Pain caused by internal cardiac defibrillation has been associated with increased patient morbidity and the technique’s lack of acceptance for atrial defibrillation. Several methods of pain reduction have been proposed including prepulse inhibition and reduced-amplitude defibrillation waveforms. In this work, the relative analgesic efficacies of prepulse and reduced-voltage waveforms were compared to the conventional truncated exponential biphasic waveform (TE). A highly adaptable arbitrary waveform defibrillator was developed to deliver the desired novel waveforms both internally to the heart and to the skin.

Four human research studies were performed to evaluate the waveforms. Three studies delivered shocks through internal defibrillation leads to the heart and were performed on conscious volunteers. Pain was reported using a Visual Analog Scale (VAS), oral pain score, and independent observer of muscle contraction. A fourth study involved cutaneous shocks of equivalent energy delivered to the forearm of volunteers. Pain was assessed using only the VAS. Startle response, or eye-blink evoked from the shock, was also recorded to assess the effect of prepulse inhibition on pain.

Results showed that peak waveform voltage was the primary contributor to pain. Reduction in waveform voltage had the largest effect on perceived pain, whereas waveform energy and shape did not affect pain. A specific reduced-voltage waveform, the “plateau” waveform, resulted in a pain threshold shift of more than 2.3 times. Specifically, a plateau waveform with 2.3 times the energy of a TE waveform produced the same pain. The addition of prepulses, at the amplitude, duration and delay studied, did not significantly reduce pain for either internal defibrillation or cutaneous shocks. Prepulses did not further reduce pain when combined with the plateau waveform, even though prepulse inhibition occurred, as shown by a reduction in startle response. This work also showed that the results from a cutaneous shock-waveform study are directly comparable to internal cardiac shocks, producing similar pain reductions and threshold shifts.