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Table 1 Summary of the device generations and select findings

From: Development and utilization of implantable cardiac monitors in free-ranging American black and Eurasian brown bears: system evolution and lessons learned

Device Features Species/usage Findings
GEN 1 80 cc 104 h recording capacity Programmable to allow duty cycling of recording intervals Ursus americanus (Colorado and Wyoming, USA) n = 6 devices in 6 bears Longest asystole = 13.3 s Extreme RSA identified Avg HR increased when electromyograms (EMGs) were present Longest duration of data collection = 68 days (HR Avg = 13.5 ± 3.8 bpm) No significant changes in the QRS or QT intervals during hibernation Rate dependence of QT interval lost during hibernation Extreme foreign body response
GEN 2 9 cc 3-year battery life Records daytime HR, nighttime HR, activity, and episodes with ECGs Ursus americanus (Minnesota, USA) n = 65 devices in 39 bears Longest asystole = 14.4 s Maximum HR = 261 bpm (bear shot by hunter) Respiratory rate increased as investigators approached the den, serving to increase the average HR Anesthesia eradicated the RSA
   Ursus arctos (Sweden) n = 35 devices in 33 bears Maximum HR = 240 bpm (07 Oct 13 and 19 Oct 13; 2-year-old female) Longest asystole = 15.8 s (26-Feb-2013; 2-year-old female)
GEN 2 with BearWare GEN 2 features with Avg HR every 2 min Activity at 15-min intervals ECGs for the 10 extremes for tachycardias and asystoles Ursus americanus (Minnesota, USA) n = 69 devices in 42 bears Longest asystole = 33.8 s (03-Mar-2015; 4-year-old female) Maximum HR = 261 bpm (02-Sep-2010; adult female)
   Ursus arctos (Sweden) n = 71 devices in 56 bears Longest asystole = 39.4 s (03-Nov-2016; 3 1/2-year-old female) Maximum HR = 222 bpm (07-May-2014; 2-year-old female)
GEN 3 with Telemetry Stations GEN 2 features with 1.2 cc 3-year battery life Temperature Impedance Wireless capability Ursus americanus (Minnesota, USA) n = 29 devices in 21 bears with 28 telemetry stations deployed Demonstrated feasibility of remote web-based monitoring of bears in the wild Cessation of long sinus pauses during parturition Subcutaneous impedance decreased during hibernation
GEN 3 with B-Ware GEN 3 and BearWare features with Posture Rejects asystoles > 60 s and tachycardias > 275 bpm Ursus americanus (Minnesota, USA) n = 10 devices in 10 bears Results pending
  1. Avg average, HR heart rate, RSA respiratory sinus arrhythmia, bpm beats per minute, ± standard deviation