Inappropriate shocks in a patient with a subcutaneous implantable cardioverter-defibrillator

The subcutaneous implantable cardioverter-defibrillator (ICD) is becoming more widespread. Approved by the Food and Drug Administration for use in the United Stated in 2012, the subcutaneous ICD is now being implanted for primary and secondary prevention of sudden cardiac death among individuals meeting conventional ICD implantation criteria but who do not have an indication for cardiac resynchronization therapy or permanent bradycardia pacing, a preexisting unipolar pacemaker, or recurrent ventricular tachycardia that responds to antitachycardia pacing. Although it is becoming more evident that the subcutaneous ICD is particularly desirable in patients with venous access issues like those with end-stage renal disease on hemodialysis and in patients at an increased risk of infection, more data on this therapy are needed, especially in relation to longterm outcomes and how those outcomes compare with those of transvenous ICDs. Among the clinically important outcomes are inappropriate ICD shocks. In the pivotal randomized clinical trials of the transvenous ICD, the rate of inappropriate shocks was up to 25%. This rate is concerning, given the mounting evidence that shocks—both appropriate and inappropriate—are associated with increased mortality and worse quality of life. The rate of inappropriate shocks from a subcutaneous ICD is up to 13%, and the most common causes include oversensing as well supraventricular tachycardia.