Contact Force Sensing RF Catheters for Ablation
Contact force sensing, the ability to determine the amount of pressure the catheter is exerting on the tissue, is another new development in radiofrequency catheters. Although irrigated catheters reduce the incidence of char formation, they can lead to another complication: steam pops. Steam pops occur when the heat from the radiofrequency catheter causes water inside the tissue to boil and steam. Sometimes so much steam builds up that it bursts through the tissue. Steam pops create craters in the heart tissue and can lead to a serious complication, cardiac perforation (a rip or tear in the heart).
Contact force is one of the variables that affects transmurality. By being able to monitor contact force, which is measured in grams, doctors may be able to apply just the right amount of pressure to create transmural lesions while avoiding steam pops. Interestingly, doctors may not realize how much (or how little) pressure they apply to catheters during ablation. Dr. Karl-Heinz Kuck, of St. George Hospital in Hamburg, Germany, presented data at the Boston Atrial Fibrillation Symposium showing a wide variance in contact force applied by doctors who participated in the European TOCCATA clinical trial. One electrophysiologist averaged only 10 grams of pressure, whereas others averaged 30 grams of pressure. Most doctors exceeded 100 grams of pressure at various points during ablations.
Here are the two main contact force sensing radiofrequency catheters.
TactiCath Force-Sensing Irrigated Ablation Catheter
The TactiCath Force-Sensing Irrigated Ablation Catheter (Endosense), which received regulatory approval in Europe in May 2009, has three optical fibers that emit wavelengths. When the catheter tip touches tissue, the optical fibers bend. TactiCath’s software calculates the changes in the wavelengths between the optical fibers and translates this information into a measurement of how much pressure is being applied to the heart tissue. The radiofrequency energy console shows the level of contact force—a small green bubble quickly illustrates when little contact force is being applied, whereas a large green bubble signifies a large amount of contact force. The console also displays a numerical read out of contact pressure as well as the angle of the catheter.
Results from TactiCath’s European TOCCATA trial were presented at the recent Heart Rhythm Society meeting. The trial included 34 individuals with paroxysmal atrial fibrillation who received ablation of the pulmonary veins as well as six other areas in the left atrium. Procedure success was defined as absence of afib, atrial flutter, or atrial tachycardia, and required that only a single procedure be performed on a patient. At three months, 71% of the patients were free from atrial fibrillation. However, this decreased over time, with only 44% of patients remaining in normal sinus rhythm at 12 months. While 61% of patients were free from atrial fibrillation symptoms at one year, many afib episodes were asymptomatic.
Although this suggests that patients' quality of life improved, some patients continued to have afib, which means that their atrial fibrillation could progress to persistent afib and become more difficult to treat. They would also continue to be subject to the severe risks associated with atrial fibrillation, such as stroke.
There were a few major adverse events in the TOCCATA trial. One patient had cardiac tamponade, a serious situation where fluid fills the pericardium, the “sac” surrounding the heart, and compromises the heart’s ability to pump. At three months, 12% of individuals had pulmonary vein stenosis (narrowing of the pulmonary vein), which obstructs oxygenated blood from flowing from the lungs to the heart.
TactiCath is being studied in a multi-phase clinical trial in Europe. The first phase, EFFICAS I, which completed enrollment in February 2011, is investigating the relationship between contact force and freedom from atrial fibrillation at three months. During the study, TactiCath's contact force sensing information was not provided to doctors so the results could be insightful as to how much contact force doctors routinely applied to tissue (too much or too little). In EFFICAS II, which has started to enroll patients, doctors will be able to see TactiCath’s contact force sensing data and adjust pressure as necessary. Data from these studies will form the basis of a larger randomized clinical trial in Europe. The US clinical trial, TOCCASTAR, began enrollment in January 2011.
THERMOCOOL SMARTTOUCH Irrigated Catheter
The THERMOCOOL SMARTTOUCH Irrigated Catheter (Biosense Webster) is another contact force sensing catheter, which is available in Europe and is expected to start a clinical trial in the US. Near the catheter tip is a spring coil that is surrounded by a magnetic signal emitter and three magnetic signal sensors. The coil allows the tip to bend in response to pressure applied to the catheter, causing the sensors to change position. The SMARTTOUCH then uses the changes in the position of the sensors to calculate the changes in catheter angle and contact force. If the doctors are using the CARTO electroanatomic mapping system, an advanced navigation system, the data is then transmitted to it.
At the Boston Atrial Fibrillation Symposium in 2010, Dr. Hiroshi Nakagawa, of the University of Oklahoma, presented findings from early research of the SMARTTOUCH. Eight dogs were separated into two groups—dogs in one group received 25 watts of radiofrequency energy and dogs in the other group received 40 watts. Dr. Nakagawa and his colleagues applied different levels of contact force (low, medium, high) to each group. They found that lesion depth, which is an indicator of transmurality, varied by the degree of energy and by the contact force applied. For instance, applying 25 watts of radiofrequency energy and a contact force of 40 grams created an average lesion depth of 7.4 millimeters whereas 45 watts of radiofrequency energy and low contact force resulted in an average lesion depth of only 5.3 millimeters. They also found that the incidence of steam pops varied by the amount of energy and contact force. Specifically, the steam pop rate was 13% with low power and high contact force, 38% with high power and medium contact force, and 75% with high power and high contact force.
Contact force sensing radiofrequency catheters may improve ablation outcomes as early studies have proven the link between contact force, lesion depth, and complications. However, research still needs to be done to identify the optimal contact force and energy to obtain the best outcomes.
To learn about other advancements in catheter design and alternative energy sources, see Balloon Catheters. To learn about other technology and tools used in catheter ablation, see Mapping and Navigation.
To learn more about whether catheter ablation is appropriate for you, see Are You a Candidate for Catheter Ablation.
Disclaimer: Some companies mentioned on this site may be donors to StopAfib.org but do not receive favored treatment in coverage as atrial fibrillation patients are our first priority.