eMedicine Specialties > Emergency Medicine > Cardiovascular

Asystole

Author: Richard M Caggiano, MD, FACEP, Adjunct Faculty, Department of Medicine, University of Washington School of Medicine; Director of Emergency Services, Medical Director of Employee Health, Chief Medical Officer, and Assistant Director of Trauma Services, Pullman Regional Hospital
Contributor Information and Disclosures

Updated: Jul 7, 2009

Introduction

Background

Asystole is cardiac standstill with no cardiac output and no ventricular depolarization; it eventually occurs in all dying patients.

Pulseless electrical activity (PEA) is the term applied to a heterogenous 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 often are interspersed with periods of asystole. When discussing PEA, ventricular fibrillation (VF) and ventricular tachycardia (VT) are excluded.

Rhythm strip showing asystole.

Rhythm strip showing asystole.

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Rhythm strip showing asystole.

Rhythm strip showing asystole.


Rhythm strip showing ventricular fibrillation.

Rhythm strip showing ventricular fibrillation.

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Rhythm strip showing ventricular fibrillation.

Rhythm strip showing ventricular fibrillation.


Pathophysiology

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 usually is preceded by a bradydysrhythmia due to sinus node block-arrest, complete heart block, or both.

Reflex bradyasystole/asystole can result from ocular surgery, 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. 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 VF and commonly occurs after unsuccessful attempts at defibrillation. This forebodes a dismal outcome.

Frequency

United States

The number of 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. 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 and none were discharged alive.1 This study was not limited to patients with asystole.

International

In one study from Goteborg, Sweden, asystole was the presenting rhythm in the field in 35% of patients with cardiac arrest.2

When the incidence of coronary artery disease 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 VF. 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, infection, choking, drowning, or poisoning). Infants are more statistically likely to suffer a cardiac arrest than older children or adolescents. 

Nontraumatic cardiac arrest occurred at a rate of 72.1 per 100,000 infants versus 3.73 and 7.37 per 100,000 in children and adolescents, respectively. In this study looking at 25,405 adults and 624 patients younger than 20 years old, the adult rate of cardiac arrest was 126.52 per 100,000. The pediatric patients with ventricular fibrillation or ventricular tachycardia were 4 times more likely to survive an out-of-hospital cardiac arrest than those with asystole (20% vs 5%). Patients younger than 20 years had an overall better survival rate than adults when all rhythms are included and traumatic arrests are excluded.3   

Mortality/Morbidity

Asystole is associated with a poor outcome regardless of its initial cause. In the Goteborg study, 10% of 1,635 asystolic patients survived to hospital admission and 2% survived to hospital discharge.2

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 may 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.

Race

Race is not a significant factor 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.

Sex

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 75 years of age.

Age

Prevalence of asystole as the presenting cardiac rhythm is lower in adults (25-56%) than in children (90-95%).

Clinical

History

Immediate diagnosis of asystole requires the recognition of a full cardiac arrest and a confirmed flat-line rhythm in 2 perpendicular leads. Lightheadedness or syncope may precede asystole when it follows a bradyasystolic rhythm.

Physical

If the rhythm is truly asystole and has been present for more than several seconds, the patient will be unconscious and unresponsive. A few agonal (final gasping) breaths may be noted, but detectable heart sounds and palpable peripheral pulses are absent.

Causes

  • Examples of common conditions that can result in secondary asystole include suffocation, near drowning, stroke, massive pulmonary embolus, hyperkalemia, hypothermia, MI complicated by VF or VT that deteriorates to asystole, post defibrillation, and sedative-hypnotic or narcotic overdoses leading to respiratory failure.
  • Hypothermia is a special circumstance, since asystole can be tolerated for a longer period of time under such conditions and can be reversed with rapid rewarming while cardiopulmonary resuscitation (CPR) is being performed. If available, institute cardiopulmonary bypass immediately, because it can accomplish both of these goals. Most survivors have received cardiopulmonary bypass.
  • 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 SA and the 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.
    • 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 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 VF.

More on Asystole

Overview: Asystole
Differential Diagnoses & Workup: Asystole
Treatment & Medication: Asystole
Follow-up: Asystole
Multimedia: Asystole
References
Further Reading
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References

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Keywords

flat line, asystole, cardiac arrest, heart attack, cardiac standstill, pulseless electrical activity, PEA, primary asystole, secondary asystole, bradyasystolic rhythm, bradydysrhythmia, bradyasystole, asystolic cardiopulmonary arrest, asystolic cardiac arrest

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Contributor Information and Disclosures

Author

Richard M Caggiano, MD, FACEP, Adjunct Faculty, Department of Medicine, University of Washington School of Medicine; Director of Emergency Services, Medical Director of Employee Health, Chief Medical Officer, and Assistant Director of Trauma Services, Pullman Regional Hospital
Richard M Caggiano, MD, FACEP is a member of the following medical societies: American College of Emergency Physicians
Disclosure: Nothing to disclose.

Medical Editor

Edward Bessman, MD, Chairman, Department of Emergency Medicine, John Hopkins Bayview Medical Center; Assistant Professor, Department of Emergency Medicine, Johns Hopkins University
Edward Bessman, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Gary Setnik, MD, Chair, Department of Emergency Medicine, Mount Auburn Hospital; Assistant Professor, Division of Emergency Medicine, Harvard Medical School
Gary Setnik, MD is a member of the following medical societies: American College of Emergency Physicians, National Association of EMS Physicians, and Society for Academic Emergency Medicine
Disclosure: SironaHealth Salary Management position; South Middlesex EMS Consortium Salary Management position

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

David FM Brown, MD, Assistant Professor, Department of Medicine, Division of Emergency Medicine, Harvard Medical School; Associate-Chief, Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital
David FM Brown, MD is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine
Disclosure: Schering  Honoraria Speaking and teaching

 
 
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