Rate Control in Atrial Fibrillation: Cardizem vs Lopressor

For acute rate control in atrial fibrillation with rapid ventricular response, diltiazem (Cardizem) achieves target heart rate faster and more effectively than metoprolol (Lopressor) in patients with preserved left ventricular function, while both agents are equally safe. 1

Patient Selection Algorithm

Use Diltiazem (Cardizem) When:

LVEF ≥40% or preserved left ventricular function 2
No signs of decompensated heart failure 2
Rapid rate control is the priority (diltiazem achieves target HR <100 bpm in 50% of patients within 5 minutes vs 10.7% with metoprolol) 1
Patient has bronchospastic disease (COPD or asthma), where calcium channel blockers are preferred over beta-blockers 2, 3

Use Metoprolol (Lopressor) When:

LVEF ≤40% or heart failure with reduced ejection fraction (HFrEF) 2
Signs of congestive heart failure are present 2
Patient has coronary artery disease or recent acute coronary syndrome 2
Diltiazem is contraindicated or unavailable 3

Evidence Supporting Diltiazem Superiority in Appropriate Patients

Acute Rate Control Efficacy:

At 5 minutes: 50.0% of diltiazem patients vs 10.7% of metoprolol patients achieved HR <100 bpm (p<0.005) 1
At 30 minutes: 95.8% of diltiazem patients vs 46.4% of metoprolol patients achieved target rate (p<0.0001) 1
Mean time to rate control: Diltiazem achieved control more rapidly with greater magnitude of heart rate reduction 1

Safety Profile:

No difference in hypotension or bradycardia between diltiazem and metoprolol 1, 4
No adverse events observed in patients with LVEF ≤40% when appropriate agent selection was used 4
Both agents demonstrated comparable safety in multiple retrospective cohorts 5, 4, 6

Guideline-Based Recommendations

First-Line Agents by Clinical Context:

For LVEF >40%:

Beta-blockers, diltiazem, or verapamil are all recommended as first-choice drugs 2
However, diltiazem demonstrates faster onset and superior acute rate control 2, 1
Initial target resting heart rate <110 bpm 2

For LVEF ≤40%:

Beta-blockers and/or digoxin are recommended 2
Diltiazem and verapamil should be avoided due to negative inotropic effects 2
Use smallest dose of beta-blocker to achieve rate control 2

Critical Safety Contraindications

Avoid Diltiazem When:

Decompensated heart failure or LVEF <40% 2, 3
Pre-excitation syndromes (Wolff-Parkinson-White) 3
Severe hypotension 3
High-grade AV block without pacemaker 3

Avoid Metoprolol When:

Severe bronchospasm or acute asthma exacerbation 2
Decompensated heart failure (use cautiously even in stable HFrEF) 2
High-grade AV block without pacemaker 7

Practical Dosing Approach

Acute IV Administration:

Diltiazem:

15-25 mg IV bolus over 2 minutes 2
May repeat or start continuous infusion if needed 2, 8
Onset of action within minutes, peak effect at 20 minutes 8

Metoprolol:

2.5-10 mg IV bolus, may repeat as required 2
Slower onset compared to diltiazem 1
Maximum beta-blockade achieved at approximately 20 minutes 7

Long-Term Oral Therapy: