Sudden cardiac arrest is an abnormal heart rhythm most often caused by ventricular fibrillation (an irregular heart rhythm from the lower chambers of the heart). When the heart’s ventricles are fibrillating, they cannot pump blood to the brain and vital organs. If not treated promptly, this leads to death. Sudden cardiac arrest is common and affects 350,00 people in the US each year. Surviving sudden cardiac arrest requires prompt cardiopulmonary resuscitation (CPR) and defibrillation with an Automatic External Defibrillator (AED). Timing is everything; if an AED shock is provided within one to two minutes of going into sudden cardiac arrest about 50% of victims will live. However after 10 minutes, less than 10% will survive. We have all seen this in real time recently. Due to the quick response and the coordinated efforts of a team who practiced for just this type of situation, Damar Hamlin is alive today. However, most sudden cardiac arrests do not happen in a controlled environment such as a cardiac care unit. The big question then is how to get responders and AEDs to sudden cardiac arrest victims as fast as possible.
If a patient has cardiac arrest in the hospital, doctors and nurses with advanced cardiac training can often successfully resuscitate the patient. If someone suffers sudden cardiac arrest outside of the hospital, it is a different story. In studies it has been shown that 8% of cardiac arrests occur in a public setting and witnessed by bystanders, but the vast majority of out of hospital cardiac arrests occur in the home (75%). The overall survival rate for out of hospital cardiac arrest is only between 2% and 14%. One of the biggest barriers to successfully resuscitating a patient out of the hospital is getting trained responders to the victim. Once a cardiac arrest has been called to 911 or emergency services, a dispatch is placed to first responders; police, fire and ambulance corps. However, if it takes emergency responders more than ten minutes to locate and get to the victim, the outcome is usually not good. If bystanders near a victim are able to start CPR and, even better, use an AED, the chance of survival increases dramatically. Resuscitation by bystanders is associated with survival rates between 53% and 66%. For comparison, survival rates for emergency medical personnel is between 28% and 43%. Most studies show a 2 fold better chance of living if the patient is treated immediately by a bystander. There are a number of volunteer responder programs around the world, including Denmark, Netherlands, United Kingdom, Australia, US and Canada. The idea is to alert volunteer trained responders about a cardiac arrest and direct them to the victim so that prompt CPR can be initiated. The programs work in the following way. Once a cardiac arrest has been called in to a central dispatching agency, registered volunteers in the vicinity of the arrest are contacted via text message. Some responders are directed to the nearest available AED, while others are sent straight to the patient to start CPR. The system keeps notifying volunteers until a critical mass have responded and are on their way. How many responders are needed to optimally manage a sudden cardiac arrest? When 3 or morevolunteersresponded before emergency medical services, there was a greater chance for bystander defibrillation with an AED.
The other huge barrier to successful resuscitation is getting an AED to the victim as soon as possible. AEDs have become ubiquitous. About 500,000 to 1 million were sold in the US last year and there are about 3.2 million AEDs in public settings. Yet, there is still a shortage. AEDs in public places (for example gyms, casinos, airports, arenas, shopping malls) should be prominently mounted with easy to see signs. In addition, emergency services and security personnel should know the exact locations of AEDs. What is the optimal density of AEDs? In a large public space how close together should AEDs be placed? In 1999 AEDs were installed in O’Hare airport in Chicago. AEDs were placed a “brisk 60-to-90 second walk apart”. The survival rate for cardiac arrest at the airport is 56%. The American Heart Association recommends an AED within a 3-to-5 minute round trip walk from anywhere in a public place. This translates to each AED covering about 100 yards in each direction.
In case of sudden cardiac arrest in the home, getting an AED to the person is very problematic. As described above, formal programs will send out texts to responders and direct them to the location of a known AED. What is the optimal density of AEDs in residential areas? One study from the Netherlands found that approximately 2 AEDs per square kilometer (5 AEDs per square mile) in residential areas was optimal coverage. However, in Holland there is a national registry for all public and private AEDs, including location. When emergency services are called, responders are directed to the nearest AED. Another study from Copenhagen concluded that the optimal coverage was 16 AEDs per square kilometer (41 AEDs per square mile) in residential areas. Keeping in mind that the Netherlands and Denmark are each about 16,000 square miles, that is not an insurmountable number of AEDs to provide residential coverage. The United States is 3,531,905 square miles.Novel ideas that are being piloted include delivering an AED via a drone to the victim and having ultraportable AEDs carried by volunteer responders.
You may ask, “How does this information help me? I can’t afford to outfit the US with millions of AEDs.” This is a valid question, but there are still lessons for the general public. The first is to get trained in CPR. The local hospitals have CPR classes for the community. You never know when you might need these skills. Next, even if you lack formal training, this should not deter you from attempting to save a life. AEDs are easy to use and they help guide the responder through the process of deploying them. Next, if you see a resuscitation in progress, go and help. Remember, the more hands, the greater the chance to save a life. Lastly, advocate in your community for greater AED density.
