Heart Block

Question 1

What does the cardiac conduction system comprise?

Answer 1

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

Question 2

What are the major causes of bradycardias?

Answer 2

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

Question 3

What is sick sinus syndrome?

Answer 3

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

Question 4

What is sinus sick syndrome also known as?

Answer 4

• Sinus node dysfunction
• Sinus node disease

Question 5

What are the causes of sick sinus syndrome?

Answer 5

• 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.

Question 6

What is a first degree HB?

Answer 6

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

Question 7

What are the ecg changes for first degree HB?

Answer 7

• PR interval greater than 0.2s

Question 8

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

Answer 8

• 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.

Question 9

What will the ECG changes be for Mobitz type 1?

Answer 9

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

Question 10

What is Mobitz type 2?

Answer 10

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

Question 11

What are the ECG changes for Mobitz type 2?

Answer 11

• PR interval remains normal
• QRS complexes dissappears

Question 12

What is a 2:1 block?

Answer 12

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

Question 13

What causes a 2:1 block

Answer 13

• Mobitz 1
• Mobitz 2

Question 14

What is 3rd degree HB?

Answer 14

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

Question 15

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

Answer 15

• escape rhythms

Question 16

What are the two types of escape rythms?

Answer 16

• junctional escape beat
• ventricular escape beat

Question 17

What are the characteristics of junctional escape rhythm?

Answer 17

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

Question 18

What are the features of ventricular escape beat?

Answer 18

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

Question 19

What causes escape rhythm to occur?

Answer 19

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

Question 20

What causes heart blocks?

*use VITAMIN CDE

Answer 20

• 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

Question 21

What is a Trifascicular block?

Answer 21

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

Question 22

What are the types of Fascicular blocks?

Answer 22

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

Question 23

How would you Mx HB?

Answer 23

• 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

Question 24

Describe Atropine

• MOA
• Cardiac effects
• uses

Answer 24

• selective muscarinic antagonist
• block vagal activity - speed AV conduction
• treat vagal bradycardia

Question 25

What are the ECG features of RBBB?

Answer 25

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

Question 26

What are the ECG features of LBBB?

Answer 26

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

Question 27

What is sick sinus syndrome?

Answer 27

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