Ventricular Conduction Disturbances

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# Ventricular Conduction Disturbances - PowerPoint PPT Presentation

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 -

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Presentation Transcript
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.

2.

3.

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

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
• pulmonary embolism
• after bypass graft surgery
• Permanent or transient
• RBBB by itself requires no treatment
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
• Causes
• long standing hypertension
• valvular lesion
• cardiomyopathy
• coronary artery disease
• Precursor
• Valvular heart disease
• Hypertensive heart disease
• Cardiomyopathy
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

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
• 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