(A) Baseline EGM: sinus rhythm, EKG lead aVL. (B) Electrogram during TENS testing, Test 2.1 (chest, 80 Hz) with 40 mA. Detection of TENS currents and false interpretation as VS and intermittent interpretation as VT and VF. Undersensing due to noise, correct interpretation as noise detection (VN). High-frequency TENS interference signals are visible in all three leads (aVL, RV–EGM, Schock–EGM) and are marked with an arrow (↓). Intermittently, the interference signals are being falsely interpreted as a VS. Tachycardia programming: VT zone, 170 b.p.m., 353 ms; VF zone, 220 b.p.m., 273 ms. Depending on the detection, they are either falsely interpreted as VT (a) or VF (b) (oval circle). Intermittently, the TENS signals are also being correctly marked as noise (VN) (b). While some intrinsic QRS complexes are also being marked as noise (c) if they fall into the noise interval. During noise detection you can also see that some QRS complexes are not being detected at all which means there is US. aVL, EKG lead aVL; EGM, electrogram; EKG, electrocardiogram; RV, right ventricular; TENS, transcutaneous electrical nerve stimulation; US, undersensing; VF, ventricular fibrillation; VN, ventricular noise; VS, ventricular sense; VT, ventricular tachycardia;