Thursday, January 6, 2011

ECG Interpretation Review #13 (BBB, Wide QRS, Is this LBBB vs RBBB vs IVCD)

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QUESTION: Interpret the 12-lead ECG below.
  • What type of conduction defect is present?  - Is this LBBB?
  • Clinically - Is anything else going on?  (Has there been anterior infarction?)
Figure 1 (ECG reproduced from our Expanded ECG pdf File - Case A-12, pg 134)
Note - Enlarge by clicking on Figures -
INTERPRETATION:  The rhythm is regular with the exception of the 4th beat which is early (See Lead II Rhythm Strip at bottom of tracing).  Upright P waves are present in lead II with a fixed PR interval. Thus, the rhythm is sinus at a rate of 75/minute with a PAC (Premature Atrial Contraction)The PR interval is approximately one large box (or at most a tad more) 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.  Practically speaking - IF the QRS complex is wide and the rhythm is supraventricular (ie, not wide due to ventricular tachycardia or WPW) - then there are 3 possibilities: 1) Typical RBBB; 2) Typical LBBB; or 3) IVCD (Figure 2).
Figure 2 - Assessment of QRS Widening - for which there are 3 possibilities.
(ECG reproduced from ECG PB book - pg 21)
  • Figure 2 in ECG Review #3 showed the expected morphology for typical RBBBRight Bundle Branch Block (an rSR' complex in right-sided lead V1 - and wide terminal S waves in left-sided leads I and V6). Clearly, Figure 1 above does not manifest the morphology of RBBB.
  • Figure 2 in ECG Review #11 showed expected morphology for typical LBBBLeft Bundle Branch Block (upright, monophasic QRS in left-sided leads I and V6 - and a predominantly negative QRS in right-sided lead V1). Although QRS morphology in Figure 1 above is consistent with LBBB in lead V1 - it is clearly not consistent with it in either I or V6. 
  • By the process of elimination - the conduction defect in Figure 1 above is IVCD (IntraVentricular Conduction Delay).
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TECHNICAL NOTE: If you right-click on the above links for tracings from ECG Reviews #3 and 11 - you can open these figures in a New Window!
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About IVCD: The ECG appearance of IVCD is difficult to characterize.  This is because IVCD is often the end result of a number of different pathophysiologic processes - rather than reflecting a discrete defect in the conduction system (as usually occurs with RBBB or LBBB).  Examples of conditions that may lead to IVCD include myocardial infarction; cardiomyopathy with ventricular fibrosis; chamber enlargement; and/or any combination of these (with or without a component of bundle branch block).  Thus, many patients with IVCD have at least some type of underlying heart disease. The "beauty" of the above algorithm (Figure 2) - is that it greatly simplifies the diagnosis of conduction defects.  IVCD is present IF:
  • The QRS complex is wide (ie, at least 0.11 second).
  • Neither typical RBBB nor typical LBBB is present.
Figure 3 - Schematic example of IVCD. QRS morphology is not typical for  either RBBB or LBBB.
(ECG reproduced from ECG PB book - pg 24)
Thus, in Figure 3 - the rsR' pattern in V1 and the wide terminal S wave in lead I are both consistent with RBBB.  However, the notched, upright complex in lead V6 is clearly not consistent with RBBB (but rather with LBBB).  Since typical morphology for either RBBB or LBBB is not present in all 3 of the KEY leads (leads I,V1,V6) in Figure 3 - the reason for QRS widening must be IVCD . . .
    Returning to Our Systematic Approach: The QT interval is difficult to interpret and less relevant in the setting of conduction defects such as IVCD. The axis in Figure 1 is indeterminate (negative QRS in leads I and aVF). That said - the concept of axis is elusive with IVCD, and there is really no need to comment on it in this setting. 
    • Chamber Enlargement - None that we can call (given the presence of IVCD).
    • Q-R-S-T Changes - Nonspecific changes (Nothing more can be said given IVCD).
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    Note - In Figure 3 of ECG Review #11 - we illustrated a KEY rule for assessment of ST-T wave changes with typical RBBB or LBBB (that the ST segment and T wave should be oppositely directed to the last QRS deflection in the 3 key leads).  This rule does not work for IVCD. With rare exceptions - it is extremely difficult to assess ST-T wave changes for ischemia or infarction in the setting of IVCD.
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    CLINICAL IMPRESSION:  Our final interpretation of the ECG in this case (Figure 1) is as follows: "NSR. Occasional PAC. IVCD. Non-specific ST-T wave changes. Suggest clinical correlation."
    •  Despite the deep QS complexes in leads V1,V2,V3 of this tracing - one cannot call prior anterior infarction because there is IVCD
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       - See also ECG Blog Review #3 - and Review #11 - 
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