4.4 | The feasibility of MI block
In the Marshall-PLAN study by Derval et al,15 it was
demonstrated that achieving a complete and durable MI block is crucial
for improving atrial tachyarrhythmia-free survival in PeAF ablation.
However, obtaining a complete MI block for RFCA is a challenge due to
anatomical complexities such as tissue thickness, local blood flow, and
epicardial musculature connections, including CS sleeves or a Marshall
bundle.16 Additional techniques, such as ablation
inside the CS and ethanol infusion into the vein of Marshall, are
usually necessary. PFA is a nonthermal ablation method. The main
challenge of MI block for PFA is tissue thickness and epicardial
connections, excluding the temperature weakening of the blood flow.
A recent study proved MI block with PFA was successfully achieved in a
high percentage (100%), but 2 patients developed severe coronary
vasospasm of the circumflex artery.12 In our cohort,
MI block was achieved in 81.3% of cases. The different success rates
might be due to the different PFA catheter electrode configurations and
energy waveforms from different manufacturers’ systems. We hypothesized
that increasing electrode number, catheter contact surface area,
application number, and energy output could improve the acute success
rate of MI block, but bring about a higher risk of severe coronary
vasospasm or severe haemolysis which was not observed in our study.
Further studies with more cases are required to adjust the energy
parameters and catheter electrode configuration to optimize efficacy and
minimize procedural risks. Can focal PFA catheter ablation inside the CS
damage the epicardial connections and bring about risks of coronary
vasospasm, still needs further investigation. Both our study and the
study by Baptiste Davong et al, PFA achieved a high success rate of
acute MI block without ethanol infusion into the vein of Marshall or
epicardial ablation in CS. Therefore, PFA could be a good alternative to
obtain an MI block when RFCA fails, especially in cases without the vein
of Marshal or the vein of Marshall cannot be catheterized. Thus, PFA
could be recommended for perimitral left atrial flutter cases.