III class - Antiarrhythmic, which retard the repolarization

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Description of the pharmacological group

Medicinal properties

Antiarrhythmic preparations - medicines, which have the normalizing effect on the disrupted rhythm of the heart contractions.

III class - preparations, which retard the repolarization

Antiarrhythmic medicines of the III class

For antiarrhythmics of III class (cordarone (amiodarone), bretiliya tosylate, ibutilide, sotalol and other) relate different in the special features of the mechanism of the action of medicines, but them all is united the ability to lengthen action potential via the blockade of the transmembrane potential dependent potassium channels during the phase of repolarization and to thus lengthen the refractory period of cardiomyocytes.

Table. Characteristic of the antiarrhythmic medicines of the III class

The preparations of this group to one extent or another decrease the ability of the pacemaker cells of sinoatrial and atrioventricular units to generate cardiac rhythm, i.e. they slow down their automatism. The basic electrophysiological properties of the antiarrhythmic medicines of the III class are given in the table. Besides the antiarrhythmic action of antiarrhythmics III class is inherent even anti-fibrillary activity; therefore they just as β- adrenoblockers, they adapt in the clinical practice for the preventive maintenance of sudden coronary death in patients with the sharp myocardial infarction.

In contrast to antiarrhythmics of the I class, of which is characteristic the phenomenon of direct frequency dependence, antiarrhythmics of the III class they possess opposite property - for them are characteristic the phenomenon of inverse frequency dependence, i.e., they more they are effective with “slow” arrhythmias. Exception is amiodarone, for which is characteristic neither “direct” nor “inverse” frequency dependence.

On EKG under the action antiarrhythmics of the III class is lengthened the interval QT.

In the clinical practice the medicines of this class use for treating of supraventricular as well as ventricular tachyarrythmias and extrasystoles. Exception is bretiliya tosylate, which is used is only in urgent (pressing) cardiology when necessary the preventive maintenance of the fibrillation of the ventricles of heart. Bretylium tosylate also uses for treating (stopping) the fibrillation of the ventricles of heart when electrical defibrillation proves to be ineffective.

Amiodarone) (sin.: cordarone) although relates to the antiarrhythmic medicines of the III class, to one degree or another render to the heart muscle the effects, inherent of all antiarrhythmics four classes besides the slow potassium channels it, i.e., blocks the rapid Na⁺- transmembrane ionic channels (1 class), it possesses the β- adrenoblocking activity (II class) and the properties of the antagonists of the ions Ca²⁺ (IV class).

At present in the clinical practice of amiodarone is considered as highly effective antiarrhythmic of medicines, effective practically with any form of tachyarrythmias.

However, amiodarone is characteristic the sufficiently wide spectrum of side effects (hypo-or hyperthyroidism, interstitial pulmonary fibrosis and / or alveolar pneumonitis, visual disturbances, arrhythmogenic, etc.), which is in many respects caused by the presence in its chemical structure of iodine atoms and by the special features of its pharmacokinetics, in particular by the ability to be accumulated (to be cumulated) in different organs and tissues of organism. At present many arrhythmologs consider that amiodarone should be assigned when other antiarrhythmic medicines they prove to be ineffective, i.e., for treating resistance arrhythmias.

Sotalol (sin.: sotalex) just as amiodarone, is not “true” antiarrhythmic III class, since it possesses the still and sufficiently expressed β- adrenoblocking activity. In the clinical practice sotalol use from the same indications, as amiodarone, i.e., for treating of different ventricular and supraventricular tachyarrythmias, and also preventive maintenance of sudden coronary death in patients with the sharp myocardial infarction, but on the effectiveness it is somewhat inferior to amiodarone. At the same time the spectrum of the side-line action of sotalol is insignificant and caused in essence by its β- adrenoblocking properties (bradycardia, hypotonia, headache, bronchospasm so forth); therefore in the clinical practice sotalol is at present used sufficiently widely.

Are in recent years in the wide clinical practice inculcated so-called “true” antiarrhythmics of the III class, for example the preparation of ibutilide, whose antiarrhythmic action is connected with their ability to block transmembrane potassium channels and to thus lengthen the plateau of action potential. In the present stage “true” antiarrhythmics of the III class in the clinical practice they use predominantly for treating the supraventricular disturbances of cardiac rhythm.