Beta-blocking agents act by antagonizing the effects of catecholamines on the heart. Such levels of catecholamines may be appropriate in critically ill patients either endogenously or as a consequence of inotropic support for the failing myocardium. Therefore such agents must be used cautiously in critically ill patients. Conventional agents such as propranolol, atenolol, or metoprolol have comparatively long half-lives, and adverse hemodynamic effects from administration may persist. Beta-blocking agents are particularly useful in arrhythmias with a significant sympathetic component such as is seen in some supraventricular arrhythmias and ventricular tachycardia arising from the right ventricular outflow tract. Beta-blocking agents may also be useful in the acute control of ventricular rate in atrial fibrillation.
The recent introduction of esmolol, an ultra-short-acting b-blocker with complete elimination within 30 min by blood esterases, enables transient use of b-blockade in situations such as postoperative hypertension and where b-blockade may be beneficial but hemodynamic effect is uncertain. The usual dosage range is 50 to 400 g/min.
Xamoterol is a b-blocker with a high degree of intrinsic sympathomimetic activity. It may have a role as an adjuvant agent in patients with refractory ventricular arrhythmias who do not settle on amiodarone alone.
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