Transcript Chapter 10 – Conduction Defects

AXIS – Chapter 8
• Direction of the current of ventricular depolarization.
• Depolarization of the heart proceeds down and to the left in the Frontal
Plane
• I + AVF + = Normal Quadrant
• I+ AVF - = LAD
• I- AVF - = Extreme LAD
• I- AVF+ = RAD
“Mean Electrical Axis is in the Frontal Plane”
Lead I is zero
Determining AXIS:
1. Determine quadrant by I and AVF
2. Determine lead with most isoelectric QRS complex
3. The axis is perpendicular to the lead with the most isoelectric QRS and falls
in the quadrant previously determined.
I + AVF + = Normal Quadrant
AVL is most biphasic (-30 degrees)
Normal Axis 60 degrees
I + AVF - = LAD
AVR is most biphasic (-150 degrees)
LAD -60 degrees
I + AVF + = Normal
AVF is most biphasic (90 degrees)
Normal Axis 0 degrees
I - AVF + = RAD
AVR is most biphasic (-150 degrees)
Right Axis Deviation 120 degrees
I and AVF are isoelectric
Most of the limb leads are isoelectric, meaning the
mean electrical axis of this patient is not in the frontal
plane, but traveling perpendicular to the frontal plane
Indeterminate Axis
Chapter 10 – Conduction Defects
Right Bundle Branch Block
• Right bundle branch is “cut”.
• May be ischemic or have degenerative changes.
• Septum is activated by fibers that originate from the LBB.
Depolarization occurs from L to R.
• Note normal ECG: R wave for V1 & V2 is small with a large S wave,
whereas V5 & V6 has a large R wave and no “s” wave.
RBBB
For various reason the classical
pattern is not always there.
Wide QRS (>0.12 secs)
rSR’ in V1 & V2
qRs in V5 & V6
However in all cases the R wave
is larger than normal for right
chest leads and the QRS is
wide.
Figure 5.3 CEP Text
Right Bundle Branch Block
RBBB
Right Bundle Branch Block
LBBB
LBBB
• Right BB is normal and LBB is “cut” and will
depolarize slowly. Septal activation is also effected.
• Net Vector of current is toward the Left Ventricle so
there will large R waves in V5 & V6 and Q waves in
V1 & V2.
• LV slower depolarization = wide QRS in the chest
leads.
• Pattern: Wide R (maybe notched) wave in V5 & V6
Wide QS in V1 & V2.
• Incomplete BBB: > 100 ms <120 ms or 2.5-3.0
boxes
Left Bundle Branch Block
Figure 5.2 – Clinical Exercise Physiology Text
LBBB
Rate Related (Exercise Induced) BBB
• The stress of exercise or high heart rate can
cause a BBB due to ischemia or degenerative
changes. STOP THE TEST!
Secondary ST-T changes from BBB
• LBBB
– ST Elevation in V1
– ST Depression/T
wave inversion V6
• RBBB
– ST Depression/T
wave inversion in V1
Intraventricular Conduction Delay
Figure 10.6
Above ECG pattern is neither that of a RBBB or a LBBB.
QRS is abnormally long (>100 ms or 2.5 boxes)
No recognizable characteristics of either block.
Fascicular (Hemi)blocks
“failure of one of the fasicles”
• Fascicle = bundle of nerve fibers
• LBB has 2
• One may function normal
and the other may not.
• Mild increase in QRS duration
but a major axis shift
Left Anterior Fascicular Hemiblock
Axis shifts to LEFT.
Right posterior
functions normally
while left anterior
fails (?)
I+ AVF - = LAD (-60)
AVR most isoelectric
Criteria: Axis shifts to LEFT.
S wave in AVF is deeper than the height of R wave in I
The axis is more negative than 45 degrees and there is a Q
in aVL = abnormal septal activation.
Left Posterior Fascicular Hemiblock
left anterior fascicle
of LBB is normal but
the posterior fascicle
fails.
I- AVF+ = RAD (120)
AVR is most isoelectric
Axis is greater than +120. Rhythm is Afib