What Causes Sudden Cardiac Arrest (SCA)?
The most common cause of SCA is a dangerous and abnormal heart rhythm called ventricular fibrillation (VF). In VF, the electrical signals that control the lower chambers of the heart (ventricles) become disorganized or chaotic. This sends the ventricles into fibrillation, an extremely rapid and irregular quivering that cannot effectively pump blood to the body.
The most common cause of SCA is a dangerous and abnormal heart rhythm called ventricular fibrillation (VF). In VF, the electrical signals that control the lower chambers of the heart (ventricles) become disorganized or chaotic. This rapid and irregular heart rhythm causes the ventricles to fibrillate or quiver, and the heart cannot effectively pump blood to the body.
With no blood getting to the brain, a person experiencing VF loses consciousness within seconds. SCA and death can follow within minutes unless the heart is quickly shocked back into its normal rhythm. This is done using a defibrillator (a machine that delivers an electrical shock to the heart). The vast majority of VF victims die from SCA before they reach a hospital. However, prompt action by bystanders to alert first responders, and begin CPR, can improve the outcome.
Who's At Risk for SCA?
Sudden Cardiac Arrest (SCA) occurs abruptly and without warning, and two-thirds of SCA deaths occur without any prior indications of heart disease. In fact, SCA can happen to people of all ages and health conditions.
While signs and symptoms are often not present, there are certain risk factors for SCA, which include:
- A previous heart attack: The majority of people who die of SCA show signs of a previous heart attack
- A family history of sudden death, heart failure, or massive heart attack
- An abnormal heart rate or rhythm of unknown cause
- An unusually rapid heart rate that comes and goes
- Episodes of fainting of unknown cause
- Some congenital heart defect before and after surgical repair
- A low ejection fraction (EF): The ejection fraction is a measurement of how much blood is pumped by the ventricles with each heart beat. A healthy heart pumps 55 percent or more of its blood with each beat; less than 35 percent indicates an elevated risk of SCA
Sudden Cardiac Arrest (SCA) Prevention
The time it takes for help and treatment to occur is a life and death situation during SCA. Ninety-five percent of those who experience SCA die because they do not receive life-saving defibrillation within four to six minutes, before brain and permanent death begin to occur. If a SCA emergency is suspected, the following steps are recommended:
- Know the signs of SCA and react quickly. SCA strikes immediately and without warning. Victims will fall to the ground/collapse, become unresponsive and will not breathe normally, if at all.
- Call 911 as soon as possible.
- Start CPR as quickly as possible. If you don't know CPR, conduct Hands-Only CPR, which is providing chest compressions by pushing hard and fast in the middle of the victim's chest with minimal interruptions at approximately 100 beats per minute (or hum the Bee Gees song "Staying Alive"). Studies of real emergencies have shown Hands-only CPR, to be equally or more effective than conventional CPR.
- If available, use an automated external defibrillator (AED) as soon as possible. AEDs are a computerized medical device that can check a person's heart rhythm and recognize and deliver a shock to a heart that needs it.
AEDs are increasingly available at public locations, such as airports, gyms, malls, and office buildings. These devices will only deliver a shock when an irregular heart rhythm is detected and usually do not cause any major harm with shock.
Prevention and Treatment
While there are often no signs or symptoms prior to SCA, there are things people can do to decrease the likelihood of experiencing SCA.
- Live a healthy lifestyle: exercise regularly, eat healthy foods, maintain a healthy weight and avoid smoking.
- Treat and monitor all health conditions including high blood pressure, high cholesterol and diabetes. Ask a doctor about ejection fraction monitoring to determine if there is a risk.
- Control or stop abnormal heart rhythms that may trigger life-threatening arrhythmias through proper medication, implantable cardioverter defibrillators (ICDs), and in some, cases surgical procedures.
- Know family heart history and understand the risks for other cardiovascular-related conditions, like heart failure. Communicate these to a physician.
While treatment guidelines recommend ICDs as the standard of care for patients at risk for SCA, a large percentage of patients at highest risk do not receive this treatment, especially African Americans and women.1
In addition, studies have shown that African Americans are significantly less likely than Caucasians to have electrophysiology (EP) study (which would identify abnormal heart rhythms) or to get an ICD.2 While reasons for this are still being investigated, it has been shown that sudden cardiac death rates are higher among African Americans.3
1 National Medical Association. (2008). Sudden Cardiac Arrest: Advancing Awareness and Bridging Gaps to Improve Survival. Washington, DC: NMA.
2 Agency for Healthcare Quality and Research. (2003). Treatment to Prevent Sudden Cardiac Death. Washington, DC: AHRQ.
3 CDC. (2002). State-Specific Mortality from Sudden Cardiac Death --- United States, 1999. MMWR, 123-6.
Terms & Resources
Sudden Cardiac Arrest (SCA) Awareness
October is Sudden Cardiac Arrest Awareness Month, which represents a critical initiative by the Heart Rhythm Society to raise awareness for Sudden Cardiac Arrest (SCA) and help the public become more familiar with what it is, how it affects people, and what can be done to help save lives.
The Society's award-winning "Apples and Oranges" campaign uses a simple analogy to educate people about the difference between a heart attack and SCA. More than 65 percent of Americans not only underestimate the seriousness of SCA, but also believe SCA is a type of heart attack. The campaign targets heart attack survivors, who are at the highest risk for SCA, and stresses the importance of maintaining a healthy heart lifestyle and learning critical risk markers, especially their Ejection Fraction (EF).
This public service announcement explains the dangers of SCA and features Emmy-award winning journalist Shaun Robinson.
About Sudden Cardiac Arrest
- More than 350,000 deaths occur each year as a result of sudden cardiac arrest.
- SCA claims one life every two minutes, taking more lives each year than breast cancer, lung cancer, or AIDS.
- To decrease the death toll from SCA, it is important to understand what SCA is, what warning signs are, and how to respond and prevent SCA from occurring.
Responding to SCA — Time is Everything
Time-to-treatment is critical when considering the chance of survival for an SCA victim. Ninety-five percent of those who experience SCA die because they do not receive life-saving defibrillation within four to six minutes, before permanent brain injury and death occur. Learn more about the steps to take when responding to a potential SCA emergency.
SCA Related Organizations & Websites
A number of organizations are involved in Sudden Cardiac Arrest awareness, education, and support. Note that this list is intended to serve as a convenience — inclusion of a link does not imply the Heart Rhythm Society' endorsement of either the linked website, the organization operating such website, or any products or services of that organization.