Review
Frequency and Causes of Implantable Cardioverter-Defibrillator Therapies: Is Device Therapy Proarrhythmic?

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Implantable cardioverter-defibrillator (ICD) shocks diminish patients’ quality of life, increase health care resource utilization, and may lead to other adverse sequelae. Better understanding of the factors that lead to ICD therapies, and better strategies to avoid unnecessary therapies, are needed to optimize patient outcomes. Data from major randomized clinical trials involving the use of ICDs and cardiac resynchronization therapy–defibrillator devices were reviewed to determine control group mortality rates, control group sudden death rates, and the frequency of appropriate and inappropriate ICD therapies. In all studies that classified deaths, appropriate ICD therapies outnumbered control group sudden cardiac deaths by a factor of 2 to 3. Some of these episodes can be explained by device programming, by the treatment of potentially unsustained tachycardias, and by errors of episode classification. Another underexplored possibility is that device therapy is proarrhythmic. Reasons for frequent therapies and methods to prevent them are discussed, as well as the notion of device proarrhythmia and the potentially detrimental effects of ICD shocks. These issues clearly affect the overall benefit of device therapy and have important implications for patient management and health care delivery.

Section snippets

Methods

We performed a Medline search for all English-language reports cross referencing the following keywords: implantable cardioverter-defibrillator, cardiac resynchronization therapy, and cardiac resynchronization therapy–defibrillator with appropriate therapy, inappropriate therapy, shocks, mortality, sudden death, and cardiac arrest. We initially reviewed major randomized controlled clinical trials published after 1995. Studies involving ICDs without sufficient data retrieval capabilities to

Results

Key aspects of the 7 major ICD trials reviewed are listed in Table 1.8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 Available mortality and ICD therapy rates from the ICD trials appear in Figure 1. A number of important ICD trials (e.g., the Coronary Artery Bypass Graft Patch Trial, the Multicenter Automatic Defibrillator Implantation Trial) were not included in our analysis for the reasons stated in the Methods section.

Inappropriate ICD therapies were common in the trials for which they were

Discussion

Recent ICD trials have demonstrated relatively high rates of inappropriate and appropriate therapies. This discussion focuses on the causes of inappropriate and appropriate ICD shocks, as well as methods to decrease their incidence. The adverse effects of potentially avoidable therapies and their clinical implications are addressed.

In contemporary trials, 25% to 35% of all ICD therapies have been classified as inappropriate.15, 24, 26 Supraventricular tachyarrhythmias (including sinus

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  • Cited by (0)

    Dr. Essebag is the recipient of a Clinician Scientist Award from the Canadian Institutes of Health Research, Ottawa, Ontario, Canada.

    Dr. Josephson is a consultant for the Medtronic Foundation, Inc., Minneapolis, Minnesota

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