How to Manage a High Defibrillation Threshold in ICD Patients: and Does it Really Matter?

In the 30 years since its introduction, implantable cardioverter defibrillator (ICD) hardware and programming has evolved greatly. Coupled with a better understanding of how patient factors and anti-arrhythmic drug therapy affect ICD function, these changes have resulted in a modern ICD system which is highly effective at terminating ventricular arrhythmias. This has led to a marked decrease in the conduct of intraoperative defibrillation testing. Still, clinicians are faced with patients who have had unsuccessful intraoperative defibrillation testing or who have experienced one or more failed clinical shocks for ventricular arrhythmias. Thus, clinicians caring for ICD patients must understand the expected performance of modern ICD systems, understand the issues with intraoperative defibrillation testing, and have a strategy for dealing with patients when their ICD has failed to terminate a clinical or induced ventricular arrhythmia. This review will focus on the clinical approach to such patients, including trouble-shooting and system revision.