Shock Strength for the Implantable Defibrillator: Can You Have Too Much of a Good Thing?

In addition to therapeutic effects, most treatment modalities have toxic effects that become more pronounced as the dosage is increased. Choice of the dosage to be administered involves an attempt to maximize therapeutic effects while minimizing toxic effects. Although considered most frequently for drugs, therapeutic and toxic effects also occur for various forms of energy applied to the body, including electrical shocks to halt fibrillation. Until relatively recently, the implanting physician has had only twro choices of dosage for the impiantabie defibriiiator, shock energies of approximately 26 and 30 joules (J). Newer impiantabie defibrillators offer a much wider choice of shock energies, ranging approximately from 0.1 to 40 J. Most considerations about choosing the shock strength for these newer devices have dealt with the therapeutic rather than the toxic effects of the shock. This is appropriate, since the patient will not be alive to experience any toxic effects if the shock is too weak to defibrillate. It is worthwhile to consider the toxic effects of the shocks as well, however, since they can de-

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