EXAM#1: CONDUCTION DEFECTS Flashcards
How many fasicles does the RBB have?
1x
How many fasicles does the LBB have?
2x
- Anterior fasicle
- Posterior fasicle
What are the three unifasicular blocks?
RBBB
LAFB
LPFB
What are the three bifasicular blocks?
LBBB
RBBB + LAFB/LPFB
What is happening in a BBB?
One ventricle activates before the other (b/c conduction is blocked)
What is the indication of a BBB?
Wide QRS (0.12 sec of wider)
What lead should you evaluate a BBB in?
V1; use the “turn signal method”
What are the classic findings for a LBBB?
- Borad QS in V1
- Slurred R-wave in V6
*Note that this is associated with a poor prognosis
What are the classic findings of a RBBB?
- rSR’ in V1
- Borad S-wave in V6
What does the broad S-wave in V6 indicate in a RBBB?
Depolarization traveling away from lead V6
What are the criteria for a LAFB?
1) Left axis (down in I, up in II and III)
2) Normal QRS duration
What degree is required for the LAD in LAFB?
-45 degrees
What is more common LAFB or LPFB? Why?
LAFB b/c the LPF has DUAL blood supply
How do you differentiate between LPFB and RVH with RAD?
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
What is the classic bifasicular block? How does this differ from a LAFB alone?
RBBB + LAFB
- Wide QRS (0.12sec) with “up turn signal” in V1
Is a LBBB uni or bifasciular?
Bifasicular
What are the criteria for a LBBB?
V1 with wide QRS and “down turn signal”
What is the difference between a trifasicular block and complete AV block?
Trifasicular= RBBB + LAFB + 1st degree AV BLOCK
Complete= block of all fasicles
What is the definition of a 1st degree AV block?
PR interval greater than 0.2 sec (5 small boxes)
Is a first degree AV block related to IHD?
No
What is the definition of a 2nd degree AV block?
Not all atrial impulses reach the ventricles
Where does a Type I 2nd degree AV block occur?
AV node
Note that there is a longer than normal refractory period in the AV junction
Where does a Tpye II 2nd degree AV block occur?
Purkinje system
List the etiologies of a 2nd degree AV block.
1) Vagotonia
2) Acute inferior MI
3) Drugs
4) Aortic valve disease
What is the definition of a Type I 2nd degree AV Block?
PR interval that progressively lengthens until AV conduction is lost
*Longest cycle is less than twice the length of the shortest cycle
What almost always precedes a Type II 2nd degree AV block?
Bundle Branch Block
What is the definition of a Type II 2nd degree AV block?
Dropped ventricular conduction without lengthening of the PR interval
What is an alternative name for a 3rd degree AV block?
Trifasicular block
What is the definition of a 3rd degree AV block?
No atrial impulses are reaching the ventricles
*Clinical outomce depends on ventricular escape rhythm.
How will a 3rd degree AV block appear on ECG?
Independent atrial and ventricular rhythms
What is AV dissociation?
Presence of independent atrial and ventricular rhythms
*This is not a block–the atrial and ventricular rhythms will be very similar
What are the etiologies of AV dissociation?
1) Acceleration subsidiary pacing site
2) Decreased sinus automaticity
3) Re-entrant ventricular tachycardia
What will a 2nd degree AV block Type II commonly progress to?
Type 3
How do you tell the difference between 3rd degree AV Block and AV dissociation?
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
