Derivation of a Defibrillator Implant Criterion Based on Probability of Successful Defibrillation

Abstract

Common criteria for implant of a cardioverter defibrillator include verification of a 2:1 energy safety margin or a fixed safety margin of 10 joules. These criteria have been established empirically. We present a statistically model based on defibrillation efficacy curves which may be used to establish a criterion which would meet a predetermined target. As an example, an implant criterion is derived based on a goal of 1-year sudden cardiac death survival of at least 99% by selecting an expected first-shock efficacy to meet that target. Logistic regression was performed on data from over 1,500 defibrillator implants including successful epicardial and transvenous electrode system implants as well as data from unsuccessful implants. A random sample from these curves was used to generate a representative sample of 1,000 potential implant candidates. By assuming successful defibrillation using a series of shocks at specified energies, i.e., choosing an implant criterion, the probability of successful defibrillation of the patient by a single shock at a predetermined maximum output can be established. Independent data are used to validate the model's accuracy in predicting defibrillation efficacy within the derived example.

Should You Use DFT or ULV to Assess Defibrillation Efficacy?

“…Within the range of starting shock strengths and step sizes used clinically, these methods approximate the DFT 60 to DFT 80 . 10,11 Clinical measurement of DFT has only fair reproducibility. In a study of 25 patients, the correlation coefficient between two successful determinations of the DFT was 0.64.…”

Reappraisal of implant testing of implantable cardioverter defibrillators**Editorials published in the Journal of the American College of Cardiologyreflect the views of the authors and do not necessarily represent the views of JACCor the American College of Cardiology.

“…There is an inverse relationship between the fraction of patients who pass any defibrillation implant criterion and the subsequent success rate for conversion of spontaneous device-detected VF (8). Given the high, a priori probability of successful defibrillation at implants performed by trained implanters, the rules of conditional probability dictate that many patients with reliable defibrillation will not pass a highly specific implant criterion.…”

“…The commonly used, 10-J safety margin identifies only ϳ50% of patients who have unreliable defibrillation (8). Increases in DFTs that compromise defibrillation efficacy occur in up to 15% of patients who are programmed to a 10-J safety margin (9).…”

Ist die DFT-Testung noch ein Muss?

“…Klinisch eingesetzte Verfahren zur intraoperativen Bestimmung der Defibrillationseffektivität sollten mit einer Mindestzahl von Defibrillationsversuchen eine möglichst genaue Festlegung der mittleren Defibrillationswahrscheinlichkeit der untersuchten Testenergie und der zu erwartenden Streubreite des Erfolgs konsekutiver Defibrillationsversuche ermöglichen [3,5,9,14,27].…”

“…Unterschiedliche Testverfahren wie "stepdown"-Protokolle, Verifikationsprotokolle, binäre Suchprotokolle und die Bestimmung des "upper limit of vulnerability" wurden in die klinische Praxis eingeführt und erreichten unterschiedliche Verbreitung [3,5,15,27,32]. Die Bestimmung der "step-down defibrillaton threshold" erfolgt durch konsekutive Defibrillationsversuche mit jeweils reduzierter Defibrillationsenergie.…”