An unusual cause for inappropriate defibrillator shock.
Abstract
A 50-year-old lady with dilated cardiomyopathy and scar VT underwent
single chamber implantable cardioverter-defibrillator (ICD, Medtronic
Ltd, Evera XT VR, DVBB2D1) implantation 2 months back. A Sprint Quattro
secure 6947 DF1 dual coil lead was placed at RV apex. Now, she presents
with an episode of ICD shock while having breakfast. The device
interrogation shows a 36 J shock in VF zone (Fig 1A). However, the
stored electrograms (EGM) reveal distinct QRS complexes in the far-field
EGM; hence, suggesting the shock is related to oversensing. Fig 1B shows
2 panels of another recent episode. Fortunately, there was aborted
therapy as there was intermittent resolution of the oversensing. The
lead impedance was normal but threshold was high. Is it possible to
predict the reason for the oversensing from the EGM and how to
troubleshoot?