Digitalis Toxicity

Chapter 18 Digitalis Toxicity


This chapter focuses on the arrhythmias and conduction disturbances caused by digitalis toxicity. Digitalis glycosides (especially, digoxin) are still widely prescribed, and digitalis toxicity remains an important clinical problem and a source of potentially lethal medical errors. Familiarity with this topic, therefore, is essential for all frontline clinicians, not just specialists.


Digitalis toxicity has a wide range of presentation, from nonspecific symptoms such as nausea to potentially fatal brady- and tachyarrhythmias. Clinical management and avoidance of medical errors should center on prevention and early recognition.



Mechanism of Action and Indications


Digitalis refers to a class of cardioactive drugs called glycosides which exert both mechanical and electrical effects on the heart. The most commonly used digitalis preparation in current practice is digoxin.


The mechanical action of digitalis glycosides is to increase the strength of myocardial contractions in selected patients with dilated hearts and systolic chronic heart failure (CHF). Their therapeutic electrical effects relate primarily to decreasing automaticity and conductivity in the sinoatrial (SA) and atrioventricular (AV) nodes, in large part by increasing parasympathetic (vagal) tone. Consequently, digitalis is used for controlling the ventricular response in atrial fibrillation (AF) and atrial flutter, which are characterized by the excessive transmission of stimuli from the atria to the ventricles through the AV junction.


Since a number of more efficacious and safer medications have become available, the use of digitalis is mostly limited to the patients with AF, systolic CHF, and hypotension who cannot tolerate beta blockers or calcium channel blockers, or it is used as an adjunct to therapy. More rarely, digoxin is still used in the treatment of certain reentrant types of paroxysmal supraventricular tachycardia (PSVT), for example, during pregnancy, when other drugs might be contraindicated.


Although digitalis has indications in the treatment of certain forms of chronic systolic heart failure and selected supraventricular arrhythmias, it also has a relatively low margin of safety. The difference between therapeutic and toxic concentrations is narrow.




Symptoms and Signs of Digitalis Toxicity


Digitalis toxicity can produce general systemic symptoms as well as specific cardiac arrhythmias and conduction disturbances. Common extracardiac symptoms include weakness, anorexia, nausea, and vomiting. Visual effects (altered color perception) and mental changes may occur.


As a general clinical rule virtually any arrhythmia and all degrees of AV heart block can be produced by digitalis. However, a number of arrhythmias and conduction disturbances are commonly seen with digitalis toxicity (Box 18-1). In some cases, combinations of arrhythmias will occur, such as AF with a relatively slow ventricular response and frequent ventricular ectopy (Fig. 18-3).


Jun 11, 2016 | Posted by in CARDIOLOGY | Comments Off on Digitalis Toxicity
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