1. Understanding Bundle Branch Blocks4
Understanding
Bundle Branch Blocks
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2. Chapter 4 Objectives Locate the J point on the ECG
Describe the benefits of Lead MCL-1
Describe the properties of the intraventricular conduction system
Using Lead MCL-1 (V1), determine the presence and location of bundle branch block
Describe the hemodynamic and conduction system problems associated with a bundle branch block
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3. Bundle Branch A&P 36 Block of left or right bundle branch
Fascicle of the conduction system
Facilitates syncytium
Bundle branch blocks = ventricles out of sync
Point out that a bundle branch block is an intraventricular block like a hemiblock. But unlike a hemiblock, axis deviation is not a diagnostic feature of a bundle branch block.
BBB is a complete block of the left or right bundle branch.
The bundle branches are fascicles of the electrical conduction system of the ventricles that carry the impulse that causes depolarization to reach all the myocardial cells at once.
This causes the ventricles to depolarize in sync with each other in a property called syncytium. This is necessary for optimum cardiac output. A bundle branch block makes the ventricles contract out of sync.
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4. Pathophysiology of BBB
Caused by ischemia acutely
Can be a result of congenital defects
Can be secondary to hypertension or degenerative heart disease
Some people live with a BBB and the limitations
Emphasize that the bundle branches are made up of “living breathing cells” that need a good blood supply.
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5. What happens in a BBB? Unaffected bundle branch depolarizes normally
Diseased bundle branch does not deliver the impulse to the ventricle
Wave of depolarization is spread from the unaffected side, cell to cell, to the other ventricle
It takes longer to depolarize in this fashion, so the QRS is widened as a result
Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ

6. Unique Pattern Ventricles out of sync37
Unique Pattern
Ventricles out of sync
Right BBB can produce a classic rsR’ (r prime) complex in Lead V1
LBBB can produce a QRS complex
This is to have the student relate to the classic patterns that are sometimes seen with a right and left BBB. Getting them used to it now will serve them well when differentiating wide complex tachycardia later.
RSR’ (r s r-prime) in lead MCL-1 or V1 that is wider than 120 ms is diagnostic of a RBBB.
A true “QRS” complex in MCL-1 or V1 that is wider than 120 ms is diagnostic of a LBBB.
Not all BBB have that classic pattern, but when they do, it is easy to see and diagnose!
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7. Diagnosing BBB Circle the J point Find the terminal deflection37
Diagnosing BBB
Circle the J point
Find the terminal deflection
Shade in an arrowhead pointing up or down
Apply “turn signal” criteria
(Step 1) The J point is where the QRS complex ends and the ST segment begins. In most cases it is easy to find. But in some cases, it may be necessary to measure for the start of the QRS to the end of the QRS duration.
The terminal deflection is where the complex came from right before it touches the J point. This deflection will determine the origin of the bundle branch block using the “turn signal” criteria.
For easy identification, we draw a line with the terminal deflection (step 2).
(Step 3) The arrowhead made by the terminal deflection is then shaded in to easily identify which direction (by arrowhead) the terminal deflection is. This step can be omitted if the students can identify that the terminal deflection is up or down in step 2.
If the terminal deflection points down, then we push our turn signal down which indicates a left turn (which we then call LEFT BBB).
If the terminal deflection points up, then we push the turn signal up, indicating a right turn (which we call a RIGHT BBB).
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8. 38
Example: LBBB
Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ

9. Example: RBBB
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10. Practice Cases Bundle Branch Blocks
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11. 40
Left BBB
QRS width is 135 ms. Negative terminal deflection in Lead V1.
Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ

12. 41
Right BBB
QRS duration is 186 and there is an rsR’ complex in Lead V1.
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13. Incomplete Left BBB
QRS is only 118 ms. There is a negative terminal deflection in Lead V1. This is known as an incomplete LBBB because of the morphology, and the QRS is >110 ms but less than 120 ms.
Note the notch on the R wave in Lead I. Frequently (but not always) a LBBB will look like this in Lead I.
Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ

14. 42
Left BBB
QRS is 136 ms and there is a negative terminal deflection in Lead V1.
Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ

15. Right BBB QRS is 144 ms. Positive terminal deflection in lead V1.
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16. Right BBB 43 Note: rSR’ complex in V1 (diagnostic).
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17. Left BBB
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18. Right BBB 44 Note: rsR’ complex in V1. QRS is 128 ms.
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19. Left BBB
QRS is 152 ms. Negative terminal defection in V1. The notch in Lead I also appears.
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20. Right BBB 45 QRS is 146. Positive terminal deflection in V1.
Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ

21. Left BBB QRS is 144 ms. Negative terminal deflection in V1.
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22. 46
Left BBB
Another clue to LBBB could be a notch in the R wave in Lead I. QRS is 150 ms. Negative terminal deflection in V1.
Page, 12-Lead ECG for Acute and Critical Care Providers © 2006 by Pearson Education, Inc. Upper Saddle River, NJ