ECG IV: Abnormal intraventricular conduction

Question 1

what are the unifascicular blocks?

Answer 1

left unifascicular block

RBBB

Question 2

what are the left unifascicular blocks?

Answer 2

LAFB

LPFB

Question 3

what are the bifascicular blocks?

Answer 3

LBBB
right bundle plus LAFB
right bundle plus LPFB

Question 4

what are the requirements for normal QRS and T waves?

Answer 4

normal RV and LV chamber sizes
normal myocardial perfusion
normal rapid impulse conduction
normal activation sequence (no pre-excitation)

Question 5

what events occur in bundle branch blocks?

Answer 5

one ventricle activates first; other side is activated by impulses spreading from the first
QRS duration is therefore prolonged (wider QRS)

Question 6

what is the resulting QRS appearance in a bundle branch block? why?

Answer 6

resembles a ventricular premature or paced beat

impulse propagation via muscle, not special conduction tissue

Question 7

which bundle branch block has a worse prognosis?

Answer 7

LBBB

Question 8

broad QS in V1 and broad, slurred R wave in V6 is indicative of what condition?

Answer 8

LBBB

Question 9

broad QRS (more than 0.12 s) with an rSR’ pattern in V1 and deep, broad S wave in V6 is indicative of what condition?

Answer 9

RBBB

Question 10

what is seen on the ECG in a LBBB?

Answer 10

broad QS in V1 and broad, slurred R wave in V6

Question 11

what is seen on the ECG in a RBBB?

Answer 11

broad QRS (more than 0.12 s) with an rSR’ pattern in V1 and deep, broad S wave in V6

Question 12

left anterior fascicular blocks (LAFBs) have what characteristics with respect to

axis
lead morphologies
QRS duration
QRS voltage

Answer 12

axis - left, at least -45 degrees (most important)
leads - small Q in I, avL; small R in II, III, avF
QRS duration - NORMAL
QRS voltage - increased

Question 13

left posterior fascicular blocks (LPFBs) have what characteristics with respect to

axis
lead morphologies
QRS duration
QRS voltage

Answer 13

axis - right, usually +120 or more
leads - small R in I, avL; small Q in II, III, avF
QRS duration - NORMAL
QRS voltage - increased

Question 14

is there evidence of RVH in left posterior fascicular blocks?

Answer 14

no

Question 15

left bundle branch blocks (LBBBs) have what characteristics with respect to

QRS duration
lead morphologies

Answer 15

QRS - wide (more than 0.12 s)
V1 - QS or rS complex
V6 - no Q, monophasic R wave
lead I - monophasic R, no Q

Question 16

what is the most common trifascicular block?

Answer 16

RBBB, LAFB, first degree AV block

Question 17

trifascicular blocks require what therapy?

Answer 17

pacemaker

Question 18

do fascicular blocks widen the QRS?

Answer 18

no

Question 19

what are the features of abnormal intraventricular conduction with respect to

duration
amplitude
morphology
vector

Answer 19

duration - widened QRS
amplitude - LBBB increases QRS amplitude, RBBB does not
morphology - BBBs have opposite effects on QRS
vector - LBBB often causes L axis, so does LAFB; LPFB produces R axis, RBBB axis