How do calcium channel blockers (CCBs) treat atrial fibrillation?

From the Guidelines

Calcium channel blockers help manage atrial fibrillation by slowing the heart rate, though they don't actually "fix" or convert the arrhythmia back to normal rhythm. Medications like diltiazem and verapamil work by blocking L-type calcium channels in the heart, particularly in the atrioventricular (AV) node, as recommended by the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1. This reduces calcium influx into cardiac cells, which slows electrical conduction through the AV node and decreases heart rate. By controlling rapid ventricular response in atrial fibrillation, these medications help improve symptoms like palpitations, shortness of breath, and fatigue. They're particularly useful in patients who cannot tolerate beta-blockers. Non-dihydropyridine calcium channel blockers (diltiazem, verapamil) are preferred for rate control, while dihydropyridines (amlodipine, nifedipine) have minimal effect on the AV node and aren't typically used for this purpose. Some key points to consider when using calcium channel blockers for atrial fibrillation include:

• The negative inotropic effects of nondihydropyridine calcium channel blockers, which might result in hypotension, and caution should be used in patients with heart failure, as noted in the 2011 ACCF/AHA/HRS focused updates incorporated into the ACC/AHA/ESC 2006 guidelines 1.
• The potential for drug interactions, particularly with verapamil and diltiazem, due to their inhibitory effect on drug transport mediated by P-glycoprotein and metabolism by the cytochrome P 450 3A4 enzyme, as discussed in the 2022 study on individualized beta-blocker treatment for high blood pressure 1.
• The possibility of combining beta-blockers with nondihydropyridine calcium channel blockers, such as diltiazem or verapamil, in patients who do not respond satisfactorily to separate treatment with either drug class, as suggested in the 2022 study 1. However, the most recent and highest quality study, from 2022, provides the most relevant guidance on the use of calcium channel blockers in atrial fibrillation, emphasizing their role in rate control and symptom management 1.

From the Research

Mechanism of Calcium Channel Blockers in Atrial Fibrillation

• Calcium channel blockers, such as verapamil and diltiazem, are used to control ventricular response rate in patients with atrial fibrillation 2, 3, 4, 5.
• These medications work by blocking the influx of calcium ions into the cardiac muscle cells, thereby reducing the contractility of the heart and slowing the ventricular rate 2, 3.
• The use of calcium channel blockers can help to alleviate symptoms such as palpitations, shortness of breath, and fatigue associated with atrial fibrillation 3, 4.

Efficacy of Calcium Channel Blockers

• Studies have shown that calcium channel blockers, such as verapamil and diltiazem, are effective in reducing ventricular rate in patients with atrial fibrillation 3, 4.
• A systematic review of the literature found that verapamil and diltiazem were efficacious for heart rate control at rest and during exercise in patients with atrial fibrillation 3.
• Another study found that intravenous diltiazem and verapamil were comparable in terms of efficacy and effect on systolic function in patients with rapid atrial fibrillation and flutter 4.

Safety and Tolerability

• Calcium channel blockers are generally well-tolerated, but can cause side effects such as hypotension, dizziness, and headache 4, 5.
• The use of calcium channel blockers in patients with congestive heart failure requires careful consideration, as they can exacerbate heart failure in some cases 5.
• A recent study found that the initiation of diltiazem or verapamil in patients with heart failure with preserved ejection fraction or atrial fibrillation may be associated with fewer heart failure hospitalization events, but also with more all-cause deaths 6.

Comparison with Other Medications

• Calcium channel blockers are often compared with beta-blockers, which are also used to control ventricular response rate in patients with atrial fibrillation 2, 3, 6.
• A study found that beta-blockers were more efficacious than calcium channel blockers in controlling resting heart rate, but calcium channel blockers were more effective during exercise 3.
• Another study found that the use of nondihydropyridine calcium channel blockers, such as diltiazem and verapamil, was associated with a lower risk of heart failure hospitalization compared with beta-blockers 6.