24 bb bs

12-Lead Electrocardiographya comprehensive course

Adam Thompson, EMT-P, A.S.

Bundle

Branch

Blocks

Bundle Branches

Bundle Branch Blocks

• Right Bundle Branch Block (RBBB)– The single right fascicle is blocked.

• Left Bundle Branch Block (LBBB)– Both left fascicles are blocked.

• Non-Specific Intraventricular conduction delay (IVCD)– BBB that doesn’t meet RBBB or LBBB criteria.


• May mimic an MI• The side that is blocked conducts last and

takes longer.


• Normal conduction without a block. 1

32

2

3

4

Mean vector

Cardiac vector


• With a RBBB, the right fascicle is blocked, so the left ventricle is conducted first and then the impulse returns to the right.

1

2

3


• With a LBBB, the right ventricle is conducted first, and the impulse travels back to the left.

1

2

3


V1


J-Points

The J-point is the exact point where the QRS ends

V1


V1


= RBBB

= LBBB

V1

V1


V1

RBBB

LBBB

Right Bundle Branch Block

• RBBB morphologies

V1


• To properly differentiate between bundle branch blocks, you must also assess leads I and V6.

• A slurred S-wave in leads I and V6 indicate a RBBB.


I & V6


aVR V4

II aVL V2 V5

III aVF V3

V1

V6

I


Slurred S-Wave I & V6


+

+

+ A B A

B

Mean vector moves towards positive electrode = positive QRSMean vector moves away from positive electrode = negative QRSMean vector is perpendicular to positive electrode = equiphasic QRS


1

2

3

I & V6+

Left Bundle Branch Block

• Duration greater than 0.12 sec• Broad monomorphic R-wave in I & V6• Terminal S-wave in V1.


V1


aVR V4

II aVL V2 V5

III aVF V3

I

V6

I V1

Intraventricular Conduction Delay

• A Non-specific IVCD is less common than a RBBB or LBBB

• They are wide, atrial rhythms that usually look like a left or right BBB in V1, but do not match the criteria in I & V6.

Non-Specific IVCD

aVR V4

II aVL V2 V5

III aVF V3

II V1

V6

Non-Specific IVCD

BBB Chart

RBBB LBBB IVCD

V1 TERMINAL R-WAVE

TERMINAL S-WAVE

TERMINAL R/S-WAVE

I & V6 TERMINALS-WAVE

TERMINAL R-WAVE

Anything is possible

24 bb bs

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