Practice Essentials
The incidence of digitalis toxicity has declined in recent years, due to decreased use along with improved technology for monitoring of drug levels and increased awareness of drug interactions. Nevertheless, cardiac glycoside toxicity continues to be a problem in the United States because of the wide use of digoxin (a preparation of digitalis) and its narrow therapeutic window.
It is important to learn about the source, amount, time of ingestion, presence of any coingestant, and patient’s own comorbidities. Acute digitalis toxicity can result from unintentional, suicidal, or homicidal overdose of the digitalis preparation digoxin, or accidental ingestion of plants that contain cardiac glycosides. Chronic toxicity in patients on digoxin therapy may result from deteriorating renal function, dehydration, electrolyte disturbances, or drug interactions. Alterations in cardiac rate and rhythm from digitalis toxicity may reproduce almost every known mechanism of dysrhythmia. See the image below.
Bidirectional tachycardia in a patient with digitalis toxicity.
Signs and symptoms
Digitalis toxicity produces CNS, visual, GI, and cardiac manifestations. Nausea, vomiting, and drowsiness are among the most common extracardiac manifestations.
CNS symptoms of digitalis toxicity include the following:
Drowsiness
Lethargy
Fatigue
Neuralgia
Headache
Dizziness
Confusion or giddiness
Hallucinations
Seizures (rare)
Paresthesias and neuropathic pain
Visual aberration often is an early indication of digitalis toxicity. Yellow-green distortion is most common, but red, brown, blue, and white distortions also occur. Drug intoxication also may cause the following:
Snowy vision
Photophobia
Photopsia
Decreased visual acuity
Yellow halos around lights (xanthopsia)
Transient amblyopia or scotomata
GI symptoms in acute or chronic toxicity include the following:
Anorexia
Weight loss
Failure to thrive (in pediatric patients)
Nausea
Vomiting
Abdominal pain
Diarrhea
Mesenteric ischemia (a rare complication of rapid IV infusion)
Cardiac symptoms
Cardiac symptoms include the following:
Palpitations
Shortness of breath
Syncope
Swelling of lower extremities
Bradycardia
Hypotension
Dyspnea
See Clinical Presentation for more detail.
Diagnosis
Studies in patients with possible digitalis toxicity include the following:
Serum digoxin level
Electrolytes
Renal function studies
ECG
Serum digoxin level
Therapeutic levels are 0.6-1.3 to 2.6 ng/mL
Levels associated with toxicity overlap between therapeutic and toxic ranges
False-negative assay results may occur with acute ingestion of nondigoxin cardiac glycosides (eg, herbal compunds, such as foxglove or oleander)
Levels determined less than 6-8 hours after an acute ingestion do not necessarily predict toxicity
The best way to guide therapy is to follow the digoxin level and correlate it with serum potassium concentrations and the patient’s clinical and ECG findings.
Electrolytes
In acute toxicity, hyperkalemia is common
Chronic toxicity is often accompanied by hypokalemia and hypomagnesemia
Electrocardiography
Digoxin toxicity may cause almost any dysrhythmia
Classically, dysrhythmias associated with increased automaticity and decreased AV conduction occur
Sinus bradycardia and AV conduction blocks are the most common ECG changes in the pediatric population, while ventricular ectopy is more common in adults
Nonparoxysmal atrial tachycardia with heart block and bidirectional ventricular tachycardia are particularly characteristic of severe digitalis toxicity
See Workup for more detail.
Management
Supportive care of digitalis toxicity includes the following:
Hydration with IV fluids
Oxygenation and support of ventilatory function
Discontinuation of the drug, and, sometimes, the correction of electrolyte imbalances
GI decontamination
Activated charcoal is indicated for acute overdose or accidental ingestion
Binding resins (eg, cholestyramine) may bind enterohepatically-recycled digoxin
Treatment of electrolyte imbalance
For hyperkalemia, use insulin plus glucose, and sodium bicarbonate if the patient is acidotic
Treatment with digoxin Fab fragments is indicated for a K+ level greater than 5 mEq/L
Hemodialysis may be necessary for uncontrolled hyperkalemia
Correct hypokalemia (usually in chronic intoxication)
Concomitant hypomagnesemia may result in refractory hypokalemia
Digoxin immune Fab
Digoxin immune Fab is considered the first-line treatment for significant dysrhythmias from digitalis toxicity. Other indications for its use, in the absence of specific contraindications, include the following:
Ingestion of massive quantities of digitalis (in children, 4 mg or 0.1 mg/kg; in adults, 10 mg)
Serum digoxin level greater than 10 ng/mL in adults at steady state (ie, 6-8 hours after acute ingestion or at baseline in chronic toxicity)
Hyperkalemia (serum potassium level greater than 5 mEq/L)
Altered mental status attributed to digoxin toxicity
Rapidly progressive signs and symptoms of toxicity
Management of dysrhythmias
In hemodynamically stable patients, bradyarrhythmias and supraventricular arrhythmias may be treated with supportive care
Short-acting beta blockers (eg, esmolol) may be helpful for supraventricular tachyarrhythmias with rapid ventricular rates, but may precipitate advanced or complete AV block in patients with sinoatrial or AV node depression
Phenytoin and lidocaine are useful for ventricular tachycardia if immune therapy is ineffective or unavailable
Phenytoin may suppress digitalis-induced tachydysrhythmias
Atropine has proved helpful in reversing severe sinus bradycardia
Magnesium sulfate may terminate dysrhythmias, but is contraindicated in the setting of bradycardia or AV block and should be used cautiously in patients with renal failure
Cardioversion for severe dysrhythmias due to digitalis can precipitate ventricular fibrillation and asystole but may be used if the patient is hemodynamically unstable and has a wide, complex tachycardia and if fascicular tachycardia has been ruled out
Criteria for hospital admission
New cardiac dysrhythmias
Severe bradyarrhythmias
Advanced AV block
Acute prolongation of the QRS interval
Severe electrolyte abnormalities, especially hypokalemia or hyperkalemia
Dehydration
Inability to care for self
Suicidal ideation
See Treatment and Medication for more detail.