What medications are used to treat irregular heart rates, specifically atrial fibrillation and ventricular arrhythmias?

Medications for Irregular Heart Rate

For atrial fibrillation with rapid ventricular response, beta-blockers (metoprolol, esmolol) or non-dihydropyridine calcium channel blockers (diltiazem, verapamil) are first-line agents for rate control in hemodynamically stable patients, with IV diltiazem showing superior efficacy for acute rate control in the emergency setting. 1, 2

Atrial Fibrillation Rate Control

Acute Setting (IV Administration)

First-line agents for hemodynamically stable patients:

• Beta-blockers 1:

  • Metoprolol: 2.5-5 mg IV bolus over 2 minutes, up to 3 doses; onset in 5 minutes 1
  • Esmolol: 500 mcg/kg IV bolus over 1 minute, then 50-300 mcg/kg/min infusion; onset in 5 minutes 1
  • Propranolol: 0.15 mg/kg IV; onset in 5 minutes 1

• Non-dihydropyridine calcium channel blockers 1:

  • Diltiazem: 0.25 mg/kg IV over 2 minutes, then 5-15 mg/h infusion; onset in 2-7 minutes 1
  • Verapamil: 0.075-0.15 mg/kg IV over 2 minutes; onset in 3-5 minutes 1

Evidence shows diltiazem achieves rate control faster than metoprolol: In a randomized trial, 95.8% of diltiazem patients reached target heart rate <100 bpm by 30 minutes versus only 46.4% with metoprolol (p<0.0001), with no increased adverse effects 2. For patients already on chronic beta-blockers, diltiazem achieved 68.8% success versus 42.4% with additional metoprolol 3.

Second-line agents:

• Digoxin: 0.25 mg IV every 2 hours up to 1.5 mg; onset delayed 60+ minutes with peak effect at 6 hours 1

  • Class I recommendation for heart failure patients 1
  • Less effective as monotherapy in acute settings due to delayed onset 1

• Amiodarone: 150 mg IV over 10 minutes, then 0.5-1 mg/min infusion 1, 4

  • Class IIa recommendation when other measures fail or are contraindicated 1
  • Particularly useful in critically ill patients or those with heart failure 1

Chronic Oral Maintenance

Beta-blockers (Class I recommendation) 1:

• Metoprolol: 25-100 mg twice daily or 50-400 mg daily (extended-release) 1
• Atenolol: 25-100 mg daily 1
• Carvedilol: 3.125-25 mg twice daily 1
• Beta-blockers achieved rate control in 70% of patients versus 54% with calcium channel blockers in the AFFIRM trial 1

Non-dihydropyridine calcium channel blockers (Class I recommendation) 1:

• Diltiazem: 120-360 mg daily (extended-release) 1
• Verapamil: 120-360 mg daily (extended-release) 1
• These are the only agents associated with improved quality of life and exercise tolerance 1
• Preferred over beta-blockers in patients with bronchospasm or COPD 1

Digoxin (Class I recommendation) 1:

• 0.125-0.375 mg daily 1
• No longer first-line except in heart failure or sedentary patients 1
• Ineffective during high sympathetic states and exercise 1

Amiodarone (Class IIb recommendation) 1:

• Loading: 800 mg daily for 1 week, then 600 mg daily for 1 week, then 400 mg daily for 4-6 weeks 1
• Maintenance: 200 mg daily 1
• Reserved for refractory cases due to significant toxicity profile 1

Critical Contraindications

Pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome):

• AVOID: Digoxin, diltiazem, verapamil, beta-blockers—these can paradoxically increase ventricular rate and precipitate ventricular fibrillation 1, 5
• Use: Procainamide, flecainide, or immediate electrical cardioversion 1, 5

Heart failure with reduced ejection fraction:

• Avoid or use cautiously: Verapamil, diltiazem (negative inotropes) 1
• Preferred: Beta-blockers (initiated cautiously), digoxin, or amiodarone 1

Dronedarone is contraindicated in permanent atrial fibrillation due to increased risk of stroke, MI, and cardiovascular death 1

Ventricular Arrhythmias

Polymorphic Ventricular Tachycardia

Torsades de pointes (long QT interval):

• IV magnesium is first-line treatment 1
• Stop all QT-prolonging medications and correct electrolyte abnormalities 1
• Consider pacing or IV isoproterenol for bradycardia-associated cases 1
• Avoid isoproterenol in familial long QT syndrome; use beta-blockers instead 1

Polymorphic VT without long QT (ischemia-related):

• IV amiodarone and beta-blockers may reduce recurrence (Class IIb) 1
• Immediate defibrillation for hemodynamic instability 1

Sustained Ventricular Tachycardia

Flecainide (for sustained VT):

• Starting dose: 100 mg every 12 hours 6
• Increase by 50 mg twice daily every 4 days as needed 6
• Maximum: 400 mg/day 6
• Must be initiated in-hospital with rhythm monitoring due to proarrhythmic risk 6
• Contraindicated in patients with recent MI or structural heart disease due to increased mortality (CAST trial) 6

Rate Control Targets

The ventricular rate is considered adequately controlled when 1:

• At rest: 60-80 bpm
• Moderate exercise: 90-115 bpm

Adequacy should be assessed with 24-hour Holter monitoring or submaximal stress testing 7. Combination therapy may be necessary when monotherapy fails to achieve targets 1, 7.