Tripolar versus bipolar ablation: insights into lesion growth and geometry using a novel ablation approach for therapy-refractory ventricular arrhythmias

Figures

• 

  Fig. 1. Upper panel: Schematic illustration of the experimental setup containing a saline-filled container, cross-sectioned porcine myocardium, two ablation catheters, a radiofrequency (RF)-generator, a thermometer, a dispersive return electrode for tripolar ablation, an infusion pump, saline infusion and a video camera. Bipolar and tripolar ablation setups were used. Lower panel: Experimental setups for unipolar, bipolar and tripolar ablation. For bipolar ablation, two ablation catheters were placed on opposing sites of the tissue cross-sections. Tripolar ablation was performed by adding a dispersive return electrode to the bipolar setup. Parts of the figure were created with biorender.com.

• 

  Fig. 2. Left panel: Comparison of lesion geometry created by bipolar and tripolar ablation in myocardial cross-section. Right panel: Schematic illustration of lesion parameters measurements and lesion volume calculation. The following parameters were measured for each lesion at both the active and the passive catheter sites: lesion depth (distance from point (A) to (A’)), lesion diameter (distance from point (B) to (B’)), depth from the surface to the diameter (distance from point (A) to (M)) and diameter at myocardial surface (distance from point (C) to (C’)) were measured. The overlapping diameter of the opposing lesion is illustrated as distance from point (D) to (D’) (‘kissing lesion’). Lesion volume was calculated using these geometric parameters by modeling the lesion as the sum of a truncated cone and a spherical shell, or a spherical segment when lesion overlap was present.

• 

  Fig. 3. The mean relative transmurality (transmurality in relation to the initial myocardial thickness at the onset of radiofrequency ablation, measured as the distance between the active and return catheters) of bipolar ablation compared to tripolar ablation. Bipolar ablation demonstrates a shorter time to transmurality and tripolar ablation approach requires more time to reach transmurality. Overall, the thermal propagation is not linear and slower in TA than in BA. Every data point represents mean value (including all power settings) with error bars indicating 95% confidence intervals. The solid lines represent GAM-based regression curves (non-parametric) to illustrate temporal progression. RF = radiofrequency.

• 

  Fig. 4. Mean maximal diameter at the active (blue) and return (blue) catheter before and after reaching transmurality. Every data point represents mean value with error bars indicating 95% confidence intervals. The solid lines represent GAM-based regression curves (non-parametric) to illustrate temporal progression.

• 

  Fig. 5. Mean impedance during RF application in bipolar (red) and tripolar ablation (blue). The use of an additional dispersive return electrode in tripolar ablation results in an initially lower mean impedance compared to bipolar ablation. Notably, the impedance level in bipolar ablation does not reach the same low levels observed in tripolar ablation during the RF application Every data point represents mean value with error bars indicating 95% confidence intervals. The solid lines represent GAM-based regression curves (non-parametric) to illustrate temporal progression. RF = radiofrequency.

• 

  Fig. 6. Scaled representation of lesions generated by bipolar and tripolar ablation at different power settings at the time transmurality was achieved. Overall lesion size varies due to differences in myocardial thickness and ablation duration until transmurality was achieved. Bipolar ablation produced more evenly distributed lesion depths, whereas tripolar ablation resulted in a deeper and wider lesion at the active catheter. W: watt.

• 

  Fig. 7. Mean lesion volume at the active catheter (red) and return catheter (blue) during bipolar ablation (left, a and c) and tripolar ablation (right, b and d). In the upper panels (a, b), the x-axis shows time to radiofrequency (RF) onset (absolute RF application duration). In the lower panels (c, d), time is aligned to transmurality (transmural lesion at timepoint 0, black dotted line, negative values indicate time before transmurality). Every data point represents mean value with error bars indicating 95% confidence intervals. The solid lines represent GAM-based regression curves (non-parametric) to illustrate temporal progression. RF = radiofrequency.