AV Blocks

Question 1

Intraventricular blocks occur where?

Answer 1

-occur INSIDE the ventricles somewhere, past the AV node

Question 2

Atrioventricular blocks occur where?

Answer 2

-occur most often in the AV node but could be anywhere above

Question 3

1st degree AV block

-definition or morphology of ECG?:

Answer 3

-PR interval >0.20 sec

Question 4

2nd degree AV block

-definition:

Answer 4

-one or more (not all) atrial impulses fail to reach the ventricles with no prematurity
AKA MOBITZ BLOCK (I or II)

Question 5

2nd degree AV block Type 1

-morphology on ECG?

Answer 5

• PR interval lengthens until conduction is lost (4 P:3 QRS periodicity)
• AV node becomes more and more refractory/ischemic/whatever with each P-wave impulse until it can’t send the P-wave through
• grouped QRS complexes
• first cycle is longer than next cycles
• longest cycle is less than twice the length of the shortest cycle

Question 6

2nd degree AV block - eitiologies?

Answer 6

• vagotonia (type 1 - due to vomiting)
• acute MI (inferior wall)
• drugs (digitalis, beta blockers, antiarrhythmics)
• aortic valve disease
• most commonly occurs in the AV node (type 1)

Question 7

1st degree AV block -

-etiologies:

Answer 7

• some of population has this variant = normal/benign
• PR interval increases with age
• no relationship to ischemic heart disease

Question 8

Why is 2:1 AV block special?

Answer 8

cant tell if its a type 1 or 2 second degree block because you cant see the PR interval prolonging but then you drop a QRS

Question 9

2nd degree AV block type 2:

• morphology:
• where is the block most commonly?

Answer 9

• atrial impulse fails to reach the ventricles without a prolonging PR interval
• commonly in purkinje system
• MUCH WORSE PROGNOSTICALLY –> can progress to 3rd degree block or death

Question 10

2nd degree AV block type 2:

-ECG/

Answer 10

• PR interval DOES NOT lengthen before the AV conduction is lost
• almost always has BBB pattern

Question 11

3rd degree AV block

-definition?

Answer 11

• no atrial impulses reach the ventricles

- equivalent to bilateral BBB or same thing trifascicular block

Question 12

3rd degree AV block on ECG?

Answer 12

• no correlation between P and QRS waves
• fusion occurs sometimes where P is randomly interposed on QRS
• Atrial rate is a lot faster than the ventricular rate

Question 13

AV dissociation

• what is it?
• causes?

Answer 13

(NOT EQUIVALENT TO 3rd AV BLOCK)
-independent atrial and ventricular rhythms
-causes:
acceleration of subsidiary pacing site;
decreased sinus node automatici;
reentrant ventricular tachycardias

Question 14

AV dissociation vs 3rd degree block:

Answer 14

-3rd degree=atrial beating fast and ventricles beating slow

AV dissociation=similar rates of beating!