What is the first choice drug for managing tachycardia with irregular irregularity, likely atrial fibrillation?

First-Line Drug for Tachycardia with Irregular Irregularity (Atrial Fibrillation with Rapid Ventricular Response)

Intravenous beta-blockers are the first-choice drugs for acute rate control in hemodynamically stable patients with atrial fibrillation and rapid ventricular response. 1, 2

Immediate Assessment

Before initiating treatment, rapidly determine hemodynamic stability:

• Hemodynamically unstable patients (severe hypotension, ongoing ischemia, altered mental status, pulmonary edema) require immediate synchronized electrical cardioversion, not pharmacologic therapy 1, 2, 3
• Hemodynamically stable patients should receive pharmacologic rate control as outlined below 1, 2

First-Line Pharmacologic Options for Stable Patients

Beta-Blockers (Preferred First-Line)

IV beta-blockers are the drugs of choice for acute rate control in most individuals without heart failure or bronchospasm (Class IIa, Level of Evidence A) 1, 2:

• Metoprolol: 5 mg IV over 1-2 minutes, repeated every 5 minutes as needed up to 15 mg total 1
• Esmolol: 500 mcg/kg (0.5 mg/kg) IV bolus over 1 minute, followed by infusion of 50 mcg/kg/min, titrated up to 300 mcg/kg/min as needed 1
• Atenolol: 5 mg IV over 5 minutes, repeat 5 mg in 10 minutes if needed 1
• Propranolol: 0.5-1 mg IV over 1 minute, repeated up to 0.1 mg/kg total 1

Nondihydropyridine Calcium Channel Blockers (Alternative First-Line)

Diltiazem or verapamil are equally effective alternatives to beta-blockers in stable patients without heart failure 1, 2:

• Diltiazem: 0.25 mg/kg IV over 2 minutes, followed by 5-15 mg/hour infusion 1
• Verapamil: 0.075-0.15 mg/kg IV over 2 minutes 1

Special Populations Requiring Different Agents

Patients with Heart Failure or Severe LV Dysfunction

In patients with congestive heart failure or severe LV dysfunction, use digoxin or amiodarone instead of beta-blockers or calcium channel blockers 1, 2:

• Digoxin: 0.25 mg IV every 2 hours up to 1.5 mg total loading dose 1
• Amiodarone: 150 mg IV over 10 minutes, followed by 1 mg/min infusion for 6 hours, then 0.5 mg/min (maximum 2.2 g/24 hours) 1

Critical Pitfall: Wide-Complex Irregular Tachycardia

If the rhythm is wide-complex and irregular, suspect pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome) 1, 3:

• AVOID AV nodal blocking agents (adenosine, beta-blockers, calcium channel blockers, digoxin) as these can paradoxically accelerate ventricular response and cause hemodynamic collapse 1, 3
• Requires immediate electrical cardioversion or rhythm control agents (procainamide, ibutilide, amiodarone) with expert consultation 1

Rate Control Targets

Target ventricular rate of 60-80 bpm at rest and 90-115 bpm during moderate exercise 1, 2

Key Contraindications and Side Effects

• Beta-blockers: Avoid in asthma, severe COPD, decompensated heart failure, and pre-excited atrial fibrillation; watch for hypotension, bradycardia 1
• Calcium channel blockers: Avoid in severe LV dysfunction, decompensated heart failure, and pre-excited atrial fibrillation; watch for hypotension, heart block 1
• Digoxin: Slow onset (2 hours), less effective for acute control, risk of toxicity and bradycardia 1
• Amiodarone: Risk of hypotension, bradycardia, phlebitis; consider potential for conversion to sinus rhythm which may be undesirable if duration >48 hours without anticoagulation 1

Anticoagulation Consideration

Do not attempt cardioversion (electrical or pharmacologic) if atrial fibrillation duration >48 hours unless patient is unstable, due to thromboembolic risk 1, 3