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People who recover from cardiac arrest are at risk of suffering a recurrent episode. A subset of this group (60 to 80 percent) exhibits abnormalities in heart function during electrocardiogram (ECG) testing; these patients respond well to medication that alleviates the abnormalities. This improvement appears to prevent recurrence of cardiac arrest. The remaining 20 to 40 percent of patients show no abnormalities during ECG testing; this group is thought to be at a particularly high risk for sudden cardiac death. Seventy-one survivors of a single episode of cardiac arrest were evaluated. During testing, 26 of these patients had no inducible ECG abnormalities, such as ventricular tachycardia (abnormally rapid patterns of contraction of the ventricle). After a 16-month follow-up, 11 of the 26 patients suffered recurrent cardiac arrest, and 10 of these patients died. Analysis of the clinical data pertaining to these patients revealed that several variables were more likely to be associated with recurrent cardiac arrest. Among the 11 patients who suffered a recurrence, 55 percent had dilated cardiomyopathy (a defect in the functioning of the heart muscle), and 64 percent experienced premature ventricular contractions. Twenty-four-hour ambulatory ECG-guided therapy (wearing a portable ECG machine) did not improve the survival rate for these patients. Further studies are needed to determine the optimal treatment strategy for this high-risk group of patients. (Consumer Summary produced by Reliance Medical Information, Inc.)