Excerpt from Asystole

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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.

For a related CME activity, see CME - Combination Vasopressin and Epinephrine Do Not Improve Cardiac Arrest Outcomes. 

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).

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.

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%).

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