Role of Defibrillation Threshold Testing in the Contemporary Defibrillator Patient Population

INTRODUCTION: Defibrillation threshold (DFT) testing has been performed to prove functionality of the implantable cardioverter defibrillator (ICD). Over the past years it has become increasingly controversial because of possible morbidity and mortality. The goal of this study was to determine unsuccessful shock testing and report strategies used to overcome these problems. METHODS AND RESULTS: A total of 314 patients with a de novo implantation of an ICD and 127 patients receiving a generator exchange were identified retrospectively. All patients underwent defibrillation threshold testing after induction of VF using a low-energy T-wave shock during the intervention, 2 shock tests after de novo implantations, 1 after generator change. A safety margin of 10 J or more was requested. Seven (2.3%) patients in the de novo group and 2 patients (1.4%) in the generator exchange group could not be defibrillated using the standard approach. All of those patients had either chronic amiodarone therapy, secondary prevention or a cardiac resynchronization therapy device (CRT). In univariate analysis, amiodarone therapy, dilated cardiomyopathy, and lower ejection fraction were predictors of failure. CONCLUSION: Our study's results as well as a review of the current literature favor shock testing, especially in patients with specific risk factors as mentioned above.