Defibrillation Testing

Abstract

In 3 decades of clinical use of the implantable cardioverterdefibrillator (ICD), defibrillation threshold (DFT) testing has remained an integral part of the implantation procedure. The prevailing rationale for the routine evaluation of DFTs has been to ensure appropriate sensing of ventricular fibrillation, system integrity, and effective defibrillation (1-3). Early ICD systems using monophasic waveforms with epicardial patches or transvenous leads were associated with a substantial incidence of elevated DFTs, requiring additional intervention to ensure clinical efficacy (1-3). Technically, the DFT is a probabilistic phenomenon requiring multiple shocks to determine with precision. Clinically, the DFT is commonly approximated with 1 or more shocks to See page 981 terminate induced ventricular fibrillation and ensure a safety margin between the DFT and the maximum output of the ICD. Inadequate safety margins of Ͻ10 J between the DFT and maximum ICD energy delivery have been associated with worse clinical outcomes (3). Contemporary ICD systems using active cans, pectoralis pulse generators, biphasic waveforms, and intravascular high-voltage leads have considerably lowered the incidence of elevated DFTs (4 -13). The reliability of current ICD systems has led implanting physicians to abandon the practice of routine testing of defibrillation efficacy before hospital discharge and annually. Observational studies also have noted an elimination of DFT testing in one-third of initial implants and two-thirds of replacements (14 -16). Indeed, based on a growing body of evidence, the clinical utility of the determination of defibrillation efficacy during de novo implants has been questioned (4 -13). With this background, it is appropriate to re-evaluate whether DFT testing still should be routinely performed at the initial ICD insertion procedure.Multiple arguments and lines of evidence support the routine evaluation of DFTs at ICD insertion (1-3). The prospective randomized trials demonstrating efficacy of the ICD for primary and secondary prevention of sudden death have required DFT testing. Evaluation of DFTs allows verification of sensing, integrity of the high-voltage system, and programming lower initial shock energy for ventricular fibrillation at 10 J over the DFT (1-3). Testing of defibrillation efficacy represent a historical standard of care, and eliminating the DFT testing may present a medical legal issue for the physician performing the implantation (1-3). However, the evidence supporting continued DFT testing is limited by the absence of a prospective randomized trial with appropriate clinical outcomes.The arguments and evidence against the determination of the DFTs include the risks of major complications related to the testing (1-18). Death, stroke, myocardial infarction, and anesthesia-related complications related to DFT determination are reported in Ͻ1% of implants. However, registry and observational data may under-report the frequency of complications. Inadequate safety margins with current ICDs are ver...

Incidence of ineffective safety margin testing (<10 J) and efficacy of routine subcutaneous array insertion during implantable cardioverter defibrillator implantation

“…In 3 decades of clinical use of the implantable cardioverter defibrillator, defibrillation threshold testing has remained an integral part of the initial implantation procedure [12] . The prevailing rationale for the routine evaluation of SMT has been to ensure appropriate sensing of ventricular fibrillation, system integrity, and effective defibrillation [12] . Early in the development of the transvenous ICD, defibrillation threshold testing was performed by connecting the transvenous lead to an external cardioverter defibrillator using high-voltage cables.…”

“…Contemporary ICD systems using active cans, biphasic waveforms, and intravascular high-voltage leads have considerably lowered the incidence of SMT <10 J [15] , [16] . The reliability of current ICD systems has led implanting physicians to abandon the practice of routine testing of defibrillation efficacy before hospital discharge and annually [12] , [13] . Based on a growing body of evidence the clinical utility of the determination of defibrillation efficacy during de-novo implants has been questioned in observational studies [15] , [17] as well as in randomized trials [18] , [19] .…”

Highlights of the Year in JACC 2012

“…The authors acknowledge that the sudden death rate was low and may have been insufficient to show a difference in the clinical effect of defibrillation threshold testing, although the shock rate was sufficiently high. In addition, as noted in the accompanying editorial by Estes (89), this study may not have addressed a higher-risk population with high DFTs, and this study did not follow patients beyond 2 years, and in some patients shocks do not occur until after 2 years follow-up.…”