AV Blocks

Question 1

Describe a first degree atrioventricular block?

Answer 1

PR interval is prolonged and equal in time

Question 2

Is there always a QRS after every P wave with a first degree heart block?

Answer 2

YES YES YES 1:1

Question 3

What are some things that can cause a first degree heart block?

Answer 3

digoxin, beta-blockers, calcium channel blockers, CAD, infectious disease, congenital lesions

Question 4

Do you treat a first degree AV block?

Answer 4

NO, but remember they can progress to a second or third degree block.

If drug is possible cause, consider discontinuation or switching to new one

Question 5

Describe a second degree Mobitz I (wenchkbach).

Answer 5

AV conduction (PR interval) gets progressively longer until an impulse eventually doesnt make it to the ventricles, causing a skipped QRS complex. After the skip, the cycle repeats itself.

Question 6

Where does the block occur in the conduction system with a mobitz I?

Answer 6

above the bundle of his.

Question 7

What things can cause a mobitz I?

Answer 7

digoxin

myocarditis

inferior wall MI

Question 8

Does a mobitz I need to be treated?

Answer 8

Not usually, the ventricular rate is normally adequate enough to keep patient hemodynamically stable.

If a drug is the suspected cause, consider discontinuation.

Monitor for progression to third degree block.

Question 9

What will take over once a mobitz I progresses to a third degree block?

Answer 9

a junctional pacemaker will take over at a rate of around 40-60 BPM

Question 10

Describe a mobitz II.

Answer 10

occurs at or below the bundle of his.

fixed PR interval with an eventual nonconducted P wave (can be 2:1, 3:1, 4:1)

Question 11

Does a mobitz II disturb the SA node? What does this mean?

Answer 11

NO NO NO

This means the the PP interval is generally regularunaffected.

Question 12

What often accompanies a mobitz II? What can that mean?

Answer 12

BBB - QRS may be wide

Question 13

What can cause a mobitz II?

Answer 13

anterior wall MI or a fibrotic disease of the conducting tissue.

Question 14

Why is a mobitz II so dangerous?

Answer 14

it is often permanent, may deteriorate rapidly to a third degree block with a slow ventricular rate of 20-40 BPM

Question 15

How do you treat a mobitz II?

Answer 15

atropine or cardiac pacing if the patient becomes symptomatic or if anterior wall MI.

Long-term - permanent pacing

Question 16

Describe a third degree AV block.

Answer 16

also called a complete heart block - sinus node fires normally, but the impulses never reach the ventricles

Question 17

If the sinus impulses never reach the ventricles, how do they depolarize?

Answer 17

escape pacemakers conduct the ventricles either in the junction (40-60, narrow QRS), or in the ventricles (20-40, wide QRS), depending on where the block is and the severity.

Question 18

How would a third degree heart block look on an ECG?

Answer 18

P waves and QRS are present, however they dont correlate with one another.

Question 19

Is a third degree block consider to cause AV dissociation?

Answer 19

YES YES YES

Question 20

PP and RR intervals with third degree block?

Answer 20

separately are regular PR is irregular

Question 21

If the third degree block is present and the escape pacemakers are of ventricular origin and the patient is showing symptoms of low CO, how is it treated?

Answer 21

temporary pacing wire can be inserted to stabilize, after stabilized permanent pacemaker is inserted.