FAQ

Double sequential external defibrillation is a procedure where two defibrillators are used at the same time during the treatment of cardiac arrest (1). Two sets of pads are placed on the patient who receives two shocks. One rescuer presses both shock buttons in rapid succession, ie. sequentially, less than one second apart. All other ACLS treatment will be according to existing guidelines.

DSED has been researched since 1940 in animal studies. The first human study was published in 1994 by Hoch et al (2). Many case series and case reports have been published since (3–8), but the scientific strengths of the studies are of variable degree. The first RCT was published in 2022 by Cheskes et al. (9), and it showed increased survival and improved neurological outcome compared to standard treatment in OHCA. The study researched the use of DSED initiated after three failed single-shocks.

DSED is currently used for the treatment of refractory ventricular fibrillation, a malignant heart rhythm that persists after three attempts with single-shock defibrillation. Canada, USA and New Zealand (10) are a few of the countries that have implemented the procedure in ground ambulance guidelines.

It is currently unknown whether earlier use of DSED may improve survival outcomes than those seen with standard defibrillation. This has never been tested before. Therefore, Dual Defib Trial aims to research the effect of DSED as an initial shock treatment.

The Dual Defib Trial is an investigator-initiated research project that will evaluate the difference between one and two defibrillators in OHCA treatment. The project will be a multicentre trial where participating ambulance stations are randomized to a six-month adherence to either standard or DSED procedure. This is followed by six months adherence to the opposite procedure. After one year, the procedures will be randomized again and follow the same pattern. The trial will be launched in mid-Norway with the possibility of new ambulance stations being consecutively included. The number of total patients included is 356, approximately 178 patients in both groups.

Before launching the RCT, a feasibility pilot study will test the integrity of the project. All OHCA patients treated by included ambulance stations will be included until feasibility of the study is accomplished. All registered patients in the pilot are sought included in the intervention group in the RCT.

For more information, read the Dual Defib Trial protocol. (LINK)

Included patients in both the pilot and the clinical study that receive DSED-treatment, will receive two defibrillations from first shock onwards. The other trials provide first shock with standard defibrillation. Also, the Norwegian ACLS guidelines state a 3-minute algorithm (11) compared to the 2-minute algorithm that is performed in other countries.

The procedure is completed by a two-member team, and both sets of pads are placed by one team member during ongoing CPR treatment:

The first set of pads are placed in anterior-lateral position; beneath the right collarbone and beneath the left armpit in the midaxillary line. This is done without interruptions in chest compressions.

The second set of pads is placed in anterior-posterior position; slightly to the left of the sternum and beneath the left shoulder blade close to the spine. The first pad is placed on the sternum while CPR-performer quickly provides access for pad placement and resumes chest compressions without delay. The second pad is placed on the back while CPR-performer tilts or logrolls the patient onto themselves. This is easiest done by grabbing the patient´s left hip with both hands. The pad-placer can push the patient´s back to further gain access to the area where the pad is placed. 

It is important that no pads are in contact with each other so that risk of current passing from one defibrillator to the other is as small as possible.

It is true that establishing two defibrillators will take more time than establishing one as in standard defibrillation treatment. However, we have scrutinized the actual time difference (12), and found that only 14 seconds separate the two procedures. In addition, there was no time difference in applying DSED procedure on a normal weight patient and an obese patient.  This means that the time difference is very short when added to the total response timeline of ambulance dispatch to arrival on-site.

There are three proposed mechanisms of effect (13):

1 – Increased energy

The total energy (Joule) delivered to the heart by the two shocks allows for defibrillation of a critical mass of myocardium that has tendency of recurrent VF. Some studies also suggest that as little as 10% of delivered energy reaches the heart when pads are placed in anterior-lateral position in standard defibrillation.

2 – Shock setup

The first shock lowers the electric potential threshold of cardiomyocytes, preparing or conditioning the cells for a second shock now received with a higher degree of success. This is why the two shocks must come in rapid sequence to not delay the second shock.

3 – Multiple vectors

The orthogonal (90 degree angle) vector that is created by the two sets of pads changes the distribution of current reaching the posterior parts of myocardium where recurrent VF is most likely to reappear.

The procedure has been thoroughly tested for the past decade and found safe. The published literature describes hundreds of patients treated with DSED. There have been no severe adverse effects described, but a small number of minor skin burns and software issues have been seen.

All adverse incidents have been analyzed and produced the following safety measures that can be applied to make the procedure safe:

1. Do not let pads touch each other.
2. Use only two identical defibrillators.
3. Place pads in the described procedure and not parallel to each other.
4. Aim to release defibrillations sequentially with less than one second apart – not synchronized.