Updated: Mar 31, 2020
  • Author: Sandy N Shah, DO, MBA, FACC, FACP, FACOI; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Asystole is also known as flatline. It is a state of cardiac standstill with no cardiac output and no ventricular depolarization, as shown in the image below; it eventually occurs in all dying patients.

Rhythm strip showing asystole. Rhythm strip showing asystole.

Pulseless electrical activity (PEA) is the term applied to a heterogeneous group of dysrhythmias unaccompanied by a detectable pulse. Bradyasystolic rhythms are slow rhythms; they can have a wide or narrow complex, with or without a pulse, and are often interspersed with periods of asystole. When discussing pulseless electrical activity, ventricular fibrillation (VF) (see the following image) and ventricular tachycardia (VT) are excluded.

Rhythm strip showing ventricular fibrillation. Rhythm strip showing ventricular fibrillation.


Asystole can be primary or secondary. Primary asystole occurs when the heart's electrical system intrinsically fails to generate a ventricular depolarization. This may result from ischemia or from degeneration (ie, sclerosis) of the sinoatrial (SA) node or atrioventricular (AV) conducting system. Primary asystole is usually preceded by a bradydysrhythmia due to sinus node block-arrest, complete heart block, or both.

Reflex bradyasystole/asystole can result from ocular surgery, [1, 2] retrobulbar block, eye trauma, direct pressure on the globe, maxillofacial surgery, hypersensitive carotid sinus syndrome, or glossopharyngeal neuralgia. Episodes of asystole and bradycardia have been documented as manifestations of left temporal lobe complex partial seizures. [3, 4] These patients experienced either dizziness or syncope. No sudden deaths were reported, but the possibility exists if asystole were to persist. The longest interval was 26 seconds.

Secondary asystole occurs when factors outside of the heart's electrical conduction system result in a failure to generate any electrical depolarization. In this case, the final common pathway is usually severe tissue hypoxia with metabolic acidosis. Asystole or bradyasystole follows untreated ventricular fibrillation and commonly occurs after unsuccessful attempts at defibrillation. This forebodes a dismal outcome.



Causes of primary and secondary asystole are briefly reviewed in this section.

Primary asystole

Primary asystole develops when cellular metabolic functions are no longer intact and an electrical impulse cannot be generated. With severe ischemia, pacemaker cells cannot transport the ions necessary to affect the transmembrane action potential. Implantable pacemaker failure may also be a cause of primary asystole.

Proximal occlusion of the right coronary artery can cause ischemia or infarction of both the sinoatrial (SA) and the atrioventricular (AV) nodes. Extensive infarction can cause bilateral bundle-branch block (ie, infranodal complete heart block).

Idiopathic degeneration of the SA or AV node can result in sinus arrest-block and/or AV heart block, respectively. This process is slow and progressive, but the symptoms may be acute and asystole may result. An implantable pacemaker is usually required for these conditions.

Occasionally, asystolic sudden death occurs from congenital heart block, local tumor, or cardiac trauma. [5]

Asystole can occur following an indirect lightning strike (ie, direct current [DC]) that depolarizes all the cardiac pacemakers. A rhythm may return spontaneously or shortly after cardiopulmonary resuscitation (CPR) is initiated. These patients may survive intact if given immediate attention. Alternating current (AC) from man-made sources of electrical current usually results in ventricular fibrillation (VF).

Secondary asystole

Examples of common conditions that can result in secondary asystole include suffocation, near drowning, stroke, massive pulmonary embolus, hyperkalemia, hypothermia, myocardial infarction (MI) complicated by VF or ventricular tachycardia (VT) that deteriorates to asystole, post defibrillation, and sedative-hypnotic or narcotic overdoses leading to respiratory failure.

Hypothermia is a special circumstance, because asystole can be tolerated for a longer period under such conditions and can be reversed with rapid rewarming while CPR is being performed. If available, institute cardiopulmonary bypass immediately, because it can accomplish both of these goals. Most survivors have received cardiopulmonary bypass.



The number of US adults in cardiopulmonary arrest who had bradyasystole as the initial arrest rhythm is difficult to measure accurately. Reports vary and may be skewed by the patient population studied and/or by the method of reporting the initial rhythm. For example, in a 1991 study of 185 patients in cardiopulmonary arrest at the time of arrival to the emergency department, 9% had survived to hospital admission but none were discharged alive. [6] This study was not limited to patients with asystole. [6] In one study from Goteborg, Sweden, asystole was the presenting rhythm in the field in 35% of patients with cardiac arrest. [7]

Race is not a significant factor in asystole except as it relates to the underlying conditions that may lead to a cardiac arrest, such as chronic hypertension, renal failure, coronary artery disease, congestive heart failure, or cardiac dysrhythmias.

Individuals with low CAD incidence

When the incidence of coronary artery disease (CAD) in the population of a country is relatively low, asystole is relatively more common as a manifestation of cardiopulmonary arrests. This is because cardiac ischemia more frequently results in ventricular fibrillation (VF).


The prevalence of asystole as the presenting cardiac rhythm is lower in adults (25-56%) than in children (90-95%). In fact, asystole is most likely to be found in cardiopulmonary arrests occurring in children; this is usually secondary to another noncardiac event (ie, respiratory arrest due to sudden infant death syndrome [SIDS], infection, choking, drowning, or poisoning). [8] Infants are more statistically likely to suffer a cardiac arrest than older children or adolescents.

The Resuscitation Outcomes Consortium Epistry-Cardiac Arrest trial, nontraumatic cardiac arrest occurred at a rate of 72.1 per 100,000 infants versus 3.73 per 100,000 in children and 7.37 per 100,000 in adolescents. [9] Investigators found the adult rate of cardiac arrest was 126.52 per 100,000 when they evaluated 25,405 adults and 624 patients younger than 20 years.

Pediatric patients with VF or ventricular tachycardia (VT) were 4 times more likely to survive an out-of-hospital cardiac arrest (20%) than those with asystole (5%), and patients younger than 20 years had an overall better survival rate than adults when all rhythms are included and traumatic arrests are excluded. [9]


The frequency of asystole, as a percentage of all cardiopulmonary arrests, is higher in women than in men; however, the frequency of cardiac arrest in general is proportional to the underlying incidence of heart disease, which is more common in males until around age 75 years.



The prognosis in asystole depends on the etiology of the asystolic rhythm, timing of interventions, and success or failure of advanced cardiac life support (ACLS).

Resuscitation is likely to be successful only if it is secondary to an event that can be corrected immediately, such as a cardiac arrest due to choking on food (a cafe coronary), and only if an airway can be established and the patient can be rapidly reoxygenated. Occasionally, primary asystole can be reversed if it is due to pacemaker failure, which could be either intrinsic or extrinsic, and this is corrected immediately by external pacing.

Generally, the prognosis is dismal regardless of its initial cause; in particular, individuals with postcountershock asystole have an even worse survival rate. [10, 11] In the Termination of Resuscitation study, when no shock was advised in patients with unwitnessed cardiac arrest, there were no survivors. [12, 13] In the Goteborg, Sweden, study, 10% of 1,635 asystolic patients survived to hospital admission, but 2% survived to hospital discharge. [7]

The most recent American Heart Association guidelines to improve cardiocerebral resuscitation (CCR) have validated studies that show improved outcomes in all adults with out-of-hospital cardiac arrest in ventricular tachycardia and ventricular fibrillation only. [14]


Complications from asystole include permanent neurologic impairment and complications from cardiopulmonary resuscitation (CPR) or invasive procedures (eg, liver laceration, fractured ribs, pneumothorax, hemothorax, air embolus, aspiration, gastric/esophageal rupture). If asystole persists for fifteen minutes or more, the brain will have been deprived of oxygen long enough to cause brain death. Death often occurs.


Patient Education

Advice about electrical storm safety and prevention of hypothermia is appropriate for those likely to be exposed to these conditions.

For patient education information, see Heart Health Center as well as Cardiopulmonary Resuscitation (CPR), Heart Attack, and Coronary Artery Disease.