Sudden cardiac arrest leads to an estimated 436,000 deaths in the US each year, and only 1 in 10 leave the hospital alive, according to the American Heart Association’s (AHA) 2025 update. Every minute without a shock from an automated external defibrillator (AED) decreases survival odds by 7–10%. Yet many people still confuse causes of cardiac arrest with a heart attack or assume it occurs only in older adults. In reality, SCA is an electrical failure of the heart, often triggered by ventricular fibrillation, where chaotic impulses stop the heart from pumping blood. It can hit healthy, young adults and even teens without warning. That misunderstanding is deadly because it delays CPR and defibrillation. These actions restart the heart in those first critical minutes.
The solution starts with knowledge of what disturbs the electrical functioning of the heart, how to identify warning signs, and acting quickly with cardiopulmonary resuscitation (CPR). So, continue reading to find out the most significant causes that lead to sudden heart failure, the process of the heart’s electrical system, and the practical measures to enhance survival.
What Is Cardiac Arrest and How Does It Differ from a Heart Attack?
Cardiac arrest is a sudden electrical failure of the heart. It occurs when the heart’s electrical system malfunctions and produces abnormal rhythms such as ventricular fibrillation or ventricular tachycardia. Within seconds, the person collapses, loses consciousness, and has no pulse.
Although it is electrical in nature, cardiac arrest often stems from
- Underlying coronary artery disease
- Structural heart problems
- Inherited rhythm disorders
These conditions make the heart more vulnerable to fatal arrhythmias.
A heart attack (myocardial infarction), on the other hand, is a circulatory problem. It occurs when blood flow to part of the heart muscle is blocked, usually by a clot in a coronary artery. This causes:
- Chest pain
- Pressure
- Shortness of breath
The heart still usually keeps beating. If the blockage isn’t relieved quickly, the damaged heart muscle can destabilize the electrical system and trigger cardiac arrest.
For example, when a seemingly healthy athlete suddenly collapses on the field with no pulse, it’s usually cardiac arrest, not a heart attack. A blocked artery would rarely act that quickly but a sudden arrhythmia can stop the heart in seconds.
Cardiac Arrest vs Heart Attack vs Heart Failure
| Feature | Cardiac Arrest | Heart Attack | Heart Failure |
| Main problem | Electrical malfunction stops heartbeat | A blocked artery cuts off blood flow | The heart muscle is too weak to pump |
| Onset | Sudden, without warning | Often gradual or sudden | Gradual, over weeks or months |
| Heartbeat | Stops completely or becomes chaotic | Usually continues | Continues but is weak |
| Symptoms | Sudden collapse, no pulse, unconsciousness | Chest pain, pressure, sweating, shortness of breath | Fatigue, breathlessness, leg swelling |
| Immediate danger | Death within minutes without CPR and AED | Heart muscle damage and can lead to arrest | Chronic decline; risk of fluid buildup |
| Example | Athlete collapses suddenly | Chest pain after exertion | Swollen ankles and fatigue over time |
How the Heart’s Electrical System Fails in Cardiac Arrest?
The heart is powered by an internal electrical system that keeps it beating in a steady rhythm. When this system malfunctions, the heart may stop pumping blood effectively, resulting in cardiac arrest. Here’s how the electrical system failure is among the major causes of cardiac arrest:
Normal Pathway
Sinoatrial node (SA node) → spreads signals across atria → atrioventricular node (AV node) → bundle branches → Purkinje fibers → coordinated contraction of ventricles.
Failure Mechanisms In Cardiac Arrest:
- Ventricular Fibrillation (VF): Chaotic signals → ventricles quiver instead of pumping.
- Ventricular Tachycardia (VT): Abnormally fast signals → ventricles contract too quickly to fill with blood.
- Pulseless Electrical Activity (PEA): Electrical signals present → but the heart muscle fails to contract.
- Asystole (“flatline”): No electrical activity → no heartbeat at all.
These failures interrupt the heart’s ability to circulate oxygen-rich blood. Brain injury can begin in just 4-6 minutes without oxygen, which makes fast CPR and defibrillation important. Unlike gradual conditions, cardiac arrest is sudden and almost always fatal unless treated immediately.
What Causes Cardiac Arrest?
Most cardiac-arrest deaths occur due to a handful of well-defined mechanisms, such as VF or VT. Knowing them clarifies who is at highest risk, which warning signs deserve instant action, and which “reversible causes” rescuers must correct on scene. Here’s what causes sudden cardiac arrest:
Coronary Artery Disease (CAD)
CAD underlies roughly two-thirds of sudden cardiac deaths in adults. Plaque builds up inside the coronary arteries, limiting oxygen to the heart muscle. When a plaque ruptures, three things happen in rapid succession:
- A clot forms and stops blood flow to part of the myocardium.
- Oxygen-starved muscle becomes electrically unstable within minutes.
- The injured zone can trigger Ventricular Fibrillation (VF) or pulseless Ventricular Tachycardia (VT), the two rhythms seen in most adult arrests.
Even if VF is terminated, a large infarct leaves scar tissue that continues to provoke dangerous arrhythmias for months. Therefore, the first six months after a heart attack carry the highest arrest risk. Risk also persists years later due to remodelling.
Primary Arrhythmias
In some people, the problem lies in the heart’s electrical wiring rather than in blocked arteries. These are called primary arrhythmias. They often come from inherited conditions that affect how electrical signals move through heart cells. Examples include Long QT Syndrome, Brugada Syndrome, Wolff-Parkinson-White Syndrome, and certain inherited muscle disorders like hypertrophic cardiomyopathy or arrhythmogenic right ventricular cardiomyopathy.
The key arrhythmias that can lead to cardiac arrest are:
- Ventricular fibrillation (VF): Chaotic, uncoordinated quivering; no forward flow.
- Sustained ventricular tachycardia (VT): More than 100 beats/min, so fast that the ventricles cannot fill.
- Extreme bradyarrhythmias or high-grade heart block: The rate slows below perfusion threshold, often progressing to asystole.
These conditions don’t occur only in the elderly. They can appear in children, teenagers, and even elite athletes who seem completely healthy. Some sudden collapses on the field are later traced to inherited heart rhythm disorders or structural abnormalities that had gone undetected.
If there’s a family history of unexplained fainting, sudden cardiac death, or known heart rhythm problems, seek evaluation from a cardiologist specializing in inherited heart diseases. Screening may include an ECG, echocardiogram, or exercise test. In some cases, genetic testing can identify conditions like hypertrophic cardiomyopathy or long QT syndrome before they turn deadly.
Reversible Causes of Cardiac Arrest: The ACLS 4H & 4T Checklist
During patient resuscitation in cardiac arrest, medical professionals utilize the “4H & 4T” model to rapidly evaluate reversible causes. These include conditions that, when addressed during resuscitation, can revive circulation.
4H – Metabolic and Environmental Causes
| Cause | What It Means | What Bystanders Can Do | What Medical Teams Do |
| Hypoxia | Lack of oxygen due to airway obstruction or severe lung disease | Open airway, start CPR, use AED, give rescue breaths if trained | Advanced airway support, oxygen, ventilation |
| Hypovolemia | Severe blood loss or dehydration lowers circulating volume | Control visible bleeding, call 911, and start CPR | IV fluids, blood transfusion |
| Hydrogen ion imbalance (acidosis) / Hypo- or Hyperkalemia | Dangerous pH or potassium shifts disrupt heart rhythm | Share known medical history, start CPR | IV medications (bicarbonate, calcium, insulin–glucose) |
| Hypothermia | Core temperature < 30 °C slows heart and enzyme activity | Move person to a warm place, remove wet clothing | Active rewarming, advanced monitoring |
4T – Mechanical and Toxic Causes
| Cause | What It Means | What Bystanders Can Do | What Medical Teams Do |
| Tension Pneumothorax | Collapsed lung compresses heart | Start CPR, relay trauma details | Needle decompression |
| Cardiac Tamponade | Fluid around heart prevents pumping | CPR, rapid EMS activation | Emergency pericardiocentesis |
| Toxins | Drug overdose or poisoning | Share details of any substances, start CPR, use naloxone if available | Specific antidotes, advanced detox measures |
| Thrombosis (Coronary or Pulmonary) | Blocked artery or pulmonary embolism stops circulation | CPR, rapid AED use | Reperfusion therapy, thrombolytics, surgery |
Mastering this mnemonic helps clinicians and trained lay responders working alongside emergency physicians to treat the cause, not just the rhythm. Doing so improves the odds of restoring spontaneous circulation before the brain reaches its 4–6-minute ischemic limit.
Myocarditis & Inflammatory Cardiomyopathies
Infections (like Coxsackie-B or COVID-19), autoimmune disease (systemic lupus erythematosus (SLE), rheumatoid arthritis, or giant cell myocarditis), or toxins can inflame the heart muscle. This damages cells and disrupts normal electrical signals. The result can be sudden heart failure or dangerous rhythm problems, sometimes occurring days after a mild viral illness.
Congenital Coronary & Structural Anomalies
Some people are born with hidden heart abnormalities, such as:
- Abnormal coronary artery origin
- Severe, undiagnosed narrowing of the aortic valve
- Complex congenital defects repaired in childhood (like Tetralogy of Fallot)
These can cause cardiac arrest from reduced blood supply, obstruction, or scar-related arrhythmias, often during teenage years when exertion levels increase.
Note: Routine pre-participation screening with ECG or echocardiography in young athletes is debated due to cost and false-positive concerns. Still, in certain cases, such screening has been life-saving by revealing silent but dangerous heart defects before collapse occurs.
Aortic Dissection with Pericardial Tamponade
A tear in the main artery (aortic dissection) can rupture into the sac around the heart. This causes sudden pressure buildup (tamponade), preventing the heart from pumping and leading to arrest. Emergency surgery, not just drainage, is the only treatment.
Commotio Cordis (Blunt Chest Trauma)
A sudden impact to the chest, such as from a baseball, hockey puck, or kick, can disrupt the heart’s electrical cycle if it occurs at a vulnerable point at a 10-20 millisecond window (just before the T-wave peak). This can trigger ventricular fibrillation (VF) even in a healthy heart. Therefore, commotio cordis is also listed among the causes of cardiac arrest. Survival depends on immediate defibrillation, as CPR alone is usually not sufficient.
Read more: What are the Causes of Sudden Cardiac Arrest?
What Are the Symptoms and Early Signs of Cardiac Arrest?
A cardiac arrest usually announces itself in seconds. Yet public-registry studies show that up to half of patients recall some form of warning within the previous 24 hours. Recognizing both the obvious symptoms and their subtler precursors allows bystanders to act before the heart’s electrical silence becomes irreversible.
Sudden Collapse and Loss of Responsiveness
The most definitive sign is an abrupt collapse followed by unresponsiveness. Within moments, the person will have no detectable pulse because the heart is no longer pumping blood effectively. Attempting to shake the individual leads to no reaction, and the eyes may remain open but vacant. This combination of collapse, unresponsiveness, and pulselessness signals the classic onset of sudden cardiac arrest rather than a fainting spell or seizure. It requires immediate activation of emergency services and the start of CPR.
Abnormal or Absent Breathing
As the heart stops, normal breathing ceases almost immediately. Some victims exhibit agonal respirations, gasping, and gurgling movements that are ineffective for oxygen exchange. Others show no chest movement at all. Lay rescuers often mistake agonal breaths for recovery, delaying CPR. A quick check for chest rise combined with pulse assessment helps confirm that the gasps are reflexive, not life-sustaining. If breathing is absent or abnormal, guidelines direct rescuers to begin chest compressions at once and apply an AED as soon as it arrives.
Minutes-to-Hours Warning Clues
Up to one-third of patients experience symptoms shortly before collapse, but they are easy to dismiss as fatigue or stress. Act on these red flags—especially if they occur together or escalate rapidly:
- Chest pressure, tightness, or discomfort that comes and goes.
- Sudden shortness of breath or unexplained wheezing.
- Heart palpitations: a racing, fluttering, or pounding heartbeat.
- Dizziness, light-headedness, or an abrupt sense of impending fainting.
- Unusual weakness or extreme fatigue not proportional to activity.
If you notice any of these signs, call emergency medical services and get an AED if one is nearby. Early medical evaluation can uncover a treatable arrhythmia or coronary event before it triggers full arrest.
Signals Up to 24 Hours in Advance
New data from Cedars-Sinai show that about 50% of sudden cardiac-arrest victims report at least one key symptom the day before the event. The patterns differ by sex:
- Men most commonly experience intermittent chest pain or pressure.
- Women more often report new-onset shortness of breath or overwhelming fatigue.
Can Cardiac Arrest Happen to Anyone? Risk Factors
Cardiac arrest is not limited to older adults. Registry data show it affects people across all ages, from infants with congenital electrical disorders to athletes with undiagnosed cardiomyopathy. What changes with age is the risk profile, not the basic mechanism: the heart’s electrical system fails, circulation stops, and collapse follows within seconds. Understanding the key risk factors helps identify who is most vulnerable.
Coronary or Structural Heart Disease
Prior heart attack, diagnosed coronary artery disease, heart failure, and cardiomyopathies (dilated or hypertrophic) are major contributors. Scar tissue left after a myocardial infarction remains electrically unstable for months, increasing the risk of lethal arrhythmias even when symptoms improve.
Electrical & Genetic Disorders
Inherited rhythm disorders, such as Long QT, Brugada, catecholaminergic polymorphic VT, Wolff-Parkinson-White, can trigger cardiac arrest in structurally normal hearts. These conditions may strike children, teens, or young adults. A family history of sudden unexplained death before age 50 should prompt specialist evaluation with ECG, echocardiography, and genetic testing.
Traditional Cardiovascular Risk Factors
High blood pressure, diabetes, high cholesterol, smoking, obesity, and inactivity speed up artery damage and double arrest risk.
These fall into two main categories:
Modifiable Risk Factors – You can change these
- High blood pressure
- Diabetes
- High cholesterol
- Smoking
- Obesity
- Physical inactivity
Non-Modifiable Risk Factors – You can’t change these
- Age
- Sex
- Family history or genetics
Situational & Lifestyle Triggers
Severe low oxygen (drowning, overdose), electrolyte shifts (vomiting, diuretic use), and stimulant drugs (cocaine, amphetamines) can precipitate arrest in otherwise healthy individuals. Newer research also links poor sleep, long sitting time, and even short-term air pollution spikes to higher arrest incidence.
High-Risk Populations
Risk rises sharply after age 45, but infants represent another peak due to congenital disorders. Men account for two-thirds of out-of-hospital arrests, though women face lower survival odds once arrest occurs. Chronic kidney disease, sleep apnea, and chronic lung disease further increase vulnerability.
Also read: Why Are Young People Dying Of Heart Attacks?
What to Do When Cardiac Arrest Occurs?
When the heart stops, the clock starts ticking. Brain cells begin to die within minutes, and survival depends on immediate action. The AHA calls this sequence the “Chain of Survival.” Each link, including recognition, CPR, defibrillation, and advanced care, must occur without delay.
Immediate Bystander Actions (First 60 Seconds)
Check that the scene is safe. Tap the person and shout to assess responsiveness. If they do not respond and show no normal breathing, or only gasping, assume cardiac arrest. Call for help. Direct someone to dial emergency services and bring the nearest automated external defibrillator (AED).
Starting CPR
Begin high-quality chest compressions. Place your hands on the center of the chest, press at least 2 inches deep, and maintain a rate of 100–120 compressions per minute. Allow the chest to recoil fully between pushes. This circulation buys time until defibrillation restores an effective rhythm.
Using an AED
Modern AEDs are built for use by the public with no medical training required. They’re often mounted in gyms, airports, schools, malls, offices, and sports arenas, where cardiac arrests are most likely to occur.
If someone collapses and has no pulse or is not breathing, turn the AED on, expose the chest, and follow the voice prompts. The device will guide you through pad placement, analyze the heart rhythm, and tell you if a shock is needed.
Role of EMS
Paramedics continue CPR, secure the airway, give medications, and treat reversible causes. They transport the patient to a cardiac-capable hospital where advanced therapies, such as controlled cooling or emergency catheterization, are available. Early notification activates specialized teams, strengthening the final link in survival.
Prevention With Medical Screening & Lifestyle Changes
Studies indicate that as much as 70% of sudden cardiac death happens in people with recognizable risk factors. With the combination of focused screening and lifestyle modification, much of the risk can be eliminated.
Clinical Screening
Adults with coronary artery disease, heart failure, unexplained syncope, or a family history of sudden death should be evaluated. Electrocardiography (ECG), echocardiography, exercise stress testing, or nuclear imaging may be used to evaluate blood flow and structure. Holter monitoring, event recorders, and genetic testing are indicated in families with inherited arrhythmias or unexplained sudden death. Coronary calcium scoring or CT angiography in intermediate-risk adults can help in getting the best treatment, i.e., statin or aspirin therapy.
Managing Medical Conditions
Control of blood pressure, cholesterol, and blood glucose stabilizes plaques and decreases electrical instability. Beta-blockers, ACE inhibitors, and mineralocorticoid antagonists reduce sudden-death risk in patients with heart failure. Some patients with severely low ejection fractions can be suggested implantable cardioverter-defibrillators (ICDs), which continuously monitor and correct life-threatening rhythms.
Lifestyle Habits That Protect the Heart
- Exercise: A minimum of 150 minutes a week of moderate aerobic exercise enhances rhythm stability.
- Diet: A diet based on the Mediterranean with vegetables, whole grains, and omega-3 fat decreases fatal arrhythmias.
- Avoidance: Stop smoking, reduce alcohol consumption, and stay at a healthy weight.
- Sleep & Stress: Get 7–9 hours of sleep and use stress-management skills. Stress and inadequate sleep raise arrhythmia risk.
Turning Awareness Into Action Against Cardiac Arrest!
Sudden cardiac arrest does not strike at random. It follows certain patterns. From coronary artery disease and arrhythmias to reversible “4 H & 4 T” causes of cardiac arrest, the warning signs are there for those prepared to see them. Studies consistently show that survival rates climb when CPR starts immediately and an AED is used within minutes. Every delay, however, narrows that window of life. The real message is clear: preparation saves. Recognizing risks, managing health factors, and acting without hesitation can mean the difference between loss and recovery.
Enroll in an accredited online CPR/AED certification course today. In just a few hours, you’ll practice high-impact skills, such as pad placement, compression depth, and pediatric versus adult protocols, to become an asset in a time of emergency.
