the beginning of the P wave to the beginning of the QRS complex

Question 4

What does the PR interval represent?

Answer 4

The time between atrial depolarisation and ventricular depolarisation

Question 5

What drugs can cause 1st degree heart block? (4)

Answer 5

1) beta blockers

2) rate-limiting CCBs e.g. diltiazem

3) digoxin

4) magnesium

Question 6

What occurs in Mobitz type I AV block?

Answer 6

There is progressive prolongation of the PR interval until eventually the atrial impulse is not conducted, and the QRS complex is dropped.

Question 7

Why can an inferior MI cause AV block?

Answer 7

As the RCA supplies the AV node

Question 8

Mx of Mobitz type I if patient is asymptomatic?

Answer 8

No mx required

Question 9

Mx of Mobitz type I if patient is symptomatic?

Answer 9

Pacemaker may be considered

Question 10

What happens in Mobitz type II?

Answer 10

There is consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction.

The intermittent dropping of the QRS complexes typically follows a repeating cycle of every 3rd (3:1 block) or 4th (4:1 block) P wave.

Question 11

Is Mobitz type II sometimes a normal variant?

Answer 11

No - always pathological

Question 12

ECG findings in second-degree AV (type 2)?

Answer 12

1) Rhythm: irregular (may be regularly irregular in 3:1 or 4:1 block)

2) P wave: present but there are more P waves than QRS complexes

3) PR interval: consistent normal PR interval duration with intermittently dropped QRS complexes

4) QRS complex: normal (<0.12 seconds) or broad (>0.12 seconds)

Question 13

When will the QRS complex be broad in second-degree AV block (type 2)?

Answer 13

The QRS complex will be broad if the conduction failure is located DISTAL to the bundle of His.

Question 14

Symptoms & exam findings in second-degree AV block (type 2)?

Answer 14

Symptoms:
- palpitations
- pre-syncope
- syncope

Exam:
- ‘regularly irregular’ pulse

Question 15

Management of second-degree AV block (type 2)?

Answer 15

1) Patients should be placed on a cardiac monitor as soon as possible (due to risk of progression to complete AV block).

2) Investigate underlying cause

3) Temporary pacing or isoprenaline may be required if the patient is haemodynamically compromised due to bradycardia.

4) A permanent pacemaker is usually inserted if there are no reversible causes identified.

Question 16

What 2 types of escape rhythms can 3rd degree (complete) heart block consist of?

Answer 16

1) narrow complex escape rhythms

2) broad complex escape rhythms

Question 17

Narrow complex escape rhythms in complete heart block:

a) QRS interval?
b) where do they originate?
c) typical HR?

Answer 17

a) <0.12s
b) above bifurcation of bundle of His
c) >40bpm

Question 18

Narrow complex escape rhythms in complete heart block:

a) QRS interval?
b) where do they originate?
c) typical HR?

Answer 18

a) >0.12s
b) below bifurcation of bundle of His
c) <40bpm (more significant clinical features e.g. heart failure, syncope)

Question 19

What 3 infections can cause complete heart block?

Answer 19

1) Lyme disease

2) Chagas disease

3) Infective endocarditis

Question 20

ECG findings in 3rd degree heart block?

Answer 20

1) Rhythm: variable

2) P wave: present but not associated with QRS complexes

3) PR interval: absent (as there is atrioventricular dissociation)

4) QRS complex: narrow (<0.12 seconds) or broad (>0.12 seconds) depending on the site of the escape rhythm (see introduction)

Question 21

Management of 3rd degree heart block?

Answer 21

1) Place on cardiac monitor

2) Transcutaneous pacing/temporary pacing wire or isoprenaline infusion may be required. Some rhythms (particularly narrow-complex escape rhythms) may respond to atropine.

3) A permanent pacemaker is usually required.

Question 22

What is the main complication of 3rd degree heart block?

Answer 22

Sudden cardiac death due to ventricular arrhythmias

Question 23

What do the following ECG components represent:

1) p wave
2) PR interval
3) QRS complex
4) T wave

Answer 23

1) Atrial depolarisation

2) Conduction through the AVN to the ventricles (i.e. time between atrial and ventricular depolarisation)

3) Ventricular depolarisation

4) Ventricular repolarisation

Question 24

What is the main feature of bundle branch blocks?

Answer 24

Broad QRS complexes

Question 25

What are the causes of damage to the right bundle branch?

(i.e. causing RBBB)

Answer 25

1) lung pathology:
- COPD
- pulmonary emboli
- cor pulmonale

2) Primary heart muscle disease (ARVC)

3) Congenital heart disease (e.g. ASD)

4) Ischaemic heart disease

5) Primary degeneration of the right bundle

Question 26

What does the left bundle branch split into?

Answer 26

Anterior & posterior fascicles

Question 27

Each branch of the left bundle branch may be damaged in isolation.

Is anterior or posterior fascicular block more common?

Answer 27

Anterior

Question 28

In the mx of angina in patients already taking a beta blocker, but a CCB is contraindicated, what can be given next?

Answer 28

A long-acting nitrate, ivabradine, nicorandil or ranolazine

Question 29

When is aortic valve replacement considered in aortic stenosis?

Answer 29

1) patient is symptomatic

2) if asymptomatic but valvular gradient >40 mmHg and with features such as LV systolic dysfunction