Relationship of BBB Patterns to PVCs and Paced Beats

Now that you understand why the QRS is prolonged to 0.12 s or greater in BBB, you can also understand why PVCs are always 0.12 s or greater. It is, again, because the ventricles are being activated by the slow process of muscle-to-muscle conduction, rather than being rapidly depolarized through the Purkinje system.

You can also now understand that we can frequently determine the general location from which a PVC is arising by looking at its pattern in the precordial leads. A PVC arising in the left ventricle will produce a vector slowly spreading to the right ventricle, and will, thus, produce a pattern similar to the pattern of RBBB (Figure 7.14).

On the other hand, a wave of depolarization arising from a PVC in the right ventricle will slowly spread toward the left ventricle, simulating the pattern of LBBB (Figure 7.15).

Figure 7.15. Premature ventricular contraction arising from the right ventricle, producing a LBBB pattern.

Figure 7.15. Premature ventricular contraction arising from the right ventricle, producing a LBBB pattern.

Figure 7.16. Paced beats from a pacemaker that is placed, as usual, in the apex of the right ventricle, producing a LBBB pattern.

Exactly the same phenomenon occurs when a pacemaker fires from the apex of the right ventricle. Electrocardiographically, it produces a similar pattern to a PVC arising from the right ventricle. Pacemakers that are properly placed in the right ventricle therefore produce a LBBB pattern (Figure 7.16).

Was this article helpful?

0 0

Post a comment