Novel method for visualization of the papillary muscle using Ensite mapping system: intracardiac echography-guided tagging surface mapping

Background

Reconstructing the geometry of the papillary muscle (PPM) using the EnSite mapping system is technically challenging. Consequently, PPM electrical activity is often represented by the ellipsoidal geometry of the left ventricle (LV), which can lead to electro-anatomical discordance. Although point density exclusion electroanatomic mapping (PDX) has been described as a method for constructing PPM geometry with EnSite, it is time-consuming and yields variable results due to the difficulty of reliably tracking the complex motion of the high-density Grid mapping catheter (HD Grid) along the PPM surface. We developed a novel technique that employs intracardiac echocardiography (ICE) to delineate PPM geometry within the LV and project corresponding electrograms onto this structure (ICE-guided tagging surface mapping, ITS).

Methods

We enrolled patients referred for catheter ablation of left-sided cardiac arrhythmias and accessed the LV via an anterograde approach. ITS mapping was initiated by constructing the LV geometry in the vicinity of the posteromedial PPM (PM-PM) using an TactiFlex ablation catheter. When the catheter was visualized by ICE at the PM-PM surface, anatomical tags were placed (Figure 1A). A PM-PM shell was subsequently generated from the cluster of tags (Figure 1B). Electrical data were then acquired using the HD Grid catheter and projected onto the PM-PM geometry (Figure 1C).

Retrospectively, PDX mapping was also performed in the same patients (Figure 2), and procedure time, PM-PM volume, and peak frequency of the modeled PM-PM were compared between ITS and PDX. ITS procedure time was defined as the interval from the LV mapping with the ablation catheter to the projection of HD Grid potentials onto the reconstructed PM-PM shell. PDX procedure time was from the LV mapping with the HD Grid catheter to the projection of HD Grid potentials onto the HD Grid–derived PM-PM.

Results

PM-PM reconstruction was performed in seven patients without structural heart disease. The median number of ICE-identified PM-PM tags in ITS mapping was 6 (interquartile range: 4–8). There were no significant differences between ITS and PDX in PM-PM volume or the number of HD Grid points projected onto the geometry {1.88 (1.39–2.66) vs. 1.18 (0.49–2.36) cm³; p = 0.20, and 126.5 (67.0–275.2) vs. 179.5 (84.5–278.7) points; p = 0.69, respectively}. The peak frequency at the PM-PM apex was 234 (108.5–369.7) Hz with ITS and 221 (101.2–345.0) Hz with PDX (p = 0.73). Procedure time was significantly shorter with ITS than with PDX {224 (209.2–362.5) vs. 518 (433–599.7) seconds; p = 0.0092}.

Conclusion

The ITS method enables more rapid PPM reconstruction than conventional PDX while achieving comparable geometric and electrophysiological quality. Furthermore, because ITS is based on ICE-derived anatomy, it is expected to provide superior reproducibility. This technique may represent a valuable tool for PPM-targeted ablation.