Cardiac arrest

Last revised by Henry Knipe on 23 Feb 2024

Cardiac arrest is the term used for the abrupt loss of cardiac pump function such that an adequate circulation cannot be maintained. Despite recent modest improvements in survival, it usually leads to death, if not immediately treated. Arrests may be in-hospital or out-of-hospital. 

The epidemiology of cardiac arrest varies based on whether we are considering in- or out-of-hospital arrests, although at least one large study (from 2020) shows that the previously assumed marked differences in these two groups may be illusory 9.

Worldwide, the incidence of cardiac arrest is not known 1, however, studies in the US have shown that there are almost 300,000 in-hospital arrests per annum 1. Age-wise, cardiac arrests have a mean age of occurrence in the mid-sixties, with a small majority being men (58%) 1. Non-shockable rhythms are much more common, accounting for about 80% of arrests.

A retrospective study of over 3,000 young (<35 years) out-of-hospital cardiac arrest patients in London, UK, found that three-quarters were over 18 years old, the majority being male, and cardiac etiology was the commonest underlying cause. Common non-cardiac causes of arrest in young adult males were attempted suicides, especially hanging and overdoses 8.

In infants less than 12-months-old, sudden infant death syndrome (SIDS) was the commonest trigger for cardiac arrest in the large young patient study performed in London, UK 8.

Patients may initially be awake, although once the heart stops, loss of consciousness rapidly ensues due to a critical lack of perfusion of the brain.

Cardiac arrest is usually straightforward to recognize, with classic signs and symptoms:

Over half of all cardiac arrests are secondary to a cardiac cause, with respiratory deterioration accounting for most of the remainder (up to 40%) 1. Many arrests will be multifactorial.

The so-called reversible causes should always be considered during the acute management of an arrest 1,6,7.

  • hypovolemia, usually massive hemorrhage

  • hypothermia e.g. near drowning, exposure

  • metabolic e.g. hypo-/hyperkalemia, hypoglycemia, hypocalcemia, severe acidosis

  • toxins: includes carbon monoxide, opioids, methadone, benzodiazepines

The "reversible causes" represent a re-ordering of the causes so far described to ensure that key etiologies are always considered 7.

"4 Hs and 4 Ts"

Cardiac arrest can be subtyped according to whether the presenting arrhythmia can be successfully treated with a shock from a defibrillator or not. The majority of cardiac arrests are with non-shockable rhythms.

Point of care ultrasound (PoCUS) has been used to assess cardiac arrest patients in emergency departments.

Cardiac arrest is diagnosed clinically however occasionally a patient will be periarrest or have arrested just prior to, or even during, an imaging exam. Several case reports have described the findings on CT in this patient cohort 3,4:

Described CT features include:

Cardiopulmonary resuscitation (CPR) is the gold standard care performed for all patients in cardiac arrest 1. The algorithms have been modified somewhat over the years as the real-life evidence base has expanded. 

Successful CPR results in 'return of spontaneous circulation' (ROSC).

Survival post-arrest remains poor, with a maximal 25% in-hospital cases reaching discharge 2 with the chance of survival outside-hospital being much worse.  Nevertheless, long term disability may still be an issue.

Poor prognostic factors for in-hospital arrests from a large meta-analysis 2:


  • male sex

  • older age

  • chronic renal disease

  • malignancy


  • prolonged resuscitation time

  • tracheal intubation

However, several conditions were correlated with improved outcomes for in-hospital arrests, including

  • witnessed arrest

  • arrest in a monitored environment

  • daytime arrest

  • shockable rhythm

It is also known that shockable rhythms are associated with a better prognosis in the out-of-hospital arrest scenario 2,5.

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