asystole

Asystole is a state of cardiac arrest defined by the absence of electrical activity in the heart, resulting in no effective cardiac output. On an electrocardiogram, it appears as a flat or nearly flat line with no identifiable P waves, QRS complexes, or other activity.

Causes are diverse and often involve profound disturbances in oxygenation, metabolism, or structure. Common contributors include severe hypoxia, extreme acidosis, electrolyte abnormalities (notably hyperkalemia or severe hypokalemia), hypothermia, toxins, massive pulmonary embolism, or advanced structural heart disease. In the context of cardiac arrest, asystole is one of the non-shockable rhythms, alongside pulseless electrical activity (PEA). Reversible causes are commonly summarized as Hs and Ts.

Presentation and diagnosis involve sudden collapse with loss of consciousness and no detectable pulse or breathing. During monitoring, asystole is identified by a lack of electrical activity on the ECG, with careful differentiation from artifacts or very fine electrical activity.

Management requires immediate action: begin high-quality chest compressions, ensure airway and ventilation, and call for help. Defibrillation is not indicated for true asystole; epinephrine (1 mg IV/IO) is given every 3–5 minutes. Ongoing assessment should focus on identifying and correcting reversible causes (improving oxygenation, correcting electrolyte and acid–base disturbances, treating hypothermia, relief of tamponade, thromboembolism, or tension pneumothorax as appropriate). Consider termination of resuscitation only according to local guidelines and prognosis.

Prognosis is generally poor, with markedly reduced survival if the arrest duration is prolonged, though outcomes improve with rapid recognition, immediate CPR, and prompt treatment of reversible factors.

See also: cardiac arrest, pulseless electrical activity, ventricular fibrillation.