Experts from Medtech Big 100 device developers — Medtronic, Johnson & Johnson MedTech, Abbott and Boston Scientific — discuss the various shapes of their pulsed field ablation (PFA) catheters.
From flowers and loops to globes, baskets and balloons, there’s no standard shape for the pulsed field ablation (PFA) catheters coming out of Medtronic, Boston Scientific, Abbott and Johnson & Johnson MedTech’s Biosense Webster.
PFA’s tissue-selective energy kills cardiomyocytes (heart muscle cells) to block irregular signals that cause atrial fibrillation (AFib), but spares phrenic nerves and nerves in the esophagus.
These PFA catheter shapes offer unique abilities for cardiac ablation to treat AFib, said engineers and leaders at these companies — some of the world’s largest medical device manufacturers — in interviews with Medical Design & Outsourcing.
Medtronic PulseSelect
In late 2023, Medtronic’s PulseSelect became the first PFA system to win FDA approval for treating AFib. Medtronic tested other form factors — such as focal and linear catheters — before choosing the 25 mm loop shape for PulseSelect, said Tim Laske, VP of research and business development for Medtronic Cardiac Ablation Solutions.
“PulseSelect has nitinol superstructure, which allows it to compress down [for delivery] through a 10-Fr catheter, and then it’s deployed in a very predictable shape,” Laske said.
The catheter also “has a 20-degree forward cant that gives you an indication of when you’re in contact with a tissue,” he said. “Then as you make contact, it also biases toward all of the electrodes touching the tissue, not just the ones that are in contact.”
PulseSelect’s loop shape allows for single-shot ablation, which is the delivery of energy across multiple parts of the pulmonary vein for a procedure that can be simpler and faster.
Read more: How Medtronic designed the PulseSelect pulsed field ablation system for AFib
Medtronic is also advancing PFA catheters developed by Affera, which Medtronic bought in 2022.
Medtronic Affera Sphere-9 and Sphere 360
Affera’s Sphere-9 and Sphere-360 catheters both use their nitinol lattice as a single spherical electrode to deliver energy for ablation. When released from its introducer inside a patient’s heart, the Sphere-9 expands into a globe shape for focal ablation.
The larger Sphere-360, however, is a single-shot catheter that’s adjustable for different shapes. That includes a sphere, a linear configuration, a pancake shape for a maximum diameter of 34 mm, or anything in between.
The Affera catheters’ nitinol lattices are both compliant, meaning they flex when forced against heart tissue, adjusting to the pulmonary vein’s shape for better contact and more effective ablation, Laske said.
“Nitinol is superelastic, and depending on how you design the struts, you can have more or less stiffness associated with that. So we want a catheter that will give you good contact with the tissue,” he said. “If you apply additional force, it’ll tend to just flatten a bit — particularly true with the Sphere-9 — and adjust to the pulmonary vein’s shape. The compliance gives you a little more forgiveness in ensuring that you have good, robust contact across the entire surface you’re trying to ablate.”
The FDA has not yet authorized Affera’s PFA catheters for treating AFib, though the Sphere-9 device is under review.
Read more from our interview with Laske about the design and features of the Affera Sphere-9 and Sphere-360 catheters.
Boston Scientific Farapulse
Boston Scientific was the second PFA catheter manufacturer to win FDA approval with its Farapulse system.
The Farapulse system’s Farawave PFA catheter can adapt to individual patient anatomies with its variable basket and flower shapes.
The single-shot catheter’s shape is also important — along with the waveform — in creating the shape of the electric field for tissue selectivity to kill cardiomyocytes but not nerves, Boston Scientific SVP and Global Chief Medical Officer Dr. Ken Stein said.
“If you can create the right shape of an electrical field — that gets back to catheter design — and if you provide just the right amount of energy, and that gets to things like the waveform, then you can tune it in a way that is relatively selective for heart tissue,” he said.
Abbott Volt
Abbott designed its balloon-in-basket Volt PFA catheter to support the efficient deployment of energy into the heart tissue, using electrodes that only face outward and insulated nitinol splines that are flat, not round. It’s a hybrid catheter that can be used for both single-shot and focal ablation.
Abbott said the investigational catheter’s design improves the accuracy, quality and efficiency of ablation to minimize the number of applications needed to treat a patient. The balloon acts as an insulator for the blood inside the patient’s beating heart, reducing the incidence of hemolysis and thermal effects such as bubble formation.
The balloon also helps stabilize the basket inside the pulmonary vein, where the device’s round shape allows a physician to place the catheter at the ablation target site, apply energy, and rotate the device slightly to achieve a spline offset for a second energy application.
“We have data showing if you use a balloon versus a basket without the balloon it makes a difference [in] lesion depths by 20% to 30%,” said Dr. Christopher Piorkowski, the chief medical officer of Abbott’s electrophysiology division.
Abbott is testing the Volt system under an FDA investigational device exemption (IDE) and anticipates European approval in the form of a CE mark in 2025.
“We’ve invested heavily in our PFA portfolio, which you will start to see hit the market …. definitely next year,” Abbott CEO Robert Ford said in July.
Read more from our interview with Piorkowski: Abbott bets on balloons in pulsed field ablation battle
Johnson & Johnson MedTech Biosense Wester Varipulse
Biosense Webster went with a loop shape for its 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.
The pre-shaped Varipulse catheter is made of laser-cut nitinol, allowing it to curl into an adjustable, contractable loop to help ensure adequate tissue contact among varying cardiac anatomies, and making it easier to maneuver the catheter inside the cramped left atrium.
“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,” Biosense Webster Senior Director of Medical Affairs Tushar Sharma. “In terms of electrode spacing … 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.”
Biosense Webster won a CE mark for the Varipulse catheter in February 2024 and filed for FDA approval in March.
Read more from our interview with Sharma: High voltage in the heart: PFA catheter design tips from Biosense Webster
— Associate Editor Sean Whooley contributed to this report.