Sudden cardiac arrest (SCA) is the abrupt failure of your heart to pump blood, causing circulation to stop completely and immediately. This emergency is different from a heart attack, where blood flow to the heart is blocked but the heart usually keeps beating. In SCA, the heart’s electrical system malfunctions, leading to immediate collapse and loss of consciousness. Because every minute counts—your chance of survival drops by 7-10% each minute without help—immediate action from bystanders, including calling for help, performing CPR, and using a defibrillator (AED), is your best chance for a full recovery.
Overview
Sudden cardiac arrest (SCA) is the abrupt loss of heart function, breathing, and consciousness, typically caused by a severe electrical short-circuit in the heart. When the heart stops pumping effectively, blood circulation ceases, and without immediate emergency treatment, death occurs within minutes.
You must understand that SCA is not the same as a heart attack (myocardial infarction). A heart attack occurs when a blocked artery cuts off blood flow to a part of the heart muscle, but the heart usually continues to beat. Cardiac arrest means the heart has stopped beating effectively. However, heart attacks are a leading cause of SCA because the damaged muscle becomes electrically unstable, often triggering the arrest.
During SCA, the heart’s electrical system malfunctions, causing life-threatening abnormal rhythms. The most common rhythms are ventricular fibrillation (VFib), where the lower chambers quiver uselessly, or ventricular tachycardia (VT), where the lower chambers beat too fast to properly fill with blood. When the heart stops pumping, blood pressure instantly drops to zero. Your brain stops receiving oxygen, and you lose consciousness within 10-15 seconds. Breathing stops or becomes ineffective gasping.
Your survival depends almost entirely on the speed of treatment. The chain of survival—immediate recognition, calling for help, starting CPR, and using a defibrillator—must happen within minutes. With immediate bystander action, survival rates in some settings can reach 70-90%, proving that your readiness to act is life-saving.
Causes
Sudden cardiac arrest results directly from electrical malfunctions in the heart, but various underlying heart conditions create the instability that allows these malfunctions to happen.
- Coronary artery disease (CAD) is the most common underlying cause in adults. Plaque buildup in your coronary arteries reduces blood flow, making the heart muscle electrically unstable. Heart attacks, where an artery suddenly completely blocks, commonly trigger SCA because the oxygen-deprived muscle develops chaotic electrical activity.
- Previous heart attacks leave permanent scars in the heart muscle. These scars disrupt normal electrical pathways and can trigger SCA many years after the initial event.
- Cardiomyopathy is a condition where the heart muscle is diseased or damaged, significantly increasing your risk. Whether your heart is enlarged and weakened (dilated cardiomyopathy) or the muscle has thickened abnormally (hypertrophic cardiomyopathy), the tissue becomes electrically unstable and prone to dangerous rhythms.
- Severe heart failure from any cause makes the heart more vulnerable to electrical problems. The stretched and weakened muscle develops abnormal, life-threatening rhythms more easily.
- Inherited heart conditions cause SCA in young people, often with structurally normal-appearing hearts. These genetic conditions, such as Long QT syndrome or Brugada syndrome, affect the heart’s electrical system. Since these often run in families, sudden death in young relatives is a serious warning sign that prompts genetic screening.
- Other triggers include drug use (particularly cocaine and methamphetamine, which increase heart oxygen demand and trigger spasms), high-voltage electrocution, and severe electrolyte imbalances (especially low potassium or magnesium), which make the heart electrically unstable.
- Sometimes, despite a thorough investigation, cardiac arrest occurs without any identifiable cause.
Symptoms
Sudden cardiac arrest causes immediate collapse—you go from appearing perfectly normal to unconscious within seconds.
Although many people have no warning at all (sudden collapse is the first symptom), some may experience brief warning signs in the hour before SCA. These can include chest pain (suggesting a heart attack), palpitations or a feeling that your heart is racing, or brief moments of dizziness or lightheadedness.
The collapse itself is dramatic and unmistakable:
- The person suddenly becomes unresponsive, not reacting to shouting or shaking.
- Consciousness is lost within 10-15 seconds as the brain is starved of oxygen.
- Breathing stops or becomes abnormal. The occasional gasps, called agonal breathing, are reflexive and ineffective. You should recognize these gasps as a sign of cardiac arrest, not effective breathing.
- No pulse can be felt.
- Skin color changes within minutes, typically becoming pale, gray, or bluish.
- Seizure-like activity (jerking or stiffness) can sometimes occur as the brain is deprived of oxygen. Never mistake this for a typical seizure—if someone collapses suddenly and is not breathing, it is cardiac arrest.
These critical symptoms happen within seconds of each other. The entire sequence from normal to cardiac arrest takes less than a minute.
Diagnosis and Immediate Response
Diagnosing cardiac arrest relies on rapid assessment by bystanders or emergency responders, not medical tests. Since every second counts, diagnosis must be immediate and action-oriented.
When someone suddenly collapses, you must check for responsiveness by shouting and tapping their shoulder. If they do not respond, assume cardiac arrest.
Next, check for normal breathing by looking at the chest for rise and fall. If they are not breathing normally (either not breathing at all or only gasping), assume cardiac arrest. Crucially, do not waste time trying to find a pulse. Delays checking for a pulse waste precious seconds, and even trained personnel often cannot reliably feel one quickly.
If the person is unresponsive and not breathing normally, cardiac arrest is assumed, and treatment begins immediately. You must call emergency services or have someone else call while you start CPR.
Once emergency personnel arrive, they use an electrocardiogram to confirm cardiac arrest and identify the specific rhythm. This is important because:
- Shockable Rhythms (like VFib) require immediate defibrillation.
- Non-Shockable Rhythms (like asystole) require continued CPR and medications but not electrical shocks.
After successful resuscitation, extensive evaluation determines what caused the SCA, including EKG, blood tests, echocardiography, and angiography. Understanding the cause is the key to guiding long-term treatment and preventing recurrence.
Treatment
Treatment for sudden cardiac arrest happens in two phases: First, emergency resuscitation to restore circulation, and second, ongoing treatment to prevent recurrence.
Immediate Bystander Action (Emergency Treatment)
- Act Immediately: Recognition must be instant. If someone collapses and is unresponsive and not breathing normally, assume cardiac arrest and act now.
- Call for Help: Call emergency services immediately or have someone else call while you begin CPR. Put the phone on speaker to receive instructions.
- Start CPR: Place the heel of one hand on the center of the chest and push hard and fast. Compressions should be at least 2 inches deep for adults, at a rate of 100-120 per minute. Hands-only CPR—continuous chest compressions alone—is very effective and should be started immediately.
- Use an AED: Automated External Defibrillators (AEDs) should be used as soon as available. These devices provide voice prompts, guiding you through every step, including placing pads on the chest and pressing the shock button if advised. You should not be afraid to use an AED; it only delivers a shock if a shockable rhythm is detected.
- Continue: Continue CPR and follow AED prompts until emergency personnel arrive or the person shows clear signs of life.
Long-Term Treatment
Once circulation is restored, the focus shifts to preventing recurrence:
- Most survivors receive an Implantable Cardioverter-Defibrillator (ICD) before hospital discharge. This small device continuously monitors your heart rhythm and automatically delivers shocks if life-threatening rhythms recur, providing immediate treatment without needing bystander help.
- If a heart attack triggered the arrest, emergency angioplasty is performed to open blocked arteries.
- If inherited conditions or structural heart disease caused the arrest, optimizing treatment with medications (like beta-blockers) and lifestyle changes reduces future risk.
What Happens Without Treatment
Without immediate treatment, sudden cardiac arrest is fatal within minutes. There are no exceptions—if the rhythm isn’t converted, you will not survive.
When circulation stops, the brain begins dying within 4-6 minutes from oxygen deprivation. Permanent damage occurs quickly because the brain is extremely sensitive to a lack of oxygen.
After 10 minutes without effective circulation, survival becomes rare even with aggressive resuscitation.
Even with bystander CPR, which maintains some minimal circulation, defibrillation is necessary for the most common rhythm, ventricular fibrillation. CPR alone cannot convert these rhythms to normal—it only buys time until a defibrillator arrives.
The harsh reality is that the overall survival rate from out-of-hospital cardiac arrest is only 10-12% nationally, primarily because treatment doesn’t arrive in time. However, communities with widespread CPR training and many public AEDs demonstrate much higher survival rates, sometimes 2-3 times higher. This emphasizes why prevention and widespread bystander readiness are so important.
Prevention
Preventing sudden cardiac arrest means identifying and treating high-risk individuals and proactively addressing the underlying heart conditions.
For people with known heart disease, optimizing treatment reduces risk significantly. This includes taking all prescribed medications (like beta-blockers and statins) and aggressively controlling conditions like high blood pressure, cholesterol, and diabetes.
Implantable Cardioverter-Defibrillators (ICDs) prevent death in high-risk individuals. These devices are recommended for survivors of cardiac arrest, people with severely weakened hearts, or those with certain inherited conditions at high risk. The device ensures a deadly rhythm doesn’t cause death by delivering immediate treatment.
Family screening is crucial when inherited conditions cause SCA. Close relatives should undergo evaluation, including ECGs and possibly genetic testing, to allow protective measures before tragedy strikes.
General population measures reduce risk: Not smoking, maintaining a healthy weight, exercising regularly, and avoiding recreational drugs (especially cocaine and methamphetamine) all promote a healthy heart and prevent coronary artery disease.
Regular medical checkups allow early detection of heart disease before it causes a sudden, life-threatening event.
Recovery After Cardiac Arrest
Surviving sudden cardiac arrest is the start of a complex recovery process that affects your physical, neurological, and emotional health.
If circulation was restored within a few minutes with minimal brain injury, recovery can be excellent. Many people return to their previous lives, often with a renewed appreciation for life.
Brain injury from prolonged oxygen deprivation creates a more complex recovery. Many people regain full function over time, but others may have permanent challenges affecting memory, thinking, or movement. Targeted temperature management (cooling the body) is a key treatment used after SCA to reduce brain injury and improve neurological outcomes.
Emotional recovery is significant. Many survivors experience post-traumatic stress, anxiety, or depression. Counseling and support groups are essential for helping you cope with the emotional aftermath and the installation of your ICD.
An ICD is implanted in most survivors before discharge, providing crucial, life-long protection against recurrence. Your return to normal activities, including driving and work, depends on your neurological recovery and the stability of your underlying heart condition.
What Bystanders Should Know
Being prepared to act during a cardiac arrest can save a life—and it could be someone you know and love.
Learn CPR. Many organizations offer quick classes teaching hands-only CPR (continuous chest compressions). This training empowers you to act confidently during emergencies.
Know where nearby AEDs are located. Seconds count when retrieving them. Check your workplace, gym, and local shopping areas.
Do not hesitate. If someone collapses, check responsiveness and breathing quickly (5-10 seconds). If they are unresponsive and not breathing normally, assume cardiac arrest and act immediately.
Push hard and fast during CPR. Effective compressions require significant force—press down at least 2 inches on adults. You cannot make things worse; you are only giving them a chance to live.
Use AEDs without fear. The device will guide you through every step and only shock when appropriate.
Don’t give up. Continue efforts until emergency personnel arrive.
When someone collapses in cardiac arrest, you are their best chance for survival—your immediate action in the first few minutes determines whether they live or die.
Reference: Sudden Cardiac Arrest
