Antiarrhythmics are drugs that are used in the symptomatic and preventive treatment of cardiac function impairment due to tachycardia and irregular rhythm.
They act by modifying the automatism, refractory periods and the conduction velocity of cardiac cells. However, the goals of antiarrhythmic treatment are to control symptoms and improve survival.
However, the efficacy of antiarrhythmics is moderate and they have a narrow therapeutic margin. In some cases, they can even be lethal if they are not used properly.
Types of antiarrhythmics
Depending on their main mechanism of action, antiarrhythmics are classified as follows:
Class I antiarrhythmics
The antiarrhythmics of this group they act by blocking sodium channels. Among them, the most used are flecainide and propafenone.
They can become dangerous in patients with certain types of heart problems; especially if they have a previous infarction or depression of cardiac contraction function.
In turn, depending on its characteristics, this group is divided into:
- IA class: disopyramide and procainamide are included; They are intermediate kinetics. They act by prolonging the duration of the action potential, repolarization and the PR, QRS and QT intervals.
- IB class antiarrhythmics: Lidocaine and phenytoin. These drugs have rapid kinetics and reduce or shorten the action potential. They can also shorten repolarization and the QT interval.
- IC class: are the most used. They have a slow kinetics. They affect the action potential and repolarization little. However, they prolong PR and QRS, and have no effect on QT.
Class II antiarrhythmic drugs
In this group are beta blockers. The most commonly used are atenolol, propanolol, metoprolol and bisoprolol.
Stresses its brady-effect, that is, reduction of the heart rhythm on the sinus and atrioventricular node. These drugs can be used in patients with and without structural heart disease.
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Class III antiarrhythmics
This group acts by blocking potassium channels. The most commonly used are amiodarone and sotalol. Amiodarone is relatively safe in patients with structural heart disease.
Structural heart disease refers to a series of cardiovascular conditions that are different but related, since they are all the result of a similar problem. For example, by a disruption of the natural flow of blood through the internal chambers and valves of the heart.
On the other hand, As for amiodarone, it has frequent and / or serious side effects extracardiac level. An example is that it can cause toxicity in the thyroid glands and in the lungs.
Class IV antiarrhythmic drugs
Class IV antiarrhythmics they act by blocking calcium channels. Among them, the most used are verapamil and diltiazem.
Although they are weak as antiarrhythmics, they have bradycardiating properties, acting on the sinus and atrioventricular node. Further, they can be dangerous in patients with depression of cardiac contractile function.
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There are two other drugs that do not belong to any group of the above and that they are also used in the treatment of arrhythmias.
- Digoxin: acts by shortening the atrial and ventricular refractory periods. In addition, it has vagotonic properties, so it prolongs conduction and refractory periods in the atrioventricular node.
- Adenosine: Reduces speed or blocks conduction in the atrioventricular node. It can also reverse conduction-dependent tachycardias through the atrioventricular node.
Indications of antiarrhythmics
Antiarrhythmics are recommended to treat the following cases:
- End or control an episode of arrhythmia.
- Prevent recurrence of an arrhythmia.
- Avoid the appearance of serious arrhythmias in specific situations.
Further, are indicated in certain tachycardias documented, according to its effectiveness, safety and proven benefit. In these situations, they are used to relieve symptoms, improve the performance of the heart and prevent a degeneration to a malignant arrhythmia.
When the patient has sustained supraventricular tachycardia, amiodarone, verapamil, digoxin and adenosine are used. Instead, if there is ventricular tachycardia, intravenous lidocaine is used. It will be administered during myocardial ischemia, and intravenous amiodarone may also be used.
On the other hand, digoxin, beta blockers, verapamil and amiodarone are administered to depress atrioventricular conduction. When you need to suppress extrasystoles, lidocaine is given. However, flecainide, amiodarone and beta blockers are used to prevent supraventricular and ventricular tachycardias.
Although cardiac ablation techniques have experienced great development, treatment selection is conditioned by the type of arrhythmia and the patient's profile; especially, if there is basic heart disease.