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 reported as a complication after radiofrequency (RF) ablation of the fast atrioventricular (AV) nodal pathway. The purpose of this study was to evaluate the prevalence of this complication and its mechanism using heart rate variability analysis. Methods and Results. Time and frequency domain analysis of heart rate was performed in the electrophysiology laboratory immediately before and immediately after RF ablation in 64 patients with supraventricular tachycardia. Ablation targets in these 64 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 undergoing diagnostic study but not ablation underwent identical analysis immediately before and at the conclusion of their procedure. Patients undergoing ablation also had time and frequency domain analysis performed 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 significant increase in mean heart rate and significant reductions in heart rate variability expressed as SD, MSSD, and PNN50 in patients undergoing AV nodal modification or posteroseptal accessory pathway ablation. Frequency domain analysis revealed marked attenuation of high frequency (0.15 to 0.40 Hz) components, indicating parasympathetic denervation. These acute changes were not seen after ablation of left lateral accessory pathways or after diagnostic study without ablation. Time and frequency domain analysis of 24-hour ambulatory Holter monitors performed 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 suggestive of reinnervation. Conclusions. RF ablation in the anterior, mid, and posterior regions of the low interatrial septum may disrupt preganglionic or postganglionic parasympathetic fibers located in these regions that are destined to innervate the sinus node. Such fibers become more scarce along the left AV groove with increasing distance from the posteroseptal space. Parasympathetic denervation may be one mechanism for persistent inappropriate sinus tachycardia after RF ablation.