Of the 1902 patients enrolled in the ADVANCE III trial , 477 received a defibrillator for secondary prevention ; 248 patients were randomly assigned to a long detection setting ( 30 of 40 intervals ) and 229 to the nominal setting ( 18 of 24 intervals ) for ventricular arrhythmias with cycle length 320 ms. Eight-five percent of patients were men , with a mean age of 65 12 years , a previous history of ventricular fibrillation in 37 % of the cases , and a mean ejection fraction of 38 13 % .