Figure 5.

Simultaneous recording of unipolar and bipolar electrograms from the same position. A unipolar electrogram is independent on the direction of the activation front and the activation time is at the point of steepest negative dV/dt in the signal. Setup for the bipolar recordings is as indicated in Figure 4. If the activation front comes from the left (A), the bipolar electrogram is mainly negative (as in Figure 4) and the activation time is at peak negative. If the activation front comes from the right (B), the bipolar electrogram inverts and becomes mainly positive. The activation time is now at peak positive. Finally if the activation front is parallel to the line between the poles (C and D), the signal output is virtually zero and an activation time cannot be determined