In neurophysiologic intraoperative monitoring, double train transcranial electrical stimulation (dt-TES) for motor evoked potentials (MEP) consists of an initial, facilitating train of stimuli followed by a second, testing, train. The optimal number of pulses per train has not been determined. The authors wanted to determine the optimal combination of pulses per train that produced the highest MEP amplitude.
Dt-TES of 4 + 4, 2 + 7, and 7 + 2 pulses were attempted in 20 patients and compared with single train TES of nine pulses. Latencies of the MEP responses were also compared. Additionally, statistical comparisons were made of the differences between the amplitude and latency measurements within the patients.
The mean age of the patients was 44.3 years (range, 9–84 years). Dt-TES of 2 + 7 pulses resulted in significantly higher mean amplitudes than dt-TES of 4 + 4 and 7 + 2 pulses and single train TES of nine pulses (p < 0.001). The MEP latency with dt-TES of 2 + 7 pulses was longer than the latencies of single train TES of nine pulses and dt-TES of 4 + 4 and 7 + 2 pulses.
Asymmetric dt-TES with 2 + 7 pulses improved MEP amplitudes. This type of stimulation may be preferable to single train TES and dt-TES with symmetric pulse trains.