In January this year, Aotearoa New Zealand became the second country (after Canada) to adopt an innovative new procedure for patients suffering cardiac arrest.
Known as “double sequential external defibrillation” (DSED), it will change initial emergency response strategies and potentially improve survival rates for some patients.
Surviving cardiac arrest fundamentally depends on effective resuscitation. When the heart is functioning normally, electrical pulses travel through its muscle walls creating regular, coordinated contractions.
But if normal electrical rhythms are disturbed, the heartbeat can become uncoordinated and ineffective, or stop altogether, causing cardiac arrest.
Defibrillation is a fundamental resuscitation method. It gives the heart a powerful electrical shock to end abnormal electrical activity. This allows the heart to restore its regular rhythm.
Its success depends on the underlying dysfunctional heart rhythm and the proper position of the defibrillation pads that deliver the shock. The new procedure will provide a second option when standard positioning is not effective.
Using two defibrillators
During standard defibrillation, a patch is placed on the right side of the chest, just below the collarbone. A second pad is placed under the left armpit. Shocks are applied every two minutes.
Early defibrillation can dramatically improve your chance of surviving cardiac arrest. However, about 20% of patients whose cardiac arrest is caused by “ventricular fibrillation” or “pulseless ventricular tachycardia” do not respond to the standard defibrillation method. Both conditions are characterized by abnormal activity in the ventricles of the heart.
DSED is a novel method that delivers rapid sequential shocks to the heart using two defibrillators. The pads are placed in two different places: one on the front and side of the chest, the other on the front and back.
A single operator activates the defibrillators in sequence, moving one hand from the first to the second. According to a recent randomized trial in Canada, this approach could more than double the chances of survival for patients with ventricular fibrillation or pulseless ventricular tachycardia who do not respond to standard shocks.
The second shock is believed to improve the chances of eliminating persistent abnormal electrical activity. It delivers more total energy to the heart, traveling along a different pathway closer to the left ventricle of the heart.
Evidence of success
New Zealand ambulance data from 2020 to 2023 identified around 1,390 people who could potentially benefit from new defibrillation methods. This group has a current survival rate of only 14%.
Recognizing the potential of DSED to dramatically improve the survival of these patients, the National Ambulance Sector Clinical Working Group updated clinical procedures and guidelines for emergency medical services personnel.
The guidelines now specify that if ventricular fibrillation or pulseless ventricular tachycardia persists after two shocks with standard defibrillation, the DSED method should be administered. It is necessary to have two defibrillators and the staff must be trained in the new method.
Although the existing evidence on DSED is compelling, until recently it was based on theory and a small number of potentially biased observational studies. The Canadian trial was the first to directly compare DSED with standard treatment.
Of a total of 261 patients, 30.4% treated with this strategy survived, compared to 13.3% when standard resuscitation protocols were followed.
The trial design minimized the risk of other factors confounding the results. It provides confidence that the improvements in survival were due to the defibrillation approach and not regional differences in resources and training.
The study also corroborates and is based on existing theoretical and clinical scientific evidence. However, as the trial was stopped early due to the COVID-19 pandemic, researchers were able to recruit less than half the numbers planned for the study.
Despite these and other limitations, the international group of experts that advises on best resuscitation practices updated its recommendations in 2023 in response to the trial results. He suggested (with caution) that emergency medical services consider DSED for patients with ventricular fibrillation or pulseless ventricular tachycardia who do not respond to standard treatment.
Training and implementation
Although evidence is still emerging, the implementation of DSED by emergency services in New Zealand has implications beyond patient care at a national level. It is also a key step to advance knowledge about optimal resuscitation strategies worldwide.
There are always concerns when moving an intervention from a controlled research environment to the relative disorder of the real world. But the balance of evidence was carefully considered before the decision was made to change procedures for a group of patients who have a low chance of survival with current treatment.
Before using DSED, emergency medical personnel undergo mandatory education, simulation, and training. Implementation is closely monitored to determine its impact.
Hospitals and emergency departments were informed of the protocol changes and were given the opportunity to ask questions and provide feedback. As part of the rollout, St John Ambulance Service will conduct case reviews as well as wider monitoring to ensure patient safety is prioritised.
Ultimately, those involved are optimistic that this change in the management of cardiac arrest in New Zealand will have a positive impact on the survival of affected patients.
Vinuli Withanarachchie, PhD candidate, Faculty of Health, Massey University; Bridget Dicker, Associate Professor of Paramedicine, Auckland University of Technology, and Sarah Maessen, Research Associate, Auckland University of Technology
This article is republished from The Conversation under a Creative Commons license. Read the original article.