Antiarrhythmics

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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Synonym(s)

Antiarrhythmics

Definition
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The term "antiarrhythmic agent" refers to a heterogeneous group of drugs that can be used to treat cardiac arrhythmias. According to the classification proposed by Vaughan Williams (Classification from 1970), antiarrhythmics are divided into 4 classes (I to IV according to Vaughan Williams) according to their electrophysiological mechanisms of action:

Classification
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Class I Antiarrhythmics: Heterogeneous group of drugs, which also have very different structures. Four important effects of class I arrhythmics can be derived from the blockade of the Na+ channels. This leads to a reduction in the speed of impulse propagation, the extension of the refractory period, the suppression of pathological impulse formation and the reduction of the automatism of heterotopic pacemaker cells. In the presence of class I antiarrhythmics, the so-calledrecovery reflects the affinity with which the substances bind to the channel protein. The values ofrecovery are the basis for the further subclassification of class I antiarrhythmics (class Ia, Ib, Ic). For Class I antiarrhythmics,recovery is 1-10s, for Class Ib <1s and for Class Ic >10s. The ECG often shows an extension of the QRS duration, less frequently an extension of the PQ interval. The effects of class I antiarrhythmics are potential and frequency dependent. High-frequency pulse series or early-onset extrasystoles are suppressed very effectively.

  • Class Ia Antiarrhythmics (sodium channel blockers):
    • Ajmalin
    • quinidine (quinidine is hardly used nowadays due to considerable side effects; increases the risk of developing torsade de pointes tachycardia)
    • Prajmalin
  • Class Ib antiarrhythmics (lidocaine type). Representative:
    • Lidocaine (reserve medication for acute ventricular dysrhythmia)
  • Class Ic Antiarrhythmics (mixed type). Representative: Class Ic Antiarrhythmics (mixed type):
  • Class II - Beta-blockers: Beta-blockers lower the sinus frequency (negative chronotropic) by blocking the β1 adrenoceptors in the heart muscle, slow down the AV conduction (negative dromotropic) and reduce myocardial excitability (negative bathmotropic). Representative:
  • Class III - Potassium channel blocker: By blocking potassium channels, repolarization is slowed and thus the action potential is prolonged. Representative:
    • Amiodarone
    • Bretylium
    • Dofetilide
    • Dronedarone
    • Ibutilide
    • Sotalol
    • Vernacalant
  • Class IV - Calcium channel blockers: Calcium channel blockers of the phenylalkylamine or benzothiazepine type lower the heart rate by blocking L-type calcium channels and delay the AV transition. Representative:
  • Other antiarrhythmics
    • Adenosine: After binding to the A1 adenosine receptor, adenosine leads to the activation of a Gi-modulated potassium channel and a short-term blockade of the AV transition lasting a few seconds. The drug is used for the diagnosis and acute therapy of cardiac arrhythmias in which the AV node is involved.

Note(s)
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The original classification of antiarrhythmic drugs according to Vaughan-Williams is incomplete because the newer specific channel and receptor blockers are not taken into account.

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Last updated on: 29.10.2020