13.01.4 Class II

Class II agents are β-adrenoceptor antagonists. As discussed previously, a whole range of things can cause activation of the sympathetic nervous system; myocardial infarction, stress, exercise, pheochromocytoma (adrenaline secreting tumours), and hyperthyroidism (Figure 13.4). With sympathetic nervous system (SNS) activation, there is the release of noradrenaline and adrenaline and the activation of cardiac β-adrenoceptors, which can initiate or make worse tachyarrhythmias. b₁-adrenoceptor antagonism leads to decreased effects of the sympathetic nervous system (SNS) on the heart, and a reduction in tachyarrhythmias (Figure 13.4).

Figure 13.4 Mechanisms of β-adrenoceptor arrhythmias (Copyright QUT, Sheila Doggrell)

Of the β-adrenoceptor blockers, sotalol is the one that is often preferred in cardiac tachyarrhthymias. Sotalol is a non-selective β-adrenoceptor blocker that is used in the treatment of tachyarrhythmias, where an overactive sympathetic nervous system is implicated. Sotalol has two isomers – the L-isomer (L-sotalol) is the non-selective β-adrenoceptor blocker

Esmolol is an ultra-short acting β-adrenoceptor blocker used intravenously to treat atrial flutter and atrial fibrillation associated with operations. When atrial flutter or fibrillation occurs during an operation, esmolol can be administered intravenously, to bring the heart back to normal sinus rhythm, and then the infusion can be stopped and the esmolol is rapidly metabolised.