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Heart Block Flashcards

1
Q

What does the cardiac conduction system comprise?

A
  • SA node
  • AV node
  • Bundle of His
  • Left bundle branch
    • LAF
    • LPF
    • Septum
  • Right bundle branch
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2
Q

What are the major causes of bradycardias?

A
  • Sinoatrial
    • sick sinus syndrome
  • Atrioventricular donduction disease
    • 1st degree
    • 2nd degree
      • Mobitz type 1
      • Mobitz type 2
    • 3rd degree
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3
Q

What is sick sinus syndrome?

A
  • inability for SA node to create heart rate that’s appropriate for body’s needs
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4
Q

What is sinus sick syndrome also known as?

A
  • Sinus node dysfunction
  • Sinus node disease
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5
Q

What are the causes of sick sinus syndrome?

A
  • Idiopathic degeneration of the sinus node (most common)
  • SA and AV nodal fibrosis.
  • Myocardial ischaemia
  • Friedreich’s ataxia, muscular dystrophy.
  • myocarditis, pericarditis, rheumatic heart disease
  • Hyperkalaemia, hypoxia, hypothermia, hypothyroidism, hyperthyroidism.
  • Drugs - eg, digoxin, calcium-channel blockers, beta-blockers, sympatholytic agents, anti-arrhythmic drugs.
  • Toxins - eg, result of sepsis.
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6
Q

What is a first degree HB?

A
  • delayed atrioventricular conduction through the AV node
  • every atrial impulse still leads to ventricular contraction
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7
Q

What are the ecg changes for first degree HB?

A
  • PR interval greater than 0.2s
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8
Q

What is a Wnckebach’s phenomenon (Mobitz type 1)?

A
  • atrial impulses become 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 then repeats.
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9
Q

What will the ECG changes be for Mobitz type 1?

A
  • Increasing PR interval until p wave no longer conducts ventricles
  • cycle repeats
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10
Q

What is Mobitz type 2?

A
  • Intermitted failure or interruption of AV conduction
  • Results in missing QRS complexes
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11
Q

What are the ECG changes for Mobitz type 2?

A
  • PR interval remains normal
  • QRS complexes dissappears
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12
Q

What is a 2:1 block?

A
  • 2 P waves for each QRS complexes
  • every second p wave not strong enough to stimulate QRS complex
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13
Q

What causes a 2:1 block

A
  • Mobitz 1
  • Mobitz 2
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14
Q

What is 3rd degree HB?

A
  • Complete block of AV node
  • no observable relationship between p and QRS complex
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15
Q

What causes QRS complexes to appear in 3rd degree HB?

A
  • escape rhythms
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16
Q

What are the two types of escape rythms?

A
  • junctional escape beat
  • ventricular escape beat
17
Q

What are the characteristics of junctional escape rhythm?

A
  • QRS: Narrow
  • Rythm: Regular / regulary irregular
  • P waves: No definitive
  • Flat baseline / p waves bury in QRS / retrograde p waves
18
Q

What are the features of ventricular escape beat?

A
  • Rate: depend on underlying rhythm
  • Regularity: irregular
  • P wave: no
  • PR interval: no
  • QRS width: wide
  • Dropped beats: absent
19
Q

What causes escape rhythm to occur?

A
  • when the rate of supraventricular impulses arriving at the AV node or ventricle is less than the intrinsic rate of the ectopic pacemaker
20
Q

What causes heart blocks?

*use VITAMIN CDE

A
  • V - MI
  • I - endocarditis, lyme disease
  • T - hypothermia
  • A - sarcoidosis, SLE
  • M - hypokalaemia, hypocalcaemia, hypomagnesaemia
  • I - bisoprolol, beta blocker, verapamil, digoxin, memantine, radiofrequency ablation for WPWS
  • N - x
  • C - congenital complete HB
  • D- Degenerative connective tissue disease (most common)
  • E - Hypothyroidism
21
Q

What is a Trifascicular block?

A
  • conducting diseases in all three fascicles:
    • right bundle branch block
    • left a/p fascicle
    • First degree AV block
22
Q

What are the types of Fascicular blocks?

A
  • Bifascicular block
    • RBBB + LAFB
      • manifested as LAD
    • RBBB + LPFB
      • manifested as RAD
  • Trifascicular block
    • any bi fascicular block + prolonged PR
23
Q

How would you Mx HB?

A
  • Stable
    • observe
  • Unstable/risk of asystole (Mobitz type 2 or complete hb)
    • atropine 0.5mg IV
  • No improvement
    • Atropine 0.5mg IV (up to 6 doses for a total to 3mg
    • NA 1mg 1:10,000 every 3-5mins
    • Transcutaneous cardiac pacing
    • permanent pacemaker
24
Q

Describe Atropine

  • MOA
  • Cardiac effects
  • uses
A
  • selective muscarinic antagonist
  • block vagal activity - speed AV conduction
  • treat vagal bradycardia
25
Q

What are the ECG features of RBBB?

A
  • QRS equal to or more than 120ms
  • M-shaped QRS in V1
  • Prominent S wave in 1 and aVL
26
Q

What are the ECG features of LBBB?

A
  • QRS equal to or more than 120ms
  • Broad R wave in 1, aVL, V6
  • lack of septal q wave in 1 and V6
27
Q

What is sick sinus syndrome?

A
  • sinus node dysfunction with an atrial rate inappropriate for normal requirements

Cardiology (15 decks)

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