Inappropriate Implantable Cardioverter-Defibrillator Shocks: Incidence, Predictors, and Impact on Mortality

Study Questions:

What are the prognostic implications of inappropriate implantable cardioverter-defibrillator (ICD) shocks?


This was a retrospective review of 1,544 patients (mean age 61 years) who received an ICD for the primary or secondary prevention of sudden death at a single institution in 1996-2006. Stored electrograms were reviewed every 3-6 months during a mean follow-up of 41 months. The causes of inappropriate ICD shocks were categorized as supraventricular tachycardia, sinus tachycardia, or abnormal sensing.


The cumulative rate of inappropriate shocks was 7% at 1 year, 13% at 3 years, and 18% at 5 years. The strongest independent predictors of inappropriate shocks were history of atrial fibrillation (hazard ratio [HR], 2.0) and age <70 years (HR, 1.8). The majority (76%) of inappropriate shocks were triggered by supraventricular tachycardia. A first inappropriate shock was associated with a 60% higher risk of mortality. Subsequent inappropriate shocks were associated with additional 40% increases in the risk of death, up to a 3.7-fold higher mortality risk after five inappropriate shocks.


Inappropriate shocks are associated with a significantly higher mortality rate in ICD recipients.


In large-scale clinical trials such as MADIT II and SCD-HeFT, inappropriate ICD shocks were shown to be associated with a higher mortality rate. The present study demonstrates that this is also the case in community practice. Although ICD shocks, whether appropriate or inappropriate, can cause myocardial injury, it is unlikely that a single shock causes enough injury to account for a 60% increase in risk of death. More likely, inappropriate shocks are a marker of comorbidities (e.g., atrial fibrillation) that are associated with a higher mortality rate.

Clinical Topics: Arrhythmias and Clinical EP, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias

Keywords: Incidence, Tachycardia, Supraventricular, Follow-Up Studies, Death, Sudden, Cardiac, Defibrillators, Implantable

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