Minimizing Inappropriate or “Unnecessary” Implantable Cardioverter-Defibrillator Shocks

Abstract

L ife-saving shocks are the raisons d'être of implantable cardioverter-defibrillators (ICDs). Paradoxically, shocks also cause much of the morbidity associated with ICDs. Consistently, shocks reduce quality of life, 1,2 and rarely, they may cause proarrhythmia. 3,4 Additionally, shocks have been reported to be associated with excess mortality. 5 Experts disagree about whether shocks are responsible for this excess mortality, 6 but they do agree that ICDs should deliver the fewest shocks necessary to protect patients from ventricular tachycardia (VT) or ventricular fibrillation (VF).Minimizing ICD shocks requires a comprehensive approach, beginning with patient selection, 7 general medical care (eg, preventing electrolyte abnormalities), and general cardiac care (preventing ischemia and treating heart failure). It includes the use of antiarrhythmic drugs and catheter ablation both to prevent VT or supraventricular tachycardia (SVT) and to control the ventricular rate in atrial fibrillation (AF) as well as the appropriate choice of hardware and device programming. This review focuses on ICD features and programming to minimize shocks. OverviewFigure 1 summarizes the sequential processes required for an ICD to deliver a shock. The sense amplifiers convert the continuous electrogram (EGM) from the tip of the right ventricular (RV) lead into a series of instantaneously sensed events representing ventricular depolarization. This series of sensed events is processed by ICD algorithms, including those for initial detection; SVT-VT discrimination; and in some models of ICDs, enhancements to minimize oversensing. If the rhythm is classified as a VT, antitachycardia pacing (ATP) can be delivered. The ICD then performs a redetection process, which results in determination that the devicedefined VT either has terminated or persists. If VT is redetected, the process iterates until all programmed ATPs are delivered. The ICD then charges the high-voltage capacitors, during which time a final round of ATP may be delivered. After capacitor charging, the ICD confirms that VT/VF is present before delivering a shock. Each step provides opportunities to minimize unnecessary shocks. Although Figure 1 shows the ICD process, we consider features and programming in the approximate order that most electrophysiologists program ICDs: (1) rate and duration for initial detection, (2) SVT-VT discrimination, (3) ATP and shock strength, (4) redetection/confirmation, and (5) sensing enhancements.Historically, shocks were classified as appropriate if delivered during VT/VF and inappropriate if delivered during other rhythms. However, some shocks delivered during VT may be avoided by programming ATP or permitting nonsustained VT to spontaneously terminate. In this review, we classify shocks as either necessary to ensure patient safety or unnecessary. Necessary shocks are those that terminate ventricular tachyarrhythmias that would not spontaneously terminate or cannot be terminated by ATP. Unnecessary shocks include those that have been traditional...

2015 HRS/EHRA/APHRS/SOLAECE expert consensus statement on optimal implantable cardioverter-defibrillator programming and testing

“…We summarize the most commonly used discriminators. More comprehensive discussions are available in the literature [107][108][109][110][111].…”

“…Approaches to minimizing Twave oversensing include reprogramming ventricular sensitivity, altering sensing bandwidth, and changing the sensing bipole [109,123,145]. One manufacturer provides an algorithm that withholds therapy after rate and duration criteria for VT/VF are fulfilled if a specific pattern of T-wave oversensing is identified [146].…”

Incidence of Atrial Tachyarrhythmias in Patients With Early Repolarization Syndrome

“…35) Optimal ICD programming to minimize inappropriate ICD shock such as higher detection rates, prolonged detection intervals, and supraventricular tachycardia discriminators is critically important. 36) Considering the high incidence of inappropriate shock and high ventricular rate during VF episodes, a more conservative approach in detection of VF (from 200 bpm to 240 bpm or higher) is required. 37) Anti-arrhythmic drugs are considered the first-line therapy to prevent the development of AF.…”

Optimal Programming of Implantable Cardiac-Defibrillators

“…[11][12][13] Although therapy delivered for a ventricular tachyarrhythmia is considered appropriate, a growing body of evidence has shown that programming antitachycardia pacing (ATP) or delaying shocks to permit nonsustained episodes to terminate significantly reduces the frequency of shock delivery. Koneru et al 14 have used the term unnecessary shocks to refer to inappropriate shocks delivered for rhythms other than VT/VF and to include shocks delivered for VT that would have responded to ATP or terminated spontaneously if given time. Optimal programming minimizes unnecessary shocks.…”

“…In the only currently available s-ICD, rate is programmable but not duration. The 25% to 75% time from detection to shock is 13 to 16 seconds, 14 so that the use of a detection rate of 200 bpm results in a therapy delay slightly longer than that in the delayed-therapy arm of MADIT-RIT. Recommended programming parameters for the primary prevention indication at our institution are presented in the Table.…”