Shocks After Initial ICD Discharge and Driving Restrictions

Study Questions:

What is the time course of subsequent shocks after initial implantable cardioverter-defibrillator (ICD) discharge, and what are the implications for driving?


This was a retrospective analysis of a nationwide cohort of 14,230 ICD recipients enrolled in a remote monitoring program. Participants experienced at least one shock. The risk of driving after an ICD shock was estimated using the risk for harm (RH) formula. The likelihood of loss of consciousness associated with an ICD shock was estimated using a cautious value of 32% and an estimate of 14% based on contemporary data.


The cumulative incidence of receiving a second shock was 15% at 1 month and 29% at 6 months. The time from implantation to initial shock had an inverse association with the likelihood of receiving a second shock (lowest quartile of time at 6 months, 32%; highest quartile of time at 6 months, 25%). The number of ICD therapy zones was also significantly associated with the incidence of a second shock (1 therapy zone, 21% at 3 months to 52% at 3 years; 3 therapy zones, 27% at 3 months to 57% at 3 years). When a likelihood of loss of consciousness of 32% associated with an ICD shock was used, the RH while driving fell below the accepted threshold of five events per 100,000 ICD recipients at 4-6 months after an initial shock. However, when a contemporary estimate for loss of consciousness associated with an ICD shock of 14% was used, the RH fell below the threshold at 1 month after an initial shock.


The incidence of a second shock after an initial ICD discharge was lower than previously reported and depended on programmed ICD variables.


American Heart Association/Heart Rhythm Society guidelines promulgated in 2007 recommend driving restrictions for 6 months after appropriate ICD therapy in recipients of primary prevention devices. These were based on event rates in patients with somewhat different clinical profiles and who were managed very differently, both in terms of the medical therapy as well as the ICD programming prevalent at the time. Given the lower risk of syncope with ICD shocks in the current era, the 2007 guidelines may be too restrictive in limiting driving among ICD recipients who experience shocks.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure

Keywords: Arrhythmias, Cardiac, Automobile Driving, Defibrillators, Implantable, Heart Failure, Primary Prevention, Incidence, Risk, Shock, Syncope

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