What is Sudden Cardiac Arrest (SCA)?

More appropriately called sudden cardiac death, sudden cardiac arrest (SCA) is a condition in which the heart stops suddenly and unexpectedly. It is caused by an electrical malfunction of the heart called Ventricular Fibrillation (VF)—an ineffective quivering of the heart muscle (arrhythmia) that makes it unable to pump blood to the body and brain. Eighty to eighty-five percent of the time, victims of SCA present this VF rhythm.

Once the blood stops circulating, the SCA victim quickly loses consciousness and finally the ability to breathe. With no pulse and no respiration, someone in cardiac arrest is clinically dead, but there is a brief window during which many victims can be brought back to life. The chance of survival drops rapidly—about ten percent with each passing minute. Thus, patient survival depends on immediate recognition of SCA, early access to the emergency medical services system, early cardiopulmonary resuscitation (CPR), and early defibrillation. The faster the shock is delivered, the better the outcome for the victim. This is the target window where public access defibrillation programs go to work. Sudden cardiac arrest is not the same as a heart attack or a myocardial infarction (MI). A heart attack is the death of a portion of the heart muscle caused by sudden decrease in blood supply to that area. Decrease in blood supply may be due to a blockage in the arteries which supply blood to the heart. A heart attack can precipitate a SCA, but so can a stroke, an anaphylactic reaction, an asthma attack, or a sudden blow to the chest cavity. Although someone suffering a heart attack is more likely to develop abnormal heart rhythms, SCA is different from a heart attack in the following ways:

• A heart attack (myocardial infarction, MI) occurs when blood supply to the heart is severely reduced or stopped due to a blockage of the veins or arteries leading to and from the heart. The heart muscle begins to die. A heart attack can, but does not always trigger sudden cardiac arrest. SCA is caused by an abnormal heart rhythm.
• A heart attack is often preceded by atypical chest, arm, upper abdomen, or jaw pain. Pain may spread to the shoulders, neck or arms. Nausea, dizziness, shortness of breath and sweating are common. The victim may experience unexplained anxiety, weakness, fatigue, palpitations, a cold sweat, and/or paleness. There is rarely a warning before SCA.
• Heart attack patients usually remain conscious during and after the attack and are able to breathe on their own. SCA victims always stop breathing, lose consciousness, and present erratic heart beats. They have no pulse or blood pressure. Unless the condition is reversed, death follows in a matter of minutes.

In summary, sudden cardiac arrest is not a synonym for heart attack. It may be helpful to remember the analogy that sudden cardiac arrest is an electrical defect, while a heart attack is the result of a plumbing or mechanical problem.

Sudden Cardiac Arrest is a Worldwide Killer

In the United States, an estimated 220,000 to 350,000 people are struck by sudden cardiac arrest each year. The American Heart Association estimates more than 600 people a day are victims of SCA.ⁱ The annual incidence of SCA is higher than the annual occurrences of car accidents, breast cancer, prostate cancer and house fires combined, more than stroke or AIDS.ⁱⁱ One adult dies from SCA every one to two minutes. The typical survival rate hovers around 5 percent, which means, using the conservative estimate of 250,000 victims, that only about 12,000 people survive. The other 238,000 die. Sudden cardiac arrest claims approximately 30-40,000 lives per year in Canada and about 300,000 lives in Western Europe.ⁱⁱⁱ

SCA Can Happen To Anybody

The National Center for Early Defibrillation describes SCA as a public health crisis.^iv Many people mistakenly believe that sudden cardiac arrest only strikes elderly men. While risk does increase with age (the average victim's age is 65), SCA strikes people of all ages; it has claimed victims in infancy, pre-teens, teens, and those in their twenties, thirties and forties. It can happen to men and women, sedentary people and elite athletes, as well as apparently healthy people and others with known heart conditions. Although pre-existing heart disease is a common cause of cardiac arrest, many victims have never had any heart problems and SCA is often the first symptom.^v

Who is at risk of SCA? As we have indicated, SCA by its very nature is unpredictable, not limited to any specific gender, age, race or cultural group. That said, SCA victims tend to fit in these categories:

• People with poor diet
• Smokers
• Overweight individuals
• Males are a statistically larger group, though females may also suffer SCA
• Patients who have had previous heart attacks with associated risks
• People with a family history of SCA or heart problems
• People who don't exercise

SCA Can Happen Anywhere

Two out of every three deaths from SCA happen outside a hospital, which makes it even more imperative to have a defibrillator accessible wherever people work and live. Most victims of sudden cardiac arrest collapse at home, but many are stricken in the workplace, at play, or in community settings. The site of a SCA event is as unpredictable as the victims it claims. Because a third of sudden cardiac arrest events do occur in hospital, hospitals are also logical sites for AED programs.

Early Defibrillation is the Key to Survival

The only effective treatment for VF is an electrical shock delivered by a defibrillator, a medical device which delivers a controlled electrical current, or shock, through the chest to the heart, stunning the heart muscle. This shock interrupts the random, chaotic electrical impulses of ventricular fibrillation and allows the heart's natural pacemaker, the sinus (SA) node, to re-establish beating in a normal rhythm.^vi This process is called defibrillation.

It doesn't matter who delivers the shock-a doctor, a paramedic or a layperson—as long as it is delivered quickly. It is important to remember that while cardiopulmonary resuscitation (CPR) helps maintain the flow of oxygen to the brain and vital organs, it cannot convert VF back into a normal, life-sustaining rhythm. According to the American Heart Association, the average adult will stay in VF for 4-8 minutes before the heart rhythm goes asystole or flatlines, indicating there is no electrical activity in the heart. At that point a defibrillator is not the treatment of choice. CPR keeps the patient in VF longer, keeping the window of opportunity for defibrillation open longer.

We know, based on studies at cardiac rehabilitation centers, that of those SCA victims receiving defibrillation therapy within the first minutes after collapse, more than 90 percent survive to be discharged from hospital. The National Center for Defibrillation warns that, "In more typical community settings, victims of SCA rarely survive. Why? Most victims do not have immediate access to prompt, definitive treatment. Too much time elapses before the defibrillator arrives—if it arrives at all."^vii

CPR is Not Enough

People mistakenly believe that cardiopulmonary resuscitation (CPR) maintains blood and oxygen flow to the brain at levels comparable with a normal heartbeat. In reality, CPR temporarily provides minimal blood flow and oxygen, buying time by keeping oxygenated blood circulating to the victim's heart, brain and vital organs until definitive intervention can occur. The CPR technique includes airway management, mouth-to-mouth or mask ventilation, and external chest compression.

While better than being untreated, sudden cardiac arrest victims receiving only CPR will survive 2 to 5 percent of the time. On the other hand, timely administration of defibrillation has a better chance of succeeding if CPR has been administered. After prescribed periods of CPR, the defibrillator will analyze the victim's heart rhythm and administer more shocks if necessary.

Dr. Richard Cummins, an American Heart Association official and a pioneer in out-of-hospital cardiac arrest treatment, has succinctly stated the reality: "Rather than independently saving lives, CPR helps early defibrillation succeed."

Time is of the Essence

Emergency Services do their part by attempting to bring early defibrillation to the patient along with early Advanced Cardiac Life Support or ACLS. Emergency Services do make a difference in the majority of calls they attend. However, when it comes to SCA, time is against them.

The unfortunate truth about organized Emergency Services systems is that they cannot always provide defibrillation as early as they need to. This is not reflective of low quality Emergency Services departments-it is the reality of the logistical difficulties which can arise trying to get the defibrillator to the patient. Large complexes, tall buildings, locations far from the city core or traffic congestion impact the time it takes for EMS to reach the patient in large metropolitan areas; in rural areas, great distances may prevent EMS from saving lives. For example, the average emergency response time in New York City is 12 minutes. There, 1 to 2 percent of SCA victims survive. Seattle's average response time is 7 minutes with a 30 percent survival rate. In Rochester, Minnesota, response times average 6 minutes and 45 percent of SCA victims survive.^viii

Paramedics are trained to do a good job of providing early Advanced Cardiac Life Support, but without early defibrillation, early ACLS is often not effective. Failure to restore a normal heart rhythm within 4 to 6 minutes can result in irreversible brain damage. After 10 minutes the survival rate may be only 2 percent-or less.

Even in some of the best EMS systems in the world, where response times are 4 to 8 minutes, EMS has a SCA survival rate of approximately 5 percent. Survival rates plunge 10 percent every minute defibrillation is delayed. The following chart illustrates why this is the case.^ix

Event Awareness of patient collapse 911 phone call (evaluation) Dispatch of crew Response time Locate patient Assess patient; prepare for defibrillation Time to defibrillation Chance of Survival

Time 2 minutes 1 minutes 1 minutes 4 minutes 1 minutes 1 minutes 10 minutes 0-10 percent

As this chart demonstrates, when defibrillation is delayed for more than 10 minutes, survival becomes doubtful.^x Survival rates can be higher if a victim is defibrillated during the first minutes after collapse. In one study of casino gaming facilities in Las Vegas, for example, survival rates reached 74 percent when the shock was administered within 3 minutes of collapse.^xi

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