Long-term incidence of inappropriate shocks in patients with implantable cardioverter defibrillators in clinical practice-an underestimated complication?

Background: Implantable cardioverter defibrillators (ICD) are life-saving device therapy, and patients often carry devices for decades with interim pulse generator exchanges. Inappropriate shocks are associated with impaired quality of life and increased mortality, but available data on their incidence and etiology outside of clinical trials is limited and usually restricted to the lifespan of a singular device. We hypothesized that the incidence in clinical practice is underestimated and aimed this study to retrospectively assess the long-term incidence and etiology of inappropriate shocks in a real-world cohort of patients with multiple ICDs over a long follow-up period.
Methods: Patients with ICDs implanted between 1998 and 2012 in two Swiss cardiology departments and at least one device exchange in the same department thereafter were included in this cohort. Retrospective analysis with follow-up until 2016 was conducted to assess incidence and etiology of inappropriate ICD shocks.
Results: Two hundred forty-nine ICDs were implanted in 100 patients (mean age: 60.1 ± 11.7; 80% male). Over a mean follow-up time of 11.2 (± 3.6) years, 555 shocks occurred in 55 patients. One hundred twenty-three (22%) shocks in 23 (23%) patients were inappropriate. Supraventricular arrhythmia and oversensing were the most frequent causes of inappropriate shock. Patients with younger age or previous supraventricular arrhythmias were at increased risk of inappropriate shocks. Patients with inappropriate shocks during the lifespan of their first ICD were at increased risk for inappropriate shocks in subsequent devices.
Conclusions: Inappropriate shocks are an underestimated and frequent problem in clinical practice with an incidence that may exceed numbers of previously reported clinical trials with shorter follow-up periods. Patients at increased risk for inappropriate shocks need careful evaluation of potential therapeutic optimization strategies including pharmacological treatment, device programming, electrophysiological ablation, device downgrading, and telemonitoring.