Which beta‑blocker and dosing regimen is appropriate for a hemodynamically stable adult with sinus tachycardia at a ventricular rate of about 125 bpm?

Beta-Blocker Selection and Dosing for Hemodynamically Stable Sinus Tachycardia at 125 bpm

For a hemodynamically stable adult with sinus tachycardia at approximately 125 bpm, intravenous esmolol is the preferred beta-blocker because of its rapid onset and ultra-short half-life, allowing for immediate titration and rapid reversal if adverse effects occur. 1, 2

Immediate Assessment Before Treatment

• Confirm hemodynamic stability: systolic blood pressure ≥90 mmHg, no altered mental status, no chest pain, no signs of shock or acute heart failure. 1
• Obtain a 12-lead ECG to differentiate true sinus tachycardia from other narrow-complex tachycardias (e.g., focal atrial tachycardia, atrial flutter with variable block, or sinus node reentrant tachycardia). 1, 3
• True sinus tachycardia demonstrates gradual onset/offset, normal P-wave morphology identical to baseline sinus rhythm, and a heart rate appropriate to the clinical context. 4
• Critical pitfall: Do not treat physiologic sinus tachycardia (secondary to pain, anxiety, fever, hypovolemia, hyperthyroidism, anemia, or substance use) with rate-control agents; instead, identify and correct the underlying cause. 1, 4

First-Line Beta-Blocker: Intravenous Esmolol

Dosing Protocol

• Loading dose: 500 mcg/kg infused over 1 minute (optional but recommended for more rapid control). 2
• Maintenance infusion: Start at 50 mcg/kg/min for 4 minutes. 2
• Titration: If target heart rate (<100 bpm) is not achieved, increase the infusion by 50 mcg/kg/min increments every 4 minutes. 2
• Maximum dose: 200 mcg/kg/min for sinus tachycardia. 2
• Advantages: Esmolol's half-life is approximately 9 minutes, allowing rapid offset if hypotension or bradycardia develops; this makes it the safest intravenous beta-blocker for titration in the acute setting. 1, 2

Monitoring

• Continuously monitor heart rate, blood pressure, and cardiac rhythm during infusion and for at least 30 minutes after discontinuation. 2
• Reduce or discontinue the infusion immediately if systolic blood pressure falls below 90 mmHg or heart rate drops below 50 bpm. 2

Alternative Beta-Blocker: Intravenous Metoprolol

• Dosing: 2.5–5 mg IV administered slowly over 2–5 minutes; repeat every 2–5 minutes as needed. 1, 5
• Maximum cumulative dose: 15 mg over 10–15 minutes. 1, 5
• Disadvantage: Metoprolol has a longer half-life than esmolol (3–7 hours), making it less titratable and slower to reverse if adverse effects occur. 1
• Use metoprolol when: Esmolol is unavailable or when a longer-acting agent is preferred after initial rate control is achieved. 1

Absolute Contraindications to Beta-Blockers

• Severe sinus bradycardia (heart rate <50 bpm). 2
• Second- or third-degree AV block or sick sinus syndrome without a pacemaker. 2
• Decompensated heart failure or cardiogenic shock. 2
• Active bronchospasm or severe reactive airway disease (asthma, severe COPD). 1, 2
• Known hypersensitivity to beta-blockers. 2

When Beta-Blockers Fail or Are Contraindicated

Intravenous Diltiazem (Preferred Alternative)

• Dosing: 15–20 mg (approximately 0.25 mg/kg) IV administered over 2 minutes; a slower infusion over up to 20 minutes reduces the risk of hypotension. 1, 5
• Efficacy: Diltiazem achieves rate control in 64–98% of cases when beta-blockers are contraindicated. 1, 5
• Contraindications: Do not use in suspected systolic heart failure, second- or third-degree AV block, sick sinus syndrome without a pacemaker, or when ventricular tachycardia cannot be excluded. 1, 5

Intravenous Verapamil (Alternative Calcium-Channel Blocker)

• Dosing: 2.5–5 mg IV over 2 minutes; clinical effect typically observed within 3–5 minutes. 1, 5
• Same contraindications as diltiazem. 1, 5

Critical Safety Warning

• Never combine intravenous beta-blockers with intravenous calcium-channel blockers because of synergistic hypotensive and bradycardic effects that can precipitate cardiovascular collapse. 5, 3

Special Clinical Scenarios

Sinus Tachycardia in Critically Ill Patients

• In surgical ICU patients with contraindications to beta-blockers, intravenous diltiazem (starting at 5–10 mg/hr, titrated up to 30 mg/hr) achieved heart rate <100 bpm in 56% of patients with minimal adverse effects. 6
• Predictors of response included older age, higher baseline mean arterial pressure, and absence of central nervous system failure. 6

Inappropriate Sinus Tachycardia (IST)

• If the patient has persistent resting heart rate >100 bpm or mean 24-hour heart rate >90 bpm with P-wave morphology identical to sinus rhythm but no identifiable physiologic cause, consider IST. 1, 7, 8, 9, 10
• Acute management: Intravenous metoprolol or esmolol can be used for immediate rate control. 1
• Chronic management: Oral beta-blockers (e.g., metoprolol succinate up to 190 mg once daily) are first-line, but are often ineffective or poorly tolerated. 7, 8, 9, 10
• Ivabradine (a selective If current inhibitor) is superior to beta-blockers for IST, achieving greater heart rate reduction during daily activity and better symptom control with fewer side effects; dosing is 5–7.5 mg twice daily. 7, 8, 9, 10
• Ivabradine reduced mean daytime heart rate from 107 bpm to 87 bpm (vs. 95 bpm with metoprolol) and was free of IST-related symptoms in 70% of patients. 8

Post-Treatment Monitoring

• Continue cardiac monitoring for at least 4 hours after achieving target heart rate to detect recurrence or bradycardia. 3
• If sinus tachycardia recurs after initial control, investigate for missed secondary causes (e.g., pulmonary embolism, sepsis, thyrotoxicosis, occult bleeding). 4
• If no secondary cause is identified and episodes are recurrent, refer to cardiology for evaluation of IST and consideration of ivabradine or catheter ablation of the sinus node (reserved for refractory cases). 1, 7, 8, 9, 10

Key Clinical Pitfalls to Avoid

• Do not treat physiologic sinus tachycardia with rate-control agents; always identify and correct the underlying cause first. 1, 4
• Do not administer beta-blockers to patients with active bronchospasm, decompensated heart failure, or high-degree AV block. 2
• Do not combine intravenous beta-blockers with intravenous calcium-channel blockers. 5, 3
• Do not assume all narrow-complex tachycardias at 125 bpm are sinus tachycardia; obtain a 12-lead ECG to exclude focal atrial tachycardia, atrial flutter, or other supraventricular arrhythmias. 1, 3
• Do not overlook inappropriate sinus tachycardia in young patients with persistent unexplained tachycardia; ivabradine is more effective than beta-blockers in this population. 7, 8, 9, 10