Harvard Heart Letter

Long-detection interval for ICDs helps avoid harmful shocks

Miniature electronic devices called implantable cardioverter-defibrillators (ICDs) detect and terminate rapid, irregular beats in the heart's lower chambers (ventricles)—a problem known as ventricular fibrillation. While these little machines are a lifesaver for people prone to potentially deadly heartbeat disturbances, the shocks they deliver can be highly uncomfortable and even damaging.

A report in the July 22, 2014, Circulation showed that a programming strategy that delayed the time between the onset of an irregular heartbeat and the delivery of the electronic impulse could prevent unnecessary and inappropriate shocks in many cases.

In the study, more than 1,900 people receiving their first ICD were assigned to either a standard- or long-detection interval. During 12 months of follow-up, participants whose ICDs were programmed for a longer detection time before delivery of the shock (about 15 to 20 seconds versus the standard 6 to 7 seconds) were less likely to have entered the hospital during the study period. There was no difference in the death rate between the long-interval and standard-interval groups. However, people in the long-interval group incurred lower hospital costs than those with standard-interval times. 

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