BBBs ST Segments and T Waves

You will note that in all of the examples of BBB that you have seen so far, the ST segments and T waves appear abnormal. Along with the abnormalities of depolarization in BBB come abnormalities of repolarization. Thus, it is characteristic of BBB that the T waves are usually inscribed in the opposite direction from the terminal portion of the QRS. This is because, as you learned earlier, it is the terminal portion of the QRS that reflects the large, slow, abnormal vector of muscle-to-muscle depolarization that is characteristic of BBB.

Note that also the ST segments are typically slurred into the inverted T waves. These ST and T wave changes are called secondary changes because they occur as the result of the intraventricular conduction delay rather than as a primary reflection of some other myocardial abnormality.

Figure 7.8 compares typical RBBB with LBBB. Note that RBBB displays the upright "M" on the right side of the precordial leads (Vi), and LBBB displays the upright "M" on the left side. Thus,if you simply remember right on the right and left on the left, you can easily distinguish between the two. Note also that the two are very easy to distinguish in lead V1 alone. Right BBB in V1 is upright and M-shaped, and LBBB in lead V1 is quite the opposite, with a deep QS.

Figure 7.8. Comparison chart of RBBB and LBBB as seen in leads V, and V6.

Summary of Findings in BBB

Figure 7.8 compares typical RBBB with LBBB. Note that RBBB displays the upright "M" on the right side of the precordial leads (Vi), and LBBB displays the upright "M" on the left side. Thus,if you simply remember right on the right and left on the left, you can easily distinguish between the two. Note also that the two are very easy to distinguish in lead V1 alone. Right BBB in V1 is upright and M-shaped, and LBBB in lead V1 is quite the opposite, with a deep QS.

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