In cases of cardiac arrest, an initial rhythm check revealing a shockable rhythm, such as ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT), usually results in higher survival rates than non-shockable rhythms like PEA or asystole. Nevertheless, defibrillation sometimes fails. When the rhythm persists after three shocks, it is called refractory VT or VF. If the rhythm briefly transitions to PEA or sinus rhythm before rapidly reverting to VT or VF, it is often referred to as recurrent VT or VF.

Background: The DOSE VF Study

This challenge was the background for DOSE VF, a randomized controlled multicenter study that generated significant interest when published in 2022. Researchers investigated whether an altered pad placement, called "vector change" (VC), or the simultaneous use of two defibrillators, called "double sequential external defibrillation" (DSED), could yield better results after three unsuccessful shocks.

"Vector change" involves moving pads from the standard anterolateral placement, i.e., one pad below the right clavicle and one below the left armpit, to an anteroposterior placement with one pad in front and one behind. The purpose is to change the current's path through the heart. With DSED, one set of pads is anterolateral and one anteroposterior, each connected to its own defibrillator. The patient then receives two rapid shocks from two different vectors.

Results and Debate

The results led to considerable debate. Survival to hospital discharge was 30.4 percent with DSED, compared to 13.3 percent with standard treatment. VC was in between with 21.7 percent. DSED also appeared to result in more successful defibrillations, more ROSC, and better neurological outcomes. However, the study was stopped early due to the pandemic and included fewer patients than planned. The effect may therefore be overestimated, which is highlighted in later discussions.

Nevertheless, the study made an impression and led to discussions among professionals about the utility of VC and DSED in refractory or recurrent VT or VF. The new Advanced Life Support guidelines from 2025 from the European Resuscitation Council (ERC) allow for considering VC after three unsuccessful shocks. DSED is still only recommended in a research context. Some believe this is a correct and cautious approach. Others point out that there should be room for more aggressive measures when already in a situation with a very low probability of success after three failed shocks.

Need for Further Research and Technological Development

In any case, there is agreement that more studies are needed. More research on VC and DSED will hopefully provide clearer answers in the coming years. If DSED proves to be effective and practically feasible, a natural question arises. Should a single defibrillator be able to deliver two shocks from two vectors? So that there is no need for two separate defibrillators in manual mode? This would require a defibrillator with four pads, not two. That should be technically possible for the industry.

Perhaps in a few years, we will have defibrillators with four pads as standard?

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Suggested further reading for the especially interested:
Here you can read the DOSE VF study and see the electrode placement if you wish: https://www.nejm.org/doi/full/10.1056/NEJMoa2207304
Here are the latest ERC guidelines: https://www.resuscitationjournal.com/article/S0300-9572(25)00281-3/fulltext