Coexistence of R-Wave Oversensing and Undersensing in an Implantable Loop Recorder: The Issue of Multiple Sensing in Implantable Loop Recorders.

BACKGROUND Implantable loop recorders (ILRs) are important tools in diagnosing unexplained syncope and palpitations through prolonged rhythm monitoring. However, ILRs can produce false-positive arrhythmia detections, due to signal oversensing and undersensing, which can complicate clinical interpretation. Oversensing typically involves P waves, T waves, or myopotentials; however, simultaneous oversensing and undersensing of multiple waveform components is rare. We report a case of R-wave oversensing of P waves and T waves, with undersensing of QRS complexes, resulting in erroneous atrial fibrillation (AF) alerts. CASE REPORT A 73-year-old woman with hypertension and hyperlipidemia presented with recurrent lightheadedness, palpitations, and hypotension. After an unrevealing initial workup, a Biotronik Biomonitor III ILR was implanted. Within 3 months, the device flagged over 200 episodes of AF and several ventricular fibrillation episodes, despite the patient remaining asymptomatic. Careful signal review revealed a triple-sensing issue of cardiac signals, leading to misclassification of arrhythmias. The sensing filter was reprogrammed from 10 Hz to 24 Hz, resulting in elimination of false-positive detections. Following reprogramming, the patient remained asymptomatic with no further inappropriate arrhythmia alerts and did not require additional interventions. CONCLUSIONS This case highlights a rare example of R-wave oversensing and undersensing by an ILR, emphasizing the importance of individualized device programming to optimize diagnostic accuracy. Additionally, it illustrates that unconventional implantation sites, such as the right parasternal region, can produce unique sensing challenges. Careful review of device signals and appropriate reprogramming can correct oversensing issues, preventing unnecessary interventions and improving patient management.