Home Health Care How pulse-field ablation can transform the treatment of atrial fibrillation

How pulse-field ablation can transform the treatment of atrial fibrillation

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Given that we are in the midst of the full-scale emergence of Pulsed Field Ablation (PFA) within the world of clinical cardiac electrophysiology, it’s imperative that PFA’s place within the discipline, including its primary advantages – both scientific and practical – be discussed. PFA can be used in several different ways, but its most valuable benefits are best illustrated through catheter ablation of atrial fibrillation (AF), and it’s important for it to be put in context.

First, AF is a big problem, impacting more than 30 million new patients globally each year. Second, AF is a solvable problem, with catheter ablation considered by many to be the most effective treatment. Third, AF ablation has its own problem, with 500,000 cases annually and a less-than-ideal safety profile. Thermal ablation – things like radiofrequency (RF), laser, ultrasound, microwave and cryoablation – impact tissues that get hot or cold enough to die. This can include nearby structures or tissues outside the heart, resulting in rare, unintentional complications. And it’s here where PFA is substantially different.

The mode of PFA injury is metabolic. It interferes with the critical metabolic functions keeping cells alive. The strong electric fields generated during PFA cause cell membranes to open, a process called electroporation. Temporary membrane failure places incredible stress on the metabolic machinery of the cell. Once the electric field collapses, cell membranes quickly reseal, and the cell can potentially go on with its normal activity. Heart tissue in and around a PFA lesion has observable blood vessels, nerves, and endothelium, all seemingly untouched while the targeted cardiac myocytes are gone.

The practical benefit from the preservation of tissue structure and blood supply is rapid tissue healing – typically resolving in 2-3 weeks. In contrast, RF ablation takes 4-6 weeks to heal with regrowth of blood supply, rebuilding of tissue factors and prolonged inflammation. Because myocytes are exquisitely sensitive to the mode of PFA injury in comparison to most other tissue types in the body, the implication is that we can more safely ablate heart tissue next to structures like the esophagus, phrenic nerve, lungs and blood vessels. It’s important to recognize that this favorable serendipity is just biology and not some special tunable feature of a PFA waveform.

I like to say PFA is easy. At a minimum, all that is required is a defibrillator and a diagnostic catheter. However, a nuanced and practical PFA technology requires more work. Contemporary PFA technologies in development utilize short bursts of kilovolt-level microsecond or nanosecond pulses delivered to target tissue through one or more electrodes. The delivery devices have some variation: flowers, baskets, rings, and rods. The current waveform and delivery strategies have wide-ranging variability. I expect the entire industry will eventually converge on a similar PFA recipe that makes sense for most cardiac ablation applications. I think we will have met success when PFA becomes boring, invisible to the operator so we can focus on treating patients. After all, PFA is just an alternative method for creating therapeutic scars in the heart.

The cornerstone of AF ablation is anatomic pulmonary vein isolation (PVI), and changing the energy source is different. The single-shot PVI devices, mimicking cryoballoon workflow, appear to be winning as the emerging clinical strategy. Most of the market leaders in our field are committing hundreds of millions of dollars to their own single-shot PFA tools. Recent data shows more than 90% single-procedure success with PVI. The second strategy involves tools that can be implemented into the more traditional point-by-point approach found with RF ablation catheter workflows. Here, linear lesions are created by ablating sequentially to either encircle a target vein or create any variety of lesions that are possible with a traditional RF catheter.

As the field of cardiac PFA evolves, there are likely to be a wide range of treatment strategies that can be optimized for each intended use. The variables for PFA waveform development are substantially more complex than traditional RF applications. These include electrode geometry, peak voltage, pulse duration, pulse repetition, pulse repetition pattern and/or phase of pulse. Understanding the target tissue physiology becomes critical to success as tissue cell size, shape, orientation in the field, cell membrane constitution, cellular energetics, PH, extracellular environment and temperature can all impact the results. The underlying complexity and variety of dosing strategies makes it almost impossible to directly compare results from different catheter-waveform treatment strategies. That said, PFA can be equally effective using different waveform structures and catheter configurations.

The key to PFA’s true value may lie in how the technology lends itself to more individualized treatment strategies and integration into contemporary 3D mapping applications. PFA lesion volume and contours follow well-defined and predictable electromagnetic rules, unlike RF ablation, where heat-transfer is substantially more complex to forecast. Because the PFA field is more predictable, physicians may be able to plan the procedures with greater confidence and tailor therapy to ablate only target tissue while protecting heart tissue not involved in the arrhythmia. Powerful mapping technologies can now visualize global activation patterns in complex arrhythmias to reveal fundamental electrophysiologic properties in heart disease. We’ve long appreciated that heterogeneous conduction abnormalities over diseased tissue exists, but it’s often hard or impractical to measure outside of research laboratories.

Technology has evolved to the point where we can measure functional electrophysiology. Constellations of previously unseen patterns and characteristics are emerging that show increasing promise in our fight to understand complex arrhythmias. There are technologies that can analyze multiple wavefronts of chamber activation and identify zones in the heart that could promote maintenance of cardiac arrhythmias like atrial flutter or AF. It is innovations like these where I see the need for a point-by-point ablation technology that creates predictable lesions. These are exciting times, like Galileo pointing his telescope to the heavens for the first time. There is a future where 3D electroanatomic maps of any arrhythmia can be quickly created, and treatment strategies can be planned based on individualized knowledge. This is where integration with PFA technologies may have a significant advantage in delivering tailored treatment with dramatically improved reliability and workflow.

Photo: Narongrit Doungmanee

 

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