[Acute electrophysiologic and echocardiographic changes induced by xamoterol in chronic chagasic patients with sinus node dysfunction].

PURPOSE: To evaluate xamoterol (Corwin)--a partial beta-adrenergic receptor agonist--in long-term chagasic patients with symptomatic sinus node dysfunction previously treated with permanent atrial pacemaker.

METHODS

Ten patients with permanent AAI pacing were studied. Initially, in spontaneous rhythm (sinus rhythm due to inhibition of the pacemaker) and under atrial pacing with rate of 60, 80 and 100ppm with temporary external programming of the pulse generator were evaluated. Basic heart rate, maximal sinus node recovery time and the point at which Wenckebach AV block was achieved were recorded. After that, echocardiographic evaluation was performed to analyze the left ventricular performance with ejection fraction calculation and the percentage of the fractional shortening during spontaneous rhythm and under atrial pacing with rate of 60, 80 and 100ppm. This protocol was repeated after 5mg of intravenous xamoterol.

RESULTS

Five men and 5 women (mean age of 46) were studied. Xamoterol increased the basic heart rate, the rate at which the Wenckebach AV block was achieved and shortened the maximal sinus node recovery time (statistically significant) suggesting a beta-adrenergic agonist action of the drug. Left ventricular performance showed significant improvement only when the values in sinus rhythm (during inhibition of the pulse generator) were compared. Under atrial pacing, left ventricular function was consistently improved in all patients but with no significance.

CONCLUSION

Xamoterol showed to be a beta-adrenergic receptors agonist in long-term chagasic patients with sinus node dysfunction at rest, when the simpatic tone was low, with evident action on the electrophysiologic parameters.