Cardizem (Diltiazem) for Rate Control vs. Rhythm Control in Atrial Fibrillation
Cardizem (diltiazem) is a rate control medication that slows the ventricular response in atrial fibrillation without restoring normal sinus rhythm—this is fundamentally different from rhythm control strategies that aim to convert and maintain sinus rhythm through cardioversion or antiarrhythmic drugs. 1
Understanding the Two Strategies
Rate Control with Diltiazem
- Diltiazem works by blocking calcium channels in the AV node, slowing conduction and reducing the ventricular rate during atrial fibrillation without converting the rhythm back to sinus. 1
- The goal is to control heart rate to <110 bpm (lenient control) or <80 bpm (strict control), with lenient control being acceptable initially unless symptoms persist. 1
- For acute rate control in hemodynamically stable patients, IV diltiazem is the preferred calcium channel blocker due to its rapid onset, safety profile, and efficacy. 1, 2
- Diltiazem achieves rate control faster than metoprolol in head-to-head comparisons, though both are effective. 2, 3
Rhythm Control Strategy
- Rhythm control aims to restore and maintain normal sinus rhythm through electrical cardioversion or antiarrhythmic drugs (amiodarone, flecainide, propafenone, sotalol, dofetilide). 1
- This approach does NOT use diltiazem—antiarrhythmic drugs with rate-limiting properties like amiodarone should only be used when rhythm control is the goal, not for simple rate control. 1
- Cardioversion (electrical or pharmacological) is required for rhythm control, followed by maintenance antiarrhythmic therapy. 1
When to Choose Each Strategy
Rate Control is Preferred For:
- Elderly patients with minor symptoms (EHRA score 1) should receive rate control as the initial approach. 1
- Patients with permanent atrial fibrillation where no attempt to restore sinus rhythm is planned. 1
- Hemodynamically stable patients with AF duration >48 hours, where cardioversion carries thromboembolic risk without proper anticoagulation. 1
- Patients with multiple comorbidities where antiarrhythmic drugs pose higher toxicity risks. 4
Rhythm Control Should Be Considered For:
- Symptomatic patients (EHRA score >2) despite adequate rate control require rhythm control therapy. 1
- Hemodynamically unstable patients require immediate synchronized cardioversion. 1
- Younger, more active patients with new-onset or paroxysmal AF and minimal structural heart disease. 1
- Patients with AF-related heart failure where restoring sinus rhythm may improve cardiac function. 1
Critical Contraindications for Diltiazem
Diltiazem must be avoided in patients with LVEF <40% or decompensated heart failure due to negative inotropic effects that can worsen hemodynamic status. 1, 2 In these patients, use beta-blockers and/or digoxin instead. 1, 5
Never use diltiazem (or any AV nodal blocker) in pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome), as it can paradoxically accelerate ventricular rate and precipitate ventricular fibrillation. 1, 6
Practical Dosing for Diltiazem Rate Control
Acute IV Administration:
- Initial bolus: 0.25 mg/kg (typically 20 mg) IV over 2 minutes. 1
- If inadequate response after 15 minutes, give second bolus of 0.35 mg/kg (typically 25 mg). 1
- Continuous infusion: 5-15 mg/hour, titrated to heart rate target. 1
- Recent evidence suggests that after an IV bolus achieves rate control, continuing a diltiazem drip may be less effective than transitioning to oral therapy or other agents. 7
Oral Maintenance:
Combination Therapy Considerations
If single-agent diltiazem fails to achieve adequate rate control, combination therapy with digoxin should be considered. 1, 5 The combination of IV diltiazem plus digoxin achieves faster rate control with fewer fluctuations than diltiazem alone. 8
Common Pitfalls to Avoid
- Do not use antiarrhythmic drugs (amiodarone, sotalol, dronedarone) solely for rate control—these are rhythm control agents. 1
- Do not attempt cardioversion (rhythm control) in patients with AF >48 hours duration without 3 weeks of therapeutic anticoagulation first, unless transesophageal echo excludes left atrial thrombus. 1, 5
- Do not discontinue rate control medications even if pursuing rhythm control, as they provide backup rate control during AF recurrences. 1
- Hypotension is the main adverse effect of IV diltiazem—monitor blood pressure closely during administration. 1
Evidence on Rate vs. Rhythm Control Outcomes
Large randomized trials (AFFIRM, RACE) demonstrate that rate control is non-inferior to rhythm control for mortality, stroke, and cardiovascular events, with fewer adverse effects. 1, 4 Rhythm control with antiarrhythmic drugs did not reduce death or serious cardiovascular events compared to rate control plus anticoagulation, and caused more adverse events including proarrhythmia. 4
Both strategies require lifelong anticoagulation based on stroke risk (CHA₂DS₂-VASc score), regardless of whether sinus rhythm is maintained. 5, 6