What is the optimal management of atrial fibrillation with tachycardia, history of Non-ST-Elevation Myocardial Infarction (NSTEMI), currently on metoprolol (Lopressor) 12.5 mg twice daily (bid)?

From the Guidelines

For a patient with atrial fibrillation, heart rate of 133, and history of NSTEMI who is currently on metoprolol 12.5 mg twice daily, I recommend increasing the metoprolol dose to achieve better rate control, with a target heart rate below 110 bpm. Increase metoprolol to 25 mg twice daily initially, with potential further titration to 50 mg twice daily if needed after reassessing in 1-2 weeks, as suggested by the guidelines 1. The current dosage of metoprolol is below the recommended range for rate control in atrial fibrillation, which is 25–100 mg BID for metoprolol tartrate 1. Additionally, anticoagulation therapy should be initiated based on the patient's CHA₂DS₂-VASc score, with direct oral anticoagulants (DOACs) like apixaban 5 mg twice daily preferred for most patients. Consider adding a rhythm control strategy if the patient remains symptomatic despite adequate rate control. Monitor for bradycardia, hypotension, and heart failure symptoms when increasing beta-blocker dosage. The current heart rate of 133 is too high and increases risk of tachycardia-induced cardiomyopathy and symptoms. Beta-blockers like metoprolol are particularly appropriate in this case given the patient's history of NSTEMI, as they provide both rate control and secondary prevention benefits for coronary artery disease, as noted in the guidelines 1. Key points to consider in management include:

• Rate control targets: heart rate below 110 bpm
• Initial metoprolol dose increase: 25 mg twice daily
• Potential further titration: up to 50 mg twice daily
• Anticoagulation: based on CHA₂DS₂-VASc score, with DOACs preferred
• Rhythm control: consider if symptomatic despite adequate rate control
• Monitoring: bradycardia, hypotension, heart failure symptoms.

From the FDA Drug Label

DOSAGE & ADMINISTRATION Myocardial Infarction Early Treatment During the early phase of definite or suspected acute myocardial infarction, initiate treatment with metoprolol tartrate as soon as possible after the patient’s arrival in the hospital. In patients with severe intolerance, discontinue metoprolol tartrate Geriatric Patients (>65 years) In general, use a low initial starting dose in elderly patients given their greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

The patient is currently on metoprolol 12.5 mg bid, which is a lower dose than the maintenance dosage of 100 mg orally twice daily.

• The patient has a history of NSTEMI and is currently experiencing atrial fibrillation with HR 133.
• The drug label does not provide specific guidance on managing atrial fibrillation with metoprolol.
• However, given the patient's history of NSTEMI and current atrial fibrillation, it is likely that the patient's current dose of metoprolol is intended to control heart rate and reduce the risk of further cardiac complications.
• Considering the patient's geriatric status and potential for decreased hepatic, renal, or cardiac function, it is reasonable to continue the current dose of metoprolol 12.5 mg bid and monitor the patient's condition closely, rather than increasing the dose 2.

From the Research

Management of Atrial Fibrillation

• The patient has a history of NSTEMI and is currently on metoprolol 12.5 mg bid, with a heart rate of 133 bpm.
• According to the study 3, metoprolol can be effective in controlling heart rate in patients with atrial fibrillation, with 80% of patients showing greater than or equal to 50% subjective improvement.
• However, the dose used in the study was 50-100 mg twice a day, which is higher than the patient's current dose of 12.5 mg bid.

Rate Control Agents

• The study 4 compared the effect of intravenous diltiazem, metoprolol, and verapamil on rate control in patients with atrial fibrillation with rapid ventricular rate.
• The results showed that there was no statistically significant difference between the three agents in achieving rate control, but the median time to ventricular rate control was shorter with verapamil (100.5 min) compared to metoprolol (297 min).
• Another study 5 compared the effectiveness and safety of metoprolol and diltiazem for rate control of supraventricular tachycardia in the emergency department, and found that there was no difference in achieving rate control between the two agents.

Dose-Related Effects of Metoprolol

• The study 6 investigated the dose-related effects of metoprolol on heart rate and pharmacokinetics in heart failure patients.
• The results showed that metoprolol CR/XL 200 mg was associated with a more pronounced suppression of heart rate than metoprolol IR 50 mg.
• The study 7 assessed the effectiveness of metoprolol in improving cardiac and motor functions in patients with chronic heart failure, and found that metoprolol treatment improved cardiac function, motor function, and quality of life in both men and women, regardless of age or dose.