EXAM#1: CONDUCTION DEFECTS

Question 1

How many fasicles does the RBB have?

Answer 1

1x

Question 2

How many fasicles does the LBB have?

Answer 2

2x

• Anterior fasicle
• Posterior fasicle

Question 3

What are the three unifasicular blocks?

Answer 3

RBBB
LAFB
LPFB

Question 4

What are the three bifasicular blocks?

Answer 4

LBBB

RBBB + LAFB/LPFB

Question 5

What is happening in a BBB?

Answer 5

One ventricle activates before the other (b/c conduction is blocked)

Question 6

What is the indication of a BBB?

Answer 6

Wide QRS (0.12 sec of wider)

Question 7

What lead should you evaluate a BBB in?

Answer 7

V1; use the “turn signal method”

Question 8

What are the classic findings for a LBBB?

Answer 8

• Borad QS in V1
• Slurred R-wave in V6

*Note that this is associated with a poor prognosis

Question 9

What are the classic findings of a RBBB?

Answer 9

• rSR’ in V1

- Borad S-wave in V6

Question 10

What does the broad S-wave in V6 indicate in a RBBB?

Answer 10

Depolarization traveling away from lead V6

Question 11

What are the criteria for a LAFB?

Answer 11

1) Left axis (down in I, up in II and III)

2) Normal QRS duration

Question 12

What degree is required for the LAD in LAFB?

Answer 12

-45 degrees

Question 13

What is more common LAFB or LPFB? Why?

Answer 13

LAFB b/c the LPF has DUAL blood supply

Question 14

How do you differentiate between LPFB and RVH with RAD?

Answer 14

1) RVH is more common
2) LPFB has to have no evidence of RVH i.e.
- Tall right precordial R-waves
- RAD
- Right precordial T-wave inversions

Question 15

What is the classic bifasicular block? How does this differ from a LAFB alone?

Answer 15

RBBB + LAFB

- Wide QRS (0.12sec) with “up turn signal” in V1

Question 16

Is a LBBB uni or bifasciular?

Answer 16

Bifasicular

Question 17

What are the criteria for a LBBB?

Answer 17

V1 with wide QRS and “down turn signal”

Question 18

What is the difference between a trifasicular block and complete AV block?

Answer 18

Trifasicular= RBBB + LAFB + 1st degree AV BLOCK

Complete= block of all fasicles

Question 19

What is the definition of a 1st degree AV block?

Answer 19

PR interval greater than 0.2 sec (5 small boxes)

Question 20

Is a first degree AV block related to IHD?

Answer 20

No

Question 21

What is the definition of a 2nd degree AV block?

Answer 21

Not all atrial impulses reach the ventricles

Question 22

Where does a Type I 2nd degree AV block occur?

Answer 22

AV node

Note that there is a longer than normal refractory period in the AV junction

Question 23

Where does a Tpye II 2nd degree AV block occur?

Answer 23

Purkinje system

Question 24

List the etiologies of a 2nd degree AV block.

Answer 24

1) Vagotonia
2) Acute inferior MI
3) Drugs
4) Aortic valve disease

Question 25

What is the definition of a Type I 2nd degree AV Block?

Answer 25

PR interval that progressively lengthens until AV conduction is lost

*Longest cycle is less than twice the length of the shortest cycle

Question 26

What almost always precedes a Type II 2nd degree AV block?

Answer 26

Bundle Branch Block

Question 27

What is the definition of a Type II 2nd degree AV block?

Answer 27

Dropped ventricular conduction without lengthening of the PR interval

Question 28

What is an alternative name for a 3rd degree AV block?

Answer 28

Trifasicular block

Question 29

What is the definition of a 3rd degree AV block?

Answer 29

No atrial impulses are reaching the ventricles

*Clinical outomce depends on ventricular escape rhythm.

Question 30

How will a 3rd degree AV block appear on ECG?

Answer 30

Independent atrial and ventricular rhythms

Question 31

What is AV dissociation?

Answer 31

Presence of independent atrial and ventricular rhythms

*This is not a block–the atrial and ventricular rhythms will be very similar

Question 32

What are the etiologies of AV dissociation?

Answer 32

1) Acceleration subsidiary pacing site
2) Decreased sinus automaticity
3) Re-entrant ventricular tachycardia

Question 33

What will a 2nd degree AV block Type II commonly progress to?

Answer 33

Type 3

Question 34

How do you tell the difference between 3rd degree AV Block and AV dissociation?

Answer 34

1) AV dissociation= variable PR with similar atrial and ventricular rates
2) 3rd degree= drastically different rates with atrial going much faster than the ventricles