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Left Bundle Branch Block and Artifact

Tue, 11/25/2014 - 20:24 -- Dawn

This ECG offers several teaching opportunities.  First, it is an example of left bundle branch block (LBBB).  It was obtained from a 53-year-old man who was undergoing a cardiac cath for chest pain.  Unfortunately, we do not have access to his past medical history or the results of his cath.  The ECG criteria for a diagnosis of LBBB are:  1) wide QRS complex; 2) supraventricular rhythm; 3) negative QRS in V1 and positive QRS in V6 and Lead I.  This ECG shows normal sinus rhythm at a rate of 88 bpm and a wide QRS at 158 ms (.158 seconds).  The QRS in V1 is negatively deflected and in V6 and Lead I it is positive.

In LBBB, as with any condition that significantly widens the QRS, there will be ST-T changes.  The ST segment will deviate in the opposite direction of the QRS.  In other words, there will be ST elevation in leads with negative QRS complexes and ST depression in leads with positive QRS complexes.  LBBB causes significant difficulty for those trying to diagnose acute ST elevation using ECG alone.  Excessive ST elevation in a lead where elevation is expected OR ST elevation in a lead where depression is expected should be considered to be abnormal.  At this point, you may find it useful to review Sgarbossa's Criteria regarding determining the presence of acute M.I. in the presence of LBBB.

LBBB can be a serious functonal problem for the patient, as the slow ventricular conduction that causes the wide QRS results in less-than-optimal cardiac output.  This associates LBBB with congestive heart failure, both as a cause of CHF and a result of CHF.  Many people with LBBB and CHF can be helped by cardiac resynchronization therapy - pacing both ventricles synchronously to narrow the QRS and improve cardiac output.  For an excellent article on cardiac pacing in general and CRT (page 2299), go to the 2013 European Society of Cardiology Guidelines as reported by the European Heart Journal, (2013) 34, 2281–2329 doi:10.1093/eurheartj/eht150

Another reason we have featured this particular ECG, is that there is significant artifact in Leads I, III, and aVL.  While this artifact does not prevent us from interpreting this ECG, it is always wise to try to avoid it.  In this case, it was easily remedied by replacing the left arm electrode and preparing the skin beneath the electrode by rubbing it with a dry gauze 4x4.  You will know your students are learning ECG lead concepts if they can figure out on their own which electrode is the culprit in the artifact.  The left arm electrode is the only one shared by these three leads, and Lead II does not use the LA.

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Comments's picture
Nice example of LBBB posted by Dawn this week. I’ll just add a few comments.
  • It is always more difficult to diagnose acute MI in the presence of LBBB. That said - it is not always impossible. Clinically - what is much MORE important than simply whether troponins are elevated enough to satisfy requirements for an “infarct” - is whether the patient in front of you is likely to benefit from acute revascularization. Realize that probably no more than 5-10% (at most! ) of patients with LBBB who present to an acute care facility with chest discomfort end up having acute coronary occlusion that might benefit from revascularization. So while the ECG is disappointing in its sensitivity for picking up LBBBs with positive troponin - it is actually not bad at picking up those few patients who may benefit from acute revascularization.
  • Qualitative ECG signs such as ST elevation where there should be none ( = primary ST elevation) is the best way to identify LBBB patients with acute STEMI - just as it is for patients without LBBB. I discuss this in this pdf on Bundle Branch Block (excerpted from my ECG-2014-ePub) - beginning in Section of 05.24. My point is that even though marked - the ST elevation we see in this tracing is NOT in a lead where ST elevation is unexpected ...
  • Dr. Steve Smith has developed modified Sgarbossa criteria as a way to account for the sometimes large amplitude deflections we see in patients with LBBB. So while the J point in lead V2 shows ~ 8mm of ST elevation - the depth of the S wave in this lead is at least 35mm (if not more). I cite “modified Smith-Sgarbossa criteria” in the above pdf. Since I wrote this ePub - Dr. Smith has revised his criteria based on new findings in his research such that height of J-point ST elevation (8 mm) must now be MORE than 25% depth of the S wave in this lead in order to be “positive”. It does not meet this criterion in this tracing …
  • BOTTOM LINE: The point to remember is that original Sgarbossa criteria failed to account for LBBB tracings with large amplitude. The finding of such deep (>25-30mm) anterior S waves in association with LBBB suggests this patient has LVH. This amount of J-point ST elevation is NOT abnormal given S wave depth. This ECG shows LBBB, probable LVH - but nothing more.
NOTE: For those wanting an ECG video review of ECG criteria for BBB - Please check out my Video on this topic - GO TO - -

Ken Grauer, MD   [email protected] 

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