Conduction blocks

Question 1

What is first degree heart block

Answer 1

occurs where there is delayed atrioventricular conduction through the AV node

Question 2

ECG for first degree heart block

Answer 2

pr interval is greater than 0.2 seconds
5 small or 1 big square

Question 3

What is second degree heart block

Answer 3

where some of the atrial impulses do not make it through the AV node to the ventricles. This means that there are instances where p waves do not lead to QRS complexes

Question 4

names of the three types of second degree heart block

Answer 4

Mobitz1
Mobitz2
2:1 BLOCK

Question 5

What happens in mobitz type 1

Answer 5

• atrial impulses becomes gradually weaker until it does not pass through the AV node.
• After failing to stimulate a ventricular contraction the atrial impulse returns to being strong
• cycle repeats

Question 6

ecg for mobitz 1

Answer 6

• increasing PR interval until the P wave no longer conducts to ventricles
• This culminates in absent QRS complex after a P wave.
• This cycle repeats itself.

Question 7

what occurs in mobitz type 2

Answer 7

• intermitted failure or interruption of AV conduction
• Normal pr intervals

Question 8

ecg for mobitz type 2

Answer 8

• pr intervals are the same
• missing qrs complexes

Question 9

what is 2:1 block

Answer 9

2 p waves for each qrs complex , every second p wave is not a strong enough atrial pressure to stimulate a QRS complex

Question 10

what is third degree heart block

Answer 10

• COMPLETE HEART BLOCK
• no observable relationship between p waves and QRS complexes

Question 11

treatment for stable av node blocks

Answer 11

observation

Question 12

treatment for unstable or risk of asystole

Answer 12

• first line- atropine iv 500mcg
• no improvement:
• atropine repeated up to 6 doses
• other inotropes
• transcutaneous cardiac pacing

Question 13

What occurs in left bundle branch block

Answer 13

right ventricle contracts before the left

Question 14

define bundle branch block

Answer 14

a block in the conduction of one of the bundle branches , so the ventricles don’t receive impulses at the same time

Question 15

describe normal cardiac conduction

Answer 15

• The sino-atrial node acts as the initial pacemaker
• Depolarisation reaches the atrioventricular node
• Impulses travel simultaneously down the bundle of His via the left and right bundle branches. The septum is depolarised from the left.
• Both the left and right ventricular walls are depolarised simultaneously

Question 16

diagnostic criteria for RBBB

Answer 16

• QRS- > 120 ms
• RSR pattern in V1-V3
• Wide , slurred S wave in lateral leads

Question 17

Explain MaRroW for RBBB

Answer 17

Complexes in V1 resemble M and V6 resembles W

Question 18

Describe the steps in right bundle branch block

Answer 18

• The sino-atrial node acts as the initial pacemaker
• Depolarisation reaches the atrioventricular node
• Depolarisation through the bundle of His occurs only via the left bundle branch. The left branch still depolarises the septum as normal.
• The left ventricular wall depolarises as normal.
• The right ventricular walls are eventually depolarised by the left bundle branch, this occurs by a slower, less efficient pathway.

Question 19

Diagnostics for LBBB are

Answer 19

• QRS duration > 120ms (3 small squares)
• Dominant S wave in V1
• Broad, monophasic R wave in lateral leads – I, aVL, V5-V6
• Absence of Q waves in lateral leads
• Prolonged R wave > 60ms in leads V5-V6

Question 20

WiLliaM mnemonic for LBBB

Answer 20

Complexes in v1 resemble W
Complexes in v6 RESEMBLE m

Question 21

Why might LBBB occur

Answer 21

• conduction system degeneration
• myocardial pathologies
• after cardiac procedures
• STEMI - rare

Question 22

What does the left bundle branch split into

Answer 22

anterior and posterior fasicles

Question 23

anterior fasicle block may cause ….?

Answer 23

left axis deviation

Question 24

posterior fasicle deviation causes …. r

Answer 24

right axis deviation

Question 25

A systolic murmur occurs ...

Answer 25

after S1

Question 26

A diastolic murmur occurs ....

Answer 26

after s2

Question 27

name the two systolic murmurs ASMR

Answer 27

Aortic stenosis mitral regurgitation

Question 28

name the two diastolic murmurs ARMS

Answer 28

Aortic regurgiation mitral stenosis

Question 29

What can cause first degree heart block

Answer 29

- High vagal tone (e.g. athletes) - Acute inferior MI - Electrolyte abnormalities (e.g. hyperkalaemia) - Drugs: NHP-CCBs, beta-blockers, digoxin, cholinesterase inhibitors

Question 30

Causes of mobitz type 2

Answer 30

- Infarction: particularly anterior MI which damages the bundle branches - Surgery: mitral valve repair or septal ablation - Inflammatory/autoimmune: rheumatic heart disease, SLE, systemic sclerosis, myocarditis - Fibrosis: Lenegre's disease - Infiltration: sarcoidosis, haemochromatosis, amyloidosis - Medication: beta-blockers, calcium channel blockers, Digoxin,

Question 31

Definitive management of mobitz type 2

Answer 31

Permanent pacemaker

Question 32

Clinical features of third degree heart block

Answer 32

Patients may present with syncope or cardiac arrest. ECG shows severe bradycardia and dissociation between the P waves and the QRS complexes.