Can “tissue tickness” guide our ablation strategy?
Schillaci et al. have tested the KODEX-EPD system in patients with cavo-tricuspid isthmus-dependent atrial flutter, showing that the tickest atrial wall was pretty close to tricuspid valve (3.6±0.5 mm vs 2.4±0.3 mm, p<0.001) and a trend towards a progressive decrease of atrial wall thickness was observed moving the mapping catheter from the tricuspid valve to the inferior vena cava. This should suggest that more RF power needs to be transferred deeply in the atrial portion close to the valve as compared to the area towards the inferior vena cava. They claim to have used power between 30 and 40 Watts all along the line with a “point-by-point” RF delivering approach, reaching an acute bidirectional block in each patient. It would have been conceivable that RF delivering would be at higher power close to the tricuspid valve as to achieve a deeper lesion (and hopefully a durable one). Unfortunately, they do not describe any significant change in RF delivering while they are ablating. In fact, it is well known that missing the atrial portion close to the tricuspid valve is one of the reasons of resumption of conduction through the cavo-tricuspid isthmus. Moreover, the possibility to measure the substrate thickness before RF delivery could change the way to perform RF ablation, allowing a tailored energy delivering thus increasing the efficiency of the ablation procedures  and potentially reducing the risk of complications.
The dream of “an eye through”By measuring the myocardial tissue thickness in any part of each cardiac chamber, we might envision to titrate the transfer of energy in relation to specific tissue characterization. This could be particularly crucial in the atria, where the wall thickness is reduced compared to the ventricles or close to the valves. Tailoring the power can increase the safety profile and reduce the likelihood of complications. None of the currently available 3D non-fluoroscopic mapping systems provides detailed information about the tissue thickness; the incorporation of a function (i.e. Wall Viewer) capable to yield thickness measurement could greatly improve our ability to effectively produce “durable” lesions and, thus improve the long-term clinical outcome of ablation procedures. Furthermore, one of potential advantages of the application of “tissue thickness measurement” over the cardiac MRI, is the real time information provided that can guide the strategy of ablation based on the “ ablating by measuring” conceptFuture applicationsTheoretically, the analysis of tissue characterization in terms of wall thickness can be of value in the ventricles as well; just imaging to investigate not only the scar extension in ischemic or non-ischemic ventricular arrhythmias but also viewing “in depth” the pathological area could guide the ablation strategy, accordingly. Needless to say that the lesion created through different energy sources (RF, Cryo, Laser, PFA, etc) and the ablative techniques employed (impedance-driven, irrigated-tip electrode, high power-short duration) can have different and variable impact on effectiveness and durability of the lesion itself also in relation to the tissue thickness. Schillaci et al. have had the privilege to test the novel KODEX-EPD function showing the potential capability of the system to analyze the myocardial wall thickness and provide crucial information during RF energy delivering. They need to be congratulated for having paved a new avenue in the field and now we hope other EP “runners” could join the “ultramarathon” of ablation and produce brilliant results. References
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