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Amlodipine
10%
48/489
Ezetimibe
4%
20/489
Adenosine
18%
89/489
Nifedipine
22/489
Verapamil
63%
306/489
Select Answer to see Preferred Response
The drug used to provide rate control for this man's atrial fibrillation is verapamil, based on the mechanism of action described in the question stem. Verapamil is an L-type calcium channel blocker (CCB) that decreases calcium ion influx occurring during phase 0 and latter part of phase 4 in cardiac slow-response tissue (i.e. SA and AV nodes). CCBs are considered class IV antiarrhythmics; other antiarrhythmic classes include I (affect sodium channels), II (beta blockers), and III (affect potassium channels). Non-dihydropyridine CCBs like verapamil primarily affect cardiac tissue, unlike dihydropyridine CCBs like amlodipine and nifedipine. Figure A is an EKG strip showing the irregularly irregular ventricular response in atrial fibrillation. Incorrect Answers: Answers 1 & 4: Amlodipine and nifedipine are dihydropyridine CCBs that have more of an effect on vascular smooth muscle. Answer 2: Ezetimibe prevents cholesterol reabsorption at the small intestine brush border. Answer 3: Adenosine does affect the slow-response cardiac tissue (i.e. AV node), but does so by increasing outward K+ flux, leading to hyperpolarization.
4.8
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