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Stored data are shown from an episode of ventricular tachycardia after successful therapy in a 22-year-old woman with recurrent ventricular tachycardia. From top to bottom, the tracings represent electrograms from the atrial, ventricular, and shock leads and from an annotated marker channel. Ventricular activity (arrow) initiates the tachycardia, and a change occurs in the QRS complex on the shock-lead electrogram. The initial beat after the arrow is a fusion complex, which is followed by a wider complex during the rest of the episode. The first break in the rhythm strip denotes that criteria for the detection of tachycardia in the ventricular-fibrillation zone have been met. The ventricular tachycardia, with 1:1 retrograde conduction, continues. The second break corresponds to the delivery of a 21-J shock (not shown in the printout). After the shock, there are a few beats of a different ventricular rhythm that gradually slows and breaks. This phenomenon is frequently observed after a shock. By the end of the strip, sinus rhythm is restored.
The greatest benefit of implantable cardioverter–defibrillators occurs among patients with advanced heart disease. In both the AVID trial and the meta-analysis,26 little advantage over drug therapy was seen in subjects with an ejection fraction that was greater than 35 percent. According to Sheldon et al.,28 when the CIDS population was stratified according to age, ejection fraction, and functional status, defibrillator therapy was shown to improve survival primarily for patients in the quartile at highest risk. Patients with arrhythmias that were thought to be due to a transient or reversible cause were excluded from the AVID trial, but they continued to be at high risk,29 presumably either because the transient cause was likely to explain a recurrence or because the patients had an underlying chronic instability. In the absence of any contraindication, such patients may therefore be considered candidates for treatment with an implantable defibrillator.
Electrophysiological studies performed after resuscitation were not significant predictors of re-current arrhythmias during follow-up among the subjects in either the AVID trial 30 or CASH. 21 Patients in whom clusters of shocks were delivered in a brief time — reflecting a phenomenon sometimes termed an electrical storm — have an increased risk of death in the next several months, but not of sudden death, even if, as is usually the case, they survive the acute episode.31 Defibrillator therapy and anti-arrhythmic-drug treatment had similar effects on the quality of life among the subjects in the AVID trial and CIDS, with a reduced quality of life associated with sporadic shocks in the defibrillator groups. The use of bet-adrenergic blocking drugs is associated with improved survival even among patients receiving amiodarone.