Factors determining the susceptibility of the isolated guinea pig heart to ventricular fibrillation induced by sinusoidal alternating current at frequencies from 1 to 1000 Hz

Abstract

We determined the threshold for ventricular fibrillation by means of sinusoidal alternating current (AC) from 1 to 1000 Hz on isolated perfused guinea pig hearts. Current was applied via electrodes located in the aorta and at the apex of the heart. The duration of current flow was kept constant at 1 s. Electrical activity was recorded with epicardial electrodes attached to the ventricles. Additional experiments were performed in isolated papillary muscles with intracellular microelectrodes. The fibrillation threshold, expressed as peak-to-peak current strength, attains a minimum at about 30 Hz and rises by a factor of 5 at 1 Hz, and by a factor of 14 at 1000 Hz. In the frequency range from 30 to 1000 Hz the rise of the fibrillation threshold can be attributed to the increase of the threshold for stimulation due to the progressive shortening of the AC periods. Thus no change of the fibrillation threshold occurs if DC pulses of constant duration are used in the same range of frequencies. Below 30 Hz there is only a slight increase of the threshold for stimulation, which cannot entirely account for the rise of the threshold for fibrillation. A likely cause of the reduced susceptibility of the heart to fibrillation at the lower frequencies is the reduced number of extrasystoles preceding the onset of fibrillation, which results in a less pronounced state of inhomogeneous excitability.

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

“…1,2 Fibrillation threshold testing shows that cardiac tissue is most sensitive to long duration, 11 sinusoidal stimulation at around 30-60 Hz. [3][4][5] The data from the present study are quite contradictory showing that (1) duration and energy have little impact on efficacy for polyphasic waveforms and (2) the optimal frequency is much higher, around 200 Hz.…”

“…However, fundamental data, like the sensitivity to parameters (magnitude and frequency), remain largely lacking. Fibrillation threshold testing 3,4 suggests that cardiac tissue is most sensitive to sinusoidal stimulation between 30 and 60 Hz. These data also suggest that increased stimulus duration increases efficacy, 5 in contrast to defibrillation studies that suggest that truncation improves efficacy 6 .…”

Frequency dependence of the cardiac threshold to alternating current between 10 Hz and 160 Hz

“…403-440, a=0.9, b=0.8) to AC sinusoidal stimulation studies of perception (ANDERSON et al, 1957) and muscle tetanus (DALZIEL, 1972). For cardiac AC sinusoidal stimulation, the Reilly equation adequately fits (REILLY, 1998) the VF threshold from dogs (KUGELBERG, 1976) and guinea pigs (WEIRICH et al, 1983).…”

“…The use of corrected and combined data for the VF graphs may have introduced some changes in the graphs' shapes. Had we presented uncombined, uncorrected data, the graphs would have been more cluttered, and our conclusions would not have changed as the uncorrected and uncombined data are also bowlshaped (see VIGMOND et al, 2001 ;HOFFMEISTER, 2001 andWEIRICH et al, 1983 for examples). However, combining electrode sizes for both VF and EFFECT data sets may be misleading.…”

Opinion of the Scientific Panel on Animal Health and Welfare (AHAW) on a request from the Commission related to welfare aspects of the main systems of stunning and killing the main commercial species of animals

“…Cardiac ventricular fibrillation threshold testing in experimental models suggests that cardiac tissue is most sensitive to stimulation between 30 and 60 Hz of sine wave alternating current and increased stimulus duration increases efficiency (Weirich et al, 1983). However, successful induction of cardiac ventricular fibrillation would depend upon the delivery of sufficient electrical current to the myocardium.…”