Centers of Excellence I Texas Cardiac Arrhythmia Institute I Austin, Texas
The evolution of RF technology to reduce complications and improve outcomes
Advancements in radiofrequency (RF) catheter ablation technology have been incremental over the past 30 years in efforts to improve safety, procedural efficiency and patient outcomes. While some newer technologies have gained a lot of attention in electrophysiology (EP) over the past several years, RF remains the solid frontline treatment.
The addition of tissue contact force sensing and irrigated catheter tips have been seen by physicians as major advancements and helped reduce the number of repeat ablation procedures due to reconnection from insufficient lesions. Irrigated catheter tips better control temperature for lesion creation and reduce complications caused by steam pops, or ablations penetrating into underlying tissues such as the esophagus and phrenic nerve. Fewer reconnections also means fewer repeat procedures.
The newest generation of RF ablation technology released in 2023 introduced new features that further improve RF. Some operators using it say it’s the pinnacle of RF technology to date. The QDOT MICRO™ catheter combines all the major advances over the past 20 years, plus new features such as micro electrodes and more accurate temperature sensors embedded in the tip. These help the operator visualize the tip with a window on the CARTO™ 3 mapping system to aid in reducing or eliminating fluoroscopy during procedures.
The thermocouples in the tip also improve safety and efficacy by avoiding steam pops and increasing physician confidence that they’re creating effective lesions faster. Thus, the catheter enables ablations at higher temperatures for shorter duration, creating shallower lesions and avoiding damage to underlying structures, such as the esophagus or the phrenic nerve. The system also uses less saline to cool the catheter tip leading to a reduction in fluid overload complications to patients.
“Every year, some company will come out and say that they've got some late and great thing and almost all of it ends up being nothing. But every five or six years, it will be something and we'll look at it and say, ‘OK, this is significant,’” says Rodney Horton, MD, director of the Texas Cardiac Arrhythmia Institute in Austin, Texas. “QDOT was one of those. The catheter would take signals that we would struggle to make go away and they would just melt away like butter. That is something that we had really never seen using radiofrequency prior to this technology.”
“Overall, it's clearly a superior technology in term of vision, quality, and efficiency.”
Andrea Natale, MD, Executive Medical Director, Texas Cardiac Arrhythmia Institute and National Medical Director, Cardiac Electrophysiology, HCA Healthcare
Horton was skeptical about the device at first, thinking it was just more hype about minor incremental changes. Not so. The new catheter combines all the previous RF advancements, he notes, but also improves control and gives the operator more information about the lesions they are creating.
“We had several iterations of improvement in ablation technology with open irrigation versus closed irrigation, and other ways of getting deeper, more transmural lesions,” he says. “This catheter took all the things that had been iterated in the past, and now enables us to measure direct tissue temperatures. It dramatically improved the efficacy and timing of these procedures as well as safety.”
The measurement of tissue temperature combined with contact force sensing also enhances the operator’s ability to perform zero-fluoro RF ablations, according to Horton. This adds an additional way to help visualize the procedure without using X-ray
Increasing efficacy through improved technical innovation
Innovations with open irrigated catheters, contact force sensing and temperature sensing have improved ablation procedure outcomes over the past decade. Refinements with the catheter have now increased safety and reduced the need for repeat procedures even further.
Better RF temperature monitoring prevents steam pops
A limitation of using RF energy within the heart is the composition of the blood surrounding that is 90% water and thus boils at 100 degrees Centigrade. RF temperatures around 100 degrees or more cause dangerous steam pops which can damage cardiac tissue and potentially cause serious complications. Both Horton and Natale agree there needs to be a careful balance between being safe while still being effective.
“We're always challenged if you give too much energy, then water pops and it boils,” Horton says. “But if you don't give enough energy, you're not really getting an effective lesion.”
Open, irrigated catheters have helped and as they’ve become more efficient with cooling, the number of complications from steam pops have dropped dramatically. This catheter takes this a step further with real-time measurement of direct tissue temperatures. A new window added to the CARTO(TM) 3 mapping system shows a temperature color-coded image of the catheter tip. The image shows how much energy is being transferred into the tissue and helps visualize the contact force being applied. The image also shows if temperature is uneven—indicating the tip is at an angle rather than the ideal 90-degree contact—so the operator has a better idea of the lesion quality.
“It gives me direct feedback using temperature signals,” Horton explains. “Basically, it's color coded as the temperature of the tissue reaches 45 degrees centigrade, which is devitalized tissue, and it turns red. It will go from blue, which is cold, to orange, to yellow to red. I actually follow it from a color standpoint. And so once it reaches the desired color, then I come off. My overall lesion time is a lot of times about seven or eight seconds, which is a lot shorter than what we would ordinarily use before. It gives me that feedback very quickly, and very visually that allows me to shorten the duration of the lesion because I don't want to ablate longer than I need to.”
Andrea Natale, MD, executive medical director the Texas Cardiac Arrythmia Institute and national medical director of cardiac electrophysiology for HCA Healthcare, also has altered his RF technique based on the temperature color feedback on the mapping system.
“I like to make sure that the temperature is red, which means 50 degrees for at least a good 10 seconds before I move,” he says. “It is one of the pieces of information that I like to have and I think it's very valuable. Besides, you can follow the direction of the catheter in three-dimensional geometry that can help you to really reduce the amount of fluoro that you need to do the entire procedure.”
QDOT also changed the way they control the power used, because the device drives the power automatically. The operator no longer sets the power based on what they think is appropriate. Instead, the device shows the tissue temperature so the operator knows when enough energy has been delivered.
High energy, short duration RF helps overcome esophagus and nerve damage
There’s a careful balancing act to create lesions deep enough in cardiac tissue to terminate arrhythmias, while not damaging healthy tissue or critical, underlying structures. Some areas around the heart are very thin with just a couple millimeters of tissue thickness. Ablations there can burn vital structures such as the esophagus or phrenic nerve and bring on very serious complications.
“If you don't ablate deep enough, it won't work,” Horton says. “. If you go too deep, then you could potentially have collateral damage.”
Natale says that in the past, the thin tissue area of the esophagus had a higher rate of reconnection because operators tended to move more quickly there and deliver less energy for a shorter duration of time.
“We moved and stopped the delivery sooner than 10 seconds, usually just after five seconds, because the temperature would increase,” he says. “And those are things that can, if you ignore it, lead to a complication called atrioesophageal fistula, which is deadly in most patients. After we saw that, we implemented a variety of strategies that go from cooling the esophagus or moving the esophagus with a special catheter. The one we like the most in our lab is cooling the esophagus to allow us to deliver at least for 10 seconds on every spot. We also try to avoid stacking up lesions on top of each other because that doesn't give time to the tissue to cool down. So we move away and then go back instead of doing lesions on top of each other.”
Also since the catheter’s energy has different modes, it can be tailored when physicians are ablating the posterior wall where the esophagus is located. “If you're using intracardiac echo, you can actually see how close you are to the esophagus,” Horton says. “That tissue is thin. You don't want to go beyond that. So the shorter you apply the lesions, the shallower the lesion will be. A lot of people do this, they will ablate with different power settings and different force settings depending on what part of the heart they're ablating. There are some areas that we know for sure are very thick, and so we would do the opposite with those to try and get deeper lesions.”
The QMode+ setting on the catheter allows operators to deliver high power for a short duration, say 4 seconds. This creates much shallower lesions of about 2 or 3 millimeters in depth. Overall, this drives toward more predictable and reproducible outcomes.
Overcoming fluid overload with irrigated RF catheters
The introduction of open irrigated RF catheters several years ago helped rapidly cool the ablation tip for better temperature control and better lesion creation. However, the trade-off was the infusion of up to several liters of saline into the patient over the course of a long ablation procedure. This often led to hypervolemia issues that complicated post-procedure patient management such as prepulmonary edema or wet lung.
“Now the problem is that if you have to inject a whole lot of saline to get the catheter temperature at the surface down just so that you can get the power into the tissue,” Horton notes. “Then you end up giving the patient a couple of liters of saline during the procedure, which is not an inconsequential amount of fluid.”
He and Natale agree this catheter enhances procedure efficacy and safety with better fluid efficiency so less saline is used. This is accomplished through better energy transfer. The efficiency of QDot energy transfer also shortens ablations times, which also reduces the need for additional saline.
“We give way less fluid to cover the same area, so clearly faster because we can drive better power, better lesion quality, but with lower fluid administration,” Natale says. “For the patient and for us, it is a more effective and efficient procedure.”
Improving contact force sensing capabilities
The amount of contact force against the tissue is another determining factor in how much energy is delivered to create good lesions. It also can serve as a warning to avoid potential issues from pushing too hard, which can cause perforations and lead to steam pops. Contact force sensing catheters, introduced a decade ago, show how much pressure the operator is applying to the catheter tip, which greatly helps improve lesion quality and safety.
Horton notes that because ablation catheters can be stiff, too much axial force can cause mechanical injury, including larger, deeper lesions or perforation. The power setting options and contact force sensing on QDOT™ helps eliminate these issues.
“Having the options of ablating shallower, having the contact force and really paying attention to the contact force allows you to limit the risk exposure to patients,” he says.
Natale says the working parameters of the catheter and being able to see the contact force visually on the screen really helps prevent steam pops.
“So if you try to keep the contact force low, we virtually don't see steam pops anymore,” Natale says. “It is extremely unusual. So that really drives the safety quite a bit.”
New RF technology is ‘eye opening’
Natale and Horton appreciate the big picture. As they see it, this new catheter combines 20 years of RF innovation plus innovative features that make it the ideal device in RF ablation technology. By offering more precise procedure guidance, improved lesion quality, more control of lesion depth, shorter procedure times and improved outcomes, it has become their catheter of choice to treat a wide variety of patients.
“Overall,” Natale notes, “it's clearly a superior technology in term of vision, quality, and efficiency.”
Longer term, they see its place in their lab for many years to come, especially for repeat ablation work.
“You get a bit more predictable outcomes,” Horton adds. “Your endpoint is signal mitigation and elimination, and that's something you can achieve easier and with more reproducibility with the QDot compared to the prior technologies. This was something that was fairly eye opening to me once we started using it.”
The Biosense Webster QDOT MICRO™ Catheters and related accessory devices are indicated for catheter-based cardiac electrophysiological mapping (stimulating and recording) and, when used in conjunction with a compatible radiofrequency generator, for the treatment of:
• Type I atrial flutter in patients age 18 or older.
• Drug refractory recurrent symptomatic paroxysmal atrial fibrillation, when used with compatible three-dimensional electroanatomic mapping systems.
The Biosense Webster QDOT MICRO™ Catheters provide real-time measurement of contact force between the catheter tip and heart wall, as well as location information when used with CARTO™ 3 Navigation System.
Dave Fornell has covered healthcare for more than 17 years, with a focus in cardiology and radiology. Fornell is a 5-time winner of a Jesse H. Neal Award, the most prestigious editorial honors in the field of specialized journalism. The wins included best technical content, best use of social media and best COVID-19 coverage. Fornell was also a three-time Neal finalist for best range of work by a single author. He produces more than 100 editorial videos each year, most of them interviews with key opinion leaders in medicine. He also writes technical articles, covers key trends, conducts video hospital site visits, and is very involved with social media. E-mail: dfornell@innovatehealthcare.com