Anterior vs. posterior position of dispersive patch during radiofrequency catheter ablation: insights from in silico modelling.

AIMS: To test the hypothesis that the dispersive patch (DP) location does not significantly affect the current distribution around the catheter tip during radiofrequency catheter ablation (RFCA) but may affect lesions size through differences in impedance due to factors far from the catheter tip. METHODS: An in silico model of RFCA in the posterior left atrium and anterior right ventricle was created using anatomic measurements from patient thoracic computed tomography scans and tested the effect of anterior vs. posterior DP locations on baseline impedance, myocardial power delivery, radiofrequency current path, and predicted lesion size. RESULTS: For posterior left atrium ablation, the baseline impedance, total current delivered, current distribution, and proportion of power delivered to the myocardium were all similar with both anterior and posterior DP locations, resulting in similar RFCA lesion sizes (< 0.2 mm difference). For anterior right ventricular (RV) ablation, an anterior DP location resulted in slightly higher proportion of power delivered to the myocardium and lower baseline impedance leading to slightly larger RFCA lesions (0.6 mm deeper and 0.8 mm wider). CONCLUSIONS: An anterior vs. posterior DP location will not meaningfully affect RFCA for posterior left atrial ablation, and the slightly larger lesions predicted with anterior DP location for anterior RV ablation are of unclear clinical significance.

Limitations of Baseline Impedance, Impedance Drop and Current for Radiofrequency Catheter Ablation Monitoring: Insights from In silico Modeling.

Background: Baseline impedance, radiofrequency current, and impedance drop during radiofrequency catheter ablation are thought to predict effective lesion formation. However, quantifying the contributions of local versus remote impedances provides insights into the limitations of indices using those parameters. Methods: An in silico model of left atrial radiofrequency catheter ablation was used based on human thoracic measurements and solved for (1) initial impedance (Z), (2) percentage of radiofrequency power delivered to the myocardium and blood (3) total radiofrequency current, (4) impedance drop during heating, and (5) lesion size after a 25 W−30 s ablation. Remote impedance was modeled by varying the mixing ratio between skeletal muscle and fat. Local impedance was modeled by varying insertion depth of the electrode (ID). Results: Increasing the remote impedance led to increased baseline impedance, lower system current delivery, and reduced lesion size. For ID = 0.5 mm, Z ranged from 115 to 132 Ω when fat percentage varied from 20 to 80%, resulting in a decrease in the RF current from 472 to 347 mA and a slight decrease in lesion size from 5.6 to 5.1 mm in depth, and from 9.2 to 8.0 mm in maximum width. In contrast, increasing the local impedance led to lower system current but larger lesions. For a 50% fat−muscle mixture, Z ranged from 118 to 138 Ω when ID varied from 0.3 to 1.9 mm, resulting in a decrease in the RF current from 463 to 443 mA and an increase in lesion size, from 5.2 up to 7.5 mm in depth, and from 8.4 up to 11.6 mm in maximum width. In cases of nearly identical Z but different contributions of local and remote impedance, markedly different lesions sizes were observed despite only small differences in RF current. Impedance drop better predicted lesion size (R2 > 0.93) than RF current (R2 < 0.1). Conclusions: Identical baseline impedances and observed RF currents can lead to markedly different lesion sizes with different relative contributions of local and remote impedances to the electrical circuit. These results provide mechanistic insights into the advantage of measuring local impedance and identifies potential limitations of indices incorporating baseline impedance or current to predict lesion quality.