Background: Atrial tachycardia (AT) can originate from the proximal coronary sinus (CS). However, detailed electrophysiologic characteristics of the tachycardia are not available.
Objectives: We describe the electrophysiologic characteristics, response to adenosine 5'-triphosphate, and results of radiofrequency ablation of AT with the earliest activation in the proximal CS.
Methods: In 7 of 54 patients (age 57 +/- 18 years) with nonmacroreentrant "focal" AT undergoing electrophysiologic study and radiofrequency ablation, the earliest atrial activation site was located in the proximal CS.
Results: The earliest activation site was inside the CS 13 +/- 3 mm from the ostium. The AT could be induced and terminated by atrial extrastimuli or burst pacing. In all patients, the AT was also terminated by a very small dose of adenosine 5'-triphosphate (4.2 +/- 1.1 mg). Rapid ventricular pacing during the tachycardia produced ventriculoatrial dissociation. Radiofrequency ablation directed at the earliest atrial activation site was effective in only three patients (group A). In the remaining four patients (group B), after the radiofrequency energy deliveries, the earliest activation site shifted to an adjacent site with a small increase in the cycle length. Three group B patients underwent successful ablation in the slow pathway region. No recurrence was observed over a follow-up period of 22 +/- 5 months.
Conclusion: AT with earliest activation in the proximal CS is sensitive to a small dose of adenosine 5'-triphosphate. In some patients, radiofrequency applications in the slow pathway region are effective even if the local activation is not early.