Theophylline is commonly used in the treatment of bronchial obstruction. In experimental studies the drug showed positive chronotropic effects.1,2 During long-term therapy, oral theophylline suppressed symptoms in young patients with paroxysmal bradyarrhythmias3; moreover, it diminished the frequency and severity of bradycardia in newborn infants with apnea-bradycardia.4 In some electrophysiologic studies intravenous theophylline showed improvement in sinus nodal function.3,5 The mechanism by which the drug exerts positive chronotropic action is controversial. One study suggests that the primary effect of theophylline at therapeutic concentrations is antagonism of adenosine receptors.6 An increase in plasma catecholamines in both normal subjects and patients with chronic obstructive pulmonary disease has also been shown after intravenous administration5; however, this investigation, to our knowledge, has not been carried out after oral therapy. The present study evaluates the effects of oral theophylline on sinus nodal function in patients with sinus bradycardia, and defines whether drug-induced improvement of sinus nodal function could be related to direct effects (or effects mediated by nonautonomic receptors) or by autonomic actions. © 1990.
