Safety and efficacy aspects of pulsed field ablation catheters as a function of electrode proximity to blood and energy delivery method

Figures

• 

  Figure 1. The 3 catheter designs selected for comparison. Top row: A balloon (in situ) with surface electrodes, a spherical design (shown with a cutoff) using flexible circuit splines with back-insulated electrodes, and a circular decapolar design with ring electrodes. Bottom row: Balloon deployed at antrum of left pulmonary veins, and circular catheter at the same position. The spline electrodes (deployment not shown) were also at same position.

• 

  Figure 2. Four methods of energizing electrodes. The first 2 are unipolar methods, with the negative electrode being a pad on back of the patient. In the multi-unipolar method, all electrodes are energized positively with simultaneous current flow from all electrodes to the back electrode. In the sequential unipolar method, each electrode is energized in turn, one at a time, while others float. For interlaced bipolar methods, there is no electrode on the patient’s back. The standard interlaced method has electrodes with alternating polarities. The wide interlaced method has nonenergized floating electrodes between alternating polarity ones; 2 sequential steps are used.

• 

  Figure 3. Partial view of computed tomography–derived anatomy as modeled. Left panel: Posterior view with segment of the descending aorta (red), part of esophagus (yellow), airways and left lung (blue), left atrium (brown), and pulmonary trunk (magenta). The venae cavae, right atrium, and coronary sinus are shown in purple. Right panel: Superior view of the same, with more organs removed. The left atrial wall (gray) is 2.5 mm thick. A 6-mm-wide target at the left pulmonary vein antrum is just visible anterior to the aorta and esophagus (see text and Figure 4).

• 

  Figure 4. Target used for measurement of efficacy of lesion transmurality. A posterior, rectangular segment of left atrial myocardium is used. It is 6 mm wide and, like the rest of the atrial wall, 2.5 mm thick. Two of the catheters compared are shown here positioned against the target. Efficacy is defined as the percentage of this target’s volume that has more than 600 V/cm field strength. 100% represents a completely transmural lesion.

• 

  Figure 5. Pulsed field ablation efficacy and safety aspects of two catheter designs: circular catheter (left), and balloon catheter (right). Right superior view of left atrium, aorta, and esophagus. With the circular catheter (left), current densities of 10 to 100 Amps/sq cm are subtantially present in atrial blood. This is less efficacious and favors bubble generation and consequent embolic risk.

• 

  Figure 6. Efficacy vs current for the catheter designs and energizing methods that were compared. Efficacy is the percent of the target volume that is treated with more than 600 V/cm, with 100% representing a completely transmural lesion. In general, one can see that the balloon and flex-circuit splined catheters have the best efficacy, while the circular catheters require much higher currents to achieve similar transmural lesions. This makes sense if one considers that current is shunted via atrial blood as electrodes are closer to it. Seq = sequential.

• 

  Figure 7. Aortic and esophageal safety vs current for the catheter designs and energizing methods compared. The curves show the volume of aorta and esophagus subject to more than 600 V/cm (ie, electroporated, damaged). A lower electroporated volume is safer. The circular catheter with an interlaced energy method is the safest, while multi-unipolar systems were the worst. (Safety from electrochemical processes is not depicted here; see Figure 9.) Seq = sequential.

• 

  Figure 8. Qualitative comparison of electroporation safety outside the heart: electric fields on the left lung, and segments of the aorta and esophagus. The balloon catheter (left) is energized in multi-unipolar fashion with 2 A at each electrode, whereas the circular catheter (right) is energized in an interlaced manner with 10 A at each electrode. The scale is logarithmic, so that a brown color corresponds to log (600 V/cm) = 4.8, a qualitative electroporation safety limit. The balloon system has large regions in orange-red, since current is flowing from all electrodes towards the back of the patient. The circular catheter, with an interlaced delivery, is much better at keeping high fields confined near the target, even with the higher current.

• 

  Figure 9. Emboli-related electrochemical safety, in terms of current density to achieve 90% transmurality. Less current density means a lower rate of bubble generation, and greater safety. Relative to catheter designs that have electrodes with low exposure to blood, the circular catheter has about 4–5 times higher bubble generation, as expected, given its electrode proximity to blood electrolytes. Seq = sequential.