ECG Interpretation Review - #3 (BBB, Wide QRS, BBB with ST Changes, Ischemia, RBBB vs LBBB)

QUESTION: Interpret the 12-lead ECG below.

• What type of conduction defect is present?
• Are ST-T waves doing what you'd expect given the presence of this conduction defect?
• Clinically - What else may be going on?

Figure 1: What type of conducton defect is present?

INTERPRETATION:  The rhythm is sinus. The rate is slow (~50-55/minute) - with slight irregularity making this sinus bradycardia and arrhythmia. The PR interval is normal. The QRS is obviously long.  Recognition of QRS widening at this point is indication to STOP - and figure out WHY the QRS is wide before going on:

• Assessment of QRS Widening:  - The 3 KEY leads to assess in order to determine the reason for QRS widening are leads I, V1, and V6.  Right-sided Lead V1 shows an rSR' complex (with a taller right rabbit ear).  Left-sided Leads I and V6 both have a relatively wide terminal S wave (albeit the S in lead I is modest in size).  QRS morphology is therefore consistent with complete RBBB = Right Bundle Branch Block (Figure 2).

Figure 2 - Typical Morphology for RBBB.

Returning to Our Systematic Approach: The QT interval is less relevant in the setting of BBB (BBB by itself may prolong the QT). Regarding Axis - there is no hemiblock (Other than the presence or absence of associated left anterior or posterior hemiblock - the concept of axis means little in the setting of BBB).  There is no chamber enlargement.

• Q-R-S-T Changes - There are some relatively larger-than-expected Q waves in the lateral leads (I,V5,V6 - and especially aVL) - which could reflect infarction of uncertain age.  The tall R wave in lead V1 is from RBBB. An important finding in Figure 1 is that ST-T waves are not as one would expect for simple BBB (Figure 3).

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KEY Rule - Normally when there is typical RBBB or LBBB - the ST segment and T wave should be oriented opposite to the last QRS deflection in the 3 KEY leads (arrows in Figure 3). Deviation from this pattern in any of the 3 KEY leads (I, V1 or V6) is abnormal - and indicates a primary ST-T wave change (suggesting ischemia or infarction may be occurring).  

Figure 3 - ST-T Wave Changes Expected with BBB.
Note - The above KEY Rule for ST-T wave direction works only for RBBB and LBBB (but not for IVCD).

• In Figure 1 - One would expect ST-T waves to be opposite to the last QRS deflection in the KEY leads (ie, negative in V1 - and upright in I,V6).  Instead - there is ST flattening in leads I and V1, and a negative T wave in lead V6.  Deep, symmetric T wave inversion in leads V2 thru V6 is also clearly more than what one should see with simple RBBB.

CLINICAL IMPRESSION:  We interpret this ECG as showing sinus bradycardia and arrhythmia with complete RBBB and primary ST-T wave changes.  In addition - there are Q waves in multiple leads with a clearly deeper-than-expected Q wave in lead aVL. We worry about infarction/ischemia in addition to RBBB, which could be recent or even acute. Clinical correlation is urged.

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   - See also ECG Blog Review #11 - and Review #13 -
   - For more on BBB please see our ECG Video on BBB BASICS -
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