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?