Oversensing of atrial fibrillatory waves in a subcutaneous implantable cardioverter-defibrillator

S-ICD oversensing detected by remote monitoring using a new atrial fibrillation diagnostic algorithm

“…This can cause a reduction in R wave amplitude. Small R wave sizes (<0.5 mV) and periods of asystole (≥3 sec) can cause the S-ICD to automatically disable the SMART Pass filter, which has shown to be useful at reducing inappropriate therapies [ 2 , 3 ]. The dampened R waves led to a low signal-to-noise ratio, resulting in oversensing of P and T waves, some episodes being sustained enough to meet both AF and VT/VF detection criteria.…”

Mechanisms and management of inappropriate therapy in subcutaneous implantable cardioverter defibrillators

“…From oversensing of atrial fibrillatory waves in a subcutaneous implantable cardioverter‐defibrillator. Reproduced with permission from Karnik et al…”

“…There is a case report of oversensing of flutter waves in a patient with hypertrophic cardiomyopathy (HCM) . We recently published a report on a patient with HCM who received inappropriate shocks due to oversensing of atrial fibrillation waves . A key requirement for atrial oversensing appears to be a “baseline shift” after which oversensing begins (Figure ).…”

“…R waves with high amplitudes and rapid upstrokes (slew rate) may exceed the dynamic processing ability of the analog to digital converter (ADC) circuit and lead to a shift in the baseline. Rectification of the QRS complex in the context of this baseline shift will narrow the ratio between R wave and the T wave (or atrial flutter/fibrillatory waves), allowing for inappropriate sensing and eventual therapy . Baseline shift leading to inappropriate therapy has been reported in 0.06% of patients with S‐ICDs (personal communication, Boston Scientific technical services).…”

“…The effect of the SMART Pass filter on our patient is demonstrated in Figure A and B. Atrial oversensing (arrows) is seen after baseline shift (Figure B) and application of the filter reduces the T and AF wave amplitude, eliminating oversensing. However, undersensing of fine ventricular fibrillation would be a theoretical risk …”