Can Carizem (diltiazem) lower heart rate (tachycardia)?

Can Cardizem (Diltiazem) Lower Heart Rate?

Yes, diltiazem (Cardizem) effectively lowers heart rate in supraventricular tachyarrhythmias by slowing conduction through the AV node, making it a first-line agent for acute rate control in hemodynamically stable patients. 1

Mechanism and Efficacy

Diltiazem works by inhibiting calcium influx during membrane depolarization, which prolongs AV node refractory periods and slows AV conduction without significantly affecting sinus node recovery time (except in sick sinus syndrome). 2 This mechanism directly reduces ventricular rate in tachyarrhythmias.

Intravenous diltiazem is particularly effective for acute rate control in atrial flutter and atrial fibrillation, with success rates of 80-98% when used alongside verapamil or adenosine for various supraventricular tachycardias. 1 In clinical studies, IV diltiazem achieved an 82% overall success rate in converting or controlling supraventricular tachyarrhythmias, with most patients reaching therapeutic endpoints within 5 minutes. 3

Clinical Applications by Arrhythmia Type

Atrial Flutter and Atrial Fibrillation

• Diltiazem is useful for acute rate control in hemodynamically stable patients, working through direct AV nodal effects. 1
• Intravenous diltiazem is the preferred IV calcium channel blocker for acute rate control due to its superior safety and efficacy profile compared to verapamil. 1
• Rate control in atrial flutter is often more difficult than in atrial fibrillation, frequently requiring higher doses or combination therapy. 1

Supraventricular Tachycardia (SVT)

• Intravenous diltiazem is reasonable for acute treatment of hemodynamically stable AVNRT (atrioventricular nodal reentrant tachycardia), though adenosine remains first-line. 1
• Studies show diltiazem terminates AVNRT in the majority of cases by prolonging AH interval and AV node refractory periods. 4, 5
• For orthodromic AVRT, diltiazem can be considered after other therapies fail, but carries risk if the rhythm converts to atrial fibrillation in patients with pre-excitation. 1

Dosing and Administration

Standard IV dosing is 0.25 mg/kg (typically 20 mg) as a bolus over 2 minutes, which prolongs AH conduction time and AV node refractory periods by approximately 20%. 2, 4 A continuous infusion of 5-15 mg/hour may follow for sustained rate control. 1

Oral diltiazem is effective for chronic management, with doses up to 240 mg/day producing small increases in PR interval without usually causing abnormal prolongation. 2

Critical Contraindications and Warnings

Absolute Contraindications

Diltiazem must never be used in pre-excited atrial fibrillation (Wolff-Parkinson-White with AF), as it can enhance accessory pathway conduction, increase ventricular rate, and potentially trigger ventricular fibrillation. 1

Relative Contraindications and Cautions

• Avoid in advanced heart failure: Diltiazem has negative inotropic effects and can depress myocardial function, increasing heart failure risk. 1, 2
• Avoid in AV block or sick sinus syndrome without pacemaker: May cause abnormally slow heart rates, second- or third-degree AV block (0.48% incidence), or rarely asystole. 6, 2
• Use caution with beta-blockers or digoxin: Concomitant use produces additive effects on cardiac conduction. 2

Monitoring Requirements

• Monitor for hypotension: Decreases in blood pressure may occasionally cause symptomatic hypotension, which occurred in 2 patients in one study but responded rapidly to fluid administration. 2, 3
• Watch for bradycardia: Particularly in elderly patients, where bradycardia occurred in 6 of 37 patients (16%) but reversed quickly after cessation. 7

Comparative Effectiveness

Beta-blockers achieve similar rate control to diltiazem, with the rate-slowing effect primarily related to reduction of sympathetic tone. 1 However, diltiazem may be preferred in patients with reactive airway disease where beta-blockers are contraindicated. 1

For heart failure patients with atrial fibrillation, beta-blockers are preferred over diltiazem due to their favorable effects on heart failure natural history, while diltiazem should be avoided due to its cardiodepressant effects. 1

Special Populations

In elderly patients (mean age 70 years), diltiazem demonstrated 41% conversion to sinus rhythm in atrial fibrillation with good ventricular rate control in most others, though side effects occurred in 27% of patients. 7 Careful dose titration is essential in elderly patients and those with hepatic impairment, where half-life increases and AUC rises by 69%. 2