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Chapter 13: Drugs Used in Heart Failure
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A 73-year-old man with an inadequate response to other drugs is to receive digoxin for chronic heart failure. He is in normal sinus rhythm with a heart rate of 88 and blood pressure of 135/85 mm Hg. Which of the following is the best-documented mechanism of beneficial action of cardiac glycosides?
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(A) A decrease in calcium uptake by the sarcoplasmic reticulum
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(B) An increase in a late transmembrane sodium current
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(C) A modification of the actin molecule
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(D) An increase in systolic cytoplasmic calcium levels
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(E) A block of cardiac β adrenoceptors
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Digitalis does not decrease calcium uptake by the sarcoplasmic reticulum or increase sodium current; it does not modify actin. Cardiac adrenoceptors are not affected. The most accurate description of digitalis’s mechanism in this list is that it increases systolic cytoplasmic calcium by inhibiting Na+/K+ transport by the ATPase sodium pump and indirectly altering Na+/Ca2+ exchange. The answer is D.
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A 73-year-old man with an inadequate response to other drugs is to receive digoxin for chronic heart failure. He is in normal sinus rhythm with a heart rate of 88 and blood pressure of 135/85 mm Hg. After your patient has been receiving digoxin for 3 weeks, he presents to the emergency department with an arrhythmia. Which one of the following is most likely to contribute to the arrhythmogenic effect of digoxin?
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(A) Increased parasympathetic discharge
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(B) Increased intracellular calcium
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(C) Decreased sympathetic discharge
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(D) Decreased intracellular ATP
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(E) Increased extracellular potassium
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The effects of digitalis include increased vagal action on the heart (not arrhythmogenic) and increased intracellular calcium, including calcium overload, the most important cause of toxicity. Decreased sympathetic discharge and increased extracellular potassium and magnesium reduce digitalis arrhythmogenesis. The answer is B.
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A patient who has been taking digoxin for several years for atrial fibrillation and chronic heart failure is about to receive atropine for another condition. A common effect of digoxin (at therapeutic blood levels) that can be almost entirely blocked by atropine is
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(C) Increased atrial contractility
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(D) Increased PR interval on ECG
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