What is the rate of inappropriate shocks from implantable cardioverter-defibrillators (ICDs)?

Updated: Oct 11, 2019
  • Author: Daniel M Beyerbach, MD, PhD; Chief Editor: Jeffrey N Rottman, MD  more...
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One of the risks of ICD implant is that of inappropriate ICD shocks. An inappropriate ICD shock is one that is not precipitated by accurate detection of a malignant ventricular arrhythmia, ventricular tachycardia (VT), or ventricular fibrillation (VF). [50] Typically, inappropriate ICD shocks result when atrial arrhythmias, such as atrial fibrillation, atrial tachycardia, or atrial flutter, accelerate the ventricular rate beyond the set limit for delivery of ICD shock therapy.

However, inappropriate shocks may also result from sinus tachycardia, supraventricular tachycardia (SVT), illicit drug use (as with cocaine and methamphetamine), and ventricular oversensing. Ventricular oversensing may occur due to T-wave oversensing, electromagnetic interference (EMI), a loose setscrew in the ICD header, or ICD lead fracture.

Analysis of the MADIT II trial data revealed that 11.5% of the ICD patients received inappropriate ICD shocks and that 31.2% of all ICD shocks were deemed inappropriate. Inappropriate ICD shocks were attributed to atrial fibrillation (44%), supraventricular tachycardia (36%), and abnormal sensing (20%). Patients with inappropriate shocks had greater all-cause mortality. [51]

Drug therapy with hydroxymethylglutaryl-coenzyme A reductase inhibitors, or so-called statins, has been shown to reduce, by more than half, the frequency of inappropriate ICD shocks secondary to occurrence of atrial fibrillation and atrial flutter. [52]  However, this finding has not been reproduced in other studies.

There is some indirect evidence that the incidence of inappropriate shocks may be lower in patients with dual-chamber devices compared with patients who receive single-chamber devices. [53]

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