Electrophysiologic effects of propranolol on sinus node function in patients with sinus node dysfunction.

Abstract

SUMMARY The electrophysiologic effects of intravenously administered propranolol (0.1 mg/kg) on three parameters of sinus node function were examined in ten symptomatic patients with sinus node dysfunction. The patients ranged in age from 26 to 79 years. Symptoms ranged from fatigue to frank syncope. Sinoatrial (SA) block and sinus pauses were observed in one patient; sinus pauses alone were observed in three patients. Five (5/10) patients had intraatrial block; three (3/10) patients had atrioventricular block; four (4/10) patients had an intraventricular conduction disturbance. At the time of electrophysiologic study, two patients had a control spontaneous sinus cycle length that exceeded 1000 msec. Following propranolol, the mean spontaneous cycle length increased by 17.4% THE BRADYARRHYTHMIAS that occur in patients with sinus node dysfunction are thought to reflect disturbances of sinus node automaticity and/or sinoatrial conduction.' The normal interactions between the parasympathetic and sympathetic nervous systems modulate the spontaneous heart rate.' Catecholamines exert a positive chronotropic effect on the sinus node and have also been shown to accelerate conduction in Purkinje fibers with abnormal conduction.4' 6 If catecholamines can also shorten sinoatrial conduction time that is prolonged, then the magnitude of the disturbance(s) of sinus node automaticity and/or sinoatrial conduction could not only be determined by the extent and nature of the cellular disturbance but also by the amount of catecholamines acting at their receptor sites in cardiac cells. Hence the accelerative and restorative effects of catecholamines on sinus node automaticity and sinoatrial conduction may play an important role in determining the magnitude of the electrophysiologic disturbance(s) in patients with sinus node dysfunction. Conversely, a #-adrenergic receptor blocking agent might have marked effects on sinus node automaticity and sinoatrial conduction in patients with sinus node dysfunction. This report examines the electrophysiologic effects of propranolol on three parameters of sinus node function in patients with sinus node dysfunction. MethodsElectrophysiologic study was performed in ten patients with symptomatic sinus node dysfunction. The patients' ages ranged from 26 to 79 years. Informed consent was obtained in all patients.Patients were evaluated prior to electrophysiologic study. History, physical examination and routine laboratory data From the

Electrophysiologic effects of intravenous xamoterol in patients with sinus node dysfunction

“…Beta-adrenoceptor blocking drugs without agonist activity induce sinus bradycardia, depress sinus node automaticity, and lengthen the sinoatrial conduction time in normals [5,22,30]; they also prolong AV nodal conduction and extend the refractory periods of the AV node [30]. Similar effects on the sinus node electrophysiologic parameters were observed in patients with sinus node dysfunction [4][5][6].…”

“…Because of their tendency to aggyavate sinus bradycardia, to depress sinus node automaticity, and to enhance sinus node entrance block in patients with sinus node dysfunction, beta-blocking agents should be used with caution in such patients [4][5][6]. However, a beta blocker that does not aggravate (or even ameliorate) the sinus node electrophysiologic characteristics of patients suffering from sinus node disease would theoretically represent a desirable therapeutic alternative, especially in cases of the bradyeardia-tachycardia syndrome.…”

Effects of propafenone on sinus node function in the rabbit heart

“…At the concentrations of propafenone in this study, which are comparable to clinically relevant concentrations, this would be equivalent to an approximate concentration of propranolol of 20 ng/rnL. This is a concentration that has been shown to have significant effects on sinus node function in man (Strauss et al 1976). However, in an in vitro preparation of atrial tissue, the beta-blocking effect would be anticipated to be less pronounced in view of the minimal sympathetic tone that would exist in such a preparation and this observation has been supported by our own observations on the effects of propranolol in this preparation (Ken 1989).…”

The sinus node electrogram in patients with and without sick sinus syndrome: techniques and correlation between directly measured and indirectly estimated sinoatrial conduction time.

“…For every premature atrial stimulus delivered, the spontaneous sinus cycles (A1A1), the test cycle (A1A2) and the return cycle (A2A3) were measured. The response of the premature stimuli in the zone of sinus node reset (i.e., the latter third of zone 11) patients (64%): in 10 of 23 (43%) by method 1 and in 18 of 21 (86%) by method 2. Although sinus node electrograms could be recorded in an additional two patients, because of the difficulties associated with the exact identification of the onset of the upstroke slope, these two patients were excluded.…”