What are the contraindications for using diltiazem (calcium channel blocker) in patients with certain medical conditions, such as sick sinus syndrome, atrioventricular (AV) block, hypotension, and heart failure?

Contraindications for Diltiazem

Diltiazem is absolutely contraindicated in patients with sick sinus syndrome without a pacemaker, second- or third-degree AV block without a pacemaker, hypotension (systolic BP <90 mmHg), acute myocardial infarction with pulmonary congestion, and decompensated systolic heart failure or severe left ventricular dysfunction. 1

Absolute Contraindications

The FDA label and major cardiology guidelines establish clear absolute contraindications where diltiazem must not be used:

• Sick sinus syndrome without a functioning ventricular pacemaker 1, 2
• Second- or third-degree AV block without a functioning ventricular pacemaker 1, 2, 3
• Hypotension with systolic blood pressure less than 90 mmHg 1, 3
• Acute myocardial infarction with pulmonary congestion documented by x-ray 1
• Decompensated systolic heart failure or severe left ventricular dysfunction 2, 3
• Cardiogenic shock 2, 3
• Wolff-Parkinson-White (WPW) syndrome with atrial fibrillation or atrial flutter 2, 3

Critical Relative Contraindications (Use with Extreme Caution)

Several clinical scenarios require extreme caution or avoidance unless no alternatives exist:

• First-degree AV block with PR interval >0.24 seconds in acute coronary syndromes 3
• Concurrent beta-blocker therapy poses significant risk for symptomatic bradycardia, profound AV block, and heart failure 3, 4. The combination can result in additive effects on cardiac conduction and should be avoided unless carefully monitored 1, 2
• Wide-complex tachycardias unless the arrhythmia is known with certainty to be supraventricular in origin 3

Important Clinical Context

Heart Failure Considerations

Diltiazem and verapamil are explicitly contraindicated in patients with STEMI and associated systolic LV dysfunction and CHF. 2 While diltiazem has less negative inotropic effect than verapamil, it can still cause abrupt decompensation in patients with severe left ventricular dysfunction 5. The drug should be avoided in patients with decompensated systolic heart failure or pre-existing ventricular dysfunction 2.

Conduction System Effects

Diltiazem prolongs AV node refractory periods without significantly prolonging sinus node recovery time, except in patients with sick sinus syndrome 1. This can rarely result in abnormally slow heart rates or second- or third-degree AV block (0.48% incidence) 1. One case report documented periods of asystole (2-5 seconds) after a single 60mg dose in a patient with Prinzmetal's angina 1.

Drug Interactions Requiring Caution

Diltiazem is both a CYP3A4 substrate (major) and a moderate CYP3A4 inhibitor 2, 3. Exercise caution with:

• Apixaban, itraconazole, bosutinib, ceritinib, cilostazol, cyclosporine, everolimus, ibrutinib, idelalisib, ivabradine, lomitapide, olaparib, ranolazine, rifampin, and simeprevir 2, 3
• Reduce warfarin dose by 50% and digoxin dose by 30-50% when initiating diltiazem 3

Common Pitfalls to Avoid

• Do not use diltiazem for wide-complex tachycardias unless supraventricular origin is certain, as it may cause hemodynamic collapse in ventricular tachycardia 3
• Avoid short-acting nifedipine (not diltiazem) in acute coronary syndromes due to increased mortality 3
• Do not routinely combine with beta-blockers due to increased risk of bradycardia and heart block 3, 4
• Avoid in cocaine-associated acute coronary syndromes as first-line therapy; reserve for patients unresponsive to benzodiazepines and nitroglycerin 3

Hepatic and Renal Dysfunction

Use with caution in patients with hepatic dysfunction, as diltiazem is metabolized by the liver and rare cases of acute hepatic injury have been reported 2, 1. Renal dysfunction may also require dose adjustment 2.