Since January this year, Aotearoa New Zealand has become only the second country (after Canada) to introduce a groundbreaking new procedure for cardiac arrest patients.
It is known as ‘double sequential external defibrillation’ (DSED) and will change initial emergency response strategies and potentially improve survival rates for some patients.
Surviving cardiac arrest critically depends on effective resuscitation. When the heart is working normally, electrical pulses travel through the muscle walls, causing regular, coordinated contractions.
But when normal electrical rhythms are disrupted, heartbeats can become uncoordinated and ineffective, or stop altogether, leading to cardiac arrest.
Defibrillation is a cornerstone resuscitation method. It delivers a powerful electric shock to the heart to stop the abnormal electrical activity. This allows the heart to restore its normal rhythm.
Its success depends on the underlying dysfunctional heart rhythm and the correct placement of the defibrillation electrodes that deliver the shock. The new procedure provides a second option when standard positioning is not effective.
Use of two defibrillators
During standard defibrillation, one pad is placed on the right side of the chest, just below the collarbone. A second pillow is placed under the left armpit. Shocks are given every two minutes.
Early defibrillation can significantly increase the chance of surviving cardiac arrest. However, approximately 20% of patients whose cardiac arrest is caused by “ventricular fibrillation” or “pulseless ventricular tachycardia” do not respond to the standard defibrillation approach. Both conditions are characterized by abnormal activity in the heart chambers.
DSED is a new method that delivers rapid successive shocks to the heart using two defibrillators. The electrodes are attached in two different locations: one on the front and side of the chest, the other on the front and back.
A single operator activates the defibrillators in sequence, with one hand moving from the first to the second. According to a recent randomized trial in Canada, this approach could more than double the survival chances of patients with ventricular fibrillation or pulseless ventricular tachycardia who do not respond to standard shocks.
The second shock is believed to increase the chances of eliminating persistent abnormal electrical activity. It delivers more total energy to the heart and travels along a different path closer to the left ventricle.
Evidence of success
New Zealand ambulance data from 2020 to 2023 identified approximately 1,390 people who could potentially benefit from new defibrillation methods. This group currently has a survival rate of only 14%.
Recognizing the potential of DSED to dramatically improve survival for these patients, the National Ambulance Sector Clinical Working Group has 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 applied. Two defibrillators must be available and staff must be trained in the new approach.
Although the existing evidence for DSED is compelling, until recently it has been based on theory and a small number of potentially biased observational studies. The Canadian study 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 design of the study minimized the risk that other factors would confound the results. It provides confidence that the survival improvements were due to the defibrillation approach and not to regional differences in resources and training.
The study also confirms and builds on existing theoretical and clinical scientific evidence. However, because the trial was stopped prematurely due to the COVID-19 pandemic, the researchers were able to recruit less than half of the planned numbers for the study.
Despite these and other limitations, the international group of experts that advises on best practices for resuscitation updated its recommendations in 2023 following the trial results. It suggested (with caution) that emergency medical services consider DSED for patients with ventricular fibrillation or pulseless ventricular tachycardia unresponsive 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 an important step in increasing global knowledge of optimal resuscitation strategies.
There are always concerns when translating 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 must undergo mandatory education, simulation and training. The implementation is being closely monitored to determine its impact.
Hospitals and emergency departments have been notified of the protocol changes and have been given the opportunity to ask questions and provide feedback. As part of the implementation, St. John’s Ambulance Service will conduct case reviews in addition to broader monitoring to ensure patient safety is prioritized.
Ultimately, those involved are optimistic that this change in the treatment of cardiac arrests in New Zealand will have a positive impact on the survival of affected patients.
Vinuli Withanarachchie, PhD candidate, College 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.