High voltage in the heart: PFA catheter design tips from Biosense Webster

Tushar Sharma at J&J Medtech’s Biosense Webster discusses pulsed-field ablation (PFA) catheter shapes, sensors, electrodes and device design tips.

Biosense Webster’s pulsed-field ablation (PFA) catheter design and development starts in the heart.

That’s where PFA treats atrial fibrillation (AFib) by killing cardiac cells to isolate errant heart signals and prevent them from triggering irregular heartbeats. PFA uses electric fields to permanently open holes in the walls of heart cells through a process called electroporation. PFA catheters need to create lesions through the entire thickness of the heart’s left atrium — which ranges from 2 mm to 6 mm — to completely isolate those irregular signals.

“For pulmonary vein isolation for the treatment of atrial fibrillation, we’re typically looking at a device that needs to give us 6 mm deep lesions on average,” said Tushar Sharma, senior director of medical affairs for Johnson & Johnson Medtech’s Biosense Webster.

Determining that target depth is the first step of developing a PFA catheter, he said, which informs how large to make the electrodes that will deliver the energy to the patient’s heart tissue.

“The reason you have to start from the size of the electrodes is because you need to know — based on the target depth — how much voltage we need, and you need to have the right electrode size to support that voltage,” Sharma said. “[Then] additional parameters like the pulse amplitude, frequency, the time between pulse application and how many pulses are being delivered.”

The Varipulse catheter — submitted for FDA approval in March 2024 — has 4 mm electrodes with an effective length of 3.5 mm, Sharma said. He declined to divulge the system’s voltage, citing the need to keep Biosense Webster’s proprietary recipe for PFA energy secret.

But he offered some detail on the role voltage plays in ensuring that the cellular electroporation is permanent, while limiting the potential for thermal damage.

Though PFA’s therapeutic effect is nonthermal, the delivery of high voltage through electrodes still introduces the potential for side effects from heat. That requires special consideration when designing the entire system, from the energy generator to the tips of the catheter.

“Everything that is needed to support high voltage, that basically cascades down to individual components,” Sharma said. “That is the biggest difference when it comes to pulsed-field versus radiofrequency — you need to have the infrastructure in your devices to support high voltage.”

PFA system designers manage the heat by limiting the voltage that their catheters will deliver, but also by spacing pulses out with enough time to avoid overheating.

“The biggest difference between thermal energies and pulsed-field ablation is that the mechanism by which we create a lesion is nonthermal. It is essentially increasing the permeability of the cell membranes, which allows the cell homeostasis to be affected, and eventually, the cells die,” Sharma said. “The key components that we look at from a pulse recipe perspective are voltage and electrode, and also the number of pulses and the number of bursts. You want to keep the pores open, and that is what is going to drive the durability. At the end of the day, the winning recipe is going to be sort of a combination of the right parameters on the pulse that allow us to get an irreversible effect, but then also, at the same time, the right catheter, the right generator and the right mapping system or the right imaging system that puts it all together.”

A single-electrode catheter will give a cardiologist more versatility for different patient anatomies and the ability to access different areas of the heart. A multi-electrode — or “single-shot” — catheter allows the physician to ablate more tissue at once for faster, less complicated procedures. Device developers are designing their single-shot PFA catheters with different shapes and features, including loops, lattice spheres, balloons, baskets and flowers.

Biosense Webster went with a loop shape for the Varipulse catheter — which can deliver single-shot therapy with all 10 electrodes, as well as more focused energy with just six electrodes— to combine the best features of both types.

“It gives you the efficiency of a single-shot device where you don’t have to make multiple dots to create a circle — you’re still creating a circle,” Sharma said. “But at the same time, it’s not limited to applying it in other areas of the heart, which might be some of the limitations of a flower configuration or a balloon configuration. In terms of electrode spacing, again, it comes down to the spacing between the electrodes — is it consistent, or is it changing? The loop-style catheter really allows us to keep that spacing consistent irrespective of the areas of the heart that we are applying the therapy to.”

Read more from this interview at Medical Design & Outsourcing.