From the Guidelines
Calcium channel blockers are recommended for controlling the ventricular rate in patients with atrial fibrillation, particularly those who cannot tolerate beta-blockers or have contraindications to their use. These medications, such as diltiazem and verapamil, work by blocking calcium entry into cardiac cells, reducing electrical conduction through the AV node, and thereby limiting the number of atrial impulses that can reach the ventricles 1. This action effectively controls the ventricular rate despite ongoing atrial fibrillation.
Key Points to Consider
- Non-dihydropyridine calcium channel blockers (diltiazem, verapamil) are preferred for atrial fibrillation because they primarily affect cardiac conduction, unlike dihydropyridines like amlodipine which mainly affect blood vessels 1.
- The typical dose for diltiazem is 120-360 mg daily, and for verapamil, it is 120-480 mg daily 1.
- These medications can improve quality of life and exercise tolerance in patients with atrial fibrillation 1.
- Side effects may include constipation, headache, and hypotension, and they should be used cautiously in patients with heart failure or certain conduction disorders 1.
- For immediate rate control in emergency settings, intravenous formulations like diltiazem (0.25 mg/kg over 2 minutes) may be used, followed by continuous infusion if needed 1.
Clinical Considerations
- The choice between calcium channel blockers and beta-blockers for rate control in atrial fibrillation should be based on the individual patient's characteristics, such as the presence of contraindications or intolerance to beta-blockers 1.
- Calcium channel blockers may be preferred over beta-blockers in patients with bronchospasm or chronic obstructive pulmonary disease 1.
- The goal of treatment is to control the ventricular rate and improve symptoms, rather than converting the abnormal rhythm back to normal 1.
From the Research
Mechanism of Action
- Calcium channel blockers, such as diltiazem and verapamil, work by slowing the conduction of electrical impulses in the heart, specifically in the atrioventricular (AV) node 2.
- This slowing of conduction reduces the ventricular rate in patients with atrial fibrillation, thereby alleviating symptoms such as palpitations and shortness of breath 3, 4.
Effects on Exercise Tolerance
- Studies have shown that calcium channel blockers, such as diltiazem and verapamil, can improve exercise tolerance in patients with atrial fibrillation 3, 4, 5.
- This improvement in exercise tolerance is thought to be due to the reduction in ventricular rate, which allows for more efficient cardiac function and improved oxygen delivery to the muscles 5.
Comparison with Other Treatments
- Calcium channel blockers have been compared to other treatments, such as beta-blockers, in terms of their effectiveness in controlling ventricular rate and improving exercise tolerance 4, 5.
- While beta-blockers can also reduce ventricular rate, they may compromise exercise tolerance in some patients, whereas calcium channel blockers tend to preserve or improve exercise capacity 4, 5.
Safety and Efficacy in Specific Populations
- The safety and efficacy of calcium channel blockers in patients with atrial fibrillation complicated by congestive heart failure have been evaluated, with some studies suggesting that these drugs may be useful in the acute reduction of ventricular response, but their safety in chronic heart rate control remains to be proven 6.
- Additionally, calcium channel blockers have been shown to reduce N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels, a marker of cardiac stress, in patients with permanent atrial fibrillation 5.