Eligibility of Pacemaker Patients for Subcutaneous Implantable Cardioverter Defibrillators

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The subcutaneous implantable cardioverter defibrillator (S‐ICD) has been approved for prevention of sudden cardiac death in patients who are deemed high risk for ventricular arrhythmias.1 Previous studies have shown that the S‐ICD has similar efficacy for treating ventricular arrhythmias compared to transvenous ICDs (TV‐ICDs).2 While the S‐ICD may be advantageous in that it does not involve implantation of intravascular or intracardiac hardware, it still can be associated with a 13% rate of inappropriate shocks in 3 years based on the IDE Study and EFFORTLESS Registry.2 The majority of these are due to T‐wave oversensing (TWO), which has been reduced by implementation of a screening 3‐lead electrocardiogram. However, 7–15% of patients do not fulfill screening criteria for the S‐ICD based on their intrinsic QRS/T‐wave morphology.3
Occasionally, pacemaker‐dependent patients will subsequently develop an indication for an ICD. In such a scenario, although options for upgrade include implantation of additional transvenous ICD lead with or without extracting the existing pacing lead, such an approach may not be possible or desirable due to central venous obstruction or patient preference. The addition of an S‐ICD to an existing transvenous pacing device may be another option. Conversely, some patients that have an existing S‐ICD may develop a pacing indication and the feasibility of adding a pacing system and the impact of ventricular pacing on S‐ICD candidacy based on the screening template is unknown.
The purpose of this study was to determine the proportion of patients who qualify for an S‐ICD based on the screening tool in the presence of ventricular pacing.
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