Several preclinical studies presented at the 2008 Heart Rhythm Society (HRS) meeting held in San Francisco last week indicated that accurate, real-time measurement of the contact force at the catheter tip can have a positive impact on the safety and efficacy of radiofrequency (RF) catheter ablation procedures.
In particular, the results suggest that:
- Accurate measurement of contact force has the potential to prevent complications, such as esophageal lesions, perforations and pops;
- The force required to perforate through an ablation lesion is significantly lower than that required to perforate through healthy tissue; and
- Alternate measurement techniques, including electrogram parameters and impedance, are poor predictors of electrode-tissue contact force in RF catheter ablation.
“Our preclinical studies clearly show that accurate, reliable force control will be critical for increasing the safety and effectiveness of the catheter ablation procedure,” said investigator Hiroshi Nakagawa, MD, a professor of medicine research at the University of Oklahoma Health Sciences Center, Oklahoma City.
In the studies, researchers used TactiCath, a force-sensing ablation catheter manufactured by Geneva-based Endosense. TactiCath is a high-end, 8.5F sheath compatible, open-irrigated, steerable catheter that integrates a proprietary fiber optic sensor technology that allows the physician to know exactly how much force to apply for optimal lesion creation. It calculates contact force (g) every 100 ms (sensitivity <1 g).
“Without this measure, the physician has to estimate—and frequently guess—the level of force required,” Eric Le Royer, president and CEO of Endosense, told Cardiovascular Business News. “If the contact force is too great, the catheter tip may perforate the heart wall. If it is too slight, the procedure may be ineffective.”
In one study led by Nakagawa’s colleague Atsushi Ikeda, MD, researchers wanted to determine the relationship between average contact force, lesion size and incidence of steam pop (a phenomenon that occurs when steam builds up in the tissue) in a beating heart.
They found that at constant RF power, lesion size and incidence of steam pop increase strikingly with increasing contact force. They concluded that the ability to measure real-time contact force may prove effective in predicting RF lesion size and risk of steam pop in clinical application.
In another study, led by Dipen C. Shah, MD, from the Hospital Cantonal De Geneve, Geneva, researchers sought to quantify tissue contact. An experienced operator blinded to force readings positioned the catheter at the lateral right atrial (RA) wall, the high RA and against the interatrial septum with poor, good and excessive contact based on subjective assessment using fluoroscopy, electrograms and tactile feedback.
They found that the mean tip force was significantly greater for poor versus excessive contact and good versus excessive contact at all three RA sites. For the same subjective contact, the actual force applied was significantly higher against the interatrial septum.
Shah led another study that analyzed the force needed to perforate the cardiac wall. Researchers first created RA free wall lesions. They then used the same catheter but without RF delivery, to perforate the free walls ex vivo. The minimum perforating force through healthy tissue in all four chambers averaged 165 g. The minimum force needed to perforate ablated tissue in the RA was 96 g. Although not significant, the RA required lower force for perforation than the right ventricle. The left ventricle could not be perforated without the support of a long sheath because of catheter shaft buckling.
Ikeda and colleagues in another study found that at constant RF power and time, esophageal temperature increased with increased contact force within the left atrium. Esophageal ulcers occurred at low contact force in two dogs and at moderate to high contact force in all five dogs.
Results demonstrate the “striking role of contact force” in esophageal injury during RF ablation in the left atrium, according to the researchers.
“The future ability to titrate RF power based on real-time contact force measurement may reduce the risk of esophageal injury while preserving an effective RF lesion,” the researchers concluded.
The first human trial of TactiCath is slated to occur in Europe in mid-2008, with CE Mark expected in 2009, according to Le Royer. TactiCath is currently