A 62-year-old woman with chronic atrial fibrillation and a rapid ventricular response (heart rate 135 bpm) presents to the emergency department. Her ECG shows irregular narrow-complex tachycardia with an absent P wave and a ventricular rate of 130–140 bpm. She is hemodynamically stable. What is the drug of choice for rate control in this acute presentation?
A. Intravenous amiodarone
B. Intravenous verapamil
C. Oral digoxin
D. Intravenous diltiazem
Explanation
Acute Rate Control in Atrial Fibrillation
Key Point
In hemodynamically stable patients with rapid atrial fibrillation, intravenous calcium channel blockers (verapamil or diltiazem) are first-line agents for acute rate control.
Mechanism of Action
Diltiazem (and verapamil) are non-dihydropyridine calcium channel blockers that:
Slow AV nodal conduction by blocking L-type calcium channels
Increase AV nodal refractoriness
Reduce ventricular response rate in atrial fibrillation
Onset of action: 2–5 minutes (IV); peak effect: 5–10 minutes
Comparison of Rate-Control Agents in Acute AF
Table
Agent
Route
Onset
Peak
Hemodynamic Effect
Use in Stable AF
Diltiazem
IV
2–5 min
5–10 min
Mild ↓ BP, ↓ HR
First-line
Verapamil
IV
3–5 min
5–10 min
Moderate ↓ BP, ↓ HR
Alternative
Amiodarone
IV
5–30 min
30–60 min
Variable; ↓ BP risk
Unstable/resistant
Digoxin
Oral/IV
30–60 min
4–6 hrs
Vagomimetic
Chronic use; slow onset
High-YieldNEET PG
Diltiazem is preferred over verapamil in acute AF because it has a faster onset, better hemodynamic tolerance, and fewer negative inotropic effects. Verapamil is an acceptable alternative but is less commonly chosen in acute settings.
Why Diltiazem Is Optimal in This Case
1.
Rapid onset: Achieves rate control within 5–10 minutes
2.
Hemodynamic stability: Minimal myocardial depression; safe in stable patients
3.
Efficacy: Reduces ventricular rate by 20–30% in most patients
4.
No need for loading: Single IV bolus often sufficient
Clinical Pearl
Diltiazem IV bolus is typically 0.25 mg/kg over 2 minutes, followed by a second dose if needed. A continuous infusion can be started for sustained rate control.
Why Other Agents Are Not First-Line Here
Amiodarone: Reserved for hemodynamically unstable patients or when rate control fails; slower onset and greater hemodynamic risk
Digoxin: Slow onset (30–60 minutes); better for chronic rate control; less effective in high adrenergic states
Verapamil: Similar efficacy to diltiazem but slightly slower onset and greater negative inotropic effect
Harrison 21e Ch 226
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