What Is Sudden Cardiac Arrest—and Why Is It So Deadly?

This common condition is fatal up to 90 percent of the time.

Medically reviewed in February 2022

When you hear the term, “sudden cardiac arrest,” you might think “heart attack.” And while the conditions are linked, sudden cardiac arrest (SCA) is a distinctly different event, with different symptoms, different treatments—and a much lower survival rate. The statistics are sobering: according to the Centers for Disease Control and Prevention, there were 357,000 new out-of-hospital cardiac arrest (OHCA) cases in the US in 2015. And, up to 90 percent of people who have OHCA die before they get to the hospital.

The good news? With prompt intervention, the outcomes for SCA could be far less disheartening.

A heart-stopping condition
“With SCA, the name gives it away—the heart suddenly and unexpectedly stops beating,” says Vinayak Manohar, MD, a cardiologist with Mercy Health in Grand Rapids, Michigan. This abrupt loss of function is usually triggered by an electrical malfunction in the heart that causes an irregular heartbeat, called arrhythmia.

The most common arrhythmia in cardiac arrest is ventricular fibrillation (v-fib). During v-fib, the ventricles (the heart’s lower chambers) quiver very rapidly and erratically, preventing blood from pumping effectively. With the flow of blood disrupted, the lungs, brain and other vital organs can’t function properly and may shut down or become damaged. “When SCA occurs, you have precious minutes before you start suffering brain damage and, eventually, sudden cardiac death,” says Dr. Manohar.

Who’s at risk?
Sometimes, SCA occurs in active people who seem to be healthy and have no known medical condition, however, there are known risk factors for SCA.

Chief among them is coronary heart disease (CHD), which occurs when the arteries that supply blood to the heart become hardened and narrowed. As many as 70 percent of SCA cases in adults have been attributed to CHD, and in more than half of people with the condition, SCA is the cause of death.

Other risk factors include:

  • A previous heart attack: The majority of people who die of SCA have had a heart attack in the past, which can disrupt the heart’s electrical signals.
  • Family history: Heart issues, including heart failure or massive heart attack—or even sudden death—may increase your chances.
  • Structural damages: An enlarged heart, valve problems and heart infections can also cause SCA.
  • Genetic disorders: Hypertrophic cardiomyopathy, which causes the walls of the heart to thicken, is usually an inherited genetic disorder and the most common cause of sudden cardiac death among people under 30. An inherited heart rhythm disorder can also increase your risk.
  • Sudden severe stress: Stress triggers the sympathetic nervous system, which initiates the body’s fight or flight mode. If the stress is severe enough, there is a very small chance it could increase the risk of SCA.

Early warning signs
Despite the fact that SCA may be the first indication of a heart problem, it may not be as sudden as it’s believed to be. Research shows that symptoms frequently crop up hours, and even weeks, beforehand. Two studies on athletes, one from 2017 and another from 2018, found that symptoms like chest pain, shortness of breath, performance decline, palpitations and fainting occurred in as many as 54 percent of cases—with about 71 percent of athletes having at least one symptom a month prior.

The warning signs aren’t just limited to athletes. A 2016 study involving 839 middle-aged people who survived SCA found that half experienced some symptoms that indicated their heart was in danger of stopping in the month prior to their event. More than 90 percent of those who had symptoms said they resurfaced 24 hours before their cardiac arrest. The most common symptoms were chest pain in men and shortness of breath in women, but researchers say they can include any combination of chest pain and pressure, shortness of breath, heart palpitations and flu-like sensations such as nausea, back pain and/or abdominal pain.

The problem: These symptoms can be vague and often easily reasoned away (“I exercised too hard” or “it’s just heartburn”), which may explain why less than 20 percent of people in this study called for medical assistance. But especially for people at risk—those with coronary artery disease or multiple risk factors such as diabetes, hypertension, high cholesterol and smoking—it’s more likely these symptoms signal a real problem and shouldn’t be ignored.

Treatment options and emergency situations
SCA can be treated and reversed, provided emergency action is taken. Survival rates increase dramatically—doubling or tripling—if the victim receives immediate intervention. Luckily, bystanders witness 37 percent of SCAs, according to a 2018 report from the American Heart Association.

If you see someone suddenly collapse or fall to the ground and they’re unresponsive and breathing abnormally, if at all, it’s critical to quickly call 911 for help and initiate CPR. “People usually have enough oxygen circulating in their bloodstream to buy them a good four to six minutes, providing that oxygen can be circulated through the body,” says Manohar.

When performing compressions, push hard and fast. Press down at least 2 inches on the center of the chest at a rate of 100 to 120 beats per minute—the same tempo as the Bee Gees’ song “Stayin’ Alive.” Allow the chest to come back up to its normal position after each push. If an automated external defibrillator is available, turn on the device and follow the prompts and instructions. The device will determine whether an electric shock to the heart is needed. Otherwise, keep pushing until the person starts to breathe or move, or someone with more advanced training takes over.

Once you’ve had SCA, you’re at high risk of having it again. To prevent a second attack, you’ll likely receive an implanted cardioverter defibrillator (ICD), a device that’s surgically placed under the skin in your chest or abdomen to monitor your heartbeat. If the ICD detects a dangerous heart rhythm, it gives an electric shock to restore the heart’s normal rhythm. “Back in the day, we’d use medications to control arrhythmia, but we can get the same effect out of a defibrillator,” says Manohar. “It’s also much easier to control and comes with fewer side effects.” According to the Cleveland Clinic, ICDs are 98 to 99 percent effective in stopping life-threatening arrhythmias and are the most successful therapy to treat v-fib.

Simple ways to lower your risk
Following a healthy lifestyle can help reduce the likelihood of SCA, as well as the heart problems associated with it. This includes eating a healthy diet, losing weight if you’re overweight, managing stress, exercising regularly and quitting smoking or recreational drug use.

Also important: “Know your personal health numbers—your cholesterol, blood pressure and blood sugar—and try to keep them under control as well,” Manohar advises. Like coronary heart disease, type 2 diabetes can raise your risk of SCA—two- to four-fold, according to research.

Finally, talk to your doctor to gauge your risk for SCA and check out the Heart Rhythm Society’s assessment tool to see if you’re at risk. Being proactive now can help save your life.

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