Active Can/SVC Coil Feature
The Active Can™/SVC Coil parameter specifies the electrodes used for defibrillation and cardioversion pulses. Either the Active Can or the SVC coil can be turned off to noninvasively troubleshoot the ICD shock vectors in patients with high DFTs.
Caution: Lead coils and Active Can electrodes that are in contact during a high-voltage therapy may cause electrical currents to bypass the heart, possibly damaging the device and leads. While the device is connected to the leads, verify that therapeutic electrodes, stylets, or guide wires are not touching or connected by any material that may conduct electricity. Move objects made from conductive materials (for example, an implanted guide wire) well away from all electrodes before delivering a high-voltage shock.
This feature can be found in some Medtronic ICD and CRT-D devices. Please go to manuals.medtronic.com or consult with your local Medtronic representative regarding device models available in your geography.
The nominal setting is Can + SVC On. Other programming options are Can Off and SVC Off.
To program this feature, go to Params -> Therapies -> Shared Settings.
The Active Can/SVC Coil parameter has the following settings:
- The Can + SVC On setting connects both the Active Can (HVA) and the SVC Coil (HVX). Current flows between these electrodes and the RV Coil (HVB).
- The Can Off setting disables the Active Can feature. In this case, an SVC coil electrode must be implanted. Current flows between the SVC Coil (HVX) and the RV Coil (HVB).
- The SVC Off setting disables the SVC coil. Current flows between the Active Can (HVA) and the RV Coil (HVB).
Note: The HVA and HVX electrodes are always the same electrical polarity and always the opposite of the HVB electrode polarity.
The Active Can/SVC Coil feature determines if there is an A or X electrode active in the defibrillation vector. The direction of current is then determined by the settings for the Pathway parameter: AX>B or B>AX. AX refers to the HVA (Can) and HVX (SVC) electrodes, which may be used individually or in combination. B refers to the HVB (RV coil) electrode. The Pathway setting defines direction of current flow during the initial segment of the biphasic waveform. If the parameter is set to AX>B, current flows from the Active Can and SVC Coil to the RV Coil. If the parameter is set to B>AX, this current flow is reversed. The efficacy of the pathway parameter programming can be assessed at implant by induction testing.
There is a nonprogrammable Patient Alert if the Active Can is programmed Off without an SVC lead in place. The device sounds a high-urgency tone daily at the programmed time.
In the example below, SVC is programmed Off. Therapy pathways are programmed B >AX for shocks 1, 2, 3, 5 and AX >B for shocks 4 and 6. Therefore, defibrillation current will flow from the RV Coil (HVB) to the Active Can (HVA) during the initial segment of the biphasic waveform for shocks 1, 2, 3, 5 and from the Active Can to the RV Coil for shocks 4 and 6.
Studies have shown that using a reversed shock polarity (B > AX) may lower DFTs.1
References
- Olsovsky, M. “Effect of Shock Polarity on Biphasic Defibrillation Thresholds Using an Active Pectoral Lead System.” J Cardiovasc Electrophysiol, Vol. 9, pp. 350-354, April 1998.
Sources: Medtronic Protecta™ XT DR Clinician Manual; Medtronic Protecta™ XT CRT-D Clinician Manual.
Last updated:
27 Mar 2013