Reduction of defibrillation threshold and safety of usage of a new model of subcutaneous defibrillation lead

Abstract

This study was designed to evaluate the performance of a new single coil model of a subcutaneous defibrillation lead (Medtronic, 6996S) by assessing its capability to lower the defibrillation threshold. The 6996S lead is a permanent unipolar subcutaneous lead with a short (15 cm) defibrillation coil. Additionally, the safety of the lead and its chronic stability were evaluated. The investigation was performed in patients who underwent implantation of an ICD system consisting of a single coil RV lead with a left sub-clavicular Active Can ICD. In these patients, the DFT was determined twice during the implantation procedure with a binary search protocol, once with an ICD system which included the 6996S lead (RV → Can + SQ), and once without the 6996S lead (RV → Can). The order in which the implanted system configurations were tested was randomised. Between June 2004 and February 2006, 32 patients were enrolled into the study. Post-implantation follow-up was of at least three-month duration. The DFT test results of 31 patients have been analysed. The average DFT of (Can → RV) and (Can + 6996S → RV) were respectively 14.3 ± 9.9 J and 10.5 ± 6.2 J (p = 0.007). The addition of the 6996S lead with 15 cm coil reduced the average DFT by 27%, which is about 80% of the DFT reduction obtained with the 6996 lead with 25 cm coil. Adverse events, predominantly related to progression of heart failure, were observed in eight (26%) patients during the study and were related neither to the particular 6996S lead model, nor to the implant procedure. The short-coil (6996S) SQ lead significantly reduced mean DFT. The implant procedure is safe, but the 6996S lead requires / warrants long-term surveillance / observation due to retraction of the tip of the lead, ranging from 1 to 4 cm, found in eight of 14 patients (57%) implanted with this lead model.