Almost all patients of a cardiologist faced one way or another with various kinds of arrhythmias. Currently, the pharmaceutical industry offers a wide variety of antiarrhythmic drugs. Their classification and characteristics will be considered in this article.
Exposure pathways
To eliminate ectopic heart rhythm disturbances, antiarrhythmic drugs are prescribed. The mechanism of action of such drugs is aimed at the electrophysiological properties of the cells of the working myocardium:
- Reducing the speed of the action potential, which helps to slow down the excitation.
- Decreased myocardial excitability.
- Reducing the time of relative refractoriness, which leads to a shortening of the interval when an extraordinary impulse can provoke a contraction of the heart.
- Lengthening the period of effective refractoriness, which is important for tachycardia and for eliminating impulses that occur after too short an interval after optimal contraction.
- Increasing the speed of excitation, which promotes homogenization and prevents the phenomenon of re-entry ("re-entry").
- Inhibition of the focus of ectopic automatism, which is associated with an extension of the period of diastolic depolarization.
- Elimination of differences in the rate of excitation and refractivity.
- Decreased cardiac sensitivity to electrical discharge and the risk of ventricular fibrillation.
Classification of antiarrhythmic drugs
All medicines in this group are divided into four classes. Additionally, the first class is divided into three subclasses. This classification is based on the degree of influence of drugs on the ability of heart cells to generate and conduct electrical signals. Different classes of antiarrhythmic drugs have their own routes of action, therefore, with different types of arrhythmias, their effectiveness will differ.
The first class includes sodium channel blockers. Subclass IA includes drugs such as Quinidine, Disopyramide, Novokainamid, Giluritmal. IB subclass includes Pyromecain, Tokainid, Difenin, Lidocain, Aprindin, Trimekain, Mexiletin. Subclass IC is formed by such drugs as Etmozin, Rhythmorm (Propafenon), Allapinin, Etatsizin, Flekainid, Indekainid, Bonnecor, Lorkainid.
The second class consists of beta-blockers (Metoprolol, Nadolol, Alprenolol, Kordanum, Propranolol, Acebutalol, Pindolol, Trazikor, Esmolol).
The third class includes potassium channel blockers: Bretilia tosylate, Amiodarone, Sotalol.
The fourth class includes slow calcium channel blockers (for example, Verapamil).
The list of antiarrhythmic drugs does not end there. Cardiac glycosides, potassium chloride, sodium adenosine triphosphate, magnesium sulfate are also isolated.
First class drugs
Blockers of fast sodium channels stop the flow of sodium into the cells, which leads to a slower passage of the excitation wave through the myocardium. Due to this, the conditions for rapid circulation in the heart of pathological signals are stopped, and arrhythmia is eliminated. Let us consider in more detail the groups of antiarrhythmic drugs belonging to the first class.
Class IA Medicines
Such antiarrhythmic drugs are prescribed for extrasystole (ventricular and supraventricular), as well as to restore sinus rhythm in case of atrial fibrillation (atrial fibrillation). In addition, they are used to prevent repeated attacks.
Novocainamide and Quinidine are effective antiarrhythmic drugs for tachycardia. We will tell you more about them.
Quinidine
This medication is used in case of paroxysmal supraventricular tachycardia, as well as in paroxysms of atrial fibrillation, to restore sinus rhythm. Most often, the medicine is prescribed in the form of tablets.
Poisoning with antiarrhythmic drugs is rare, however, when taking Quinidine, side effects in the form of digestive upset (vomiting, loose stools) and headache are possible. In addition, the use of this medication can cause a decrease in platelet levels in the blood, a slowdown in intracardiac conduction, and a decrease in myocardial contractility. The most dangerous side effect is the development of a special form of ventricular tachycardia, which can cause the patient to die suddenly. That is why quinidine therapy should be carried out only with the control of an electrocardiogram and under the supervision of a specialist.
The medicine is contraindicated in case of intraventricular and atrioventricular block, cardiac glycoside intoxication, thrombocytopenia, arterial hypotension, heart failure, pregnancy.
Novocainamide
This medication has the same indications for use as Quinidine. Quite often it is prescribed for the relief of paroxysms of atrial fibrillation. With the intravenous injection of Novocainamide, a sharp decrease in blood pressure is possible, as a result of which it is necessary to introduce the solution as slowly as possible.
Among the side effects are nausea, vomiting, changes in the composition of the blood, disorders of the nervous system in the form of dizziness, headache, and in rare cases, confusion. If you use the drug constantly, lupus-like syndrome (serositis, arthritis, fever), a microbial infection in the oral cavity, accompanied by slow healing of wounds and ulcers and bleeding of the gums, can develop. In addition, Novocainamide can provoke an allergic reaction, in this case, the first sign will be the appearance of muscle weakness with the introduction of the drug.
It is forbidden to use the medication for atrioventricular block, severe forms of renal and heart failure, arterial hypotension and cardiogenic shock.
IB class
Such drugs have a weak effect on the sinus node, atrioventricular connection and atria, therefore, are ineffective in case of supraventricular arrhythmia. These antiarrhythmic drugs are prescribed for extrasystole, paroxysmal tachycardia, that is, for the treatment of ventricular arrhythmias. They are also used to treat arrhythmias that are triggered by an overdose of cardiac glycosides.
The list of antiarrhythmic drugs in this class is quite extensive, but the most commonly used drug is Lidocaine. As a rule, it is administered intravenously in case of severe ventricular rhythm disturbances, including with myocardial infarction.
"Lidocaine" is able to disrupt the functioning of the nervous system, which is manifested by dizziness, convulsions, problems with speech and vision, impaired consciousness. If you introduce the drug in a large dose, it may slow down the heart rate, reduce contractility of the heart. In addition, allergic reactions in the form of Quincke's edema, urticaria, and pruritus are likely.
"Lidocaine" is contraindicated in atrioventricular block, sick sinus syndrome . A medication is not prescribed in case of severe supraventricular arrhythmia, since the risk of atrial fibrillation increases.
IC class
Medicines belonging to this class lengthen intracardiac conduction, especially in the His-Purkinje system. They have pronounced arrhythmogenic properties, so they are currently used only to a limited extent.
The list of antiarrhythmic drugs of this class was given above, but of them only “Propafenone” (“Rhythmorm”) is mainly used. It is prescribed for supraventricular and ventricular arrhythmias, including with ERW syndrome. Since there is a risk of an arrhythmogenic effect, the medication should be used under the supervision of a doctor.
In addition to arrhythmias, this drug is capable of causing progression of heart failure and worsening contractility of the heart. Among the side effects, the occurrence of a metallic taste in the mouth, nausea and vomiting can be distinguished. Such negative effects as visual impairment, changes in the blood test, dizziness, insomnia, and depression are not ruled out.
Beta blockers
When the tone of the sympathetic nervous system rises, for example, in case of stress, with hypertension, autonomic disorder, ischemia, a lot of catecholamines appear in the blood, including adrenaline. These substances act on beta-adrenergic receptors of the myocardium, which leads to electrical cardiac instability and the appearance of arrhythmias.
Beta-blockers prevent excessive stimulation of the receptors and thereby protect the myocardium. In addition, they reduce the excitability of the cells of the conduction system, which entails a slowdown in heart rate.
Medicines of this class are used in the treatment of atrial flutter and atrial fibrillation, for the prevention and relief of supraventricular arrhythmia. In addition, they help to overcome sinus tachycardia.
Ineffective antiarrhythmic drugs under consideration for atrial fibrillation, with the exception of cases when the pathology is caused precisely by an excess of catecholamine in the blood.
For the treatment of rhythm disturbances, Metoprolol and Anaprilin are often used. These drugs have side effects in the form of slowing the pulse, reducing myocardial contractility, and the occurrence of atrioventricular block. These medications can provoke cold extremities and a deterioration in peripheral blood flow. In addition, drugs affect the nervous system, causing drowsiness, dizziness, depression, and memory impairment. They also change the conductivity in the nerves and muscles, which is manifested by fatigue and weakness.
Beta-blockers are not allowed for use in cardiogenic shock, pulmonary edema, insulin-dependent diabetes mellitus, bronchial asthma. Also contraindications are atrioventricular block of the second degree, sinus bradycardia.
Potassium Channel Blockers
The list of antiarrhythmic drugs in this group includes drugs that slow down electrical processes in the heart cells and thereby block potassium channels. The most famous medicine of this class is Amiodarone (Cordaron). Among other things, it acts on M-cholinergic and adrenergic receptors.
"Cordaron" is used for the treatment and prevention of ventricular, atrial and supraventricular arrhythmias, cardiac arrhythmias on the background of ERW syndrome. The medication is also prescribed to prevent life-threatening ventricular arrhythmias in patients with acute heart attack. In addition, it is used to reduce heart rate with constant atrial fibrillation.
If you use the product for a long time, interstitial pulmonary fibrosis may develop , skin color (the appearance of a purple tint) will change. In some cases, headaches, sleep disturbances, memory, and vision appear. Taking Amiodarone may cause the development of sinus bradycardia, constipation, nausea and vomiting.
Do not prescribe medication for the initial bradycardia, lengthening of the QT interval, impaired intracardiac conduction, thyroid disease, arterial hypotension, pregnancy, bronchial asthma.
Slow Calcium Channel Blockers
These drugs block the slow flow of calcium, due to which ectopic foci in the atria are suppressed and the automatism of the sinus node is reduced. The list of antiarrhythmic drugs in this group includes Verapamil, which is prescribed for the prevention and relief of paroxysms of supraventricular tachycardia, for the treatment of supraventricular extrasystole. Verapamil is ineffective in case of ventricular arrhythmias.
Side effects include atrioventricular block, sinus bradycardia, arterial hypotension, and in some cases, a decrease in cardiac contractility.
Cardiac Glycosides
The classification of antiarrhythmic drugs would not be complete without mentioning these agents. These include drugs such as Celanide, Korglikon, Digitoxin, Digoxin, etc. They are used to restore sinus rhythm, stop supraventricular tachycardia, reduce the frequency of ventricular contractions in case of atrial fibrillation. When using cardiac glycosides, you need to monitor your condition. Signs of digital intoxication are manifested by abdominal pain, nausea and vomiting, headaches, impaired vision and sleep, nosebleeds.
It is forbidden to use these antiarrhythmic drugs for bradycardia, ERW syndrome, intracardiac blockade. They are not prescribed in case of paroxysmal ventricular tachycardia.
The combination of antiarrhythmic drugs
With ectopic rhythms in clinical practice, some combinations of medications are used. So, “Quinidine" can be used in conjunction with cardiac glycosides for the treatment of persistent extrasystoles. With beta-blockers, “Quinidine" can be prescribed for relief of ventricular arrhythmias, which can not be treated otherwise. The combined use of beta-blockers and cardiac glycosides gives a good effect in ventricular and supraventricular extrasystoles, and also helps prevent relapses of tachyarrhythmias and ectopic tachycardia.