Impact of defibrillation testing on predicted ICD shock efficacy: implications for clinical practice

Lack of consensus regarding defibrillation testing methods for implantable cardioverter-defibrillators relates to risks of repeated fibrillation episodes.

To provide recommendations for testing protocols, repeating testing of patients with high defibrillation threshold (DFT), and interpreting testing after implantable cardioverter-defibrillator system revision.

We constructed a computer model of defibrillation probability-of-success curves using data from 564 patients. Then, we compared 13 safety margin (SM) or DFT protocols in 50,000 simulated patients to identify those with the best balance of sensitivity and predictive value for detecting patients at high risk for failed defibrillation. Conditional retesting of patients with high DFT was simulated, both without and with revision that lowered defibrillation energy by one-third.

SM protocols were more efficient than DFT protocols; 2/2 successes at 20 J or 1/1 at 16 J performed best. Patients who failed testing had a mean probability of defibrillation of 94% at 35 J, but great uncertainty regarding that probability (range 67.0%-100%). When they repeated testing, 62% passed, with 48% owing to regression to the mean. If system revision was performed before retesting, 84% passed; the fraction of patients at high risk reduced (4.7% to 2.7%, with 43% relative reduction); but 3.5% underwent unnecessary revisions. Testing and revision of patients with high DFT benefitted 2.5% of the patients.

SM protocols are superior to DFT protocols for implant testing. For patients who fail testing, there is substantial uncertainty in defibrillation efficacy. After a system revision that does not alter defibrillation efficacy, 62% of these patients pass retesting.