Rethinking the Shock: What a New Cardiac Arrest Study Reveals About Defibrillation

In a life-or-death emergency, our intuition often screams for a simple solution: more is better. Whether it's more water on a fire or more pressure on a wound, we are conditioned to believe that increasing the force of our intervention will yield a better outcome. This "more power" instinct seems especially true during sudden cardiac arrest (SCA) events where electricity from a defibrillator is used to jolt a chaotic heart back into a life-sustaining rhythm. The logical assumption is that a stronger, more powerful shock would be more effective. However, a recent large multicenter study on out-of-hospital cardiac arrests, accepted for publication in Resuscitation Plus, challenges this fundamental assumption. Thousands of defibrillation attempts were analyzed to compare a standard energy setting with a newer, high-current approach; the results reveal what makes defibrillators effective, which could reshape our understanding of SCA responses.

Takeaway 1: On the First Attempt, More Power is a Draw

The study compared two different settings on a defibrillator used during out-of-hospital cardiac arrests (OHCA): the standard 200 Joule (J) shock and a novel "MAX" option. Unlike a standard setting that delivers a fixed amount of energy, the MAX option is designed to deliver the technically highest possible electrical current based on a patient's specific chest resistance, or impedance. This adaptive approach is intended to optimize the dose for each victim.

The most counter-intuitive finding emerged from the most critical moment: the very first shock. The data showed no statistically significant difference in success rates between the higher-current MAX setting and the standard 200 J setting. This held true for two key measures of success:

• Termination of Fibrillation (TOF): Simply stopping the chaotic heart rhythm. The first shock was successful in 81% of MAX cases versus 76% of 200 J cases.

• Return of Organized Rhythm (ROOR): The return of a potentially life-sustaining, organized heart rhythm. The first shock was successful in 66% of MAX cases versus 64% of 200 J cases.

This is counter intuitive to many providers who assume that a stronger, more optimized shock would prove immediately superior.

Takeaway 2: For Stubborn Cases, Higher Current Gains the Edge

Many cardiac arrest patients don't respond to the first shock. Their heart rhythm can remain chaotic or revert to fibrillation, requiring multiple attempts to restore an organized rhythm. The research showed that when considering all shocks delivered throughout a resuscitation effort, the MAX setting demonstrated a significantly higher overall success rate.

• Overall TOF: MAX achieved an 80% success rate across all shocks compared to just 72% for the 200 J setting (p < 0.001).

• Overall ROOR: MAX also led to a significantly higher rate of organized rhythms, at 67% versus 63% for the 200 J setting (p = 0.02).

This finding was reinforced by patient-level data. In an analysis of patients who received only one type of shock setting, those treated with MAX needed fewer shocks on average to achieve success (1.17 vs. 1.36, p = 0.02). Furthermore, within three shocks, TOF was reached in 93.1% of patients receiving only MAX shocks versus 89.3% of those receiving only 200 J shocks. This evidence suggests that a higher-current approach is more effective for treating persistent fibrillation.

Takeaway 3: It's Really About the Current, Not Just the Joules

This also highlights a core principle of electrophysiology: the decisive factor for a successful defibrillation isn't the total energy delivered (Joules), but the electrical current (Amps) that successfully passes through the myocardium. A patient's body, i.e. their transthoracic impedance, acts as a resistor to the electrical shock. Defibrillators set to a fixed energy level, i.e. 200 J, it will deliver significantly less current to a high-impedance patient than to one with a low-impedance. The MAX setting is fundamentally different because it utilizes a current-based strategy; instead of targeting a fixed energy output, it adapts to the patient specific impedance needs to deliver the highest possible current. This ensures a more consistent and potent electrical dose reaches the heart muscle. This principle isn't new; current-based defibrillation was investigated decades ago, however major international guidelines continue to recommend energy-based protocols, making these findings particularly noteworthy.

Conclusion: A Smarter Shock, Not Just a Stronger One

This study offers a critical update to our understanding of defibrillation. The future of defibrillation technology may not lie in escalating energy levels, but in developing smarter, more adaptive systems that prioritize the delivery of the electricity.

The findings push us to look beyond the "more power" paradigm. An intelligent, current-based approach can finally move the needle on the ultimate goals: improved rates of resuscitation and long-term survival.

Reference:

A.M. Lechleuthner, K. Leupolz, F. Ripke, S. Dopfer, J. Stock, C. Miller, Y. Keller, M. Strohm, Effect of higher currents on defibrillation success in out-of-hospital cardiac arrest: A multicentre cohort analysis, Resuscitation Plus (2025), doi: https://doi.org/10.1016/j.resplu.2025.101205