AED survival rates without chest compressions or defibrillation are essentially zero, but with early bystander CPR and a defibrillation shock provided within less than 3 minutes after collapse, the AED survival rate can be as high as 74% for patients with ventricular fibrillation.
Studies have shown over and over again that a rapid response is the most crucial element to survival. Having an automated external defibrillator nearby and knowing how to recognize the signs of sudden cardiac arrest could save hundreds or even thousands of lives.
Survival Rates for Out-of-Hospital Cardiac Arrest Victims Who Received an AED Shock Before EMS Arrived
A population-based cohort study published in the Journal of the American College of Cardiology examined 13,769 out-of-hospital cardiac arrests documented between December 2005 and May 2007. The aim was to see how bystander CPR and AED shock therapy provided before EMS personnel arrived (if any) affected SCA survival rates to hospital discharge. This study did not document the length of time between collapse and the defibrillation shock.
Based on the available data, the researchers discovered that:
- 7% of cardiac arrest victims with no bystander CPR or defibrillation shock survived to hospital discharge.
- 9% of cardiac arrest victims with bystander CPR but no AED shock survived to hospital discharge.
- 38% of cardiac arrest victims with bystander CPR and an AED shock survived to hospital discharge.
Astoundingly, of 13,769 out-of-hospital cardiac arrests, only 32% of victims received bystander CPR and a mere 2.1% received an AED shock. By waiting for EMS personnel—who typically take between 4 and 10 minutes to arrive—the survival rates were much lower.
Survival Rates for Cardiac Arrest Patients Under Ideal Circumstances
A second large-scale study was published in 2018 in the American Heart Association’s journal Circulation. This study analyzed 49,555 out-of-hospital cardiac arrests in major U.S. and Canadian cities and, in particular, the effects of public AED use on survival rates when:
- The sudden cardiac arrest (SCA) occurred in public.
- The collapse was witnessed.
- The victim had an AED shockable rhythm—either ventricular fibrillation or pulseless ventricular tachycardia.
Under these ideal circumstances, researchers found that SCA victims had a survival rate of 66% with bystander AED use and 43% without. More specifically, victims who received a shock from a publicly available automatic external defibrillator had 2.62 times higher chance of surviving to hospital discharge and 2.73 times of functioning well after discharge compared to victims who only received a shock after emergency medical services arrived. The researchers concluded that “assisting cardiac arrest victims before emergency responders can get to the scene” is the most critical factor in better survival rates.
Time Until Defibrillation and Survival Rates
The first two studies examined cardiac arrest survival rates with respect to public access defibrillation before the arrival of emergency responders. However, other studies shed more light on the precise difference in response time when non-medical rescuers are given access to AEDs.
Lay Volunteers vs EMS in Italy
An experimental study published in Circulation in 2002 examined the impact of equipping untrained lay volunteers with automated external defibrillators. The 1285 volunteers, located in the Piacenza region of Italy, had no traditional training in cardiopulmonary resuscitation but were given access to 39 AEDs.
Over a period of 22 months, the volunteers responded to 143 cases of sudden cardiac arrest, arriving in 4.8 minutes compared to 6.2 minutes for emergency medical services. Without controlling for factors such as shockable rhythms or whether the collapse was witnessed, the faster response time tripled survival rates—10.5% of victims survived with early lay defibrillation compared to 3.3% with traditional EMS.
Police vs EMS in Florida
A similar experiment was conducted in Miami-Dade County in Florida, in which police cars were equipped with AEDs in an attempt to reduce response time in cases of out-of-hospital cardiac arrest. During the study period, police officers responded in an average of 4.88 minutes compared to 7.64 minutes for emergency personnel. The survival rate for cardiac arrest victims treated by police was 17.2% compared to 9% with EMS.
Casino Security Guards Instructed in AED Use
A further study, published in the New England Journal of Medicine in 2000, examined the effect of training casino security officers in defibrillation and providing them with AEDs. This study provides especially valuable insights into survival rates because the results were controlled for the presence of ventricular fibrillation and the exact response time.
Of 105 patients with ventricular fibrillation, the survival rate among those who received their first shock less than 3 minutes following the witnessed collapse was 74% compared to 49% for those who received their first shock after 3 minutes following the witnessed collapse. This shows that the highest survival rates are achieved when the collapse is witnessed and a defibrillation shock is administered within 3 minutes of the collapse.
How Does Rapid Defibrillation Boost Survival Rates?
The reason that rapid defibrillation boosts survival is very simple: The electric shock delivered by the AED stops the chaotic and ineffective rhythm in cardiac arrest so that a normal heart rhythm can resume. At that point, the heart can pump oxygen-rich blood around the body again.
When the heart doesn’t pump blood to the body, the brain and other vital organs begin to die, and chest compressions can only do so much before the oxygen in the blood is gone. A defibrillation shock is the only way to help the heart restart and pump oxygenated blood around the body again—preventing brain damage and increasing the chance of survival.
Why Aren’t Survival Rates 100%?
While early defibrillation can dramatically improve survival rates, some cases won’t respond to an AED or advanced cardiac life support—no matter how well or how quickly it’s applied.
One reason an AED won’t always restore a normal sinus rhythm is that some cardiac arrest victims have a non-shockable rhythm like pulseless electrical activity or asystole. An external defibrillator can only stop an abnormal heart rhythm if there is chaotic (rather than orderly or absent) electrical activity.
Another reason that AED shock therapy might not bring someone back is that there were multiple health problems or structural issues in the heart that were simply beyond treatment. However, providing chest compressions and defibrillation right away will give them the best chance.
How Public Access Defibrillation Can Save Lives
While there might be some victims who don’t survive, immediate CPR combined with rapid defibrillation is the best way to raise survival rates from cardiac arrest. To save as many lives as possible, most U.S. states today have public access defibrillation programs and laws that aim to maximize access to external defibrillators.
You can often find easy-to-use portable defibrillators like the Philips HeartStart FRx or HeartSine Samaritan PAD 350P, 360P, or 450P in:
- Schools
- Colleges
- Gyms
- Swimming pools
- Shopping malls
- Dental offices
- Police stations
- Hospitals
If there is a strong public access defibrillation program in your state, emergency personnel may have a list of the AEDs available in the immediate vicinity and can tell you exactly where to go. That’s why it’s essential to call 9-1-1 as soon as you find someone who is unconscious and unresponsive or witness someone suddenly collapse.
What to Do If You Witness a Cardiac Arrest
If you see someone collapse suddenly, become unresponsive, and stop breathing or breathe in gasps:
- Call 9-1-1 and send someone to get an AED.
- If it’s safe to approach, provide compression-only CPR (don’t give rescue breaths unless you’re trained to do so).
- Attach the electrode pads, turn the defibrillator on, and follow the instructions. The AED will analyze the patient’s heart rhythm and prompt you to administer a shock if it detects a shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia).
The most important thing to remember is that the survival rate from cardiac arrest drops by 7–10% for every minute that a patient waits for treatment. Know where your nearest AED is and don’t hesitate to use it if you see someone collapse. Their life is literally in your hands.
