Simulation of infarct zone electrograms: determining activation time in unipolar recordings

Isochronal maps of cardiac activation require the accurate identification of a unique activation time. Electrograms from infarct regions may be ambiguous with multiple deflections and temporally overlapping events, e.g., near and far sources. For unipolar recordings, -dV/dt(max) is often used to define the activation time. This concept was tested in the case of overlapping events using real recordings of both local and distant events and by controlling the time of their overlap and their relative amplitudes. Differences in actual activation time and detected activation time were as great as 20 msec in some cases. The primary factor which seemed to determine these differences was the amplitude ratio of the local event and the distant event. Infarct regions exhibit a wide variation in electrogram characteristics and the use of a fixed criterion based upon -dV/dt(max) will not be a reliable approach.<>