Final answer:
Extreme bradycardia is considered the cardinal sign of digoxin toxicity in patients with heart failure, as it indicates significant cardiovascular disturbance due to the narrow therapeutic range of digoxin. The correct option is C.
Step-by-step explanation:
The nurse would regard extreme bradycardia as the cardinal sign/symptom of digoxin toxicity in a patient being treated for heart failure.
Digoxin is a medication that can help improve the strength and efficiency of the heart, or control the rate and rhythm of the heartbeat.
However, its therapeutic range is very narrow and can easily be exceeded, leading to toxicity. Digoxin toxicity can cause a variety of symptoms, but the most significant ones affect the cardiovascular system.
Bradycardia, which is an abnormally slow heart rate, is a classic sign of digoxin toxicity. This can lead to insufficient oxygenated blood reaching tissues, potentially causing symptoms such as dizziness, fatigue, and in severe cases, cardiovascular collapse. The correct option is C.