Case summary
An 81-year old male with a history of systolic heart failure due to an underlying ischemic cardiomyopathy with a left ventricular ejection fraction of 13% and QRS duration of 130ms had undergone an uncomplicated CRT-D implantation (Quadra Assura MP, St. Jude Medical) in 2015. The patient was evaluated on the ICD-outpatient clinic because of (near-)syncope. Recent home monitoring reported non-sustained oversensing (NSRVOS) in the VT2 zone (figure 1). At the time, his device was programmed to DDDR mode with SecureSense algorithm switched on and lower rate of 50 beats per minute (bpm) and maximum tracking rate of 130 bpm. The tachycardia therapy settings were; monitor zone 150 bpm (incount 20 intervals), VT2 zone 187 bpm (incount 30 intervals) and VF zone 240 bpm (incount 30 intervals). Triggered LV-pacing was switched off and ventricular noise reversion mode was VOO.
After investigating the reason behind NSRVOS, it was determined that this was a non-physiological signal with a fairly stable amplitude with a maximum of about 0.9 mV. Previous entries of the remote monitoring revealed several episodes showing the same signal with identical frequency and amplitude. This signal was detected by the ICD resulting in the start of incount for tachy therapy and inhibition of brady pacing resulting in an asystole. So the question arose: how can we protect both brady and tachy therapy in this particular case with recurrent noise with a stable signal amplitude?