AntiarrhythmicsAntiarrhythmics are a group of drugs used to treat cardiac arrhythmias. A distinction is made between a heartbeat that is too slow and one that is too fast. A heartbeat that is too slow is when the heart beats less than 60 beats per minute at rest (bradycardic arrhythmia).
If the heart beats faster than 100 times per minute at rest, this is called tachycardic arrhythmia. An irregularly beating heart is also to be distinguished. The heart rate can be too slow, too fast or normal.
It is also important to know whether the disorder is located in the atrial (supraventricular) or ventricular region and whether the transition from atrium to ventricle is disturbed (e.g. AV block). The cardiac action is an electro-mechanical event in which the flow of the ions sodium, calcium and potassium, as well as the interaction of myocardial cells and cells that form the electrical signal (sinus node) and transmit it (AV node, etc.) are important.
It should be noted that antiarrhythmic drugs (drugs against cardiac arrhythmias) are in turn capable of triggering cardiac arrhythmias themselves; they are proarrhythmogenic. In the acute therapy of cardiac dysrhythmia, two groups of drugs are available which act on the autonomic nervous system. This nervous system consists of a sympathetic part (sympathicus), which among numerous other tasks has the task of increasing the heart rate, and a parasympathetic part (parasympathicus), which slows down the heart rate.
If the heartbeat is too slow, the parasympathetic component can be slowed down (parasympatholytics) or the sympathetic component can be promoted (sympathomimetics). Parasympatholytics include, for example, the substances atropine or ipratropium. Examples of sympathomimetic drugs are adrenalin or orciprenalin.
As a long-term therapy, a pacemaker is the drug of choice. According to Vaughan-Williams, this group of antiarrhythmic drugs is divided into classes I – IV. This class of antiarrhythmics (drugs against cardiac arrhythmia) are substances that block sodium channels (sodium channel blockers) on the cell membrane of the heart cells.
The path across the membrane through the channel into the cell is then blocked for the sodium ion. The substances only block the path when the channel is open or just inactive (use dependency). The cell membrane is stabilized.
The ability to trigger electrical signals is reduced and the heartbeat slows down. Due to the blockade, the recovery time of these sodium channels is also extended. Consequently, the probability of an early and therefore irregular heartbeat is reduced.
Class – I – antiarrhythmic drugs are divided into three subclasses according to the recovery time of the sodium channel: Of the Class – I – Antiarrhythmics, the substances Ajmalin (Class IA), Lidocaine (Class IB) and Propafenone (Class IC) are the most commonly used. They are mainly used for cardiac arrhythmia affecting the ventricles (ventricular tachycardia). Contraindications are cardiac insufficiency, the first three months after a heart attack and AV block (a form of cardiac arrhythmia in which the transmission of excitation from atrium to ventricle is disturbed).
- L-Class – IA – Quinidine-type antiarrhythmics: They block the rapid influx of sodium and are more of a 2nd choice because of the side effects and interactions.
- L-Class – IB – Lidocaine-type antiarrhythmics: They are highly use dependent and block the sodium channel in an inactive state only at high heart rates. With slower heartbeats the substance diffuses out of the channel and becomes ineffective.
- L-Class – IC – Antiarrhythmics: They block slowly, provide a long recovery time of the sodium channels and are not use dependent.
