Metoprolol Use for Tachycardia: Heart Rate Thresholds
Metoprolol is typically considered for treatment of tachycardia when the heart rate exceeds 150 beats per minute, as this is the threshold at which tachycardia is more likely attributable to an arrhythmia and may cause symptoms of instability. 1
Heart Rate Thresholds for Metoprolol Use
- Tachycardia is defined as a heart rate >100 beats per minute, but clinical significance typically occurs at higher rates 1
- Heart rates ≥150 beats per minute are more likely to be attributable to an arrhythmia rather than a physiologic response 1
- When heart rate is <150 beats per minute, symptoms of instability are unlikely to be caused primarily by the tachycardia unless there is impaired ventricular function 1
Contraindications and Precautions
- Metoprolol is contraindicated in patients with heart rate <45 beats per minute 2
- Avoid use in patients with asthma, obstructive airway disease, decompensated heart failure, and pre-excited atrial fibrillation or flutter 1
- Use with caution in patients with AV block greater than first degree or sinus node dysfunction (in absence of pacemaker) 1
- Monitor for hypotension, which is a common side effect (occurred in 23.5% of patients in one study) 3
Dosing for Tachycardia
- For intravenous administration: 5 mg over 1 to 2 minutes, repeated as required every 5 minutes to maximum dose of 15 mg 1
- For oral administration: Starting with 25-50 mg daily, with maintenance doses up to 200 mg BID for metoprolol tartrate or 400 mg daily for metoprolol succinate 1
- In studies treating multifocal atrial tachycardia, mean oral dose required was 32.5 mg, and mean IV dose was 6.5 mg 4
Efficacy in Different Types of Tachycardia
- Effective for narrow-complex supraventricular tachycardias (SVT) 1
- Useful for controlling ventricular rate in atrial fibrillation or atrial flutter 1
- Particularly effective in multifocal atrial tachycardia (MAT), with studies showing conversion to sinus rhythm in 68-100% of patients 4, 5
- In one study comparing metoprolol to diltiazem for supraventricular tachycardias, both achieved similar rate control at two hours (45.8% vs 42.6%) 3
Clinical Approach
- First, determine if tachycardia is the primary cause of symptoms or secondary to an underlying condition 1
- Assess for and correct hypoxemia, which is a common cause of tachycardia 1
- For heart rates ≥150 beats per minute with symptoms of instability, consider metoprolol if no contraindications exist 1
- For heart rates <150 beats per minute, metoprolol may still be considered if there is evidence of impaired ventricular function or if the tachycardia is symptomatic 1
- Monitor closely for bradycardia and hypotension during administration 3
Remember that while metoprolol is effective for rate control, synchronized cardioversion should be considered for hemodynamically unstable patients with tachycardia when pharmacologic therapy is ineffective or not feasible 1.