RBBB (Right Bundle Branch Block) & Primary T-wave Changes

Please answer the following 3 ECG Interpretation Quiz questions before beginning this case study. Answers will follow at the bottom of this blog post (Questions referenced from Page 14 of the Interactive 12-lead ECG Workbook).

ECG Quiz Question #1: True or False: The requirement |QRS| > or = 0.12 sec is common to both RBBB & LBBB?

A. True

B. False

ECG Quiz Question #2: In a case of RBBB (Right Bundle Branch Block), Lead I is ____ with a broad terminal S-wave.

A. Inverted

B. Upright

C. Flat

D. Biphasic

ECG Quiz Question #3: In an otherwise normal case of LBBB & RBBB, if the terminal portion of the QRS complex is positive, the T-wave will be inverted. This is described as ________ T-wave changes.

A. Primary T-wave Changes (or Concordance of the T-waves)

B. Secondary T-wave Changes (or Discordance of the T-waves)

C. Tertiary T-wave Changes (or Accordion Effect of the T-waves)

ECG Case Study: We will analyze the following 12-lead ECG of a 65-year-old male who presents with chest pain and is cold, clammy & diaphoretic with an O2 saturation of 97%.

RBBB Dr Stanleys ECG Courses Blog Image — *Interpretation @ End of Blog Post*

This month’s blog post contains:

Development of the pattern of The Right Bundle Branch Block (RBBB)
The focus will be on two ECG Leads: Lead V1 and Lead I
Primary versus Secondary T-wave Changes

Examining RBBB From Lead V1

Determine the time of the depolarization wavefront
Determine the direction of the depolarization wavefront
Make a judgement of the magnitude of the depolarization wavefront

These three determinations (time, direction, magnitude) will predict the resultant waveform. For Illustrations of the Conduction System of the RBBB (Right Bundle Branch Block | and LBBB):

Diagram #38: The Right Bundle Branch Block (RBBB) Electrical Waves from Lead V1

Please take note of the time sequence of depolarization of the ventricles as follows:

1^stthe Septum is depolarized.
2^ndthe Left Ventricle is depolarized.
3^rdthe Right Ventricle is depolarized.

Electrical wavefront Color Coded Lead V1 for RBBB ECG

Next notice the direction of these wavefronts for presentation of Depolarization Wave of Septum and the Left Ventricle

Examining RBBB from ECG Lead I

Now let us develop the waveshape of Lead I associated with the RBBB (Right Bundle Branch Block). Using the same approach as for Lead V_1,we will conclude the following: (you are again reminded to concentrate on three aspects of the depolarization wavefronts: direction, timeframe and magnitude, from the perspective of Lead I).

1^st……The initial deflection will be downward and rightward ——- Septum
2^nd…..The next deflection will be downward and leftward ——– Left Ventricle
3^rd……The next deflection will be downward and rightward —- Right Ventricle

This resultant ECG waveform from the “viewpoint” Lead I is shown schematically below. (The color coding is the same as for Lead V_1.)Remember that the vector representation of Lead I is leftward. Therefore, an electrical signal traveling leftward [the Left Ventricle (colored green) in this situation] will result in a positive deflection on the ECG.

Diagram #41: Predicted Biphasic Waveshape of Lead I in RBBB (Right Bundle Branch Block)

Please observe that this QRS complex has a negative and a positive component, mathematically described as biphasic. Regarding Lead I, our conclusion is as follows: “Lead I is biphasic with a broad terminal S-wave.”

Triad Criteria for the Classic RBBB (Right Bundle Branch Block):

1. QRS Complex Duration = 0.12 sec. (or exceeds)

2. Lead I is biphasic with a broad terminal S-Wave

3. Lead V₁V₂ V₃RSR’ (sometimes only small notch, “rabbit ears” or slur)

Primary (Concordance) & Secondary (Discordance) T-wave Changes

If you find an LBBB (Left Bundle Branch Block) or RBBB (Right Bundle Branch Block), you must further analyze all the T-Waves to categorize them as either Primary or Secondary.

If Primary T-Waves are found, this is consistent with ischemia.

If you find an LBBB, look for Primary and Secondary T’s. (If primary T-wave changes are present, consider myocardial ischemia.)
If you find an RBBB, look for Primary and Secondary T’s. (Analyze all the Leads looking for ST-Elevation, ST-Depression, T-Wave Peaking and Significant Q’s that might suggest acute ischemia or infarction.)

ECG Concordance (Primary T-waves) and Discordance (Secondary) of the T-waves Illustration

PEARL: One of the greatest booby traps of electrocardiography is the LBBB. The ST-Elevations, T-wave peaking and significant Q-waves are usually due to the distortion caused by the LBBB conduction i.e. these are usually pseudoinfarction patterns. An exception to this conclusion holds if primary T-waves are present. (When evaluating the Acute Coronary Syndrome (ACS) patient, look for the Modified Sgarbossa Criteria to diagnose the STEMI – aka ST Elevation Myocardial Infarction.)

NOTE: Occasionally you will encounter a cardiogram that demonstrates a widened QRS > 0.10 seconds but otherwise does not meet the classic criteria of the LBBB or RBBB. In order to acknowledge this finding, we label the cardiogram as an IntraVentricular Conduction Delay (IVCD). This is a convenient label to demonstrate that the electrocardiographer recognized the widening of the QRS complex and also that it did not fit the classic criteria pattern of the RBBB or LBBB.

Sometimes it is appropriate to label the tracing as an atypical LBBB or atypical RBBB.

12-lead ECG Showing RBBB with Primary T-waves Stanleys ECG Course

In the above 12-lead ECG, you will notice that 12-lead ECG Leads II, III & avF exhibit very subtle Primary T-wave changes (aka Concordance of the QRS & T–wave). Although soft in presentation on this ECG, this patient was found to have elevated cardiac markers, was diagnosed with an ST Elevation MI (Inferior STEMI) and was sent to the nearest catheterization lab for treatment. As with all cases, it is recommended that in addition to routine labs, serial ECGs, CXR and serial cardiac markers, comparison with an old ECG should be done when possible as well as consultation with the cardiologist. (ECG Case Presentation Referenced from Page 128 of the 12-lead ECG Workbook)

INTERPRETATION of Above Tracing:

High Voltage Lead avL (probably pseudo due to LAFB – Left Anterior Fascicular Block)
RBBB (Right Bundle Branch Block) with Primary (Discordance of) T-wave changes
LAFB (“Left Anterior Fascicular Block” | Bifascicular Block when seen with RBBB)
ST-elevations (coving) II, III, avF (suspicious of Acute Inferior MI | STEMI)

ECG Quiz Question #1: True or False: The requirement |QRS| > or = 0.12 sec is common to both RBBB & LBBB?

A. True

B. False

ECG Quiz Question #2: In a case of RBBB (Right Bundle Branch Block), Lead I is ____ with a broad terminal S-wave.

A. Inverted

B. Upright

C. Flat

D. Biphasic

A. Primary

B. Secondary

C. Tertiary

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