Insights into the electrophysiology of accessory pathway-mediated arrhythmias provided by the catheter ablation experience: "learning while burning, part III"

Shortening of conduction time over arborized atrioventricular accessory pathway with Mahaim fibers physiology just before interruption during radiofrequency ablation

A 21-year-old woman had paroxysmal wide QRS tachycardia with a left bundle branch block configuration and a retrograde conducted P wave just behind the QRS complex. An electrophysiological study revealed antidromic atrioventricular tachycardia involving an atrioventricular connection with decremental conduction as the anterograde limb and normal atrioventricular node as the retrograde limb. During constant pacing from the high right atrium (HRA) at the cycle length (CL) of 600 ms, the QRS configurations were not identical to those during the wide QRS tachycardia or constant pacing at the CL of less than 500 ms. The process by which this arborized atrioventricular accessory pathway with the Mahaim fibers physiology was interrupted by radiofrequency catheter ablation is described. Radiofrequency energy was delivered to the site recording a Mahaim potential at the tricuspid annulus during constant pacing from the HRA at the CL of 429 ms. The stimulus-QRS interval gradually shortened as it reached the power plateau without changing the preexcited QRS configuration. Shortening of the conduction time over the Mahiam pathway might have resulted in changing of the propagation from a slow to fast conduction zone or acceleration in response to thermal effect in a node-like structure on the atrial insertion site.

[Analysis of local electrograms and characteristics of the ablation procedure in left-sided accessory pathways that required five or more pulses of radiofrequency]

INTRODUCTION AND OBJECTIVES

Radiofrequency ablation of left sided accessory pathways requires multiple pulses in some patients due to different factors such as inadequate mapping, inappropriate tissue electrode contact and particular anatomic factors. However these characteristics have not been specifically analyzed.

METHODS

We have studied a prospective ablative series of 65 consecutive patients with left-sided pathways submitted to radiofrequency ablation by a simplified technique. In every application point, we analyzed the electrogram features, application point, impedance, potency and temperature.

RESULTS

52 patients (80%) required less than 5 radiofrequency pulses (group A) and 13 (20%) required > or = than 5 pulses (group B). The presence of a suggestive potential accessory pathway in local electrogram was similar in both groups and there were no differences in the local A-V or V-A intervals. However, in patients with pre-excitation the Delta-V interval was shorter in group A than in group B (8 ms vs 15 ms; p < 0.001). Furthermore, the impedance observed from the ablation point in group A was lower (108 +/- 12 vs 121 +/- 22 ohms; p < 0.001), and the maximum watts required to reach the predetermined temperature was higher in group A (42 +/- 16 vs 31 +/- 18 watts; p < 0.001). Final success of the procedure was 100%.

CONCLUSIONS

Patients requiring more than 5 radiofrequency pulses had electrograms and tissue contact equal or better than those requiring less than 5 pulses. This suggests that difficulties encountered in some procedures can be due to anatomical factors rather than inaccurate mapping or insufficient tissue contact.