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The concept of VF threshold is one familiar to basic
scientists. In controlled animal experiments, it is possible to deliver ever-increasing
amounts of energy until the point of ventricular fibrillation eg1.
Such would be unethical in man. With the advent of ICDs2,
it has become necessary to provoke ventricular fibrillation in man but this is done in a
relatively expedient manner rather than as a stepwise energy delivery3-5.
VF threshold is an engaging notion. It could describe an individual's vulnerability to
the potentially fatal arrhythmia. Prognostic indices have been developed in the belief
that they might reflect VF threshold. The reality is that probably few do. It would seem
intuitive that ventricular antiarrhythmic drugs, ought to raise an individual's threshold
for fibrillation. Drugs have some useful effects but with exception of betablockers and
amiodarone6-8, there is very little evidence they
effect the threshold for VF.
Surprisingly, there has not been as much interest in this area as its importance might
suggest. Perhaps it is too difficult to determine the threshold, or perhaps the threshold
is so variable as to render any single assessment meaningless..
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