EKG conduction blocks pt 2 Flashcards
(19 cards)
Define bundle branch block (BBB)
Delay or block of conduction in either right or left bundle branches
What are the characteristics of Right BBB?
RV depole is delayed…does not begin until the LV is depolarized
Wide QRS….> 0.12 sec (3 small boxes)
QRS configuration over RV (ride sided leads; V1 (& V2))
Right BBB: Explain what you’ll see in V1 and V2
1) Normal = small R wave, deep S wave due to electrical dominance of the LV
2) RBBB = RV depolarization delayed: wide QRS and characteristic shape in right leads – V1 & V2
-RBBB see initial R & S waves as LV depoles, then RV begins depole, axis swings back to right and 2nd R wave called R’ (RSR’ or “rabbit ears”) OR just large wide R waves
Left lateral leads (I, aVL, V5/6) over LV – late RV depole causes reciprocal late deep S waves in these leads
What do you normally see in V1 and V2?
Normally small R waves and deep S waves
List some main characteristics of left BBB
1) Left ventricular depole delayed results in:
2) Wide QRS complex > 0.12 sec
3) QRS in leads over LV (I, aVL, V5,6) show characteristic changes
4) QRS in leads over RV will have reciprocal, broad, deep S waves
5) Late LV depole may result in LAD but variable
List some main characteristics of right BBB
1) Wide QRS….> 0.12 sec (3 small boxes)
2) RV depole is delayed (does not begin until the LV is depolarized)
3) Wide QRS and characteristic shape in V1 + V2
4) 2nd R wave called R’ (RSR’ or “rabbit ears”) OR just large wide R waves in V1 V2
5) Left lateral leads (I, aVL, V5/6) over LV – late RV depole causes reciprocal late deep S waves in these leads
What will QRS in leads over LV (I, aVL, V5,6) show in left BBB?
These leads already have tall R wave
LBBB causes marked prolongation in the rise of the R waves – either broad on top or notched (true rabbit ears less common than RBBB)
ST and T wave changes in both kinds of BBB are what?
Abnormality of repolarization in BBB results in depressed ST segments and flipped T waves
ST and T wave changes:
1) Where are they seen in RBBB?
2) What abt LBBB?
1) RBBB – in leads V1-3 (similar to LVH with repole abnormality)
2) LBBB- left lateral leads
What are the significances of RBBs and LBBBs?
RBBB
Pathology of conduction system but also common in o/w normal hearts
LBBB
Almost always reflects pathology – degenerative disease of conduction system or ischemic CAD
True or false: BBB can be intermittent or fixed
True
Explain critical rate with BBBs
1) Ventricles may conduct the electrical impulse at a slow rate
2) Above “critical rate” a BBB develops
-Directly related to time it takes a particular BB to repole
3) If rate too fast, BB can not repole and temporary BBB develops
List the criteria for right and left BBBs
Dx of Myocardial Infarction can be very difficult in presence of ___________
LBBB
Define hemiblock
Conduction delay or block in 1 fascicle of Left bundle
Describe left anterior hemiblocks
1) Anterior fascicle lies superior and lateral to posterior fascicle
2) Conduction blocked down left anterior fascicle
All current runs down left posterior fascicle to apex
Depolarization occurs inferior to superior, right to left = shift of axis
3) Axis is now superior and left = LAD
Tall R waves laterally
Deep S waves inferiorly
Describe left posterior hemiblocks
1) All current run thru Anterior Fascicle
2) LV depoles Superior to inferior & left to right
3) Axis shift to right = RAD
-Taller R waves inferior
-Deeper S waves Laterally
Name a cause of RAD
Chronic lung disease
Combining RBBB with hemiblocks = what?
Bifascicular block
