bundle branch blocks

Question 1

what is the direction of the electrical current in the ventricles normally

Answer 1

from left (V6 closest) to right (V1), as LV significantly more muscular

Question 2

normally on an ecg, the QRS in V1 is predominately….

Answer 2

negative

Question 3

on a normal ECG the V6 QRS is predominately……

Answer 3

positive

Question 4

characteristics of a RBBB

Answer 4

• wide QRS
• V1, rSR ( small R then big R)
• V1,big negative deflection between the Rs
• V6 or lateral leads, QRS mostly negative, slurred S wave, tall R wave

BOTH LEADS: T wave in the opposite direction of the QRS

Question 5

characteristics of a LBBB

Answer 5

wide QRS, T wave discordance

V1-2,3: negative QRS, slurred long S wave

V6 and lateral leads: large positive QRS with slurred, discordant ST segment

Question 6

how to tell if its a left anterior fascicular block

Answer 6

RBBB with left axis deviation ( QRS positive in I and negative in AVF)

Question 7

how to tell if its a left posterior fascicular block

Answer 7

RBBB with right axis deviation ( negative in I and positive in AVF)

Question 8

causes of RBBB

Answer 8

RVH, pulmonary HTN, ischemic heart disease

Question 9

what perfuses the RBB predominately

Answer 9

the left anterior descending

Question 10

what causes a LBBB

Answer 10

a stemi, aortic stenosis, HTN

Question 11

what predominately perfuses the LBB

Answer 11

LAD and sometimes the RCA

Question 12

why is the QRS slurred in RBBB

Answer 12

RBB blocked, RV will depol after the LV, and it occurs slowly, muscle fibre to muscle fibre, thus a slur that draws it out