Study type: Medical/biological study (experimental study)

Frequency dependence of the cardiac threshold to alternating current between 10 Hz and 160 Hz med./bio.

By: Malkin RA, de Jongh Curry A
Published in: Med Biol Eng Comput 2003; 41 (6): 640-645
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Aim of study (acc. to author)

To examine what criteria influence the ability of alternating current to induce ventricular fibrillation in vivo.

Background/further details

Two theoretical models of stimulation threshold according to the literature were tested. One model has assumed that the mechanisms underlying alternating current stimulation of nerves are at work for ventricular fibrillation induction (bowl-shaped relationship of cardiac threshold and frequency). In a RC-like model the cardiac alternating current stimulation threshold is also frequency dependent, suggesting that some unarticulated mechanism is at work for ventricular fibrillation. 12 dogs and 20 guinea pigs were stimulated with square waves and sine waves at 10, 20, 40, 80 and 160 Hz. The stimulus frequencies were delivered in random order and stimulus strengths were increased until ventricular fibrillation was induced.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 10–160 Hz
Exposure duration: 5 s
  • guinea pigs: I = 25 µA - 3000 µA in steps of 25 µA, 50 µA or 100 µA
  • dogs: I = 20 µA - 1000 µA in steps of 20 µA, 50 µA or 100 µA
Exposure 2: 10–160 Hz
Exposure duration: 5 s
  • guinea pigs: I = 25 µA - 3000 µA in steps of 25 µA, 50 µA or 100 µA
  • dogs: I = 20 µA - 1000 µA in steps of 20 µA, 50 µA or 100 µA
Exposure 3: 10–160 Hz
Modulation type: pulsed
Exposure duration: 5 s
  • guinea pigs: I = 25 µA - 3000 µA in steps of 25 µA, 50 µA or 100 µA
  • dogs: I = 20 µA - 1000 µA in steps of 20 µA, 50 µA or 100 µA

Exposure 1

Main characteristics
Frequency 10–160 Hz
Type
Waveform
  • rectangular
Exposure duration 5 s
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
cf. remarks - - - - guinea pigs: I = 25 µA - 3000 µA in steps of 25 µA, 50 µA or 100 µA
cf. remarks - - - - dogs: I = 20 µA - 1000 µA in steps of 20 µA, 50 µA or 100 µA
Additional parameter details

for the guinea pigs: I = 25 µA - 500 µA in steps of 25 µA, I = 500 µA - 1000 µA in 50 µA steps, I = 1000 µA - 3000 µA in 100 µA steps
for the dogs: I = 20 µA - 200 µA in 20 µA steps, I = 200 µA - 500 µA in 50 µA steps, I = 500 µA - 1000 µA in 100 µ

Exposure 2

Main characteristics
Frequency 10–160 Hz
Type
Waveform
Exposure duration 5 s
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
cf. remarks - - - - guinea pigs: I = 25 µA - 3000 µA in steps of 25 µA, 50 µA or 100 µA
cf. remarks - - - - dogs: I = 20 µA - 1000 µA in steps of 20 µA, 50 µA or 100 µA
Additional parameter details

for the guinea pigs: I = 25 µA - 500 µA in steps of 25 µA, I = 500 µA - 1000 µA in 50 µA steps, I = 1000 µA - 3000 µA in 100 µA steps
for the dogs: I = 20 µA - 200 µA in 20 µA steps, I = 200 µA - 500 µA in 50 µA steps, I = 500 µA - 1000 µA in 100 µ

Exposure 3

Main characteristics
Frequency 10–160 Hz
Type
Waveform
Exposure duration 5 s
Modulation
Modulation type pulsed
Pulse width 1 ms
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
cf. remarks - - - - guinea pigs: I = 25 µA - 3000 µA in steps of 25 µA, 50 µA or 100 µA
cf. remarks - - - - dogs: I = 20 µA - 1000 µA in steps of 20 µA, 50 µA or 100 µA
Additional parameter details

for the guinea pigs: I = 25 µA - 500 µA in steps of 25 µA, I = 500 µA - 1000 µA in 50 µA steps, I = 1000 µA - 3000 µA in 100 µA steps
for the dogs: I = 20 µA - 200 µA in 20 µA steps, I = 200 µA - 500 µA in 50 µA steps, I = 500 µA - 1000 µA in 100 µ

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • before exposure
  • during exposure

Main outcome of study (acc. to author)

It was found that, for square wave and sine wave stimulation in both dogs and guinea pigs, the stimulation treshold increased monotonically with frequency from 10 Hz to 160 Hz. Between 80 Hz and 160 Hz, the alternating current stimulation threshold doubled, exactly as predicted by an RC-model.
It was concluded that the alternating current stimulation threshold is not bowl-shaped and is best understood with an RC model. As the ventricular fibrillation treshold does exhibit a bowl-shape with frequency, as opposed to the stimulation threshold which does not, the ventricular fibrillation induction frequency dependence must have different origins.

Study character:

Study funded by

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