Sudden cardiac arrest

Sudden cardiac arrest is when the heart abruptly stops pumping, so blood stops reaching the brain and other organs. It is an emergency. Without quick treatment it usually causes death within minutes. Anyone who sees a person collapse can help by calling 9-1-1, giving CPR and, if one is nearby, using an automated external defibrillator (AED).

Also called Cardiac arrest · SCA

Condition
In this atlas

Overview

Technical summary

NHLBI and MedlinePlus agree on the outline. Cardiac arrest is caused by a rhythm disturbance, with ventricular fibrillation named by MedlinePlus as the cause of most arrests and by NHLBI, with ventricular tachycardia, as the main cause. Coronary artery disease is a common condition underneath. MedlinePlus separates it from a heart attack, which is a blocked blood supply to the heart, and says an arrest can happen after or during recovery from a heart attack; NHLBI also says cardiac arrest accounts for about half of all deaths associated with heart attacks and strokes. NHLBI puts deaths from cardiac arrest in the United States between 300,000 and 450,000 a year and says nine in ten people who have an arrest outside hospital die, often within minutes. Neither page gives an age group. MeSH D006323 (Heart Arrest) is wider than this page and is stored as a broad match.

Recognition

NHLBI lists a sudden collapse with loss of consciousness, no breathing or only gasping, no response to shouting or shaking, and no pulse. MedlinePlus says loss of consciousness is usually the first sign.

Assessment

MedlinePlus says providers rarely diagnose cardiac arrest with tests while it is happening; it is usually recognized afterwards by ruling out other causes of a sudden collapse.

Classification codes

MeSH id.nlm.nih.gov linked data, retrieved 2026-10-15 D006323

Burden

No burden claims are published.

Claims and evidence

Context People in cardiac arrest outside hospital, as described in NHLBI and MedlinePlus patient pages

Recipient: Recipient not specified
Population: People who collapse and may be in cardiac arrest, and the bystanders around them. The pages are general patient information and do not give separate advice by age.
Care setting: Community and public places, then emergency services (the pages are written for bystanders).
Geography: United States (the NHLBI page cites US death figures and the 9-1-1 number).
Life stage: The pages do not state an age group.
Gestational age: Not reported
Postnatal age: Not reported
Follow-up: Not applicable (patient information pages).

Eligibility: 1 inclusion criterion; exclusion criteria not stated

Included: A person who collapses, stops responding and is not breathing normally
Excluded: None stated

Description Evidence stage unknown Certainty not assessed

NHLBI lists the signs that a person may be in cardiac arrest: a sudden collapse with loss of consciousness, no breathing or only gasping, no response to shouting or shaking, and no pulse. MedlinePlus says the first sign is usually loss of consciousness. NHLBI says survival chances improve when first responders get there quickly, which is why it stresses phoning 9-1-1 before anything else.
Applies to Recipient not specified
- People who collapse and may be in cardiac arrest, and the bystanders around them. The pages are general patient information and do not give separate advice by age.
- Community and public places, then emergency services (the pages are written for bystanders).
- United States (the NHLBI page cites US death figures and the 9-1-1 number).
- The pages do not state an age group.
- Gestational age Not reported
- Postnatal age Not reported
Follow-up Not applicable (patient information pages).
Certainty method
Not assessed

Limitations
General patient information from two government pages (NHLBI last updated 2022-05-19). NHLBI is a cite-only source, so its wording is restated and not quoted. The pages do not give an age group or a time limit for these steps.

Last checked
2026-10-15

Next evidence check due
Not scheduled
Sources and citations (6)
1. Supports Cardiac Arrest: What Is Cardiac Arrest? (NHLBI)
  
  Webpage · National Heart, Lung, and Blood Institute (NIH) · Edition Page fetched 2026-10-15. The page says it was last updated on May 19, 2022.
  
  Locator
  Page body, list item 1
  
  How it applies
  Patient information page, restated in the claim.
  
  Retrieved
  2026-10-15T13:53:21Z
  
  Source effective date
  Not reported
  
  Source state
  Current
  
  Snapshot hash
  983ed7b98dc8e782bb47746bd9a1e78f09f7a6d5be1f583b636d40b93e91748a
  
  Reuse basis
  NHLBI is part of the U.S. National Institutes of Health. The pages carry third-party material, such as glossary entries and animations, that this atlas does not use. NIH's own web policy page returned HTTP 403 to a script on 2026-10-14 in an earlier cluster (cj-nih-web-policies.html) and was not tried again here, so NHLBI's reuse terms have not been read. Public text is cite_only until they are read; the integration owner can change it to quote. Hash only; the page is not committed (fetched as ck-nhlbi-cardiac-arrest.html).
2. Supports Cardiac Arrest: What Is Cardiac Arrest? (NHLBI)
  
  Webpage · National Heart, Lung, and Blood Institute (NIH) · Edition Page fetched 2026-10-15. The page says it was last updated on May 19, 2022.
  
  Locator
  Page body, list item 2
  
  How it applies
  Patient information page, restated in the claim.
  
  Retrieved
  2026-10-15T13:53:21Z
  
  Source effective date
  Not reported
  
  Source state
  Current
  
  Snapshot hash
  983ed7b98dc8e782bb47746bd9a1e78f09f7a6d5be1f583b636d40b93e91748a
  
  Reuse basis
  NHLBI is part of the U.S. National Institutes of Health. The pages carry third-party material, such as glossary entries and animations, that this atlas does not use. NIH's own web policy page returned HTTP 403 to a script on 2026-10-14 in an earlier cluster (cj-nih-web-policies.html) and was not tried again here, so NHLBI's reuse terms have not been read. Public text is cite_only until they are read; the integration owner can change it to quote. Hash only; the page is not committed (fetched as ck-nhlbi-cardiac-arrest.html).
3. Supports Cardiac Arrest: What Is Cardiac Arrest? (NHLBI)
  
  Webpage · National Heart, Lung, and Blood Institute (NIH) · Edition Page fetched 2026-10-15. The page says it was last updated on May 19, 2022.
  
  Locator
  Page body, list item 3
  
  How it applies
  Patient information page, restated in the claim.
  
  Retrieved
  2026-10-15T13:53:21Z
  
  Source effective date
  Not reported
  
  Source state
  Current
  
  Snapshot hash
  983ed7b98dc8e782bb47746bd9a1e78f09f7a6d5be1f583b636d40b93e91748a
  
  Reuse basis
  NHLBI is part of the U.S. National Institutes of Health. The pages carry third-party material, such as glossary entries and animations, that this atlas does not use. NIH's own web policy page returned HTTP 403 to a script on 2026-10-14 in an earlier cluster (cj-nih-web-policies.html) and was not tried again here, so NHLBI's reuse terms have not been read. Public text is cite_only until they are read; the integration owner can change it to quote. Hash only; the page is not committed (fetched as ck-nhlbi-cardiac-arrest.html).
4. Supports Cardiac Arrest: What Is Cardiac Arrest? (NHLBI)
  
  Webpage · National Heart, Lung, and Blood Institute (NIH) · Edition Page fetched 2026-10-15. The page says it was last updated on May 19, 2022.
  
  Locator
  Page body, list item 4
  
  How it applies
  Patient information page, restated in the claim.
  
  Retrieved
  2026-10-15T13:53:21Z
  
  Source effective date
  Not reported
  
  Source state
  Current
  
  Snapshot hash
  983ed7b98dc8e782bb47746bd9a1e78f09f7a6d5be1f583b636d40b93e91748a
  
  Reuse basis
  NHLBI is part of the U.S. National Institutes of Health. The pages carry third-party material, such as glossary entries and animations, that this atlas does not use. NIH's own web policy page returned HTTP 403 to a script on 2026-10-14 in an earlier cluster (cj-nih-web-policies.html) and was not tried again here, so NHLBI's reuse terms have not been read. Public text is cite_only until they are read; the integration owner can change it to quote. Hash only; the page is not committed (fetched as ck-nhlbi-cardiac-arrest.html).
5. Supports Cardiac Arrest: What Is Cardiac Arrest? (NHLBI)
  
  Webpage · National Heart, Lung, and Blood Institute (NIH) · Edition Page fetched 2026-10-15. The page says it was last updated on May 19, 2022.
  
  Locator
  Page body, AED section (quote 3)
  
  How it applies
  Patient information page, restated in the claim.
  
  Retrieved
  2026-10-15T13:53:21Z
  
  Source effective date
  Not reported
  
  Source state
  Current
  
  Snapshot hash
  983ed7b98dc8e782bb47746bd9a1e78f09f7a6d5be1f583b636d40b93e91748a
  
  Reuse basis
  NHLBI is part of the U.S. National Institutes of Health. The pages carry third-party material, such as glossary entries and animations, that this atlas does not use. NIH's own web policy page returned HTTP 403 to a script on 2026-10-14 in an earlier cluster (cj-nih-web-policies.html) and was not tried again here, so NHLBI's reuse terms have not been read. Public text is cite_only until they are read; the integration owner can change it to quote. Hash only; the page is not committed (fetched as ck-nhlbi-cardiac-arrest.html).
6. Supports Sudden Cardiac Arrest (MedlinePlus health topic)
  
  Webpage · U.S. National Library of Medicine (MedlinePlus) · Edition Page fetched 2026-10-15.
  
  Locator
  Summary, symptoms
  
  How it applies
  Patient information page, restated in the claim.
  
  Retrieved
  2026-10-15T13:54:14Z
  
  Source effective date
  Not reported
  
  Source state
  Current
  
  Snapshot hash
  713e38eb67d03168df1bcf93f80abed751759ee7e044ac8697444ff28033a8d5
  
  Reuse basis
  MedlinePlus states that works produced by the federal government are not copyrighted, and lists the summaries on health topic pages and medical test information as public domain (the page titled Linking to and Using Content from MedlinePlus, fetched as ck-medlineplus-usingcontent.html, sha256 f70c0b8c67574e30377aab0c22b44038364a37e2e9f54a2ffa67597383b3de34). It names the A.D.A.M. encyclopedia, drug monographs and many images as copyrighted; this atlas uses only the page summary text. Source: MedlinePlus, National Library of Medicine. The raw page is committed at research/snapshots/ck-medlineplus-suddencardiacarrest.html (fetched as ck-medlineplus-suddencardiacarrest.html).

Clinical links

Each link reports what one cited claim says about one population. "Evaluated for" means studied, not shown to work. These links do not show that anything is effective or right for you.

Claim, not a settled fact Evaluated for this: Temperature control after cardiac arrest (Evaluated for, seen from the other side)
Applies to Adult
- Adults with coma who had had an out-of-hospital cardiac arrest of presumed cardiac or unknown cause (abstract wording). 1900 were randomly assigned and 1850 were evaluated for the primary outcome. The registry adds: unconscious with a FOUR-score below M4, stable return of spontaneous circulation for 20 minutes, eligible for intensive care without restrictions, and inclusion within 180 minutes of return of spontaneous circulation.
- Not stated in the abstract; the abstract gives no setting.
- Registry locations in 14 countries; the registry also lists Luxembourg and the Netherlands as removed countries.
- Adults (abstract); the registry minimum age is 18 years and it gives no maximum age.
Follow-up The primary outcome was death from any cause at 6 months (abstract). The registry gives 180 days.
In TTM2, an open-label trial with blinded assessment of outcomes, 1900 adults with coma who had had an out-of-hospital cardiac arrest of presumed cardiac or unknown cause were randomly assigned to targeted hypothermia at 33 degrees C followed by controlled rewarming, or to targeted normothermia with early treatment of fever (body temperature of 37.8 degrees C or higher). The primary outcome was death from any cause at 6 months. A total of 1850 patients were evaluated for it: 465 of 925 patients (50 percent) in the hypothermia group had died, as compared with 446 of 925 (48 percent) in the normothermia group (relative risk with hypothermia 1.04; 95 percent confidence interval 0.94 to 1.14; P=0.37). Of the 1747 patients whose functional outcome was assessed, 488 of 881 (55 percent) in the hypothermia group had moderately severe disability or worse (modified Rankin scale score of 4 or more), as compared with 479 of 866 (55 percent) in the normothermia group (relative risk 1.00; 95 percent confidence interval 0.92 to 1.09). Arrhythmia resulting in hemodynamic compromise was more common in the hypothermia group (24 percent vs 17 percent, P<0.001); the incidence of other adverse events did not differ significantly. The authors conclude that targeted hypothermia did not lead to a lower incidence of death by 6 months than targeted normothermia.
Limitations. Abstract of the 2021 report only; the full text was not read (NEJM pages return HTTP 403 to scripts). The comparator was targeted normothermia with early treatment of fever, not an absence of temperature management, so the trial does not test whether managing temperature at all matters. The registry lists masking as TRIPLE but its description says the clinical team was not blinded to allocation; the abstract says open-label with blinded outcome assessment. 1850 of the 1900 randomized patients were evaluated for the primary outcome. The abstract names the Swedish Research Council and others as funders. PubMed lists no erratum for this record.
Claim, not a settled fact Evaluated for this: Automated external defibrillator (AED) (Evaluated for, seen from the other side)
Applies to Recipient not specified
- People with out-of-hospital cardiac arrest in 993 community units (for example shopping malls and apartment complexes) in 24 North American regions, where trained lay volunteers responded. The abstract counts 128 treated arrests in the AED units and 107 in the CPR-only units; 70 percent of arrests were in a public location.
- Community units with a structured, monitored emergency-response system staffed by trained lay volunteers (more than 19,000 took part); later ambulance and hospital care is not described in the abstract.
- 24 North American regions (abstract wording).
- The abstract gives a mean age of 69.8 years for treated patients and sets no age limits.
- Gestational age Not reported
- Postnatal age Not reported
Follow-up The abstract gives the primary outcome (survival to hospital discharge) and no follow-up period.
In a prospective, community-based, multicenter trial of public-access defibrillation, community units such as shopping malls and apartment complexes were randomly assigned to a structured, monitored emergency-response system in which lay volunteers were trained either in CPR alone or in CPR plus the use of an AED. More than 19,000 volunteer responders from 993 community units in 24 North American regions took part. The primary outcome was survival to hospital discharge. Among treated out-of-hospital cardiac arrests, there were more survivors to discharge in units assigned to CPR plus AED volunteers (30 survivors among 128 arrests) than in units assigned to CPR-only volunteers (15 among 107; P=0.03; relative risk 2.0, 95 percent confidence interval 1.07 to 3.77). There were only 2 survivors in residential complexes. Functional status at hospital discharge did not differ between the groups, and no inappropriate shocks were delivered. The authors conclude that training and equipping volunteers to attempt early defibrillation within a structured response system can increase the number of survivors after out-of-hospital cardiac arrest in public locations.
Limitations. Abstract of the 2004 report only; the full text was not read (NEJM pages return HTTP 403 to scripts). The units, not the patients, were randomized, and the abstract counts survivors among treated arrests without giving survival percentages. The benefit reported is for arrests in public locations; the abstract reports only 2 survivors in residential complexes. The volunteers were trained and worked in a structured, monitored response system, so the result does not show what happens when untrained bystanders use an AED. Functional status at discharge did not differ. PubMed lists no erratum for this record.

Record details

Record id: cardio:sudden-cardiac-arrest
Content hash: 1500406c60f0b4b763777f9f9f9a47f8fb9784b160ba788f04d3e3f06c8e4d5e