Review Article |

Implantable Cardioverter-Defibrillator Shocks:  Epidemiology, Outcomes, and Therapeutic Approaches

Ryan T. Borne, MD; Paul D. Varosy, MD; Frederick A. Masoudi, MD, MSPH
JAMA Intern Med. 2013;173(10):859-865. doi:10.1001/jamainternmed.2013.428.
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Importance Implantable cardioverter-defibrillators (ICDs) have revolutionized the approach to the prevention of sudden cardiac death and are commonly used in a wide range of high-risk patients, including the large population of patients with severe left ventricular systolic dysfunction. The benefit of these devices derives from their therapies, including both antitachycardia pacing and high-energy shocks. However, although these therapies may be life saving, devices can also deliver inappropriate shocks.

Objective To review ICD therapies (shocks and antitachycardia pacing), their effects on health outcomes, and current methods to reduce these therapies.

Evidence Review We reviewed clinical evidence on ICD shocks and reference lists of retrieved articles. We also examined literature about the methods of reducing ICD therapy.

Findings Both appropriate and inappropriate ICD shocks are common and are associated with an adverse effect on health outcomes, quality of life, and mortality. Several methods are available to reduce the risk of inappropriate ICD therapies.

Conclusions and Relevance Implantable cardioverter-defibrillators reduce the risk of sudden cardiac death and prolong life in selected populations; however, many patients will receive an ICD shock, either appropriate or inappropriate. It is imperative that patients be counseled regarding this risk and adverse outcomes associated with shocks. Reduction of ICD shock should be individualized to ensure that patients receiving these devices experience the maximal benefits of therapy while minimizing the adverse consequences.

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Figure 1. Appropriate and inappropriate implantable cardioverter-defibrillator (ICD) shock rates from the Multicenter Automatic Defibrillator Implantation Trial (MADIT II),10 the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT),4,8 Defibrillators in Non-Ischemic Cardiomyopathy Treatment Evaluation (DEFINITE) trial,3,11 and the Antiarrhythmics versus Implantable Defibrillators (AVID) trial.9,12

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Figure 2. Reasons for inappropriate arrhythmia detection among patients with implantation of a combined cardiac resynchronization therapy–implantable cardioverter-defibrillator (ICD) device in the Multicenter InSync ICD Randomized Clinical Evaluation study.8,16

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Figure 3. Reasons for inappropriate implantable cardioverter-defibrillator (ICD) shock among patients with ischemic cardiomyopathy and reduced left ventricular ejection fraction who received a primary prevention ICD in the Multicenter Automatic Defibrillator Implantation Trial.10




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The American Medical Association is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The AMA designates this journal-based CME activity for a maximum of 1 AMA PRA Category 1 CreditTM per course. Physicians should claim only the credit commensurate with the extent of their participation in the activity. Physicians who complete the CME course and score at least 80% correct on the quiz are eligible for AMA PRA Category 1 CreditTM.
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