ALTERATIONS OF HEART-RATE AND OF HEART-RATE-VARIABILITY AFTER RADIOFREQUENCY CATHETER ABLATION OF SUPRAVENTRICULAR TACHYCARDIA - DELINEATION OF PARASYMPATHETIC PATHWAYS IN THE HUMAN HEART

Background. Persistent inappropriate sinus tachycardia has been report ed as a complication after radiofrequency (RF) ablation of the fast at rioventricular (AV) nodal pathway. The purpose of this study was to ev aluate the prevalence of this complication and its mechanism using hea rt rate variability analysis. Methods and Results. Time and frequency domain analysis of heart rate was performed in the electrophysiology l aboratory immediately before and immediately after RF ablation in 64 p atients with supraventricular tachycardia. Ablation targets in these 6 4 patients included the fast AV nodal pathway (n=3), the slow AV nodal pathway (n=14), a posteroseptal accessory pathway (n=23), and a left lateral accessory pathway (n=24). A control group of 21 patients under going diagnostic study but not ablation underwent identical analysis i mmediately before and at the conclusion of their procedure. Patients u ndergoing ablation also had time and frequency domain analysis perform ed on ambulatory 24-hour Holter tapes recorded before ablation and at 1 day, 1 month, and 6 months after ablation. Compared with preablation values, time domain analysis immediately after ablation revealed a si gnificant increase in mean heart rate and significant reductions in he art rate variability expressed as SD, MSSD, and PNN50 in patients unde rgoing AV nodal modification or posteroseptal accessory pathway ablati on. Frequency domain analysis revealed marked attenuation of high freq uency (0.15 to 0.40 Hz) components, indicating parasympathetic denerva tion. These acute changes were not seen after ablation of left lateral accessory pathways or after diagnostic study without ablation. Time a nd frequency domain analysis of 24-hour ambulatory Holter monitors per formed serially after ablation revealed resolution of abnormalities of heart rate and of heart rate variability 1 to 6 months after ablation , with reappearance of the high frequency parasympathetic component su ggestive of reinnervation. Conclusions. RF ablation in the anterior, m id, and posterior regions of the low interatrial septum may disrupt pr eganglionic or postganglionic parasympathetic fibers located in these regions that are destined to innervate the sinus node. Such fibers bec ome more scarce along the left AV groove with increasing distance from the posteroseptal space. Parasympathetic denervation may be one mecha nism for persistent inappropriate sinus tachycardia after RF ablation.