Detection of ventricular fibrillation
Trace category:
EGM
Device/Field:
ICD
Company:
Medtronic
Patient with a single-chamber ICD (Medtronic Evera) implanted for primary prevention in the context of severe ischemic heart disease.
He was admitted because of a ventricular fibrillation episode with ATP attempt and termination by internal electrical shock.
The episode was entierly asymptomatic and was discovered by remote monitoring..
ICD tachycardia zones were programmed as follows:
Initial Redétection V interval (rate)
VF On 30/40 12/16 300 ms (200 min-¹)
FVT Off
VT On 32 12 360 ms (167 min-¹)
Monitor 36 420 ms (143 min-¹)
My question:
How does the ICD detect VF while the VF counter of 30/40 has not been filled?
PR Richard Hooker
Fri, 28/10/2016 - 18:13
The device is using the Medtronic combined count algorithm as the episode falls at rates in both the VT zone and VF zone. The combined count is 7/6 of the normal interval to detect (NID) and uses the VF detection 30/40. Therefore the device detects the epsiode on the 35beat (7/6 x 30 = 35). To assess whether it is a VT or VF episode it looks at the 8 cycles before detection if one falls into the VF zone (as in this case) the device treats the episode as VF.
That's about the best sense I can make of it
Rich
Good Hope Hospital. U.K
DR Marc Strik
Sat, 29/10/2016 - 10:09
Correct! Great explanation as well!
Just wish to add for those not familiar with the combined counter that Medtronic implemented this algorithm in order not to delay detection (and therapy) for tachycardias which have coupling intervals both in the VT and VF zone.