Chapter 4 · Oversensing · Case 4
Lead fracture and multiple capacitor charges
Patient and episode
Patient
- 60-year-old male implanted with an Incepta single-chamber defibrillator; telemedicine alert for abnormal impedance measurement
Summary
- Episode classified in the VT zone
- No therapy delivered
The recording
Tap a number on the trace, or an entry in the list below
- Oversensing of fast signals on the bipolar sensing channel; no oversensing on the shock channel
- Oversensing on the ventricular channel of signals of variable amplitude and morphology; occasional large amplitude signals saturating the amplifiers; the shock channel makes it possible to differentiate these signals from spontaneous ventricular activity
- End of oversensing
From the interrogation
Points to remember
- The defibrillation lead is the weak link in the defibrillation system, with rates of malfunction varying between models
- In this patient, the combination of high impedance values and the abnormal EGM trace is highly suggestive of lead fracture; there is oversensing of fast, intermittent signals of varying morphology with very short cycle lengths close to the ventricular blanking period; some signals are very large, saturating the amplifiers; these ‘make-break’ potentials are highly suggestive of lead fracture with probable breach of the conductor rather than an insulation defect; the graph also shows a characteristic cloud of points with very short cycles
- In this asymptomatic patient, remote monitoring facilitated an early diagnosis and prevented inappropriate therapies; this helps avoids a succession of inappropriate shocks which, even if diverted, consume energy and shorten the life of the device
- In cases of lead dysfunction, anomalies generally occur in different stages: initially, the device may record multiple episodes of non-sustained VT without any anomalies in lead parameters; subsequently, a clear break in impedance, threshold and right ventricular sensing curves may be observed; as the duration of over-sensing episodes increases, multiple shocks may occur
Sensing and impedance curves
- Stable right ventricular shock impedance
- Abnormal right ventricular pacing impedance (> 2000 Ohms)
- The impedance curve shows a number of abnormal values and a clear jump when compared to previously stable values
Episode list since previous interrogation
- Multiple episodes of non-sustained VT recorded at the same time as the abnormal pacing impedance values
- 2 episodes classified as VT with no therapy delivered
Interval plot
- Appearance suggestive of lead dysfunction; the presence of a cloud of points that is generally incompatible with ventricular arrhythmia
- Very fast cycles (bordering on blanking) with slower cycles
Practice out loud
Just describe the tracing. What do you think is going on? Describing the numbers can help.
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From Boston Scientific ICD — clinical cases by P. Bordachar, M. Strik, A. Thiyagarajah, S. Ploux. Published by Cardiocases. Every numbered marker on a recording is explained in the list beneath it; tap a marker on the trace or an entry in the list.
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