Selected topics: cardiology commentary
Electrocardiographic manifestations: Digitalis toxicity1

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Abstract

Toxicity from the digitalis family of cardiac glycoside medications remains common. Successful treatment depends on early recognition; however, the diagnosis of potentially life-threatening toxicity remains difficult because the clinical presentation is often nonspecific and subtle. The hallmark of cardiac toxicity is increased automaticity coupled with concomitant conduction delay. Though no single dysrhythmia is always present, certain aberrations such as frequent premature ventricular beats, bradydysrhythmias, paroxysmal atrial tachycardia with block, junctional tachycardia, and bidirectional ventricular tachycardia are common. Treatment depends on the clinical condition rather than serum drug level. Management varies from temporary withdrawal of the medication to administration of digoxin-specific Fab fragments for life-threatening cardiovascular compromise.

Introduction

The objective of this article is to review the electrocardiographic manifestations of digitalis toxicity, particularly as they relate to the pathophysiology and management of this potentially lethal poisoning. Despite the introduction of new classes of drugs in the management of congestive heart failure (CHF) and atrial fibrillation, many patients presenting to Emergency Departments (EDs) continue to be managed with cardiac glycosides. Cardiotoxicity from cardiac glycosides, known as a class as digitalis, ranges from obvious with nausea, vomiting, and hypotension, to more subtle presentations with nonspecific symptoms. The difficulty in diagnosing patients with digitalis intoxication can be attributed to several factors, including: 1) the signs, symptoms and electrocardiogram (EKG) manifestations often can be attributed to the underlying disease process for which the drug is prescribed; 2) a narrow therapeutic window of digoxin resulting in marked variability in the sensitivity of individuals to the drug; and 3) the lack of any dysrhythmia diagnostic of toxicity 1, 2, 3. It is believed that chronic toxicity occurs in 4–10% of patients on digitalis, yet is suspected in only 0.25% of the cases 4, 5.

Section snippets

Case 1

A 50-year-old man presented to the ED complaining of shortness of breath, nausea, and palpitations. He had a history of atrial fibrillation and congestive heart failure and was taking digoxin. His primary physician had increased his dose of digoxin the week prior from 0.125 mg to 0.25 mg per day because he was having increasing episodes of palpitations.

The patient was a middle-aged man who appeared in moderate distress. Vital signs included a pulse rate of 148 beats/min, blood pressure of 96/52

Discussion

Digitalis derivatives are found in several plants, including oleander, foxglove, and lily of the valley. They are used therapeutically as digoxin or digitoxin primarily for their ability to slow conduction through the atrioventricular (AV) node in disease states such as atrial fibrillation and flutter. These agents act by inhibiting the sodium-potassium adenosine triphosphatase (ATP-ase) pump and increasing intracellular calcium concentration at the level of cardiac myocyte. (6) As a result,

Conclusion

Although digoxin continues to be a common medication utilized by patients presenting to the ED, the nonspecific signs and symptoms make the diagnosis of toxicity difficult to establish. The key to successful management is early diagnosis. Though no single dysrhythmia is always found, certain aberrations such as PAT with block, junctional tachycardia, and bidirectional ventricular tachycardia are common. The hallmark of digitalis toxicity is increased automaticity with concomitant conduction

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Selected Topics: Cardiology Commentary is coordinated by Theodore Chan, MD, of the University of California San Diego Medical Center, San Diego, California

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