Oversensing and connection defect
Tracing
Manufacturer Medtronic
Device ICD
Field Oversensing
N° 28
Patient
Patient implanted with a dual-chamber ICD (Evera XT DR) for hypertrophic cardiomyopathy; the day after implantation, highlighting of non-sustained VT episodes in the device memory in conjunction with a connection defect.
Graph and trace
The graph shows a characteristic scatter plot pattern with significant interval to interval variability and very short ventricular cycles at the limit of the programmed blanking value; no delivered therapy and diagnosis of non-sustained VT.
- the EGM reveals intervals with anarchic amplitude and frequency, unrelated to the QRS complexes, with some signals saturating the amplifiers and some intervals at the limit of the programmed blanking.
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When in the presence of inappropriate therapy early after implantation, two causes are to be particularly investigated: faulty connection of the pace/sense pin and an early dislodgement of the ventricular lead. A control interrogation of the ICD allows measuring the pacing thresholds, the R wave amplitude as well as impedances. Lead position can be verified by a chest X-ray.
A connection problem (loosened setscrew connection, incomplete contact between lead pin and header) can yield a similar presentation to that of a lead fracture: the impedance may be abnormally high and the pattern of the EGMs may be relatively similar (fast, disorganized, anarchic and sometimes high-amplitude signals saturating the amplifiers). In such instance, the chest X-ray can confirm the absence of contact between the pin connector and the header. A connector problem is most often revealed within a short time interval after the last intervention (primary implantation or change of pulse generator), the impedance variation and/or the oversensing generally occurring within a few hours to a few days after the procedure. Signs associated with a lead fracture/failure often appear later, except in cases of procedural damage (e.g. direct lesion of the lead with the electric scalpel). In case of a loose connection, manipulating the device inside in the pocket can reproduce the oversensing.
Other atypical presentations may replicate that of a lead dysfunction with combination of an abnormal impedance and oversensing: lead to lead mechanical interaction (contact between the defibrillation lead and a remaining lead fragment or an abandoned right ventricular lead), presence of air in the connector with a specific oversensing pattern corresponding to air bubbles escaping from the connector.
The differentiation between these different clinical situations is essential, albeit sometimes difficult, in order to avoid a false diagnosis of lead fracture which has important therapeutic implications (necessity to replace the lead and discussion on the necessity to extract the "defective" lead). a