What is the next step in managing an elderly male patient with atrial fibrillation (Afib) and rapid ventricular response (RVR), presenting with tachycardia and shortness of breath (SOB) on exertion?

Immediate Rate Control with IV Beta-Blocker or Calcium Channel Blocker

For this elderly male with newly diagnosed AFib with RVR (HR 144) and exertional dyspnea who is hemodynamically stable, initiate immediate IV rate control with either metoprolol or diltiazem as first-line therapy. 1, 2

Initial Assessment: Hemodynamic Stability

First, determine if the patient is hemodynamically unstable (hypotension, acute heart failure, chest pain/MI, altered mental status):

• If hemodynamically unstable: Proceed immediately to synchronized electrical cardioversion without waiting for pharmacologic rate control 3, 1, 2
• If hemodynamically stable (as appears to be the case here with only exertional SOB): Proceed with pharmacologic rate control 1, 2

First-Line Pharmacologic Rate Control

Beta-Blockers (Preferred Initial Choice)

Metoprolol is the preferred first-line agent for most patients with AFib with RVR who are hemodynamically stable 1, 2:

• Dosing: 2.5-5 mg IV bolus over 2 minutes; may repeat up to 3 doses 3
• Onset: 5 minutes 3
• Advantages: Lower adverse event rate (10% vs 19% with diltiazem), particularly in elderly patients 4

Calcium Channel Blockers (Equally Effective Alternative)

Diltiazem is an equally effective alternative 1, 2, 5:

• Dosing: 0.25 mg/kg IV over 2 minutes (typically 20 mg), followed by 5-15 mg/hour continuous infusion 3
• Onset: 2-7 minutes 3
• Advantages: Faster time to rate control (13 vs 27 minutes) and greater HR reduction at 30 minutes 6

Critical Considerations Before Choosing Agent

Assess for Heart Failure Status

• If HFrEF (reduced ejection fraction) or acute decompensated heart failure: Avoid diltiazem due to negative inotropic effects; use metoprolol instead 2, 7
• If HFpEF (preserved ejection fraction): Either agent is acceptable 6
• Note: Recent evidence suggests diltiazem may be safer in HF patients than previously thought, but beta-blockers remain preferred 6

Assess for Underlying Precipitants

Critical pitfall: Always identify and treat underlying causes, as AFib with RVR is often secondary 3, 1:

• Acute illness: Sepsis, pulmonary embolism, pneumonia, hyperthyroidism 3, 1, 7
• Cardiac causes: Acute MI, heart failure exacerbation 3, 1
• Metabolic: Electrolyte abnormalities, hypoxia 7

For acute noncardiac illness (especially sepsis), beta-blockers are preferred due to the elevated catecholamine state, unless contraindicated 3

Contraindications to Specific Agents

Avoid beta-blockers if:

• Active bronchospasm or severe COPD 3
• Hemodynamic instability requiring vasopressors 7

Avoid calcium channel blockers if:

• Decompensated heart failure with hypotension 2, 7
• Wolff-Parkinson-White syndrome (use procainamide or ibutilide instead) 3

Target Heart Rate and Monitoring

• Target HR: <100 bpm at rest 3, 5
• Monitor: Continuous cardiac monitoring for bradycardia and hypotension 4
• Time to reassess: 30 minutes after initial dose 5, 6

If Initial Agent Fails

• Repeat dosing: May give additional boluses of the same agent 3
• Add second agent: Consider adding digoxin (0.25 mg IV) as adjunct, particularly in elderly patients 3, 2
• Switch agents: If metoprolol fails, try diltiazem (or vice versa) 5
• Combination therapy: Beta-blocker plus digoxin is highly effective for refractory cases 3, 2

Anticoagulation Decision

Initiate anticoagulation as soon as possible based on CHA₂DS₂-VASc score, independent of rate control strategy 1:

• Start heparin infusion (bolus followed by continuous infusion to maintain aPTT 1.5-2x control) concurrently with rate control 3
• Transition to oral anticoagulation (warfarin INR 2-3 or DOAC) for at least 3-4 weeks 3

Common Pitfalls to Avoid

• Do not focus solely on rate control while missing underlying precipitants (sepsis, PE, thyrotoxicosis) 3, 1, 7
• Do not use diltiazem in patients with WPW syndrome - this can precipitate ventricular fibrillation 3
• Do not delay cardioversion in hemodynamically unstable patients while attempting pharmacologic rate control 3, 1
• Do not use IV beta-blockers or calcium channel blockers in hypotensive patients requiring vasopressors - use amiodarone instead 7

Transition to Oral Therapy

Once rate controlled, transition to oral maintenance therapy 2:

• Metoprolol: 25-100 mg twice daily 3
• Diltiazem: 120-360 mg daily in divided doses 3