From the Guidelines
Calcium channel blockers are a reasonable choice to control resting and exercise heart rate in patients with atrial fibrillation, particularly in those with heart failure with preserved ejection fraction (HFpEF), as they prolong AV node repolarization and increase the refractory period, preventing many rapid atrial impulses from reaching the ventricles. The mechanism of action of calcium channel blockers, such as diltiazem and verapamil, involves blocking L-type calcium channels in the AV node, which slows conduction and increases the refractory period, effectively controlling ventricular rate and reducing symptoms like palpitations and improving exercise tolerance 1. Key points to consider when using calcium channel blockers for atrial fibrillation include:
- They do not convert atrial fibrillation to normal rhythm, but rather control ventricular rate
- They should be used cautiously in patients with heart failure or those taking beta-blockers due to potential additive effects on heart rate and contractility
- Side effects may include hypotension, bradycardia, heart block, and constipation
- The rate control strategy is particularly important because rapid ventricular rates can lead to tachycardia-induced cardiomyopathy over time
- A combination of digoxin and a beta blocker (or a nondihydropyridine calcium channel antagonist with HFpEF) is reasonable to control resting and exercise heart rate in patients with AF, as stated in the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1. It is also important to note that calcium channel blockers, such as verapamil and diltiazem, have not been found effective for pharmacological cardioversion of recent-onset or persistent AF, but they act rapidly to control the rate of ventricular response, as mentioned in the 2011 ACCF/AHA/HRS focused updates incorporated into the ACC/AHA/ESC 2006 guidelines for the management of patients with atrial fibrillation 1.
From the FDA Drug Label
Electrical activity through the AV node depends, to a significant degree, upon calcium influx through the slow channel By decreasing the influx of calcium, verapamil hydrochloride prolongs the effective refractory period within the AV node and slows AV conduction in a rate-related manner.
Verapamil hydrochloride, a calcium channel blocker, prolongs the effective refractory period within the AV node by decreasing calcium influx. This action slows AV conduction in a rate-related manner. However, the provided text does not directly explain how this mechanism fixes atrial fibrillation. The text only mentions that verapamil hydrochloride may induce sinus arrest or sinoatrial block in patients with sick sinus syndrome and acceleration of ventricular rate and/or ventricular fibrillation has been reported in patients with atrial flutter or atrial fibrillation and a coexisting accessory AV pathway following administration of verapamil. Therefore, it can be inferred that calcium channel blockers like verapamil hydrochloride may not directly fix atrial fibrillation, but rather may be used to control ventricular rate in patients with atrial fibrillation 2.
From the Research
Mechanism of Action
- Calcium channel blockers (CCBs) work by prolonging AV node repolarization, which helps to control the ventricular rate in atrial fibrillation (AF) 3, 4, 5, 6, 7
- CCBs, such as verapamil and diltiazem, are commonly used for rate control in AF due to their ability to slow the conduction of electrical impulses through the AV node 3, 4, 5, 6, 7
Effects on Atrial Fibrillation
- CCBs have been shown to be effective in controlling ventricular rate in patients with AF, both at rest and during exercise 4, 5, 7
- Studies have demonstrated that CCBs, such as diltiazem and verapamil, can reduce the incidence of AF and improve symptoms in patients with paroxysmal AF 3, 4
- CCBs may also have a role in reducing the risk of embolic complications in patients with AF, although this is still being investigated 3, 6
Comparison with Other Treatments
- CCBs have been compared to other rate-control agents, such as beta-blockers and digoxin, in terms of their efficacy and safety in patients with AF 4, 5, 6, 7
- Studies have shown that CCBs may be more effective than beta-blockers in improving exercise capacity and reducing NT-proBNP levels in patients with permanent AF 7
- However, the choice of rate-control agent ultimately depends on the individual patient's characteristics and clinical presentation 3, 4, 5, 6, 7