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Proper localization of the anatomical target during ablation of the accessory pathways (AP) and the ability to detect clear AP potentials on the ablation catheter are crucial for successful AP ablation. We report a case of recurring AP conduction that was finally eliminated using a novel ablation catheter equipped with high-resolution mini-electrodes. Smaller and closer electrodes result in high mapping resolution with less signal averaging and cancellation effects. Owing to improved sensitivity, the new catheter seems effective in detecting fragmented and high frequency signals, thus allowing more effective radiofrequency application and improving ablation success.
A 35-year-old male patient with Wolff–Parkinson–White syndrome presented for radiofrequency (RF) ablation. The patient had already undergone two ablation procedures. In both procedures, acute success was achieved; however, on the first day after ablation, the conduction over the AP recurred. A third ablation was attempted using an 8 mm-tip ablation catheter (IntellaTip MiF XP, Boston Scientific, Marlborough, Massachusetts) equipped with 3 mini-electrodes (MEs) at the distal tip for electrogram (EGM) recording and pacing. In this catheter, bipolar signals can be recorded between the three 0.8 mm-wide electrodes that are equally spaced 2.5 mm center-to-center. We introduced a long guide wire through the right femoral vein, up to the superior vena cava, and through this wire, we introduced an 8-Fr sheath. The guide wire was removed to allow the introduction of the Brockenbrough needle. We punctured the interatrial septum at the level of the oval foramen guided only by radioscopy and contrast injection. After a 5000 U.I. heparin infusion, we introduced the ablation catheter through the sheath to reach the lateral part of the mitral annulus (3 o’clock position in the left anterior oblique projection). The ablation target was the site of the earliest ventricular activation with fusion between the local atrial (A) and ventricular (V) EGMs. Careful mapping of the entire mitral annulus did not reveal a local EGM with such a pattern. The shorter AV interval was 45 ms, with a clear isoelectric line between A- and V-EGMs (Fig. 1A). At this site, fractionated atrial signals fused with ventricular EGM were revealed on MEs only. We applied RF energy of up to 70 W for 60 s (Fig. 1B), thereby abolishing the conduction over the AP. At the 3 months follow-up visit, the patient remained free from any sign of pre-excitation or other symptoms.
Our case showed that the use of a catheter with small and closely spaced electrodes allowed us to accurately identify and achieve the anatomical target during AP ablation. EGM criteria to guide attempts at RF ablation of overt AP include the presence of EGM stability, an accessory AV connection potential, a continuous electrical activity, the absolute and relative amplitudes of the atrial and ventricular components of the local EGM, interval between the atrial and ventricular components of the local EGM, and timing of the atrial and/or ventricular components of the local EGM relative to the QRS complex . In our case, using the conventional bipolar mapping, we were not able to find an EGM ablation site matching any of these characteristics, finding only a relatively short AV interval with a clear isoelectric line between A- and V-EGMs. Conversely, the signals collected with the mini-electrodes showed a fragmented atrial signal (as result of the previous failed ablations) fused to an earlier ventricular activation signal during pre-excitation. This suggested that the catheter tip was correctly positioned at the AP ventricular insertion site. This concern was particularly important because, with standard technology, we were able to discern only a more proximal atrial signal (due to healthier tissue) separated from the ventricular EGM by an isoelectric line, suggesting that the ablator tip was far away from the AP ventricular insertion site. According to several preliminary reports, signals from these electrodes seem to be potentially useful for better defining the arrhythmic substrate targeted for ablation, facilitating the identification of viable tissue , . In conclusion, the use of a catheter with small and closely spaced electrodes ensures higher mapping resolution and less averaging and cancellation of signals. This results in improved sensitivity for detection of fragmented and high frequency signals, possibly improving ablation success.
No external funding was obtained for this project.
F. M. and M. M. are Boston Scientific employees. No other conflicts of interest exist.
Appendix ASupplementary data associated with this article can be found in the online version at 10.1016/j.joa.2016.12.003.