Reducing Shocks and Improving Outcomes With Implantable Defibrillators

Abstract

Implantable cardioverter-defibrillators (ICDs) have been shown to reduce mortality as primary1 and secondary prevention2- 3 of sudden death from ventricular tachycardia or ventricular fibrillation in selected patients. However, defibrillator shocks, whether for appropriate or inappropriate indications, are associated with adverse effects. These adverse effects include the acute discomfort of the shock as well as late and longer-lasting psychological trauma including depression and posttraumatic stress disorder.4 In addition to the psychological effects of shocks, there is a clear and somewhat paradoxical association between ICD shocks and increased mortality. In the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) and in the Sudden Cardiac Death in Heart Failure Trial, ICD shocks were associated with a 2- to 5-fold increased risk of death.5- 6 There has been a long-standing debate as to whether this increased mortality is a direct result of shocks having adverse effects on myocardial function leading to worsening congestive heart failure and death or whether the arrhythmias that lead to ICD shocks are markers of deteriorating myocardial function that leads to death.7- 9 Only by performing a clinical trial that randomizes patients to strategies that lead to different risks of ICD shock after receiving an implant could this important question be answered.