A 60-Year-Old Man Comes to the Office for Follow-Up Due

question 282

Multiple Choice

A 60-year-old man comes to the office for follow-up due to persistent atrial fibrillation.  He reports occasional palpitations and poor exercise tolerance.  For the past year, the patient's atrial fibrillation has been managed with a rate-control strategy using metoprolol.  Three months ago, his metoprolol dosage was increased for improved rate control, but today in the office, he reports that he was unable to tolerate the new dosage due to dizziness.  Blood pressure is 110/70 mm Hg and pulse is 105/min and irregular.  Examination shows no abnormalities.  Echocardiography reveals left atrial enlargement, an ejection fraction of 59%, and no significant valvular disease.  The patient is advised to remain on his previously tolerated metoprolol dose, and digoxin is added to the medication regimen.  Four weeks later, he reports symptom improvement.  Resting pulse is 84/min and irregular.  Which of the following best explains digoxin's effect on heart rate in this patient?

• A)Decreased atrial refractoriness
• B)Decreased cardiomyocyte action potential duration
• C)Decreased Purkinje fiber automaticity
• D)Increased parasympathetic tone
• E)Increased ventricular contractility

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Definitions:

Plasticity

The brain's ability to change and adapt as a result of experience, which can occur through the reorganization of neural pathways or the growth of new neurons.

Wiring

In neuroscience, it refers to the complex network of neurons and their connections in the brain.

Sex Differences

Refers to the biological and physiological distinctions between males and females, including chromosomes, hormones, and reproductive organs.

Biochemical Differences

Variations in the chemical processes and substances within the body that can influence mood, behavior, and cognitive functions.