Is metoprolol suitable for an adult with tachycardia at rest?

Metoprolol for Tachycardia at Rest: Heart Rate 138 bpm

Yes, metoprolol can be administered for a heart rate of 138 bpm at rest, provided there are no contraindications such as decompensated heart failure, active asthma, severe bradycardia, hypotension, or high-grade AV block. 1, 2

Clinical Context and Decision Framework

A heart rate of 138 bpm at rest falls into the tachycardic range (>100 bpm) but is below the threshold where tachycardia is more likely attributable to a primary arrhythmia (≥150 bpm). 1 At this heart rate, symptoms of instability are unlikely to be caused primarily by the tachycardia unless there is impaired ventricular function. 1

Before administering metoprolol, you must first determine whether the tachycardia is primary or secondary to an underlying condition:

• Assess for and correct hypoxemia, which is a common reversible cause of tachycardia 1
• Evaluate for fever, sepsis, hypovolemia, pain, anxiety, or other physiologic stressors 1
• If the tachycardia is secondary to these conditions, treat the underlying cause first rather than reflexively administering a beta-blocker

Absolute Contraindications to Check Before Administration

Do not administer metoprolol if any of the following are present:

• Signs of decompensated heart failure, low output state, or acute heart failure exacerbation 3, 1, 2
• Systolic blood pressure <100 mmHg with symptoms 1, 4
• Heart rate <60 bpm (though not applicable here) 3, 4
• Second or third-degree AV block without a functioning pacemaker 3, 1, 2
• PR interval >0.24 seconds 4, 2
• Active asthma or severe reactive airway disease 3, 1, 2
• Cardiogenic shock or high risk factors for shock 3, 4

Recommended Dosing Protocol

For oral administration (most common in stable patients at rest):

• Start with metoprolol tartrate 25-50 mg orally 1, 4
• Reassess heart rate and blood pressure 1-2 hours after administration 1
• Maintenance dosing can be titrated to 25-100 mg twice daily for ongoing rate control 3, 1

For intravenous administration (if more rapid control needed):

• Administer 5 mg IV over 1-2 minutes 3, 1
• Repeat every 5 minutes as needed based on hemodynamic response 3, 1
• Maximum total dose of 15 mg (three 5 mg boluses) 3, 1, 4
• Transition to oral therapy 15 minutes after last IV dose at 25-50 mg every 6 hours 4

Efficacy for Different Tachycardia Types

Metoprolol is effective for:

• Narrow-complex supraventricular tachycardias (SVT) including AVNRT 3, 1
• Atrial fibrillation or atrial flutter with rapid ventricular response 3, 1
• Multifocal atrial tachycardia (MAT), though calcium channel blockers are preferred in patients with severe pulmonary disease 3, 5, 6, 7, 8
• Sinus tachycardia when beta-blockade is indicated 1, 2

Beta-blockers were the most effective drug class for rate control in the AFFIRM study, achieving specified heart rate endpoints in 70% of patients compared to 54% with calcium channel blockers. 3

Monitoring Requirements

After administration, monitor for:

• Symptomatic bradycardia (heart rate <60 bpm with dizziness or lightheadedness) 1, 4
• Hypotension (systolic BP <100 mmHg with symptoms like dizziness or lightheadedness) 1, 4
• New or worsening bronchospasm, particularly if any history of reactive airway disease 1, 4
• Signs of worsening heart failure (increased dyspnea, fatigue, edema) 1, 4

Common Pitfalls to Avoid

• Do not assume all tachycardia requires beta-blockade – always identify and treat reversible causes first 1
• Do not administer if decompensated heart failure is present – wait until clinical stabilization 1, 4, 2
• Do not give IV metoprolol rapidly as a single bolus – this significantly increases hypotension and bradycardia risk 1, 4
• Do not abruptly discontinue metoprolol – this can cause severe exacerbation of angina, myocardial infarction, and ventricular arrhythmias, with a 2.7-fold increased risk of 1-year mortality 1, 4, 2

Alternative Therapies if Metoprolol is Contraindicated

• Calcium channel blockers (diltiazem or verapamil) are preferred if the patient has severe pulmonary disease or bronchospasm 3, 5
• Digoxin may be used but is less effective for rate control during exercise and has delayed onset (60 minutes to 6 hours) 3
• Amiodarone can be considered if other measures are unsuccessful or contraindicated, though it has higher toxicity 3