By Ken Grauer, MD

Professor Emeritus in Family Medicine, College of Medicine, University of Florida

Dr. Grauer reports no financial relationships relevant to this field of study.

Try to interpret the ECG in the figure below without the benefit of any clinical information. What do you see? Is there bundle branch block (BBB)?

This is a challenging tracing in several respects. In addition to a large amount of artifact and baseline wander, there is obvious change in QRS morphology in certain leads. However, there is hardly any difference in QRS appearance in the long lead rhythm strip at the bottom of the tracing.

It is helpful to begin by determining the underlying rhythm. The upright P wave that appears with a constant PR interval in front of virtually all beats in the long lead II rhythm strip confirms a sinus mechanism.

The clue to what is happening in this tracing lies in lead V1. There are four beats in this lead. The first and fourth complexes in lead V1 are narrow with a negative QRS. The second and third complexes begin with a similar-looking negative deflection, but terminate with a tall and wide R wave. This picture of terminal delay in conduction visible for the second and third complexes in lead V1 is characteristic of right BBB (RBBB). The other characteristic ECG finding for the terminal right-sided delay seen with RBBB is the presence of a wide terminal S wave in lateral leads. This is seen for the first three beats in lead I, as well as for the second and third beats in lead aVL. In contrast, the fourth beat in lead I and the first beat in lead aVL are conducted normally, without any terminal widening (i.e., without any S wave).

The underlying rhythm in this tracing is sinus. There is intermittent RBBB conduction, which is evident in some leads, but not at all obvious in the long lead II rhythm strip.

A subtle advanced point about this tracing is that although the ST-T waves of normally conducted sinus beats (i.e., beats 4, 5, 8, 11, 12, and 13) look unremarkable, there appears to be inappropriate ST segment coving in the two RBBB-conducted beats in leads V2 and V3. Further, the J-point of the ST segment for the three beats conducted with RBBB in lead I is elevated. The patient had positive troponin values.

For more information about and further discussion of this case, please click here.

ECG Review