Increasing the repetition frequency of electric pulse delivery reduces unpleasant sensations that occur in electrochemotherapy.

Involuntary muscle contractions and painful sensations during electric pulse delivery are the most unpleasant side effects of electrochemotherapy. The aim of this study was to determine the nature of pain caused by the application of electric pulses and to evaluate patients tolerance to the standard electric pulses of 1 Hz repetition frequency and the new 5 kHz protocol. A train of eight electric pulses of 1 Hz and 5 kHz repetition frequencies was delivered to the forearms of 40 healthy volunteers. After the conclusion of each protocol the subjects had to complete the short-form McGill Pain Questionnaire with separate visual analog scales for pain intensity and unpleasantness. All subjects selected at least one superficial and one deep pain descriptor; 85% selected at least two superficial descriptor and 60% at least two deep description. The application of 5 kHz electric pulses was less unpleasant than the standard 1 Hz pulses; however, the pain intensity did not differ between the protocols. Significantly more subjects chose the new 5 kHz protocol as their choice of treatment (P = 0.017). The frequent use of deep descriptors in our study indicates that muscle contractions contribute to the discomfort felt by the subjects during the delivery of electric pulses. The new 5 kHz protocol considerably shortens the treatment session and is also better tolerated. Therefore, the new 5 kHz electrochemotherapy protocol should eventually replace the 1 Hz pulses as new standard.