An investigator studies the effects of 2 different medications on the heart rate of patients with persistent atrial fibrillation. After participants receive therapeutic doses of medication for several days, their heart rates are measured for 24 hours at rest and during 10 minutes of moderate exercise. The results are compared against placebo and shown in the graphs below. Which of the following medications is most likely represented by the red line (drug 1)?

Question

An investigator studies the effects of 2 different medications on the heart rate of patients with persistent atrial fibrillation.  After participants receive therapeutic doses of medication for several days, their heart rates are measured for 24 hours at rest and during 10 minutes of moderate exercise.  The results are compared against placebo and shown in the graphs below.  Which of the following medications is most likely represented by the red line (drug 1)?

Quizplus · Accepted Answer

11ec160b_3b7f_1c3a_9249_239c81734168_MD0001_00 Persistent atrial fibrillation is usually managed with a rate-control strategy that focuses on maintaining an acceptable ventricular contraction rate during both rest (eg, <85/min) and moderate exercise (eg, <110-120/min) despite continued rapid and disorganized conduction of the atria. Pharmacologic agents that allow for rate control do so by slowing conduction through the atrioventricular (AV) node via various mechanisms: Beta blockers (eg, atenolol, metoprolol) (Choice B) slow AV node conduction via blockade of sympathetic tone. This mechanism allows for effective rate control both during rest and exercise. For this reason, beta blockers are often the preferred agent for rate control of atrial fibrillation. Nondihydropyridine calcium channel blockers (eg, verapamil, diltiazem) block AV nodal calcium channels to slow AV node conduction both at rest and during exercise. These drugs have similar rate control efficacy to that of beta blockers, although beta blockers are slightly superior at controlling heart rate during exercise. Digoxin slows AV node conduction via increased parasympathetic tone. This mechanism is effective at rest, when sympathetic tone is low, but it poorly controls ventricular rate during exercise, when high levels of sympathetic tone accelerate AV node conduction. For this reason, digoxin is often used only as an adjunctive agent for rate control in atrial fibrillation. (Choices A and D) Dihydropyridine calcium channel blockers (eg, amlodipine, nifedipine) and ACE inhibitors (eg, lisinopril) are vasodilators with no significant effect on the AV node. These drugs are not expected to slow heart rate either at rest or with exercise (ie, both resting and exercise curves are expected to closely match placebo). Educational objective: Digoxin slows atrioventricular node conduction by increasing parasympathetic tone. This mechanism is effective at controlling ventricular rate in atrial fibrillation at rest, but it poorly controls ventricular rate during exercise, when parasympathetic output is low relative to high levels of sympathetic tone.

An Investigator Studies the Effects of 2 Different Medications on the Heart