What is Diltiazem (calcium channel blocker) used for?

Diltiazem Indications

Diltiazem is FDA-approved for chronic stable angina and coronary artery spasm, and is guideline-recommended for acute rate control in atrial fibrillation/flutter and supraventricular tachycardia in hemodynamically stable patients. 1

Primary FDA-Approved Indications

Angina Pectoris

• Chronic stable angina: Diltiazem reduces myocardial oxygen demand through heart rate reduction and systemic blood pressure lowering at submaximal and maximal exercise workloads 1
• Vasospastic angina (Prinzmetal's): Acts as a potent dilator of both epicardial and subendocardial coronary arteries, inhibiting spontaneous and ergonovine-induced coronary artery spasm 1

Guideline-Supported Arrhythmia Indications

Atrial Fibrillation and Atrial Flutter (Class I Recommendations)

For acute rate control in hemodynamically stable patients, intravenous diltiazem is the preferred calcium channel blocker due to superior safety and efficacy compared to verapamil. 2

• Mechanism: Direct effect on AV node to slow ventricular response 2
• Efficacy: Achieves rate control in atrial flutter (though more difficult than AF), with strong correlation between plasma concentration and heart rate reduction 3
• Dosing considerations: Standard dose is 0.25 mg/kg IV bolus over 2 minutes, though lower doses (≤0.2 mg/kg) may be equally effective with significantly reduced hypotension risk (18% vs 35% with standard dosing) 4

Supraventricular Tachycardia

In hemodynamically stable ACHD patients with SVT, intravenous diltiazem is recommended (Class I, Level C-LD), though caution is required due to 20% risk of hypotension. 2

• Monitor closely for hypotension, particularly in patients with ventricular dysfunction or single-ventricle physiology 2
• May be useful for rate control of atrial tachycardia while planning conversion strategies 2

Hypertension (Off-Label but Evidence-Supported)

• Effective for mild to moderate systemic hypertension with favorable adverse effect profile 5, 6
• Demonstrated similar efficacy to diuretics in older patients 6
• In rapid uncontrolled atrial fibrillation with hypertension, diltiazem serves dual purpose of rate control and blood pressure management 2

Critical Contraindications and Precautions

Absolute Contraindications

• Advanced heart failure or LV systolic dysfunction: Diltiazem has negative inotropic effects and should be avoided 2
• Heart block or sinus node dysfunction without pacemaker: Diltiazem prolongs AH interval and AV node refractory periods by approximately 20% 2, 1
• Pre-excitation syndromes (WPW): Risk of accelerated ventricular response 2
• Concurrent beta-blocker use: Risk of severe bradycardia, though combination therapy has been used cautiously in select cases of refractory rapid AF 2

Important Drug Interactions

• Metabolized by CYP3A4: Avoid combination with ivabradine due to severe bradycardia risk 2
• P-glycoprotein inhibition: May increase levels of direct oral anticoagulants, increasing bleeding risk 2

Mechanism-Based Clinical Pearls

• Calcium channel selectivity: Less vascular-selective than dihydropyridines (amlodipine), with more pronounced effects on cardiac conduction and contractility 2
• Electrophysiologic effects: Prolongs sinus cycle length up to 50% in sick sinus syndrome; average PR prolongation of 14% at 300mg oral dose 1
• Hypotension management: Main adverse effect across all indications; occurs in up to 20% of patients receiving IV formulation 2, 4

Comparative Positioning

• Versus verapamil: Diltiazem preferred for IV rate control due to superior safety profile 2
• Versus beta-blockers: Similar rate control efficacy in atrial flutter, but beta-blockers preferred if heart failure with reduced ejection fraction present 2
• Versus dihydropyridines: Diltiazem appropriate for angina and rate control; dihydropyridines (amlodipine) better for pure vasodilation without conduction effects 2