4 left bundle branch block (lbbb) – Welch Allyn Means ECG Physicians Manual for CP Series Electrocardiographs - User Manual User Manual
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MEANS Physicians Manual
Welch Allyn
11
2.4 Left Bundle Branch Block (LBBB)
The primary condition for the diagnosis of a complete block is prolonged QRS duration. In the
program the limit is 130 ms. The normal initial QRS activity to the right and anterior is smaller
than normal or absent. Soon after the beginning of QRS the electrical forces turn posteriorly,
and somewhat to the left and mostly horizontally. The predominantly posterior activity
produces generally deep S waves in V1 and V2 while the R waves in V5 and V6 tend to
remain low. Therefore, the program requires r waves in V1 and V2 to be minor (they even
may be lacking, and in V5 and V6 q’s must be reciprocally absent). This is expressed by the
requirement of a net negative area and R/S ratio of less than 1/3 in V1. The R waves in V5
and V6 will have a delayed intrinsicoid deflection. Septal infarction should not be diagnosed in
the presence of LBBB. Finally, if LBBB and WPW both come into consideration the case is
decided by the duration of the PR interval.
Skip tests
if:
Q wave in any of I, V5, V6
or
QRS duration
130 ms
Say:
“LBBB”
if:
QRS area in V1 <
100 mVms
and
S amplitude in V6
1000 µV
or
100
QRS area in V1 <
40 mVms
and
negative QRS amplitude > 3 times positive QRS amplitude in V1
and
QRS area > 0 in V6
and
intrinsicoid deflection at
50 ms in V5 or V6
Say:
“possible LBBB”
if:
QRS area in V1 <
100 mVms
and
S amplitude in V6 > 1000 µV
or
100
QRS area in V1 <
40 mVms
and
negative QRS amplitude > 3 times positive QRS amplitude in V1
and
QRS area > 0 in V6
and
intrinsicoid deflection at < 50 ms in V5 and V6
or
QRS area
0 in V6
and
intrinsicoid deflection at
50 ms in V5 or V6
if:
test LBBB passed
and
test WPW passed
and
QRS area in V1
5 mVms
and
0
QRS axis
90
then:
Say:
“possible LBBB”
“possible WPW”
if:
PR interval > 140 ms
suppress:
“LBBB”
if:
PR interval
140 ms