For the newest article see: 2014 AF Symposium: The New Era of Catheter Ablation Technology: Force Sensing Catheters
It’s been discovered that the force applied to heart tissue during RF ablation affects the size and safety of the lesions. Too little force results in lesions that are smaller in volume and depth and may not be effective. Too much force can result in pressure- and overheating-related complications such as steam pops, coagulum formation, or charring at the electrode. In worst cases they can lead to perforation and/or stroke.
(That’s why A-Fib patients are advised to seek out A-Fib doctors with experience who perform enough ablations a year to maintain and develop the “touch,” manual dexterity, and skill necessary to produce good ablations. Unlike other arrhythmias, A-Fib ablation requires greater technical skill, more time, and more lesions.)
New force-sensing technologies help doctors apply appropriate force. Sensors on the catheter give instantaneous feedback on the force applied at the catheter tip and even the angle of the catheter.
The Contact Force Sensor Catheter (TactiCath, Endosense, SA) uses three optical fibers to measure “microdeformation”—how much the catheter tip bends when pressed against heart tissue. The force applied changes the wavelength of light in the optical fibers. The force applied during an ablation shows up on an imaging/mapping system as either yellow, green or red. Doctors can see when they make an ablation how much force they applied to a particular spot. (Posted 2011)
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Last updated: Sunday, February 15, 2015
The New Era of Catheter Ablation Technology for Atrial Fibrillation: Force Sensing Catheters-2014 Boston AF Symposium
2014 Boston AF Symposium
The New Era of Catheter Ablation Technology: Force Sensing Catheters
By Steve S. Ryan, PhD
Dr. Moussa Mansour of Massachusetts General Hospital gave a presentation entitled “Role of Force Sensing in Catheter Ablation for AF.” In particular, he referenced the Biosense Webster’s Thermocool SmartTouch irrigated tip ablation catheter with force sensing technology and the St. Jude Medical’s TactiCath (Endosense) contact-force sensing ablation catheter.
Note: The month following Dr. Mansour’s presentation at the Boston AF Symposium, the FDA approved the Biosense Webster’s Thermocool SmartTouch irrigated tip ablation catheter with force sensing technology (February 25, 2014). The main competing system, St. Jude Medical’s TactiCath (Endosense) contact-force sensing ablation catheter, was approved for use in Europe (July 22, 2014) and hopes to get FDA approval by the end of 2014.
Just the right amount of pressure
Doctors (and patients) are excited about force sensing catheters, because they allow doctors to apply just the right amount of pressure to make a good ablation lesion. Previous studies have shown that even experienced operators sometimes apply too little pressure which can result in incomplete lesions and gaps, or they sometimes apply too much pressure which can lead to overheating and can damage or even perforate the heart. Researchers found a wide variance in contact force applied by doctors, and even a variance of force by particular doctors within the same ablation procedure.
The clinical trial for the Biosense Webster SmartTouch SMART-AF demonstrated for the first time that the consistent and stable application of contact force on the heart wall positively impacts the efficacy of catheter ablation. According to Dr. Andrea Natale, “Consistent and stable application of contact force has a significant impact on patient outcomes…and represents a major advancement for the clinical community.”
How the ThermoCool SmartTouch works
The basic mechanism of the SmartTouch is a magnet and precision spring near the catheter tip. When the catheter makes contact with heart tissue, it bends allowing small amounts of electrode movement. Sensors record the micro-movements of the spring and monitor the transmitter coil location which sends signals back about the location of the spring. Changes in catheter angle and contact force are calculated by the changes in the position of the sensors.
The ThermoCool SmartTouch is usually used in conjunction with the Biosense Webster CARTO 3 electroanatomic mapping and navigation system which displays the contact force readings in real-time. (Contact force is usually measured in grams.)
How the TactiCath Works
Not yet approved by the FDA, the St. Jude Medical’s TactiCath contact-force–sensing ablation catheter uses an optical fiber system with three fibers. When the catheter tip touches tissue, the optical fibers bend changing the wavelength of the fibers. Software translates this information into a measurement of how much pressure is being applied. A console also displays the angle of the catheter. (In the TOCCATA trial, contact force (CF) measurements below 10 grams usually failed, “Clinical failure is universally noted with an average CF below 10 grams.”)
Preclinical Testing of force sensing catheters
Dr. Mansour pointed out how the same lesion depth can be achieved by a 30W energy level at 30 g contact force as a 50W at 20g.
In another study where operators were blinded to the force they were using, lower force (below 400gs FTL (Force-Time Integral) resulted in over 20% reconnections vs. only 5% with a force of over 400gs FTL (EFFICAS I) (TactiCath contact force sensing catheter).1
In a study where the force information was visible to the operator, more PVs were durably isolated (EFFICAS II) (TactiCath)2.
In another study, low contact force (0-10 [g]) resulted in 100% recurrence after 12 months; 10-20 [g] had 47% recurrence; over 20 [g] had only 20% recurrence3
Clinical Trials of Force sensing catheters
In the SMART-AF trial of the ThermoCool SmartTouch catheter, if operators stayed within their pre-selected force range 80% or more, they had a much higher success rate. In general, operators remained in their preselected force ranges 73% of the time. Possible reasons for catheter instability include the beating of the patient’s heart and their breathing motion.
Using High Frequency Jet Ventilation (which slows down the beating heart and breathing motion), improved catheter stability and contact force (FTL) (Mansour et al. HRS 2012).
Dr. Mansour’s Conclusions
• Higher contact force during ablation results in deeper lesions
• Contact force greater than 20g is associated with an improved clinical outcome
• Increased percent of time within operator-targeted force range is associated with improved clinical outcome
• Jet ventilation and steerable sheath improve the ability to achieve the desired contact force.
Contact force sensing catheters is a major medical advancement that will change the way ablations are done. Ablation lesions will be more durable and consistent. Instances of tamponade will be significantly reduced or possibly eliminated entirely. Catheter ablation success rates will rise.
Though it’s been less than 12 months since the FDA approved Biosense Webster’s Thermocool SmartTouch contact force-sensing catheter, anecdotal reports of its success are very encouraging. Experienced operators who already have a high success rate, report a 10%+ improvement using contact force sensing catheters. I’m surprised at how many top echelon EPs are already using force sensing catheters.
For example, Dr. Hugh Calkins of Johns Hopkins wrote the author:
“We have quickly adopted force sensing catheters in all of our atrial fibrillation and VT ablation procedures. The additional contact information provided with these catheters is invaluable in maximizing the safety and efficacy of radiofrequency ablation procedures.”
Unfortunately, because of the added cost and technology challenges, the low volume operators who need to use force sensing catheters the most, will probably be the last to adopt them. (See my report about low-volume operators: Catheter Ablation Complications: A 2014 In-depth Review and Comparison with Anticoagulation Drug Therapy)
As a patient, ask your EP if they use contact force-sensing catheters. If the answer is no, should you make an effort to find an EP who does use force sensing catheters? Absolutely! Force sensing catheters will improve ablation success and durability, and will reduce complications. Even if you have to travel, it’s certainly worth the effort to find an EP who uses contact force sensing catheters.
Jet ventilation is an improvement, but may not be a game changer that you want to hunt for.
I intend to research which EPs are using contact force sensing catheters and make a special “Steve’s List” of them under the Directory Doctors/Facilities page of A-Fib.com.[]Neuzil et al. AHA 2011 http://circ.ahajournals.org/cgi/content/meeting_abstract/124/21_MeetingAbstracts/A18101
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