Predictors of high defibrillation threshold in the modern era

High defibrillation threshold (DFT) is a clinical problem in 1-8% of implantable cardioverter-defibrillator implants. Some clinicians and investigators question whether the benefits of routine DFT testing outweigh the risks. Identification of the predictors of elevated DFT may allow selective application of DFT testing. However, the clinical characteristics of patients with high DFT in the modern era have not been well-defined.

All patients who underwent DFT testing in our institution during an 8-year period were reviewed for this retrospective study. High DFT was defined as less than a 10-J safety margin on initial testing. For each case, the two cases preceding and two cases following by the same implanter were selected as controls.

Of the 2,138 patients who underwent DFT testing, 48 (2.2%) met criteria for high DFT. Compared to 192 control patients, patients with high DFT were more likely to be younger (P = 0.004), have nonischemic cardiomyopathy (P = 0.036), have a longer QRS interval (P = 0.026), and have a left ventricular ejection fraction (LVEF) ≤ 0.25 (P = 0.013). On multivariate analysis, only younger age (P = 0.016) and LVEF ≤ 0.25 (P = 0.010) remained statistically significant predictors of elevated DFT.

High DFT was identified in 2.2% of ICD implants in our institution in recent years. Although younger age and depressed LVEF predicts this problem, elevated DFT occurred in patients of all ages and ejection fractions. Elimination of routine DFT testing appears to be premature given the prevalence and unpredictability of elevated DFT.