LBBB

This is a great ECG for teaching your students about some of the different causes of wide QRS.  This 89 year old man has a sinus rhythm that is around 100 bpm, and his QRS is widened at 148 ms (.148 sec).  Leads I and V6 are positive, and Lead V1 is negative, meeting the criteria for left bundle branch block. There is a left axis deviation, which is common with LBBB, although it is not always this pronounced, indicating that there is possibly another cause for LAD.  In this ECG, there are also PVCs and probable fusion beats.  The 14th beat is a PVC.  Complexes 1, 6, and 9 are possibly fusion beats. Fusion can be described as an almost simultaneous sinus beat and ventricular beat.  The depolarization waves, one coming from the top of the heart and one coming from the bottom, meet and "fuse" on the ECG.  Fusion beats will have some characteristics of the supraventricular beats and some of the ventricular beats.  They are not significant except that fusion can be said to "prove" the existence of a ventricular pacemaker - either a natural pacemaker or an electronic one.

Do you see anything else interesting in this ECG?  How would YOU describe this rhythm?

This interesting and instructive ECG was contributed by Jason Roediger, ECG Guru Extraordinaire, and one of the experts featured on our '"Ask the Experts" page. It is an excellent example of acute inferior wall M.I. with left bundle branch block. Left bundle branch block normally displays ST elevation and depression in a "negative concordance" pattern. That is, when the QRS complex is negative, we may expect ST elevation. When the QRS is positive, ST depression is seen. In this ECG, there is clearly ST elevation in Leads II, III, and aVF, and the ST segments have a distinct coved upward appearance. This shape signals to the experienced ECG interpreter that there is an acute injury.

Unfortunately, the normal deviations of the ST segment seen in left bundle branch block can make diagnosis of acute M.I. difficult. For a good example of a left BBB without acute M.I., please refer to the ECG archives on this site. Often, students are taught that it is IMPOSSIBLE to see an acute M.I. in the presence of LBBB. This is not true, as this ECG clearly illustrates. See the March 4, 2012 blog post on the ECG Guru regarding this topic.

 This wide complex tachycardia has an initial rate of 129/min. It is difficult to discern if P waves are present, although the ECG machine does give us a PR interval. The ECG meets most of the criteria for left bundle branch block: wide QRS, negative QRS in V1, positive QRS in Lead I and V6. However, it is difficult to say for certain that this is a supraventricular rhythm. Later, however, the patient's rate slowed (see top strip), revealing P waves. When the rate slowed, the left bundle branch block pattern remained. That helps confirm the original interpretation of left bundle branch block. Interestingly, the BBB is not rate-related, in that it is still present at the slower rate.
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