Is Cardizem (diltiazem) harmful to a patient with congestive heart failure (CHF)?

Diltiazem (Cardizem) Is Harmful in Patients with Congestive Heart Failure

Diltiazem should be avoided in patients with congestive heart failure (CHF), particularly those with reduced ejection fraction, due to its negative inotropic effects that can worsen heart failure symptoms and potentially increase mortality. 1, 2

Mechanism of Harm in CHF

Diltiazem causes several effects that are problematic in heart failure patients:

• Negative inotropic effects: Diltiazem reduces cardiac contractility, which can further compromise already impaired ventricular function in CHF patients 2
• Vasodilatory properties: Can cause hypotension in volume-depleted or hemodynamically unstable CHF patients 1
• Drug interactions: When combined with beta-blockers (standard therapy for CHF), diltiazem may cause additive effects on cardiac conduction, potentially leading to bradycardia or heart block 2

Evidence from Guidelines

Multiple cardiology society guidelines specifically warn against diltiazem use in CHF:

• The European Society of Cardiology (ESC) 2012 guidelines state: "Calcium-channel blockers should be discontinued unless absolutely necessary, and diltiazem and verapamil are potentially harmful because of their negative inotropic effect" 1

• The ESC 2005 guidelines explicitly state: "Calcium antagonists are not recommended for the treatment of heart failure caused by systolic dysfunction. Diltiazem- and verapamil-type calcium antagonists, in particular, are not recommended in heart failure because of systolic dysfunction" 1

• The ACC/AHA versus ESC guidelines comparison (2019) recommends against combining verapamil or diltiazem with beta-blockers in heart failure patients with atrial fibrillation (Class III recommendation - harmful) 1

FDA Warning

The FDA drug label for diltiazem specifically cautions: "Although diltiazem has a negative inotropic effect in isolated animal tissue preparations... Experience with the use of diltiazem hydrochloride alone or in combination with beta-blockers in patients with impaired ventricular function is very limited. Caution should be exercised when using the drug in such patients." 2

Recent Research Findings

Recent studies have shown mixed but concerning results:

• A 2022 study found that while diltiazem was effective for rate control in atrial fibrillation, it was associated with a significantly higher incidence of worsening heart failure symptoms compared to metoprolol (33% vs 15%, p=0.019) 3

• A 2024 study showed that worsening heart failure occurred in 17% of patients with reduced ejection fraction who received IV diltiazem for atrial fibrillation, compared to only 4.8% in those with preserved ejection fraction (p=0.005) 4

Alternative Medications for CHF Patients

For CHF patients requiring rate control (e.g., for atrial fibrillation):

1. Beta-blockers: First-line agents for rate control in CHF patients (metoprolol succinate, carvedilol, bisoprolol) 5
2. Digoxin: Can be used as an adjunct to beta-blockers for rate control 1
3. Amiodarone: May be considered in selected cases for rhythm control 1

Special Considerations

• In hypertrophic cardiomyopathy (HCM), diltiazem may be considered only if verapamil is contraindicated or not tolerated 1

• For patients with preserved ejection fraction heart failure (HFpEF), the risk may be lower but caution is still warranted 4

Clinical Pitfalls to Avoid

1. Don't mistake HFpEF for HFrEF: While diltiazem may be somewhat safer in HFpEF, it remains potentially harmful in HFrEF
2. Don't use for acute rate control in decompensated CHF: The negative inotropic effects are particularly dangerous in acutely decompensated patients
3. Don't combine with beta-blockers in CHF patients: This combination increases risk of bradycardia and heart block 1, 2
4. Don't continue diltiazem when initiating guideline-directed medical therapy for CHF: Switch to safer alternatives for rate control

In summary, the evidence strongly indicates that diltiazem should be avoided in CHF patients due to its negative inotropic effects and potential to worsen heart failure symptoms, with safer alternatives available for most clinical scenarios where rate control is needed.