Understanding Outcomes With the EMBLEM™ S-ICD in Primary Prevention Patients With Low Ejection Fraction

Implantable cardioverter defibrillator (ICD) therapy is highly effective for reducing mortality in patients with clinical markers for elevated risk for ventricular arrhythmias. However, inappropriate shocks and unnecessary appropriate shocks remain an important side effect that can significantly affect an ICD recipient's quality of life and may be deleterious to the myocardium. The MADIT RIT study demonstrated that the incidence of inappropriate and unnecessary appropriate ICD therapy can be reduced in primary prevention patients through two different programming strategies: 1) High Rate Zone Cutoff, i.e., raising the lowest rate detection cutoff to 200 bpm; and 2) Delayed Therapy Initiation, i.e., increasing the time to therapy initiation to 60 seconds for arrhythmias detected between 170-199 bpm and 12.5 seconds between 200-249 bpm. Both strategies effectively reduced the amount of ICD therapy delivered when compared to conventional programming, where the lowest rate detection cutoff was 170 bpm and the delay to therapy initiation was programmed to 2.5 seconds. Importantly, neither treatment arm was associated with significantly increased syncope or mortality. The results of MADIT RIT established preferred device settings for reducing shocks in transvenous ICD (TV-ICD) patients with a primary prevention indication. Preferred settings for subcutaneous ICDs, however, have not been established with data from prospective studies. The UNTOUCHED study will test a programming scheme designed to minimize inappropriate and unnecessary shocks in patients who have an indication for primary prevention of sudden cardiac death and low ejection fraction. Although S-ICD programming options do not permit exact replication of the programmed settings previously shown to reduce shocks in the MADIT RIT treatment arms, key elements are combined into the UNTOUCHED settings to be tested in this protocol. It is hypothesized that despite the lack of anti-tachycardia pacing, the EMBLEM S-ICD settings utilized in this study will result in an overall shock incidence similar to that observed in ICD patients from MADIT RIT.