High-resolution minielectrode mapping of the cavotricuspid isthmus: quantitative substrate characterisation and correlation with ablation requirements in the Zero MAGIC randomised trial

Background

High-resolution (HR) electroanatomical mapping with minielectrode (ME) catheters enables precise identification of discrete conduction bundles within the cavotricuspid isthmus (CTI). Quantitative assessment of this substrate may help predict ablation requirements and guide a more individualised strategy for typical atrial flutter.

Methods

In the ongoing randomised Zero MAGIC trial comparing ME-based maximum-voltage-guided (MVG) with standard linear CTI ablation, detailed HR mapping was performed in all MVG procedures using a large-tip 8-mm catheter with integrated MEs and a 15-segment CTI subdivision. High-voltage areas (HVA) were defined as ≥ 70 % of the individual maximum bipolar voltage. Dominant HVA area was defined as the percentage of CTI mapping points (ME) belonging to the largest contiguous ≥70% MV cluster (dominant conduction channel) over all valid CTI mapping points. The number of ME-defined conduction channels (MiFiCH Nch) and the proportion of CTI surface occupied by the dominant HVA (MiFiCH %HVA) were quantified and correlated with radiofrequency (RF) duration, cumulative energy, and number of RF applications required to achieve bidirectional CTI block.

Results

Mapping data were available for 37 MVG patients. ME signals displayed higher peak voltages than conventional bipolar recordings (6.0 ± 2.0 mV vs 4.7 ± 2.1 mV, p < 0.01).

Each patient showed 1.5 ± 0.6 conduction channels (range 1–3).

Correlations between substrate complexity and ablation requirements are summarised in the Table.

Patients exhibiting multiple discrete conduction bundles required longer RF delivery and higher energy to achieve CTI block, whereas those with a single dominant channel showed lower ablation burden despite similar acute success.

Conclusion

Quantitative HR-ME mapping provides detailed characterisation of CTI conduction anatomy and correlates meaningfully with ablation effort. Increased bundle number and reduced dominance of a single HVA predict higher RF requirements. These findings support HR-based substrate quantification as a promising tool for procedure planning and complexity prediction in typical atrial flutter ablation.