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Inappropriate inhibition of biventricular pacing due to diaphragmatic myopotentials amplified by the selectable sensing filter.

A 66-year-old man with a cardiac resynchronization therapy defibrillator (CRT-D: Quadra Assura 3367-40QC, St. Jude Medical Inc.) experienced asymptomatic intermittent inhibition of biventricular pacing, mainly after meals. All measured parameters of the true bipolar ventricular lead (Durata 7122Q, St. Jude Medical Inc.) were in the normal range and general provocative maneuvers could not reproduce any noise. Only Valsalva maneuvers succeeded in reproducing the noise, showing the typical signal morphology of extracardiac myopotentials (Panel A); thus, oversensing of diaphragmatic myopotentials was diagnosed. After turning off the low-frequency attenuation filter (LFA) of the CRT-D, neither inhibition of pacing for bradycardia nor inappropriate detection of tachyarrhythmias was observed, even at the highest sensitivity (Panel A). In this patient, turning off the LFA was effective in preventing oversensing of diaphragmatic myopotentials. The LFA is designed to enhance sensing performance and may reduce the possibility of oversensing T waves. Although the precise mechanism of the LFA is proprietary information, it seems to attenuate signals with low frequency components such as T waves and to amplify high-frequency signals such as R waves. Because extracardiac diaphragmatic myopotentials consist of high-frequency components, the LFA may increase the risk of oversensing of extracardiac myopotentials. Introduction Oversensing of extracardiac myopotentials is a well-recognized problem in arrhythmia management with cardiac implantable electronic devices (CIEDs). The potentials can cause two types of CIED malfunctions: intermittent inhibition of pacing for bradycardia and/or inappropriate delivery of therapy for ventricular tachyarrhythmia. Bandpass filters designed to attenuate the extracardiac myopotentials have been used to avoid these malfunctions (sensing filters), and some state-of-the-art CIED models are equipped with selectable bandpass filters in accordance with the frequency characteristics of the signal from the sensing electrodes. We present a case in which the oversensing of diaphragmatic myopotentials was successfully avoided by adjusting the setting of the sensing filter.