Antiarrhythmics of the second group: β-adrenoblockers

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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.

Antiarrhythmic medicines of the II class

At the basis of the antiarrhythmic action of β- adrenoblockers (Atenolol (sin.: Tenormin), acebutolol, propranolol (inderal) and other) lies their ability to suppress arrhythmogenic action on the heart of catecholamines - noradrenaline and adrenaline. This effect is achieved via the blockade of the β₁- adrenoreceptors, located on the cellular membrane both of the conducting, and contracting cardiomyocytes.

The basic electrophysiological effects of β- adrenoblockers appear at the level of sinoatrial and atrioventricular units, and also ectopic drivers of rhythm.

The medicines of this group slow down the rhythmical (pacemaker) activity of sinoatrial unit due to the oppression of its capability for the spontaneous diastolic depolarization, i.e., of the decrease of its automatism and, therefore, the frequency of the heart contractions. In the atrioventricular unit the β- adrenoblockers slow down conducting and lengthen effective refractory period. The basic electrophysiological properties of the antiarrhythmic medicines of the II class are given in the table.

Preparations from the group of β- adrenoblockers do not exert a substantial influence on the rate of conducting pulse on the pathologically unchanged (functioning in the physiological regime) atria and the ventricles of heart, but under the conditions of sharp ischemia of myocardium β- adrenoblockers increase the threshold of the fibrillation of ventricles and at present are considered as some of the most effective medicines for the preventive maintenance of sudden coronary death in this category of patients. Besides this the β- adrenoblockers are effective in the preventive maintenance of arrhythmias of the type of reentry, which appear in the myocardium of the ventricles of heart under the conditions of ischemia of myocardium.

At the therapeutic medium doses the β- adrenoblockers do not exert a substantial influence on the transmembrane ion currents. At the same time at the high doses some β- adrenoblockers, for example acebutolol and inderal, possess the ability to suppress the rapid entering Na⁺- current they, i.e., manifest the membrane stabilizing activity.

Arrhythmogenic action in β- adrenoblockers is observed sufficiently rarely, but in the case of applying the inadequate doses is possible the development of sharp bradycardia, ventricular bigamy (form of the disturbances of rhythm, with which extrasystole it follows each normal heart contraction), paroxysmal ventricular tachycardia.

At the therapeutic doses the β- adrenoblockers do not exert a substantial influence on EKG, but in certain cases against the background their application is possible lengthening segment PQ.

Table. Characteristic of the antiarrhythmic medicines of the II class

In the clinical practice the β- adrenoblockers use for treating of supraventricular tachycardia and extrasystole, and also for the preventive maintenance of the fibrillation of the ventricles of heart in patients with the sharp myocardial infarction.

It is necessary to remember that besides the antiarrhythmic action the β- adrenoblockers possess also the expressed anti-ischemic and hypotensive action; therefore they can be assigned to patients, whose disturbances of the rhythm of heart are developed against the background by coronary heart disease and/or arterial hypertonia.

Antiarrhythmics of the second group are used for treatment of paroxysmal tachycardia, paroxysm of atrial fibrillation