The Dilemma of ICD Implant Testing

Abstract

Ventricular fibrillation (VF) has been induced at implantable cardioverter defibrillator (ICD) implant to ensure reliable sensing, detection, and defibrillation. Despite its risks, the value was self-evident for early ICDs: failure of defibrillation was common, recipients had a high risk of ventricular tachycardia (VT) or VF, and the only therapy for rapid VT or VF was a shock. Today, failure of defibrillation is rare, the risk of VT/VF is lower in some recipients, antitachycardia pacing is applied for fast VT, and vulnerability testing permits assessment of defibrillation efficacy without inducing VF in most patients. This review reappraises ICD implant testing. At implant, defibrillation success is influenced by both predictable and unpredictable factors, including those related to the patient, ICD system, drugs, and complications. For left pectoral implants of high-output ICDs, the probability of passing a 10 J safety margin is approximately 95%, the probability that a maximum output shock will defibrillate is approximately 99%, and the incidence of system revision based on testing is < or = 5%. Bayes' Theorem predicts that implant testing identifies < or = 50% of patients at high risk for unsuccessful defibrillation. Most patients who fail implant criteria have false negative tests and may undergo unnecessary revision of their ICD systems. The first-shock success rate for spontaneous VT/VF ranges from 83% to 93%, lower than that for induced VF. Thus, shocks for spontaneous VT/VF fail for reasons that are not evaluated at implant. Whether system revision based on implant testing improves this success rate is unknown. The risks of implant testing include those related to VF and those related to shocks alone. The former may be due to circulatory arrest alone or the combination of circulatory arrest and shocks. Vulnerability testing reduces risks related to VF, but not those related to shocks. Mortality from implant testing probably is 0.1-0.2%. Overall, VF should be induced to assess sensing in approximately 5% of ICD recipients. Defibrillation or vulnerability testing is indicated in 20-40% of recipients who can be identified as having a higher-than-usual probability of an inadequate defibrillation safety margin based on patient-specific factors. However, implant testing is too risky in approximately 5% of recipients and may not be worth the risks in 10-30%. In 25-50% of ICD recipients, testing cannot be identified as either critical or contraindicated.

Clinical impact of defibrillation testing at the time of implantable cardioverter-defibrillator insertion

“…This comparison cannot be assessed statistically due to the small number of unsuccessful shocks. This rate of first shock failure is in agreement to that reported for spontaneous VF in patients with DT (80-91%) or safety margin testing (91%) at ICD implantation [2,4,5]. Similarly, a significant proportion (80-87%) of VT/fast VT episodes were successfully ATP-terminated without shock delivery, regardless of whether DT was performed.…”

“…The assessment of defibrillation efficacy has long been the standard of care during implantable cardioverter-defibrillator (ICD) insertion, and is recommended by ICDs manufacturers and scientific guidelines [1,2]. However, this strategy is currently being questioned due to the high probability of current devices to successfully defibrillate ventricular arrhythmias, the low incidence of spontaneous ventricular fibrillation (VF) (~10%) and the high efficacy of dedicated antitachycardia pacing (ATP) strategies [2][3][4][5][6][7][8].…”

“…However, this strategy is currently being questioned due to the high probability of current devices to successfully defibrillate ventricular arrhythmias, the low incidence of spontaneous ventricular fibrillation (VF) (~10%) and the high efficacy of dedicated antitachycardia pacing (ATP) strategies [2][3][4][5][6][7][8]. Moreover, defibrillation testing (DT) is not without a risk, and complications associated to VF induction, shock delivery and anesthesia may occur [2,3,[9][10][11][12]. For all these reasons, the proportion of patients undergoing any type of DT, especially among primary prevention ICD implantation, is experiencing a progressive decline in routine clinical practice [12][13][14][15].…”

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

“…The authors concluded that defibrillation efficacy without DT was noninferior to ICD implantation with DT in left-sided ICD implants. Because no major benefit or harm associated with DT was detected, in patients with a leftsided pectoral implantation it is reasonable to omit routine VF induction and DT during ICD implantation, assuming stable ICD lead position and good sensing and capture function [217][218][219][220]. This approach is particularly applicable to patients with ischemic and idiopathic dilated cardiomyopathy, given these entities were well represented in the studied cohort.…”

Impact of Subpectoral Implantation of the Implantable Cardioverter Defibrillators on Defibrillation Threshold

“…High DFT is defined as an absolute value of shock energy >25Joules (J) or a safety margin of <10J below the maximum output of the device. This is assessed by two successful shocks of same strength [8] and the reported incidence of high DFT is from 2 to 24%. Russo et al reported a 6.2% prevalence of high DFT (n=1139) [9] which was replicated in a separate study by Osswald and colleagues in a larger population (n= 2803) [10].…”