Device Interrogation:
- What type of device is this?
- What rhythm is this?
- How is the rhythm terminated?
- Is the device functioning appropriately?
- What if any programming changes should be considered?
Answer:
This device is a CRT-D. At first glance, one may think this is a dual chamber ICD, but look at the markers after the shock and you will see “BP” which means Bi-Ventricular pace.
This is a stored episode where an LV waveform channel was not selected for episode storage in this device. It is important to know what kind of device you are looking at when interpreting EGMs, and this is a good example of looking a little closer!
The rhythm is being called “VF” by the device and a HV shock is delivered. The sinus rate is approximately 100bpm; note the p waves on the atrial channel. The stored episode demonstrates undersensing and oversensing on the RV channel.
Device testing was performed and shown below:
RV threshold testing shows no capture at 6.0V. The threshold one month prior was 0.75V@0.5ms.
The Ventricular sense test shows R waves at 1.7mV, while one month prior they were 8.8mV.
Notice the R wave measurements have been as low as 0.4mV.
These findings are consistent with an RV lead dislodgment; most likely pulled back into the tricuspid annulus. One can suspect that this is true given the RV lead appears to be sensing p waves as well as variable R waves. The device is binning the intervals into the programmed VF zone, therefore causing an inappropriate shock. This is inappropriate device behavior. The ICD HV therapy was programmed off to avoid additional inappropriate shocks, and the patient was sent for an RV lead revision.
