Flecainide for cardiac arrhythmias

Anti-arrhythmic agents are classified into different classes based on their target of action. Flecainide is one of the class I anti-arrhythmic agents that acts as a sodium channel blocker. This drug is particularly indicated in the treatment of paroxysmal supraventricular tachycardia, commonly known as PSVT. This is a condition where irregular heartbeats are observed, and the term paroxysmal indicates that they are sudden-onset. Supraventricular, which means they are generated above the ventricles, so these impulses can be generated from the atria, where excessive firing of sodium channels may lead to irregular heartbeats.

Sodium ions are very important for depolarization, but when they're excessively firing, they can produce more impulses, leading to a loss of coordination. It can lead to either atrial flutter or, in severe conditions, atrial fibrillation. Sometimes impulses can also be generated from the AV node because of any re-entry type of arrhythmia. A unidirectional conduction block may lead to a circular motion of impulses that may lead to a re-entry type of arrhythmia. In such conditions, flecainide can be given as a sodium channel blocker. This drug can block excessive sodium channel activity so that it can reduce excessive heartbeats.

Among the class I antiarrhythmic agents, flecainide is classified as a class Ic agent because this drug can block the sodium channels with different kinetics. Under normal conditions, voltage-gated sodium channels are very important to produce rapid depolarization.

Flecainide is a Class Ic antiarrhythmic agent, and this drug shows a slow rate of association and dissociation with sodium channels. Flecainide can reduce the slope of phase zero action potential as it slows down the activation of sodium channels. In this way, flecainide can reduce sodium channel activity by decreasing the rate of their opening as well as closing. Interestingly, flecainide is not significantly increasing the repolarization, so under normal conditions it is having less effect on the increase in the QT interval.

Mechanism of flecainide

On the SA node as well as nodal cells, different types of ion channels are expressed: one is the sodium channel, the second is the potassium channel, and the third is the calcium channel. When an impulse reaches sodium channels, they are opened and they can enter the cells, so this sudden entry of sodium can produce a rapid depolarization within the membrane, and this phase is called phase zero. Phase 0 is the rapid depolarization phase. At the end of phase 0, because of the development of a positive membrane potential, potassium channels are immediately opened. Since potassium is outward-going, a few of the potassium ions can go outside, which leads to phase I, the partial repolarization phase.

Immediately at the end of phase 1, calcium channels are opened. Calcium can enter the membrane, and at the same time, a few of the potassium ions can go outside of the membrane. So this maintains a plateau phase,a horizontal phase where the membrane potential remains constant, and this phase is called phase 2. Now, after the end of phase 2, calcium channels are closed and potassium channels are more activated, resulting in an increased outflow of potassium that brings repolarization of the membrane. This phase is called Phase 3. In this way, when an impulse reaches the cardiac cells, all these phases work in coordination to produce cardiac contraction.

Now that flecainide is a Class Ic anti-arrhythmic agent, it is not acting on phase 2 or phase 3; it simply blocks the voltage-gated sodium channels. In the presence of flecainide, sodium cannot enter these cells, so excessive firing of sodium channels is inhibited. In this way, flecainide acts on phase 0 of the action potential, and since it binds to the sodium channels at a slow rate, it is classified as a class Ic antiarrhythmic agent.

Precautions about flecainide

Even flecainide can reduce irregular heartbeats, but it can also produce some abnormal heart rhythms, so this drug should be carefully used only in conditions like paroxysmal supraventricular tachycardia. Similarly, people with any previous history of heart attacks may have some induction of irregular heartbeats. In such conditions, flecainide should be carefully used because it can increase the risk of heart attacks by producing an abnormal heart rhythm. That's why this drug is not recommended for people with any previous history of heart attacks.

Flecainide can reduce the sudden onset of irregular heartbeats that may be associated with either atrial flutter or atrial fibrillation. However, it is not recommended for conditions like chronic atrial fibrillation. In chronic conditions, flecainide can further reduce cardiac activity by producing an abnormal heart rhythm. That's why this drug is not used for chronic conditions.

Another important consideration is that flecainide can worsen heart failure because it blocks the sodium channels, thereby reducing the depolarization of the cardiac membrane. Therefore, flecainide should be carefully used in people with any previous history of heart failure, and any symptoms like excessive tiredness, weakness, wheezing, coughing, or shortness of breath may indicate the worsening of heart failure in such people.

Similarly, this drug can produce some dizziness and lightheadedness. Patients taking flecainide should be careful while driving vehicles or working with machinery because it can produce some sudden falling sensations and dizziness. This is particularly pronounced when this flecainide is combined with other drugs that produce CNS depression. Even under normal conditions, flecainide does not increase the repolarization, but on repeated use, it can also increase the repolarization and elevate the QT interval within the ECG. So this may produce certain cardiac arrhythmias, and it may lead to some fainting sensation. Sometimes this drug can also increase the PR interval as well as the QRS interval, so any changes in the ECG should be closely monitored with the use of flecainide.

Side effects

Flecainide mainly produces some dizziness, headaches, and excessive tiredness. Some gastrointestinal side effects, like constipation and abdominal pain, can be observed. It can also produce some changes in vision, leading to blurred vision. Apart from these side effects, cardiac side effects like chest pain, palpitations, some state of confusion, coughing, and unusual bleeding can also be produced by this medication. Even it can increase the edema and leg swelling. These are the common side effects that can be produced by flecainide.

How is it given?

This drug is available as a tablet in different strengths, such as 50 mg and 100 mg. The dose is variable based on clinical use. The starting dose range is variable, ranging from 50 to 100 mg given every 12 hours to control irregular heartbeats. But the dosage interval may be variable based on the patient's conditions. In a few of the patients, it can also be given every 8 hours in order to control excessive heartbeats.

Conclusion

Flecainide is a class Ic anti-arrhythmic agent that is indicated in the treatment of paroxysmal supraventricular tachycardia. This drug can produce some cardiac side effects like chest pain and palpitations, gastro-intestinal side effects like constipation and abdominal pain, and central side effects like dizziness and confusion. It should be carefully given to people with any previous history of heart failure or heart attacks.