Transcript Ventricular Conduction Disturbances

Ventricular Conduction Disturbances
Chapter 7
Bundle Branches
• Normal conduction speed through the bundles is about 0.1 seconds
Bundle Branch Block
• Consider a blocked or slowed branch or bundle
Right
Left
Right Bundle Branch Block
First Phase will
be normal
Second Phase Normal
Third Phase ?
After the left ventricle has completely depolarized, the right ventricle continues to depolarize
Right Bundle Branch Block
1.
1. r wave in V1
q wave in V6
2. S wave in V1
R wave in V6
3. R’ wave in V1
S wave in V6
2.
3.
Right Bundle Branch Block Criteria
• V1 or V2 = rSR’ - “M” or rabbit ear shape
• V5 or V6 = qRS
• Large R waves
• Right chest leads: T wave inversion (“secondary
changes” since they reflect a delay in depolarization
not an actual change in depolarization).
• Complete RBBB: QRS > 0.12 sec.
• Incomplete RBBB: QRS = 0.10 to 0.12 sec.
Right Bundle Branch Block
V1 = rSR’
V6 = qRS
Right Bundle Branch Block
V2 = rSR’
V6 = qRS
Right Bundle Branch Block
• Clinical Significance
• Healthy heart
• Organic heart disease
• atrial septal defect
• pulmonary disease
• valvular lesions
• degenerative changes in conduction system
• chronic coronary artery disease
Left Bundle Branch Block
• RBBB affects mainly the terminal
phase of depolarization
• LBBB affects the early and
terminal phases of depolarization
• Septum is depolarized from
right to left (rather than left to
right)
• Depolarization of the left
ventricle takes longer
Left Bundle Branch Block
1. r wave in V1
R wave in V6
2. S wave in V1
R wave in V6
Left Bundle Branch Block
• Loss of septal R in V1 and
septal Q in V6.
• Wide QRS
• Negative in V1
• Positive in V6
Left Bundle Branch Block Criteria
• Wide QRS complex
• V1 = QS (or rS) and may have a “W” shape to it.
• V6 = R or notched R showing a “M” shape or rabbit ears
• Secondary T wave inversion
• Secondary if in lead with tall R waves
• Primary if in right precordial leads
Left Bundle Branch Block
RBBB versus LBBB
?
?
Left Bundle Branch Block
• Causes
• long standing hypertension
• valvular lesion
• cardiomyopathy
• coronary artery disease
• Precursor
1. Advanced CAD
Rate-Related (Exercise-Induced) Bundle Branch
Blocks
• Ischemia or other factors during exercise may produce BBB not seen at rest
• Rate-limited bundle branch block
• Exercise induced bundle branch block
Incomplete Bundle Branch Blocks
• RBBB or LBBB where QRS is between .10 and .12 with same QRS features
• Incomplete RBBB normal variant
• Incomplete LBBB a progression of LVH
Intraventricular Delay or Intraventricular
Conduction Defect
General term
for wide QRS
complexes
that are not
typical of
RBBB or
LBBB
Pacemaker Pattern
Pacemaker Patterns
Trifascicular Conduction System
Tri-fascicular Conduction System
• Right bundle
• Left anterior (superior) fascicle
• Left posterior (inferior) fascicle
• Fascicular block (or hemiblock) = a
block in either the LAF or LPF.
Fascicular Blocks
• Fascicular blocks only slightly prolongs the QRS.
• Fascicular blocks cause axis deviation as do infarcts and hypertrophy.
• Left or right axis deviation without signs of infarct or hypertrophy are fascicular
blocks.
Left Anterior Fascicular Block
• Limb leads
• QRS less width less than 0.12 sec.
• QRS axis = Left axis deviation (-45° or more)
• if S wave in aVF is greater than R wave in lead I
• small Q wave in lead I, aVL, or V6
Left Posterior Fascicular Block
• Right axis deviation (QRS axis +120° or more)
• S wave in lead I and a Q wave in lead III (S1Q3)
• Rare
Bifascicular Block
• Two of the three fascicles are blocked.
• Most common is RBBB with left anterior fascicular block.
Summary
• The last component of the QRS vector will be shifted in the direction of the last
part of the ventricles to be depolarized.
• In other words, the major QRS vector shifts toward the regions of the heart
that are most delayed in being stimulated.
• RBBB: late QRS forces point toward the right ventricle (Rabbit ears, M shape
in V1)
• LBBB: late QRS forces point toward the left ventricle (negative in V1 and R or
notched R in V6)
• LAFB: late QRS forces point in a leftward and superior direction (LAD with
deep S wave in aVF ).
Hypertrophy In The Presence of Bundle Branch
Block
• RVH and RBBB
• RAD is typically seen; also look for RAE and its peaked P waves.
• RBBB with RAD indicates RVH is likely present, too.
• LVH and RBB
• usual criteria can be used but also look for LAE