50 Hertz oversensing
Tracing
Manufacturer Abbott
Device ICD
Field Sensing
N° 23
Patient
A 34-year-old male recipient of a single chamber ICD, implanted after he suffered an episode of aborted sudden death, experienced an electrical shock while operating a power saw in the rain.
Main programmed parameters
- VF zone at 240 bpm and VT zone at 197 bpm
- 12 cycles in the VF and 18 cycles in the VT zones were needed for the diagnosis
- Maximum sensitivity programmed at 0.3 mV
- VF zone: six 36-J shocks (maximum strength); VT zone: set on monitor
- Effective discrimination in the VT zone
- VVI pacing mode at 40 bpm; VVI post-shock pacing mode at 40 bpm
Graph and trace
Narrative (tracing 17a)
Episode of VF with noise reversal; the charge was dumped.
Tracing
1: Sinus rhythm;
2: Sensing of very rapid signals, which heavily saturated the baseline, though the QRS complexes remained visible;
3: Decrease in the signals amplitude;
4: Further oversensing and diagnosis of VF episode; start of the capacitors charge;
5: Therapies abandoned after the diagnosis of ventricular noise; pacing mode of interferences rejection (000);
6: The noise criterion was no longer verified by the ICD, which classified the on-going cycles as short (F);
7: Diagnosis of VF and capacitors charge (asterisks);
8: Further diagnosis of noise;
9: Return of sinus rhythm diagnosed.
Narrative (tracé 17b)
Another episode occurred a few minutes later with delivery of 36-J shock.
Tracing
Gain : 5mm/mV
10: Intermittent sensing of 50 Hz signal (typical pattern);
11: Diagnosis of return of sinus rhythm (intermittent oversensing; 5 consecutive VS);
12: Further oversensing, though without interference diagnosed by the ICD; diagnosis of VF and capacitors charge;
13: End of charge;
14: Delivery of 36-J shock;
15: End of oversensing and diagnosis of return of sinus rhythm.
Tracing 17a1
Gain : 20 mm/mV
16: This tracing is identical with the previous tracing though the amplification has changed; therefore, the amplitude of similar signals is huge.
Tracing 17a2
Gain : 1 mm/mV
17: Tracing identical with the previous tracing though the amplification has changed; the same signals are now very low in amplitude; the low-amplitude R waves are indicative of poor sensing; the intermittence of oversensing is apparent.
Tracing 17a3
Sweep speed: 100 mm/sec
18: Tracing identical with the previous tracing, though the faster sweep speed reveals the characteristic sinusoidal aspect of 50 Hz signals (20 ms in-between signals).
Other articles that may be of interest to you
This tracing shows the usual characteristics observed in patients presenting with electromagnetic interference: 1) exposure to a source at the time of event, and 2) rapid, regular signals spanning the entire cardiac cycle. The sweep speed of Abbott instrumentation can be changed, which allows the display of the characteristic sinusoidal aspect of exposure to a 50-Hertz alternating current, with a 20-ms interval in-between each signal.
On a dual chamber ICD, the signals are usually visible on both the atrial and the ventricular channels, and are larger on the shocking than on the sensing lead channel.
The noise reversion algorithm can lower the risk of inappropriate therapy without, however, eliminating it altogether, as in this case. The main preventive measures consist in finding the emitting source and avoiding the use of poorly insulated instrumentation.