An automatic method of determining local activation time (LAT) from at least three multi-channel cardiac electrogram signals including a mapping channel and a plurality of reference channels. The method comprises (a) storing the cardiac channel signals, (b) using the mapping-channel signal and a first reference-channel signal to compute LAT values at a plurality of mapping-channel locations, (c) monitoring the timing stability of the first reference-channel signal, and (d) if the timing stability of the monitored signal falls below a stability standard, using the signal of a second reference channel to determine LAT values. Substantial loss of LAT values is avoided in spite of loss of timing stability.
