Antiarrhythmics

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:

Class I antiarrhythmics: Heterogeneous group of drugs that also have quite different structures. Four important effects of class I antiarrhythmics can be derived from the blockade of Na+ channels. This leads to a decrease in the rate of pulse propagation, prolongation of the refractory period, suppression of pathological pulse formation, and reduction in the automaticity of heterotopic pacemaker cells. In the presence of class I antiarrhythmic drugs, the so-called_TErholung reflects the affinity with which the substances bind to the channel protein. The values of_TErholung underlie the further subclassification of class I antiarrhythmic drugs (class Ia, Ib, Ic). For class I antiarrhythmics,_TErecovery is 1-10s, for class Ib <1s, and for class Ic >10s. On ECG, prolongation of QRS duration is often seen less commonly prolongation of the PQ interval. The effects of class I antiarrhythmics are potential- and frequency-dependent. High-frequency impulse series or early-onset extrasystoles are suppressed very effectively.

• Class Ia antiarrhythmics (sodium channel blockers).Representative:
  • Ajmaline
  • Quinidine (quinidine is rarely used nowadays because of significant side effects; increases risk for development of torsade de pointes tachycardia)
  • Prajmalin
• Class Ib antiarrhythmics (lidocaine-like). Representative:
  • Lidocaine (backup drug for acute ventricular arrhythmias)
• Class Ic antiarrhythmics (mixed type). Representative:
  • Propafenone
  • Flecainide
  • Aprindin
  • Moricizine
• Class II - Beta-blockers: Beta-blockers decrease sinus rate (negative chronotropic), slow AV conduction (negative dromotropic), and decrease myocardial excitability (negative bathmotropic) via blockade of β1-adrenoceptors on the myocardium. Representative:
  • Propranolol
  • Metoprolol
  • Atenolol
  • Bisoprolol
  • Nebivolol u.v. a.m.
• Class III - Potassium channel blockers: Blockade of potassium channels slows repolarization, thereby prolonging the action potential. Representative:
  • Amiodarone
  • Bretylium
  • Dofetilide
  • Dronedarone
  • Ibutilide
  • Sotalol
  • Vernakalant
• Class IV - Calcium channel blockers: Calcium channel blockers of the phenylalkylamine or benzothiazepine type decrease heart rate via blockade of L-type calcium channels and delay AV conduction. Agents:
  • Verapamil
  • Diltiazem
  • Gallopamil
  • Flunarizine
  • Diprafenone.
• Other antiarrhythmics
  • Adenosine: After binding to A1 adenosine receptors, adenosine leads to short-term blockade of AV conduction lasting a few seconds via activation of a Gi-modulated potassium channel. The drug is used for the diagnosis and acute therapy of cardiac arrhythmias in which the AV node is involved.

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.