Abstract Body (Do not enter title and authors here): Introduction/Background: The Safety Mode (SM) in Boston Scientific pacemakers provides back-up pacing if a critical device malfunction or unexpected internal error occurs. However, SM's high sensitivity (0.25mV) and unipolar configuration have been associated with deaths and serious injuries due to oversensing and pacing inhibition in pacemaker-dependent patients. SM is also present in Boston Scientific 's implantable cardioverter-defibrillators (ICD) and cardiac resynchronization defibrillators (CRT-D) but it is unknown if any adverse effects SM has been caused in patients with these devices. When a Boston Scientific ICD or CRT-D enters SM, it paces VVI or BiV, fixed rate 72.5 min^-1, unipolar autogain sensitivity 0.25mV, single zone ventricular fibrillation (VF) with a rate threshold of 165 min^-1 and 5 maximum output shocks per episode. Moreover, tachycardia and defibrillation therapy may be disabled if additional faults occur while the device is in SM.
Research Question: Is SM in Boston Scientific ICDs and CRT-Ds associated with major adverse clinical events (MACE)?
Methods: The FDA’s Manufacturer and User Facility Device Experience (MAUDE) database was searched from January 2021-May 2025 for MACE involving SM in Boston Scientific ICDs and CRT-Ds.
Results: The search found 217 worldwide SM events that Boston Scientific classified as death (n=2; 1%), injury (n=178; 82%), or malfunction (n=37; 17%). Deaths were associated with a shorted ICD lead and a ventricular arrhythmia requiring external defibrillation. Thirty-three events (15%) involved SM-related inappropriate shocks (IAS) and 3 of these also had asystole due to pacing inhibition. One injury event was ventricular tachycardia (VT) that was not treated by the ICD due to SM. Of the 165 devices removed and analyzed, the causes of SM included memory inconsistencies (n=102; 62%), electronic component defects (n=17; 10%) and latent leakage paths in the battery (n=7; 4%).
Conclusions: SM in Boston Scientific ICDs and CRT-Ds is often caused by software errors and is associated with MACE including IAS, asystole, and failure to treat VT. Importantly, VT/VF therapy is not assured when a Boston Scientific ICD or CRT-D is in SM. These findings and the experience with pacemakers suggest the Boston Scientific Safety Mode should be redesigned.