Which of the following clients is at greatest risk for digitalis toxicity?
A. A 25-year-old client with congenital heart disease.
B. A 50-year-old client with CHF.
C. A 60-year-old client after myocardial infarction.
D. An 80-year-old client with CHF.
Correct Answer: D. An 80-year-old client with CHF.
Extremely old clients are at greater risk for digitalis toxicity. Remember when it comes to adversity, the very old and very young are always at the highest risk. There are no evidence-based guidelines for the management of mild to moderate toxicity so there is a wide variation in treatment. Severe toxicity requires hospital admission and consideration of the need for digoxin-specific antibody fragments. Although digoxin-specific antibody fragments are safe and effective, randomized trials have not been performed.
Option A: Digoxin toxicity can emerge during long-term therapy as well as after an overdose. It can occur even when the serum digoxin concentration is within the therapeutic range.
Option B: The clinical features of toxicity are often non-specific. They commonly include lethargy, confusion, and gastrointestinal symptoms (anorexia, nausea, vomiting, diarrhea, and abdominal pain). Visual effects (blurred vision, color disturbances, halos, and scotomas) are rarer in contemporary practice. Cardiac arrhythmias account for most deaths.
Option C: Digoxin increases intracellular calcium in myocardial cells indirectly, by inhibiting the sodium-potassium pump in the cell membrane. Increased intracellular calcium increases cardiac contractility, but also the risk of tachyarrhythmias. Inhibition of this pump causes hyperkalemia commonly seen in toxicity. Digoxin also causes an increase in vagal activity, reducing activity in the sinus node and prolonging conduction in the atrioventricular node.