Conduction Blocks

Question 1

What type of block maintains AV synchrony?

Answer 1

1st degree AV block

Question 2

What type of block has intermittent loss of AV conduction?

Answer 2

2nd degree AV block

Question 3

What type of block has AV dissociation?

Answer 3

3rd degree (complete) AV block

Question 4

What are the MC causes of AV blocks?

Answer 4

• Progressive cardiac conduction disease d/t fibrosis and sclerosis
• Ischemic heart disease

Question 5

How does 1st degree AVB present on EKG?

Answer 5

• Prolonged PR interval

- Ratio of P:QRS is retained at 1:1

Question 6

1st degree AV block is ___ (likely/unlikely) to degrade to 2nd degree AV block?

Answer 6

UNLIKELY

Question 7

What are the etiologies of 1st degree AVB?

Answer 7

• Underlying structural abnormalities of AV node
• Increased vagal tone
• Drugs that impair or slow AV conduction (digoxin, BBs, CCBs)

Question 8

Which populations are more at risk for 1st degree AVB?

Answer 8

Young trained athletes

African Americans

Question 9

What does 1st degree AVB increase risk of developing?

Answer 9

A Fib

Question 10

How to treat 1st degree AVB?

Answer 10

-If PR

Question 11

How does 2nd degree AVB present on EKG?

Answer 11

Ratio of P:QRS is greater than 1:1 (dropped beats)

Question 12

What populations are affected by 2nd degree AVB?

Answer 12

• Young trained athletes

* Men = women

Question 13

What are the etiologies of 2nd degree AVB?

Answer 13

• Cardiac meds (Digoxin, BBs, CCBs)
• Lithium
• Inflamm diseases (endocarditis)
• Infiltrative diseases (amyloid)
• Malignancy (Hodgkin’s)
• Scleroderma

Question 14

What is Wenckebach and how does it look on EKG?

Answer 14

• 2nd degree AVB Mobitz Type I

- Progressive PR interval lengthening until dropped beat occurs

Question 15

What is Mobitz Type II?

Answer 15

• Indicative of underlying disease below AV node

- NO change in PR interval

Question 16

What type of block frequently progresses to 3rd degree AVB?

Answer 16

2nd degree Mobitz Type II

Question 17

How to treat 2nd degree AVBs?

Answer 17

• No tx for asymptomatic
• Treat underlying cause
• Avoid AV nodal blocking meds
• Pacemaker indicated in nearly all Mobitz Type II

Question 18

What is a 3rd degree AVB?

Answer 18

• Complete failure of AV node to conduct any impulses to ventricles
• Variable PR intervals
• Escape rhythm (junctional or ventricular)
• AV dissociation

Question 19

Treatment of 3rd degree AVB?

Answer 19

• Apply temp pacer
• Refer to EP
• Treat underlying cause
• Perm pacemaker in all patients!

Question 20

What does LBBB predict for young healthy vs. older pts?

Answer 20

• Does NOT predict bad outcome in young healthy

- Increased mortality in older pts

Question 21

What is a LBBB and how does it present on EKG?

Answer 21

• Delay in LV depolarization

- Wide QRS w/rabbit ears V6

Question 22

What is most important to consider with a LBBB?

Answer 22

• Difficult to identify MI through a LBBB

- New LBBB in setting of chest pain is MI until proven otherwise

Question 23

Treatment of LBBB

Answer 23

• No tx in young asymp
• Tx underlying conditions and risk factors
• Consider pacemaker in pts with syncope

Question 24

How does RBBB present on EKG?

Answer 24

Wide QRS with rabbit ears in V1-V3

Question 25

How to treat RBBB?

Answer 25

• Usually no tx needed
• If pt has syncope, consider pacemaker
• Avoid AV blocking meds