Medtronic Cardiac Ablation Solutions VP of Research and Business Development Tim Laske discusses the Sphere-9 dual-energy ablation and mapping catheter’s design and unique features.
Medtronic’s Affera Sphere-9 mapping and ablation catheter is designed to provide both radiofrequency ablation and PFA to treat AFib. [Photo courtesy of Medtronic]
Medtronic acquired the Sphere-9 catheter for pulsed field ablation (PFA), radiofrequency (RF) ablation and cardiac mapping in its 2022 purchase of device developer Affera for up to $1 billion. In 2023, Medtronic’s PulseSelect became the first PFA system approved by the FDA.
Previously: Affera founder Doron Harlev and Medtronic’s Rebecca Seidel discuss Affera’s technology
“The Sphere-9 is a tool that can be used for pulmonary vein isolation (PVI), but it’s more of a general utility catheter used to create a number of lesions outside of the pulmonary veins,” Tim Laske, VP of research and business development for Medtronic Cardiac Ablation Solutions, said in an interview with Medical Design & Outsourcing. “The approach for treating patients with atrial fibrillation really breaks down to two forms from a high-level perspective: PVI and PVI plus.”
“Some of it is philosophical, where certain physicians will always start with PVI only and find out which patients recur. And that’s most common in paroxysmal patients,” Laske continued. “For persistent [AFib] patients, some will do PVI only and watch and wait. Others feel they need to do more, generally referred to as PVI plus … [which means] pulmonary vein isolation plus whatever they deem is appropriate. It could be lines, it could be ablating and isolating the posterior wall, etc. PVI plus is more common for persistent atrial fibrillation where there are likely triggers coming from locations other than just the pulmonary veins and or substrate that is developed over time due to fibrosis or a persistent disease.”
The Sphere-9 focal catheter’s 9 mm lattice tip is smaller than the Sphere-360 single-shot PFA catheter, which has an expandable diameter of up to 34 mm. For PVI plus, cardiologists need a smaller catheter that can deliver more targeted, focal energy versus single-shot ablation (from the Sphere-360 or PulseSelect catheters) that delivers energy around the entirety of the pulmonary vein without the cardiologist having to rotate the catheter.
“The goal, of course, is to ablate the minimal amount of tissue and get the best outcome,” Laske said. “Pulsed field ablation is very fast and if you’re working with a large tool, there’s potential to ablate non-targeted tissue. Although we believe it’s very tissue selective using our particular waveforms, you want to be cautious in what you’re targeting and what collateral structures might be adjacent to it.”
Previously: What’s so special about pulsed field ablation? Medtronic EVP Sean Salmon explains
Similarities between the Sphere-9 and Sphere-360 cardiac PFA catheters
Medtronic’s Affera Sphere-360 pulsed field ablation catheter is adjustable, allowing it to take different shapes inside a patient. [Illustration courtesy of Medtronic]
The two Affera PFA catheters have another feature in common that sets them apart from PulseSelect and other ablation catheters that use multiple gold electrodes to deliver energy. The Sphere-9 and Sphere-360 catheters both use their nitinol lattice as a single spherical electrode to deliver energy for ablation.
Sphere-360 only delivers pulsed field energy to kill cardiac myocytes, while the Sphere-9’s nitinol cage delivers both RF and pulsed field energy for ablation.
“We’re uniquely using nitinol as an electrode where it’s commonly used as just a structural element,” Laske said.
“The Affera catheters deliver biphasic energy just like PulseSelect, but they’re a unipolar energy modality,” he later said. “And the Sphere-9 is a single, large electrode that’s delivering to a patch typically on the back of the patient. We’re controlling the field. There’s not a risk of crosstalk between that electrode in the back because they’re at a safe distance.”
He declined to discuss how that global nitinol electrode is designed in too much detail. But it introduced new challenges for engineers to overcome, given that PFA systems deliver significantly more voltage and more current than traditional cardiac ablation technologies.
“They’re high-voltage, very fast waveforms,” Laske said. “You have to look at means of ensuring you’re not getting polarization on your electrodes, that they’re biostable, you’re not having any material-related issues associated with voltage, and that you’re creating the field that you desire and that it’s predictable.”
Medtronic’s Affera Sphere-9 is designed with an expandable nitinol cage that acts as a single, spherical electrode to deliver both radiofrequency and pulsed field energy for ablation. The catheter’s nine smaller electrodes are isolated for mapping, pacing and other features. [Photo courtesy of Medtronic]
“[They] perform the function of electrical sensing for creating activation maps and voltage maps, they have embedded thermocouples for temperature-controlled RF and for monitoring pulse field, they have a contact-impedance-based function where you can tell is there a shifting impedance which gives you a surrogate for contact and they also can be paced through,” Laske said.
Just like the Affera Sphere-360 catheter, the Sphere-9’s nitinol lattice collapses down for catheter delivery through an 8.5-Fr introducer, which is the typical size for focal ablation.
“We feel that’s an advantage,” Laske said of the two Affera ablation catheters’ size. “A smaller introduction size [may] result in fewer complications at the introduction site, and it’s a size and form factor that physicians are generally more familiar with.”
The Sphere-9 and Sphere-360 nitinol lattices are also compliant, meaning they flex when forced against heart tissue, adjusting to the pulmonary vein’s shape for better contact and more effective ablation of cardiac myocytes.
“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,” Laske 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.”
When it is released from the introducer, the Sphere-9 expands into a sphere, while the Sphere-360 is adjustable for different shapes. The original form factor of the nitinol used to make both the Sphere-360 and Sphere-9 lattice tips is confidential, Laske said.
“What I can say is it requires laser cutting and electropolishing, as is common in use of nitinol,” he said.
PFA therapy works by creating a voltage field, and as you move the catheter’s electrodes and its field closer to the tissue, more of the field envelops the heart tissue that a cardiologist is trying to ablate. Medtronic’s PFA portfolio does not measure contact force, with Laske saying the company’s catheter testing on PulseSelect did not find force had an impact on lesion creation.
Medtronic Cardiac Ablation Solutions VP of Research and Business Development Tim Laske [Photo courtesy of Medtronic]
In a Medtronic news release announcing Sphere-9 safety and efficacy data as of May 2024, Dr. Vivek Reddy, director of cardiac arrhythmia services for the Mount Sinai Health System in New York City, called it “groundbreaking news for the electrophysiology community that could change the treatment workflow.”
“We’ve been waiting for one catheter that can be used for every arrhythmia, and these randomized results from centers that routinely use conventional point-by-point ablation indicate Affera Sphere-9 will be worth the wait with all its innovation and the rapid learning curve of the system,” Reddy said.
Read more from our interview with Tim Laske: Medtronic’s Sphere-360 pulsed field ablation catheter design has some new tricks and How Medtronic designed the PulseSelect pulsed field ablation system for AFib
This post was originally published in May 2024 and updated in October 2024 when Sphere-9 won FDA approval.
