Lecture 4: AV blocks

Question 1

Which EKG finding defines a first degree AV block?

Answer 1

PR interval >0.2 sec that is uniform

*0.2 sec = 5 small boxes or 1 large box

Question 2

Presence of what 4 underlying conditions enhances the chances of a 1st degree AV block?

Answer 2

• Atherosclerosis
• HTN
• Diabetes
• Degeneration of conduction system/fibrosis CHD

Question 3

What’s the cause of this rhythm?

Answer 3

1st degree AV block

Question 4

What’s the definition of a sinus rhythm?

Answer 4

Upright ‘P’ waves preceding QRS in lead II

Question 5

Epigastric pain, GERD, and other upper GI sx’s can be a clue for that cardiac abnormality?

Answer 5

Inferior wall MI

Question 6

What are the EKG characteristics of a 2nd degree AV block, Mobitz I (Wenckebach)?

i.e., intervals, QRS morphology…

Answer 6

• Narrow QRS
• Progressive PR-interval prolongation until ventricular beat is dropped, sequence is then repeated
• “Grouped beats”

Question 7

The progressive lengthening of the PR-interval in Mobitz I (Wenckebach) results from what?

Level of the block is where?

Answer 7

• Earlier arrival in relative refractory period of A-V conduction
• Block is at level of AV node

Question 8

List 4 etiologies which can lead to a 2nd degree AV block, Mobitz I (Wenckebach)?

Answer 8

• All things that cause 1st degree AV block
• Digitalis toxicity
• INFERIOR acute MI
• Myocarditis

Question 9

Whenever you see “grouped beating” on an EKG strip you should immediately think what?

Answer 9

2nd degree AV block - Mobitz I (Wenckebach)

Question 10

A 2nd degree AV block, Mobitz Type II may be due to what 3 underlying etiologies?

Answer 10

• Ischemic heart disease
• May be seen with acute ANTERIOR MI
• Degeneration of conduction system (i.e., aging)

Question 11

What type of acute MI is associated with a 2nd degree AV block, Mobitz Type I and Type 2?

Answer 11

• Type 1 (Wenckebach)= acuteINFERIORMI (sinceRCA supplies at or above AV node)
• Type 2 = acute ANTERIOR MI (since LAD supplies distal conduction system)

Question 12

What are the characteristic EKG findings of a 2nd degree AV block, Mobitz Type II?

Intervals, QRS…

Answer 12

• Fixed/uniform PR interval
• Occasional dropped beats (QRS) in 2:1, 3:1, or 4:1 pattern
• QRS usually wide (due to block being distal)

Question 13

A 2nd degree AV block, Mobitz Type II may occur at which 3 levels?

Answer 13

• Bundle of His
• Both bundle branches
• Fascicular branches

Question 14

What is the progression and tx like for a 2nd degree AV block, Mobitz Type II?

Answer 14

• Progressive/irreversible
• Permanent pacemaker indicated

Question 15

What is the ECG interpretation?

Answer 15

2nd degree AV block, Mobitz Type II and LBBB

Question 16

What are the EKG findings associated with a third degree heart block (aka complete block)?

Answer 16

• P waves NEVER related to QRS complexes
• 2 indpendent rhythms (A-V dissociation)

Question 17

A 3rd degree heart block can occur above or below the AV node and what serves as the escape rhythm for each type and QRS findings?

Ventricular rate?

Answer 17

• Above –> junctional rhythm/ w/ NARROW QRS (rate 40-55)
• Below –> ventricular pacemaker w/ WIDE QRS (rate 20-40)

Question 18

What are 3 of the major etiologies associated with 3rd degree heart block (aka complete AV block)?

Answer 18

• Ischemic
• Infiltrative diseases
• Cardiac surgery: by-pass/valve replacement, myocarditis, degenerative

Question 19

How do you treat a 3rd degree AV block?

Answer 19

Permanent pacemaker

Question 20

How do you interpret this rhythm and how do you treat?

Answer 20

• 1st degree AV block
• Tx: do nothing

Question 21

When looking at a strip showing a 2:1 AV block which can be caused by either a Mobitz type I or II, what general rule of thumb should be used to distinguish the cause?

Answer 21

• If PR interval is prolonged and QRS is narrow it is likely a type I (Wenckebach)
• If PR interval is normal and QRS is wide it is likely a type II, and pacemaker is warranted

Question 22

Which technique can be employed at the bedside to get a better look at the root cause of a 2:1 AV block?

Answer 22

Vagal maneuver

Question 23

How would you interpret this EKG finding?

Answer 23

3rd degree AV block

Question 24

Interpret this EKG

Answer 24

LBBB w/ 2nd degree AV block, type II