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cardiology > Conduction blocks > Flashcards

Conduction blocks Flashcards

1
Q

What is first degree heart block

A

occurs where there is delayed atrioventricular conduction through the AV node

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2
Q

ECG for first degree heart block

A

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

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3
Q

What is second degree heart block

A

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

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4
Q

names of the three types of second degree heart block

A

Mobitz1
Mobitz2
2:1 BLOCK

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5
Q

What happens in mobitz type 1

A
  • 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
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6
Q

ecg for mobitz 1

A
  • 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.
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7
Q

what occurs in mobitz type 2

A
  • intermitted failure or interruption of AV conduction
  • Normal pr intervals
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8
Q

ecg for mobitz type 2

A
  • pr intervals are the same
  • missing qrs complexes
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9
Q

what is 2:1 block

A

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

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10
Q

what is third degree heart block

A
  • COMPLETE HEART BLOCK
  • no observable relationship between p waves and QRS complexes
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11
Q

treatment for stable av node blocks

A

observation

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12
Q

treatment for unstable or risk of asystole

A
  • first line- atropine iv 500mcg
  • no improvement:
  • atropine repeated up to 6 doses
  • other inotropes
  • transcutaneous cardiac pacing
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13
Q

What occurs in left bundle branch block

A

right ventricle contracts before the left

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14
Q

define bundle branch block

A

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

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15
Q

describe normal cardiac conduction

A
  • 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
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16
Q

diagnostic criteria for RBBB

A
  • QRS- > 120 ms
  • RSR pattern in V1-V3
  • Wide , slurred S wave in lateral leads
17
Q

Explain MaRroW for RBBB

A

Complexes in V1 resemble M and V6 resembles W

18
Q

Describe the steps in right bundle branch block

A
  • 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.
19
Q

Diagnostics for LBBB are

A
  • 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
20
Q

WiLliaM mnemonic for LBBB

A

Complexes in v1 resemble W
Complexes in v6 RESEMBLE m

21
Q

Why might LBBB occur

A
  • conduction system degeneration
  • myocardial pathologies
  • after cardiac procedures
  • STEMI - rare
22
Q

What does the left bundle branch split into

A

anterior and posterior fasicles

23
Q

anterior fasicle block may cause ….?

A

left axis deviation

24
Q

posterior fasicle deviation causes …. r

A

right axis deviation

25
Q

A systolic murmur occurs …

A

after S1

26
Q

A diastolic murmur occurs ….

A

after s2

27
Q

name the two systolic murmurs ASMR

A

Aortic stenosis
mitral regurgitation

28
Q

name the two diastolic murmurs
ARMS

A

Aortic regurgiation
mitral stenosis

29
Q

What can cause first degree heart block

A
  • High vagal tone (e.g. athletes)
  • Acute inferior MI
  • Electrolyte abnormalities (e.g. hyperkalaemia)
  • Drugs: NHP-CCBs, beta-blockers, digoxin, cholinesterase inhibitors
30
Q

Causes of mobitz type 2

A
  • 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,
31
Q

Definitive management of mobitz type 2

A

Permanent pacemaker

32
Q

Clinical features of third degree heart block

A

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

cardiology (16 decks)

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