Conduction disorders

Question 1

Define RBBB

Answer 1

-delay in activation of the RV

-free wall of LV and interventricular septum are depolarised as normal

-we dont treat RBBB

Question 2

What is the criteria for RBBB on an ECG?

Answer 2

RSR’ pattern in V1-3
QRS >/ 0.12s
Q wave in V6
-deep S wave in V1 and 2

Question 3

Why does RBBB have that morphology?

Answer 3

RBB is blocked so impulses have to travel to the left side, the heart depolarises left to right. Impulses are travelling towards V1 which is why we get RSR’ and travels away from V6 so we get a Q wave, conduction continues as normal so R wave is normal .

Question 4

What is the criteria for transient RBBB?

Answer 4

-RSR’ in V1-3
-QRS< 0.12

Question 5

What conditions are associated with RBBB?

Answer 5

-RVH
-rheumatic heart disease
-cardiomyopathies
-IHD
-myocardial damage
-COPD,

Question 6

Define LBBB

Answer 6

-activation of interventricular septum is in the opposite direction to normal - right to left - being initiated from impulse in the RBB

Question 7

What happens during LBBB?

Answer 7

-impulse comes down the right side depolarising the RV as normal, depolarising the LV later and slower

-septal activity of RV depolarises away down the page V1 (QS)

-moves towards V6

Question 8

What is the criteria for Complete LBBB?

Answer 8

• broad R wave in V5,6 I and aVL
  -QRS> / 120ms
  -Dominant S wave in V1
  -Prolonged R wave peak time >60ms in V5-6
  -absent septal q waves in left sided leads
  -deep snd wide S waves in V5 and 6

Question 9

What is the criteria for transient LBBB?

Answer 9

same as complete
-QRS<0.12s

Question 10

What are some causes of LBBB?

Answer 10

-LVH
-myocardial damage
-cardiomyopathy
-CAD

Question 11

What fascicles make up the left bundle?

Answer 11

-anterior/ superior
-inferior/posterior

Question 12

what is the ECG criteria for LAFB?

Answer 12

-LAD -45 to -90
-qR in I and aVL
-rS in II, III, aVF
-prolonged R wave in aVL >45ms
-QRS <120ms

Question 13

What happens in LAFB?

Answer 13

-depolarisation spread fron endocardium to epicardium, inital vetor is directed downwards and right towards inferior leads, small R wave in inferior leads and a small Q wave in I and aVL

-major depolarisation is slightly delayed spreading up and left = tall R waves un left leads
=deep S wave in inferior leads

Question 14

What happens during LPFB?

Answer 14

-activation of the posterior inferior portion of the LV is delayed

Question 15

What do we see on an ECG with LPFB?

Answer 15

-small R waves in aVL and lead I
-non pathological Q waves in II, III and aVF
-rS in high lateral leads
QRS axis +/- 120
QRS duration <120ms

Question 16

How do we modify our axis by 15 degrees?

Answer 16

-go back to our original lead and find out if its more +ve or more -Ve (biphasic)
-also check what leads are either side of the lead perpendicular on the hexaxial reference system, look at the amplitude of the leads and choose which one is higher and move your axis towards that side

-check when its on the border of normal/abnormal

Question 17

Defien trifasicular block

Answer 17

conduction delay in all three fascicles below the AV node (RBBB, LAFB, LPFB) with first degree heart block

Question 18

How do we treat fascicular blocks?

Answer 18

-we dont, we document it

Question 19

pneumonic for LAFB and LPFB

Answer 19

LAFB = ArSI
LPFB = AqRL

Question 20

What is bifascicular block?

Answer 20

-two blocks in bundle branches carrying impulses to the ventricules

Question 21

What are the main patterns seen in an ECG with bifasicular block?

Answer 21

-RBBB + LAFB (more common, due to a single coronary artery supply (LAD) to the anterior fascicle
-RBBB + LPFB (dual blood supply RCx and LCx