Oversensing combined with abnormal impedance trends may be used to identify ICD lead failures with high sensitivity and very high specificity.

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PURPOSEThe undesirable production of secondary neutrons by cancer radiotherapy linear accelerators has been demonstrated to cause softerrors in nearby electronics through the %(n, a)'Li reaction. The "B is a component in the BPSG used as a dielectric material in some IC fabrication processes. XNTRODUCTIONBaumann el ai first reported the potential for thermal neutrons to cause soft-errors in some integrated circuits (IC) [I]. In this scenario, neutrons that are in thermal equilibrium with their surroundings (i.e., those with kinetic energq. of approximately 0.025 eV at 25OC) interact with 1°5 found in the lower inter-metal dielectric layers of an IC, resulting in the production of 7Li and a particles in the immediate vicinity of the active circuitry. Subsequent interaction of these charged species with the IC leads to soft-errors. For some ICs with normal terrestrial exposure to thermal neutrons, this mechanism has been identified as the dominant cause of soft-errors 121. Other authors have also reported measurements of soft-errors caused by this mechanism [3].In most developed countries, linear accelerators (linacs) are used for cancer radiotherapy treatment (figure 1). This equipment accelerates a beam of electrons to high energies (3 -20 MV) and directs them at a high atomic number target, typically tungsten. The bremmstrahlung X-rays produced in this interaction are filtered, collimated and directed to the patient's tumor. When operated at an electron beam energy greater than -9MV, a flux of energetic photoneutrons is produced as an undesirable byproduct. These energetic neutrons are moderated or absorbed by the shielding materials in the linac and the construction materials of the treatment FIGURE 1. A TYPICAL 18 MV LINAC USED FOR THE TREATMENT OF CANCEROUS TUMORS.room. Unabsorbed neutrons quickly reach thermal equilibrium with the environment and are available for a host of nuclear reactions that are much more probable with a low energy incident particle, A typical radiation safety survey has characterized the thermal neutron flux near the entrance to the treatment room maze at I mSv h i ' 141. EXPERIMENTAL METHODOLOGYAn experiment to determine the potential for soft-errors in electronics operating in the vicinity of a linac was undertaken. A total of 10 small S U M S (SI), known to be sensitive to thermal neutron induced soft-errors, were continuously monitored while being exposed to the ambient flux approximately 50 cm from the linac beam's iso-center. Each SRAM was alternately exposed a) without shielding, b) shielded from electromagnetic interference (EMI), c) shielded from thermal neutrons, or d) held outside the treatment room as a control. Shielding from thermal neutrons was accomplished by surrounding the memory on all sides with a minimum of 2 cm of dry boric acid. A total of 4 soft-errors were detected in the S1 devices during these exposures, 3 from the unshielded memories and 1 from an EM1 shielded memory. No errors were detected from any device shielded from thermal neutrons or outside the treat...

Implantable cardioverter defibrillators (ICD) lead dysfunctions can cause inappropriate shocks. Current ICDs store lead diagnostics and detected episodes. This stored information with intracardiac electrograms (EGM) and sensed RR interval patterns may characterize the ICD lead performance. The aim of this analysis was to determine the sensitivity and positive predictive value (PPV) of an automatic lead dysfunction identification algorithm. This algorithm uses RR and EGM data to distinguish noncardiac oversensing (OS), for example, due to conductor fracture, and cardiac OS, for example, T-wave OS, from detected episodes. The algorithm also uses lead diagnostics: sensing integrity counter trends (e.g., RR intervals <140 ms), nonsustained tachyarrhythmias episodes with a mean RR <200 ms and impedance trends to identify lead fractures. The PPV was determined using the stored memory from 1,756 ICD patients enrolled in a 13-center long-term lead study with an average follow-up of 18.3 patient-months. Sensitivity was determined in 35 patients who presented with OS or lead fracture-related adverse events confirmed by stored ICD diagnostics. The algorithm sensitivity was 97.1% (34/35). There were 43 additional patients identified by the algorithm without an adverse event. Stored ICD diagnostics confirmed lead dysfunctions in 32 of 43 patients corresponding with an 85.7% PPV (66/77). ICD memory diagnostics and episodes with intracardiac EGM may be used to identify ICD lead dysfunctions with high sensitivity and PPV. This algorithm may be implemented in postprocessing ICD environments (e.g., remote server, programmer) to rapidly identify lead dysfunction prior its clinical manifestation.