Therefore, the potential superiority of dual-chamber over single-chamber ICD settings in terms of inappropriate shocks can be assessed only in the light of optimal tachyarrhythmia discrimination algorithms

combined with optimized bradycardia parameters for minimized ventricular pacing (25). The OPTION UMI-77 in vivo (Optimal Anti-Tachycardia Therapy in Implantable Cardioverter-Defibrillator Patients Without Pacing Indications) trial was designed to compare long-term outcomes in ICD recipients with dual-chamber settings with those in patients with single-chamber settings. All patients received atrial leads and dual-chamber devices, the only difference being the pacing mode setting. The programming in both groups was optimized to minimize ventricular pacing and to reduce inappropriate NLG919 shocks using discrimination

algorithms along with standardized antitachycardia pacing (ATP) therapies. The rationale and design of OPTION have been published previously (25). The OPTION trial is a prospective, randomized, multicenter, 2-arm, single-blinded, parallel-group trial. A total of 462 patients were enrolled at 54 centers in Europe and North America between June 2006 and April 2009. Eligible patients were recipients of de novo ICDs for primary or secondary prevention of sudden cardiac death with left ventricular ejection fractions ≤40% despite optimal O-methylated flavonoid tolerated heart failure therapy. Major exclusion criteria were an indication for permanent pacemaker or resynchronization therapy; the diagnosis of hypertrophic obstructive cardiomyopathy or acute myocarditis; history of percutaneous coronary intervention, troponin-positive acute coronary syndrome, myocardial infarction, or coronary artery bypass grafting within the previous month; and permanent atrial tachyarrhythmias or cardioversion of these within the

previous month. The investigational plan was approved by the institutional review board or ethics committee at each study center. All patients provided written informed consent. Before implantation, patients were randomized to either standard single-chamber settings or dual-chamber settings, as described later, according to a 4-block permutation randomization list. Follow-up visits were scheduled at 3 months after implantation and at 6-month intervals thereafter up to 27 months. The primary endpoint of this study was 2-fold: the time to first occurrence of inappropriate ICD shock and the occurrence of all-cause death or cardiovascular hospitalization (including hospitalization for congestive heart failure, symptomatic atrial fibrillation (AF), cardioversion of AF, stroke, and undetected or untreated ventricular tachycardia).