Theophylline for Treatment of Bradyarrhythmias: When Is it Indicated?
Theophylline is a methylated xanthine which exerts several pharmacological actions of therapeutic interest. It stimulates the central nervous system, acts on the kidney to produce diuresis, stimulates cardiac muscle and relaxes smooth muscles, notably bronchial muscles. Moreover, the drug exerts positive chronotropic and dromotropic action. In fact at therapeutic plasma concentrations, theophylline produces a modest increase in sinus rate in normal individuals . An improvement in sinus node (SN) function and in atrioventricular (AV) nodal conduction has been reported after both intravenous and oral administration of the drug [2–4]. There are several mechanisms by which theophylline might exert positive chronotropic and dromotropic action; however, several observations suggest that the primary action of theophylline at therapeutic concentrations is blockade of adenosine receptors . Adenosine has been shown to slow sinus rate and depress AV nodal conduction in laboratory animals and in humans. Theophylline antagonizes the negative chronotropic and dromotropic action of adenosine by blocking extracellular adenosine receptors . Clinical studies have shown that oral theophylline can be efficacious in the treatment of symptomatic sick sinus syndrome (SSS) [2, 6–9] and of atrial fibrillation (AF) with a slow ventricular response [10, 11].
KeywordsAtrial Fibrillation Sinus Rate Permanent Pacemaker Sick Sinus Syndrome Sinus Node Dysfunction
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