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 !

  5. Since your interpretation includes myocardial ischenia and infarction of uncertain age, should it be treated as a stemi (immediate cathlab if the patient complains of chest pain), or we should go with the nstemi guideline?
    Many thx

    1. @ Tamas — As always, one needs the clinical history for optimal correlation. That said, there is NO ST elevation here — so this should not be treated as a STEMI ...

    2. Dear Ken, Thx for your answer. I was thinking of whether we should go to the cathlab ASAP if the patient has tight chest, distress etc.
      For example: a patient with symptoms and de Winter's T-waves we should go straight to tha lab, since it is a STEMI-equivalent case.

    3. @ Tamas — There ARE times when acute cardiac cath may be indicated even though the patient is not having a STEMI. Unrelieved chest pain with ischemia as is suggested on this tracing might be one of those indications — but then the reason for cath would be to define the anatomy in a case not responding to medical therapy. That said, I would emphasize my original answer to your question — which is that the tracing above is not suggestive of a stemi; and immediate cath would not be indicated unless there were unusual circumstances (such as persistent pain despite full medical therapy). Hope that answers your question.

    4. Many thx. It was satisfying. Hope you to write this blog for a long time :)