Friday, December 31, 2010

ECG Interpretation Review #11 (BBB, Wide QRS, ST Changes with BBB, LBBB vs RBBB, LVH)

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? (Is there LVH? - evidence of infarct?)
Figure 1 (ECG reproduced from our Expanded ECG pdf File)
Note - Enlarge by clicking on Figures -
INTERPRETATION:  The rhythm is regular at a rate just over 100/minute.  This qualifies the rhythm as sinus tachycardia at 102/minute. The PR interval is normal (ie, not more than a large box in duration). 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 any further:
  • 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.  We look first at left-sided Leads I and V6 - which both show a wide monophasic R wave (albeit with slight slurring on the downslope in lead I).  Right-sided Lead V1 shows an entirely negative QS complex.  QRS morphology is therefore consistent with complete LBBB = Left Bundle Branch Block (See Figure 2 and LBBB Criteria below).
Figure 2 - Typical Morphology for LBBB.
(ECG reproduced from ECG-2014-ePub )
Criteria for LBBB (illustrated above in Figure 2):
  • QRS widening to at least 0.12 second (whereas complete RBBB can occur with a slightly lesser degree of QRS widening = 0.11 second!).
  • An upright (monophasic) QRS in leads I and V6 that may (or may not) be notched.  But there should not be any q wave in either lead I or lead V6!
  • A predominantly negative QRS in lead V1.  There may (or may not) be an initial small r wave in lead V1 (lead V1 may show either a QS or rS complex).
Returning to Our Systematic Approach: The QT interval is less relevant in the setting of BBB (BBB by itself may prolong the QT). The axis is normal (close to 0 degrees) - albeit the concept of axis usually means little in the setting of BBB.  
  • Chamber Enlargement - There is probable LVH (See Impression below).
  • Q-R-S-T Changes - There appears to be a Q wave in lead III.  Otherwise - typical secondary ST-T wave changes are seen, consistent with the conduction defect (See KEY Rule and Figure 3 below).
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 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.
(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 - ST-T waves are as expected for typical LBBB (ie, opposite to the last QRS deflection in each of the 3 KEY leads).  Note that even the dramatic T wave peaking (with ST elevation) in anterior precordial leads of Figure 1 is as expected for LBBB. Lateral ST depression seen here is also not ischemic, but rather typical for LBBB. 
CLINICAL IMPRESSION:  We interpret this ECG as showing sinus tachycardia with complete LBBB - but no acute changes. Clinical correlation (and comparison with prior tracings) is needed to determine the significance of these changes, and whether they are new.
  •  It is always more difficult (but not necessarily impossible) to assess for ischemia and infarction when there is LBBB.  Two important clues we routinely look for in this assessment are: i) the presence of typical secondary ST-T wave changes of BBB (See KEY Rule and Figure 3) - and ii) that no Q wave is seen in any lateral lead (there should be a monophasic R wave but no q wave with uncomplicated LBBB - as is seen in leads I, aVL, and V6 of Figure 1). The Q wave in lead III and the QS in lead V1 of Figure 1 are not indicative of infarction given the presence of BBB.
  • Finally - It is also more difficult to assess for ventricular enlargement in the setting of LBBB. That said - the statistics are that many (if not most) patients with LBBB also have significant underlying heart diseasae (longstanding hypertension, heart failure, cardiomyopathy, coronary artery disease). By dint of their disease - many of these patients also have LVH (Left Ventricular Hypertrophy). The chance of true chamber enlargement with LBBB is extremely high (approaching 90%) - IF one finds very deep S waves (>25-30 mm) in leads V1, V2, or V3 and/or IF one finds LAA (Left Atrial Abnormality) in addition to LBBB. Given the appearance of Lead V2 in Figure 1 - we suspect there is probable LVH in this patient with complete LBBB.
   - See also ECG Blog Review #3 - and Review #13 - 
   - Please check out our ECG Video on Basics of Bundle Branch Block (


  1. Prof. Grauer,
    First of all,
    I would like to express you my profound gratitude,
    for all this educational –essential material, that you provide to all of us, free, via your Blog.

    Something that I observed on the ECG-strip of the Figure 1 :

    In lead-I, beside the characteristic Monophasic wide “R-wave” of the LBBB,
    we could observe an “upright deflection”,
    which could be considered as a “positive” “T-wave” (…)
    So, a “T-wave” deflection NON-opposite compared to its “R-wave” => a sign of Ischemia…??

    Thank you so much, in advance, for your attention.

    My best and cordial wishes for the “emerging” New Year!!

    With appreciation,
    Anastasio (Greece)

  2. Thanks for your comment & kind words Anastasio! You are correct that technically the T wave in lead I looks to be biphasic (initially negative-then positive) - which strictly speaking is not completely "typical" (ie, oppositely directed from the last QRS deflection). That said - I chose not to comment on this (nor to factor it in as "suspicious") because in the absence of other clearly primary ST-T wave changes - I think the specificity of this subtle-but-real biphasic T wave in lead I is poor for indicating ischemia ... In general - I prefer to undercall ST-T wave changes with BBB unless they are clearly abnormal (and very likely to predictive acute occlusion/ischemia).

    More on this on the web page I made on the Basics of BBB (GO TO: ) - with specifics in the PDF on "Dx of MI with BBB" that appears on this web page for free download.

    THANKS again for your comment!