(A) Baseline EGM: atrial fibrillation, biventricular pacing (BP) with VVI programming. A, atrial; RV, right ventricular; LV, left ventricular; EGM, intracardiac electrogram, I; EKG Lead I. (B) EGM during TENS testing; test, 2.1 (chest, 80 Hz) at 25 mA. Detection of TENS current and false interpretation as ventricular sense (VS), ‘V. Störung’ German for noise detection and asynchronous stimulation in V00 mode. High-frequency TENS interference signals are visible in B on the RV-EGM and Lead I and marked with an arrow (↓). Despite having a relatively low amplitude these interference signals are being falsely marked in the marker channel as a ventricular sense (VS/S) (*). This causes an inhibition of pacing with interruption of biventricular pacing (a). The patient was not pacemaker-dependent. His own bradycardic sinus rhythm prevented longer pauses and the patient remained asymptomatic. After detection of noise, the device correctly switched into ‘noise detection mode’ with pacing in VOO mode (‘-> V. Störung’). Although the cycle length of the detected TENS-signals (VS/S) is < 330 ms and does fall into the tachycardia detection zone (programming: VT zone: 182 b.p.m. (330 ms); VF-zone: 231 b.p.m. (260 ms) it is not being marked as VT/VF. This might be due to further unfulfilled VT detection criteria such as onset, stability and morphology.