Necessity of Defibrillation Threshold (DFT) Testing Even at ICD Exchange: Lesson Learnt from One Case

Background: With the popularization of high voltage ICD delivering over 35 J, omission of DFT test during ICD exchange has increased. We encountered a case that highlights the necessity of DFT test at ICD exchange. Case Report: A 70 year-old man was admitted for ICD exchange. In 2005, an ICD was implanted due to VF associated with obstructive hypertrophic cardiomyopathy. In May 2011, he was admitted for ICD exchange due to low battery. The old generator was removed. Test of the lead with an analyzer before and after connection to a new generator revealed no problem. Then a DFT test was conducted. Initial shock therapy with 15 J followed by 20 J and 35 J failed to terminate VF. Induction data showed that while the device was charged properly, only 0.2 J was delivered. To check for generator defect, the lead was connected to another generator and DFT test again showed faulty delivery. Defect of the lead was suspected. An electrical test showed that when the charge exceeded 5 J, only 0.2 J was delivered. The presence of miniscule damage in the lead causing leakage only at high voltage was suspected. A DFT test after installing the new lead yielded scheduled delivery and VF was terminated at 20 J. Discussion: In this case, a serious defect affecting vital ICD function was revealed only by DFT testing conducted at ICD exchange.