Nerve conduction studies: orthodromic vs antidromic latencies.

Variables known to affect the sensory nerve action potential (SNAP) include the method of measuring the SNAP, electrode placement and local impedance, volume conduction, temperature, age, nerve fiber composition, and duration dependent phase cancellation. There is debate, however, concerning the effect of orthodromic vs antidromic stimulation on the latency of the SNAP. This question was studied with the same methodology of those who reported a difference between antidromic and orthodromic latencies, but with control of the interelectrode distance. Twenty-five normal hands were studied. The median and ulnar digital nerves were analyzed both orthodromically and antidromically. There was careful control of interelectrode distance, which was the same for both the recording and stimulating electrodes. Studies were done with both a 3-cm and 4-cm interelectrode distance. Parameters recorded were onset latency, peak latency, terminal latency, and amplitude (baseline to negative peak, and peak to peak). Extensive statistical analysis was performed for all parameters. No differences were found between antidromic and orthodromic studies when the interelectrode distance was the same.