ASYSTOLE

 

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; with a wide or narrow complex, with or without a pulse, interspersed with periods of asystole. When discussing PEA, ventricular fibrillation and ventricular tachycardia are excluded..

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 of the SA node or AV conducting system due to sclerosis. It is usually preceded by a bradydysrhythmia, due to sinus arrest or complete heart block.

Reflex bradyasystole/asystole can result from ocular surgery, retrobulbar block, eye trauma, pressure on the globe, maxillofacial surgery, hypertensive carotid sinus syndrome, and glossopharyngeal neuralgia.

Secondary asystole occurs when factors outside of the heart's electrical system result in its failure to generate any electrical depolarization. In this case, the final common pathway is usually severe tissue hypoxia or acidosis.

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Frequency:

• In the U.S.: It is difficult to accurately measure the number of adults in cardiopulmonary arrest, who had asystole as the initial arrest rhythm. Reports vary and may be skewed by the patient population studied and/or the method of reporting the initial rhythm.
  
• Internationally: When there is a lower incidence of coronary artery disease in the population of a country, asystole is more common as a percentage of cardiopulmonary arrests. This is because cardiac ischemia more frequently results in ventricular fibrillation.
  

Mortality/Morbidity: Asystole is associated with a poor outcome - regardless of its initial cause. 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 a cafe coronary, i.e., chocking on food, and only by establishing an airway immediately following the onset of asystole.

Sex: The frequency of asystole, as percentage of all cardiopulmonary arrests, is probably the same between the sexes; however, the frequency of cardiac arrest is proportional to the underlying incidence of heart disease, which is more common in males until age 75.

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

 

CLINICAL

PATHOPHYSIOLOGY

History: The immediate diagnoses of asystole requires the recognition of a full cardiac arrest and a confirmed flat line rhythm, in two 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. There may be a few agonal breaths, but there will be no detectable heart sounds or palpable peripheral pulses.

Causes:

WORKUP

ETIOLOGY AND CLINICAL MANIFESTATIONS

Lab Studies:

Procedures:

• Ventricular fibrillation masquerading as asystole should be ruled out by checking two leads perpendicular to each other. However, with the use of a flat-line protocol based on a 3-lead check, occult VF was documented in only 3/118 asystolic patients (2.5%). It appears that VF masquerading as asystole is rare.

TREATMENT

TREATMENT

Prehospital Care:

• The only two drugs recommended by the American Heart Association are epinephrine and atropine. In spite of full vagolytic doses of atropine (0.04 mg/kg) and high-dose epinephrine (0.20 mg/kg), few patients survive to leave the hospital neurologically intact.

• Transcutaneous pacing (TCP), even when used immediately, has not significantly altered meaningful survival, resulting in a functional lifestyle. When there is no metabolic deficit, such as an arrest preceded by a conduction or impulse generation disorder, i.e., primary asystole, immediate use of TCP may be lifesaving.
  

Emergency Department Care:

• There has been a case report of a long, but successful, resuscitation from asystole of a hyperkalemic renal failure patient. The treatment included calcium chloride to reverse the physiologic effects and insulin and glucose to lower serum potassium; however, this cannot be routinely recommended for all cases of asystolic arrest.

MEDICATION

SUMMARY

Parasympathetic influences have not been fully elucidated during cardiopulmonary arrests, and the clinical benefits of atropine have yet to be confirmed. High-dose epinephrine (0.20 mg/kg) may improve the hemodynamics of cardiopulmonary resuscitation, increasing the rate of return to spontaneous circulation; however, it has not been unequivocally demonstrated to influence the final clinical outcome. Adenosine antagonists such as aminophylline have been investigated, but have not been shown to be clinically useful.

Drug Category: Anticholinergic agent - The goal is to improve conduction through the AV node by reducing vagal tone via muscarinic receptor blockade. This is only effective if the site of block is within the AV node. For patients with infranodal block, this therapy is ineffective.

FOLLOW-UP

Further Inpatient Care:

• The intensive care unit is the appropriate disposition for the occasional patient who survives asystolic cardiopulmonary arrest and requires further treatment and diagnostic evaluations.

Deterrence/Prevention:

• Primary asystole may be prevented by the appropriate use of a permanent pacemaker in those patients who have high-grade heart block or sinus arrest.

• Preventing secondary asystole requires early recognition and treatment of the preceding event.

Complications:

• Complications include death, permanent neurological impairment and complications from CPR or invasive procedures such as liver laceration, fractured ribs, pneumothorax, aspiration and gastric/esophageal rupture.

Prognosis:

• Prognosis depends on the etiology of the asystolic rhythm and success or failure of CPR.

Patient Education:

• Advice about electrical storm safety and preventing hypothermia is appropriate for those exposed to these conditions.

MISCELLANEOUS

Medical/Legal Pitfalls:

• Negligence may be claimed for failure to anticipate impending asystolic arrest, unrecognized esophageal intubation and for withholding specific therapy with hypothermia , prior to pronouncement of death.

BIBLIOGRAPHY

• American Heart Association : American Heart Association Emergency Cardiac Care Committee and Subcommittees: Guidelines for cardiopulmonary resuscitation and emergency cardiac care. JAMA 1992; 268: 2171-2302.
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