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Defibrillator therapy plus drug therapy in secondary prevention
The AVID, CIDS, and CASH secondary-prevention trials were designed to test the hypothesis that therapy with an implantable cardioverter–defibrillator was superior to antiarrhythmic-drug therapy. Patients in whom antiarrhythmic-drug therapy was thought to be required were excluded from all three trials. In actual practice, drug therapy is often used in conjunction with a defibrillator. Antiarrhythmic drugs may be needed early after resuscitation to stabilize the patient, or they may be needed to decrease the frequency of shocks, to terminate the arrhythmia along with antitachycardia pacing, or to treat atrial arrhythmias. Pacifico et al. reported that long-term therapy with oral sotalol decreased the need for defibrillator shocks. Because some antiarrhythmic drugs may influence defibrillation thresholds or tachycardia sensing, physicians should be aware of the potential for interactions and should retest the function of the defibrillator when a harmful interaction is liable to occur.
Primary-prevention trials
Even with advances in emergency medical systems, most persons who have an out-of-hospital cardiac arrest do not survive. Clinical trials of antiarrhythmic-drug therapy for the primary prevention of sudden death have had variable results, showing harm, no effect, or an inconsistent benefit. Several clinical trials evaluating the implantable cardioverter– defibrillator for the primary prevention of sudden death have been reported. The first Multicenter Au-tomatic Defibrillator Implantation Trial (MADIT) enrolled 196 subjects with coronary artery disease, spontaneous nonsustained ventricular tachycardia, an ejection fraction of 35 percent or less, and inducible ventricular tachycardia that was not suppressed with the use of intravenous procainamide. The subjects were randomly assigned to therapy with a defibrillator or “conventional” antiarrhythmic therapy, as prescribed by their primary care physicians, and they were followed for a mean of 27 months. There were 15 deaths in the defibrillator group, as com-pared with 39 deaths in the conventional-therapy group, for a relative reduction of 54 percent. Interestingly, the improvement in mortality was reported for all causes of death: arrhythmic and nonarrhythmic cardiac, noncardiac, and unknown. Similar effects on deaths from noncardiac causes have not been seen in other trials.