Friday, December 17, 2010

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 (ECG reproduced from ECG-2014-ePub )
- Note - Enlarge by clicking on Figures -


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.
(ECG reproduced from ECG-2014-ePub )
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).
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 3ST-T Wave Changes Expected with BBB.
(ECG reproduced from ECG-2014-ePub )
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.
   - See also ECG Blog Review #11 - and Review #13 -
   - For more on BBB please see our ECG Video on BBB BASICS -


  1. hi doctor
    the Q wave in avl is suspected to be ischemic not a normal variant according to the overwhelmingly positive QRS in avl ?

  2. Thank you for your comment Lot Ben. As stated - the Q in lead aVL is clearly much deeper-than-expected! There are other deeper than expected Q waves on this tracing (in leads I, V5,V6) - and in the context of clearly abnormal T inversion for RBBB - I am highly suspicious of infarction of uncertain age in lateral lead areas. Note also the subtle-but-real ST coving in lead aVL.

    There is some semantics in terminology - but rather than "ischemia" - I say the abnormal Q in aVL suggests infarction of uncertain age. This certainly could be recent given all of the T wave changes we see. Hope that explains your question.

  3. Your interpretation is excellent !

  4. Your interpretation is excellent !