New Ways to Avoid Unnecessary and Inappropriate Shocks

Abstract

Implantable cardioverter-defibrillators (ICDs) reduce mortality by terminating ventricular arrhythmias (VAs), and it has become widely accepted that this is done by delivering shocks. From the initials of ICD therapy it is known that ICD shocks are associated with reduced quality of life. Most importantly, recent accumulated evidence indicates a clear association among shocks (appropriate and inappropriate) and increased risks of heart failure (HF) and death (Poole et al, 2008). Knowing that, one of our major objectives when dealing with an ICD patient has to be reducing shocks while keeping the certainty that all the VAs are adequately terminated. When trying to reduce shocks our focus should be dual, inappropriate and unnecessary therapies. Inappropriate shocks are generally defined as those not delivered for ventricular tachycardia (VT) or fibrillation (VF), and may be due to oversensing (double counting of right and left ventricular depolarization, T-wave oversensing, noise, etc) or to atrial arrhythmias with rapid ventricular conduction. Unnecessary shocks are those that could have been avoided using other means of terminating the VT, namely antitachycardia pacing, or allowing the VT to spontaneously finish, in case of non-sustained episodes, prolonging the number of intervals needed to detect and initiate therapy. Depending on the trial, only 3–35% of shocked episodes were sustained VT/VF that absolutely require a shock for termination. When considering the number of shocks delivered for SVT, T-wave oversensing (TWOS) and lead noise, primary prevention patients may experience more inappropriate shocks than shocks for VT/VF. This highlights the need for improved shock reduction strategies. During this chapter we will review the most recent developments and algorithms to avoid inappropriate and unnecessary shocks.