The Defibrillation Efficacy of High Frequency Alternating Current Sinusoidal Waveforms in Guinea Pigs

Abstract

There have been few basic studies of alternating current (AC) defibrillation, despite growing interest in the ability of AC to terminate or alter ongoing fibrillation. Based on fibrillation threshold testing, it has been suggested that cardiac tissue is most sensitive to long duration, low strength AC stimulation at around 50 Hz. This has not been directly tested for defibrillation. Two subcutaneous electrodes were placed 40 mm apart on opposing aspects of the guinea pig thorax. Seven seconds were allowed to elapse between fibrillation initiation and defibrillation. The tested waveforms were at 50, 100, 200, 500, and 1000 Hz with 2, 4, 8, 16, and 32-cycles. The efficacy of every waveform was measured using a single stimulus in a large population of animals. Forty-one guinea pigs were used in the fixed energy group. Thirty-three guinea pigs were used in the fixed amplitude group with additional 1-cycle waveforms tested. The 200-Hz and the 2-cycle waveforms were significantly more efficacious than those at other frequencies (P < 0.02) and other durations (P < 0.001). The 50-Hz waveforms were the least successful. Amplitude, not duration or energy, was the determinate of efficacy for 2-cycle (the most efficacious) waveforms. Unlike low strength stimulation, defibrillation strength stimuli are most effective with high frequency (200 Hz) pulses (2 cycles).

Reversible Cardiac Conduction Block and Defibrillation with High-Frequency Electric Field

“…AC has been used in intact guinea pig hearts, demonstrating a frequency-dependent increase in fibrillation induction threshold (19). The defibrillation efficacy in vivo in guinea pig hearts has been evaluated at AC frequencies up to 1 kHz but with a maximum duration of 32 cycles (20). Successful termination of VF in vivo required at least 80 cycles (400-ms duration at 200 Hz) in our study.…”

Effects of high-frequency biphasic shocks on ventricular vulnerability and defibrillation outcomes through synchronized virtual electrode responses

“…Weirich et al [39] applied alternating-current (AC) defibrillation waveforms with frequencies of 30-1000 Hz on guinea pig hearts and demonstrated that the fibrillation threshold increased when high frequencies were applied. One study demonstrated that 200 Hz had a higher defibrillation success rate than 1000 Hz did; however, the study had limited sampling frequencies [40]. High-frequency AC stimulation (1000-2000 Hz) can also inhibit cardiac excitation and generate reversible conduction blocks in cardiomyocytes [41].…”