My field of electrophysiology is abuzz with excitement over the new technology of pulsed field ablation (PFA). It dominated this year's heart rhythm meetings, and it dominates my private electrophysiologist chat groups. My Google alert for "AF ablation" most often includes notices on PFA and the expansion of the atrial fibrillation ablation market.
Yet, the excitement does not match the empirical data.
Despite having strong brains, electrophysiologists adopt new things as if we were emotional shoppers. Our neighbor buys a sports car and we think we need the same car. Left atrial appendage occlusion and subcutaneous defibrillators were past examples.
The most recent example of soft thinking (especially in the United States) is the enthusiasm and early adoption of first-generation PFA systems for the treatment of AF.
Readers of cardiac news (including some of my patients) might think PFA has solved the AF puzzle. It has not.
A true breakthrough in AF would be to find its cause. PFA is simply another way to destroy (ablate) cardiac myocytes. PFA uses electrical energy (think shocks) to create pores in the cell membranes of myocytes. It's delivered through various types of catheters.
The main theoretical advantage of PFA is cardioselectivity, which is possible because myocytes have lower thresholds for irreversible electroporation than surrounding tissues. The dose of electrical energy that ablates cardiac tissue does not affect surrounding tissues. Cardioselectivity decreases the chance of the most feared complication of standard AF ablation, thermal damage to the esophagus, which is often fatal. The esophagus lies immediately behind the posterior wall of the left atrium and can be inadvertently injured during thermal ablation.
The challenge in assessing this potential advantage is that thermal esophageal damage is, thankfully, exceedingly rare. Its incidence is in the range of 1 in 10,000 AF ablations. But it might be even lower than that in contemporary practice, because knowledge of esophageal injury has led to innovations that probably have reduced its incidence even further.
Proponents of PFA would rightly point to the fact that not having to worry about esophageal injury allows operators to add posterior wall ablation to the normal pulmonary vein isolation lesion set. This ability, they would argue, is likely to improve AF ablation outcomes. The problem is that the strongest and most recent trial of posterior wall isolation (with radiofrequency ablation) did not show better outcomes. A more recent observational analysis also showed no benefit to posterior wall isolation (using PFA) over pulmonary vein isolation alone.
What About PFA Efficacy?
I've long spoken and written about the lack of progress in AF ablation. In 1998, the first report on ablation of AF showed a 62% arrhythmia-free rate. Two decades later, in the carefully chosen labs treating patients in the CABANA trial, arrhythmia-free rates after AF ablation remain unchanged. We have improved our speed and ability to isolate pulmonary veins, but this has not increased our success in eliminating AF. The reason, I believe, is that we have made little to no progress in understanding the pathophysiology of AF.
The FDA regulatory trial called ADVENT randomly assigned more than 600 patients to thermal ablation or PFA, and the primary endpoint of ablation success was nearly identical. Single-center studies, observational registries, and single-arm studies have all shown similar efficacy of PFA and thermal ablation.
Proponents of PFA might argue that these early studies used first-generation PFA systems, and iteration will lead to better efficacy. Perhaps, but we've had 20 years of iteration of thermal ablation, and its efficacy has not budged.
What About PFA Safety?
In the ADVENT randomized trial, safety results were similar, though the one death, due to cardiac perforation and tamponade, occurred in the PFA arm. In the MANIFEST-17K multinational survey of PFA ablation, safety events were in the range reported with thermal ablation. PFA still involves placing catheters in the heart, and complications such as tamponade, stroke, and vascular damage occur.
The large MANIFEST-17K survey also exposed two PFA-specific complications: coronary artery spasm, which can occur when PFA is delivered close to coronary arteries; and hemolysis-related kidney failure — severe enough to require dialysis in five patients. Supporters of PFA speculate that hemolysis occurs because electrical energy within the atrium can shred red blood cells. Their solution is to strive for good contact and use hydration. The irony of this latter fix is that one of the best advances in thermal ablation has been catheters that deliver less fluid and less need for diuresis after the procedure.
No PFA study has shown a decreased incidence of thermal damage to the esophagus with PFA ablation. Of course, this is because it is such a low-incidence event.
One of my concerns with PFA is brain safety. PFA creates substantial microbubbles in the left atrium, which can then travel north to the brain. In a small series from ADVENT, three patients had brain lesions after PFA vs none with thermal ablation. PFA proponents wrote that brain safety was important to study, but few patients have been systematically studied with brain MRI scans. Asymptomatic brain lesions have been noted after many arterial procedures. The clinical significance of these is not known. As a new technology, and one that creates substantial microbubbles in the left atrium, I agree with the PFA proponents that brain safety should be thoroughly studied — before widespread adoption.
What About Speed and Cost?
Observational studies from European labs report fast procedure times. I have seen PFA procedures in Europe; they're fast — typically under an hour. A standard thermal ablation takes me about 60-70 minutes.
I am not sure that US operators can duplicate European procedural times. In the ADVENT regulatory trial, the mean procedure time was 105 minutes and that was in experienced US centers. While this still represents early experience with PFA, the culture of US AF ablation entails far more mapping and extra catheters than I have seen used in European labs.
Cost is a major issue. It's hard to sort out exact costs in the United States, but a PFA catheter costs approximately threefold more than a standard ablation catheter. A recent study from Liverpool, United Kingdom, found that PFA ablation was faster but more expensive than standard thermal ablation due to higher PFA equipment prices. For better or worse, US patients are not directly affected by the higher procedural costs. But the fact remains that PFA adds more costs to the healthcare system.
What Drives the Enthusiasm for First-Generation PFA?
So why all the enthusiasm? It's surely not the empirical data. Evidence thus far shows no obvious advantage in safety or efficacy. European use of PFA does seem to reduce procedure time. But in many EP labs in the United States, the rate-limiting step for AF ablation is not time in the lab but having enough staff to turn rooms around.
The main factor driving early acceptance of PFA relates to basic human nature. It is the fear of missing out. Marketing works on consumers, and it surely works on doctors. Companies that make PFA systems sponsor key opinion leaders to discuss PFA. These companies have beautiful booths in the expo of our meetings; they host dinners and talks. When a hospital in a city does PFA, the other hospitals feel the urge to keep up. It's hard to be a Top Person in EP and not be a PFA user.
One of my favorite comments came from a key opinion leader. He told me that he advised his administration to buy a PFA system, promote that they have it, and keep it in the closet until better systems are released.
Iteration in the medical device field is tricky. There are negatives to being too harsh on first-generation systems. Early cardiac resynchronization tools, for instance, were horrible. Now CRT is transformative in selected patients with heart failure.
It's possible (but not certain) that electrical ablative therapy will iterate and surpass thermal ablation in the future. Maybe.
But for now, the enthusiasm for PFA far outstrips its evidence. Until better evidence emerges, I will be a slow adopter. And I hope that our field gathers evidence before widespread adoption makes it impossible to do proper studies.
John Mandrola practices cardiac electrophysiology in Louisville, Kentucky, and is a writer and podcaster for Medscape. He espouses a conservative approach to medical practice. He participates in clinical research and writes often about the state of medical evidence.
COMMENTARY
Pulsed Field Ablation for AF: Are US Electrophysiologists Too Easily Impressed?
John M. Mandrola, MD
DISCLOSURES
| July 17, 2024My field of electrophysiology is abuzz with excitement over the new technology of pulsed field ablation (PFA). It dominated this year's heart rhythm meetings, and it dominates my private electrophysiologist chat groups. My Google alert for "AF ablation" most often includes notices on PFA and the expansion of the atrial fibrillation ablation market.
Yet, the excitement does not match the empirical data.
Despite having strong brains, electrophysiologists adopt new things as if we were emotional shoppers. Our neighbor buys a sports car and we think we need the same car. Left atrial appendage occlusion and subcutaneous defibrillators were past examples.
The most recent example of soft thinking (especially in the United States) is the enthusiasm and early adoption of first-generation PFA systems for the treatment of AF.
Readers of cardiac news (including some of my patients) might think PFA has solved the AF puzzle. It has not.
A true breakthrough in AF would be to find its cause. PFA is simply another way to destroy (ablate) cardiac myocytes. PFA uses electrical energy (think shocks) to create pores in the cell membranes of myocytes. It's delivered through various types of catheters.
The main theoretical advantage of PFA is cardioselectivity, which is possible because myocytes have lower thresholds for irreversible electroporation than surrounding tissues. The dose of electrical energy that ablates cardiac tissue does not affect surrounding tissues. Cardioselectivity decreases the chance of the most feared complication of standard AF ablation, thermal damage to the esophagus, which is often fatal. The esophagus lies immediately behind the posterior wall of the left atrium and can be inadvertently injured during thermal ablation.
The challenge in assessing this potential advantage is that thermal esophageal damage is, thankfully, exceedingly rare. Its incidence is in the range of 1 in 10,000 AF ablations. But it might be even lower than that in contemporary practice, because knowledge of esophageal injury has led to innovations that probably have reduced its incidence even further.
Proponents of PFA would rightly point to the fact that not having to worry about esophageal injury allows operators to add posterior wall ablation to the normal pulmonary vein isolation lesion set. This ability, they would argue, is likely to improve AF ablation outcomes. The problem is that the strongest and most recent trial of posterior wall isolation (with radiofrequency ablation) did not show better outcomes. A more recent observational analysis also showed no benefit to posterior wall isolation (using PFA) over pulmonary vein isolation alone.
What About PFA Efficacy?
I've long spoken and written about the lack of progress in AF ablation. In 1998, the first report on ablation of AF showed a 62% arrhythmia-free rate. Two decades later, in the carefully chosen labs treating patients in the CABANA trial, arrhythmia-free rates after AF ablation remain unchanged. We have improved our speed and ability to isolate pulmonary veins, but this has not increased our success in eliminating AF. The reason, I believe, is that we have made little to no progress in understanding the pathophysiology of AF.
The FDA regulatory trial called ADVENT randomly assigned more than 600 patients to thermal ablation or PFA, and the primary endpoint of ablation success was nearly identical. Single-center studies, observational registries, and single-arm studies have all shown similar efficacy of PFA and thermal ablation.
Proponents of PFA might argue that these early studies used first-generation PFA systems, and iteration will lead to better efficacy. Perhaps, but we've had 20 years of iteration of thermal ablation, and its efficacy has not budged.
What About PFA Safety?
In the ADVENT randomized trial, safety results were similar, though the one death, due to cardiac perforation and tamponade, occurred in the PFA arm. In the MANIFEST-17K multinational survey of PFA ablation, safety events were in the range reported with thermal ablation. PFA still involves placing catheters in the heart, and complications such as tamponade, stroke, and vascular damage occur.
The large MANIFEST-17K survey also exposed two PFA-specific complications: coronary artery spasm, which can occur when PFA is delivered close to coronary arteries; and hemolysis-related kidney failure — severe enough to require dialysis in five patients. Supporters of PFA speculate that hemolysis occurs because electrical energy within the atrium can shred red blood cells. Their solution is to strive for good contact and use hydration. The irony of this latter fix is that one of the best advances in thermal ablation has been catheters that deliver less fluid and less need for diuresis after the procedure.
No PFA study has shown a decreased incidence of thermal damage to the esophagus with PFA ablation. Of course, this is because it is such a low-incidence event.
One of my concerns with PFA is brain safety. PFA creates substantial microbubbles in the left atrium, which can then travel north to the brain. In a small series from ADVENT, three patients had brain lesions after PFA vs none with thermal ablation. PFA proponents wrote that brain safety was important to study, but few patients have been systematically studied with brain MRI scans. Asymptomatic brain lesions have been noted after many arterial procedures. The clinical significance of these is not known. As a new technology, and one that creates substantial microbubbles in the left atrium, I agree with the PFA proponents that brain safety should be thoroughly studied — before widespread adoption.
What About Speed and Cost?
Observational studies from European labs report fast procedure times. I have seen PFA procedures in Europe; they're fast — typically under an hour. A standard thermal ablation takes me about 60-70 minutes.
I am not sure that US operators can duplicate European procedural times. In the ADVENT regulatory trial, the mean procedure time was 105 minutes and that was in experienced US centers. While this still represents early experience with PFA, the culture of US AF ablation entails far more mapping and extra catheters than I have seen used in European labs.
Cost is a major issue. It's hard to sort out exact costs in the United States, but a PFA catheter costs approximately threefold more than a standard ablation catheter. A recent study from Liverpool, United Kingdom, found that PFA ablation was faster but more expensive than standard thermal ablation due to higher PFA equipment prices. For better or worse, US patients are not directly affected by the higher procedural costs. But the fact remains that PFA adds more costs to the healthcare system.
What Drives the Enthusiasm for First-Generation PFA?
So why all the enthusiasm? It's surely not the empirical data. Evidence thus far shows no obvious advantage in safety or efficacy. European use of PFA does seem to reduce procedure time. But in many EP labs in the United States, the rate-limiting step for AF ablation is not time in the lab but having enough staff to turn rooms around.
The main factor driving early acceptance of PFA relates to basic human nature. It is the fear of missing out. Marketing works on consumers, and it surely works on doctors. Companies that make PFA systems sponsor key opinion leaders to discuss PFA. These companies have beautiful booths in the expo of our meetings; they host dinners and talks. When a hospital in a city does PFA, the other hospitals feel the urge to keep up. It's hard to be a Top Person in EP and not be a PFA user.
One of my favorite comments came from a key opinion leader. He told me that he advised his administration to buy a PFA system, promote that they have it, and keep it in the closet until better systems are released.
Iteration in the medical device field is tricky. There are negatives to being too harsh on first-generation systems. Early cardiac resynchronization tools, for instance, were horrible. Now CRT is transformative in selected patients with heart failure.
It's possible (but not certain) that electrical ablative therapy will iterate and surpass thermal ablation in the future. Maybe.
But for now, the enthusiasm for PFA far outstrips its evidence. Until better evidence emerges, I will be a slow adopter. And I hope that our field gathers evidence before widespread adoption makes it impossible to do proper studies.
John Mandrola practices cardiac electrophysiology in Louisville, Kentucky, and is a writer and podcaster for Medscape. He espouses a conservative approach to medical practice. He participates in clinical research and writes often about the state of medical evidence.
Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
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