Amiodarone
Amiodarone is an iodine-rich class III multichannel antiarrhythmic used for ventricular fibrillation and pulseless ventricular tachycardia in cardiac arrest, sustained ventricular tachycardia, and atrial fibrillation rhythm or rate control when other agents are unsafe. First-line arrest dosing is a 300 mg intravenous push, and long-term use requires monitoring for thyroid, liver, lung, and eye toxicity.
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What this article covers
- Overview
What it is: amiodarone is a potassium channel blocker (Vaughan Williams class III) that behaves as a multichannel agent, adding sodium and calcium channel blockade plus noncompetitive alpha and beta adrenergic blockade.
- Epidemiology
Typical patient: adults with recurrent, hemodynamically significant ventricular arrhythmia, patients resuscitated from shock-refractory VF or pulseless VT, and AF patients in whom other rate- or…
- Risk factors
Preexisting thyroid disease: underlying nodular goiter or autoimmune thyroiditis raises the risk of amiodarone-induced thyroid dysfunction.
- Pathophysiology
Multichannel blockade: amiodarone blocks the potassium current of phase 3 repolarization, fast sodium channels, and L-type calcium channels, and noncompetitively blocks alpha and beta adrenergic…
- Clinical features
Electrocardiographic effect: therapeutic amiodarone slows the sinus rate, prolongs the PR interval by slowing atrioventricular (AV) nodal conduction, and prolongs the QT interval, expected findings rather than markers of toxicity.
- Differential diagnosis
Sotalol: another class III agent for AF and VT, but a pure potassium channel blocker needing inpatient initiation with continuous ECG monitoring, with a higher torsades de pointes risk than amiodarone.
- Diagnosis
What establishes the indication: the arrhythmia diagnosis that justifies amiodarone is established first, not a test for the drug itself; sustained VT is confirmed on a 12-lead ECG showing a…
- Management
First-line in cardiac arrest: for shock-refractory VF or pulseless VT, give amiodarone 300 mg IV or intraosseous (IO) push after the second failed defibrillation attempt and after epinephrine; if the…
- Complications
Thyroid dysfunction: occurs in about 15% of treated patients, more often hypothyroidism than hyperthyroidism, and can develop at any point during therapy or after the drug is stopped because of its long half-life.
- Prognosis
Arrhythmia control: amiodarone is highly effective at suppressing ventricular arrhythmia and maintaining sinus rhythm in AF, and in ICD recipients it meaningfully reduces device shock burden.
- Prevention
Baseline screening before starting: obtain TSH, liver function tests, a chest radiograph, pulmonary function testing, and a baseline ECG for the QT interval before the first oral load or IV infusion.
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Related articles
- Atrial fibrillation
Atrial fibrillation is a supraventricular tachyarrhythmia with disorganized atrial activation and an irregularly irregular ventricular response, the most common sustained arrhythmia and a major cause of stroke. Diagnosis is by ECG showing no discrete P waves with irregular RR intervals, and management addresses rate or rhythm control, stroke prevention by CHA2DS2-VASc-guided anticoagulation, and the underlying cause.
- Ventricular tachycardia
Ventricular tachycardia is three or more consecutive ventricular beats at over 100 per minute, a wide-complex tachycardia that is life-threatening when sustained. Any regular wide-complex tachycardia is ventricular tachycardia until proven otherwise: unstable patients are cardioverted or defibrillated, and long-term risk is managed with an implantable defibrillator.
- Ventricular fibrillation
Ventricular fibrillation is chaotic, disorganized ventricular electrical activity with no effective contraction, producing immediate loss of cardiac output and cardiac arrest. It is the leading shockable arrest rhythm, and survival depends on immediate CPR and defibrillation, followed by treatment of the cause and an ICD for secondary prevention.
- Torsades de pointes
Torsades de pointes is a polymorphic ventricular tachycardia occurring on a background of QT prolongation, with a characteristic twisting of QRS complexes around the baseline. Management is intravenous magnesium, correction of the underlying QT-prolonging cause, and rate acceleration by pacing or isoproterenol; unstable episodes are defibrillated.
- Sudden cardiac arrest
Sudden cardiac arrest is the abrupt cessation of cardiac function with loss of pulse and consciousness, most often from a ventricular tachyarrhythmia on a background of coronary disease. Survival depends on immediate CPR and defibrillation of shockable rhythms, followed by treatment of the cause and secondary prevention with an ICD.
- Hyperthyroidism
Hyperthyroidism is the clinical syndrome of thyroid hormone excess, produced by a range of causes from Graves disease and autonomously functioning nodules to destructive thyroiditis and exogenous hormone ingestion. Diagnosis begins with a suppressed thyroid-stimulating hormone and elevated free thyroxine, followed by radioactive iodine uptake testing or antibody measurement to identify the cause, and first-line treatment is a beta blocker for symptom control while the underlying cause directs thionamide, radioactive iodine ablation, or thyroidectomy therapy.
- Hypothyroidism
Hypothyroidism is thyroid hormone deficiency, most commonly caused by autoimmune (Hashimoto) thyroid failure in iodine-sufficient countries, diagnosed by an elevated thyroid-stimulating hormone with a low or normal free thyroxine. First-line treatment is levothyroxine dosed at 1.6 mcg/kg lean body weight orally once daily, titrated using thyroid-stimulating hormone rechecked no sooner than 6 weeks after any dose change.