Importance of contact force in catheter ablation

PRAGUE, CZECH REPUBLIC. Despite significant, recent improvements in catheter ablation strategies to treat atrial fibrillation (AF), recurrence remains a continuing concern. Recurrence (after the blanking period) follows 20-55% of initial procedures and is almost always attributable to gaps in the isolation lines separating the pulmonary veins (PVs) and the left atrium. Isolation gaps may result either from areas omitted during initial treatment or from lesions that are not sufficiently transmural (extending through the entire thickness of the heart wall) to prevent conduction. The force (contact force or CF measured in grams) applied to the catheter, the position of the catheter in relation to the point ablated, and the length of time radiofrequency (RF) energy is applied (Force-Time Integral or FTI measured in gram-seconds) are the most important variables in determining the durability of any particular lesion.

A group of American, Czech, German and Swiss researchers now reports their experience with a new 3.5 mm irrigated catheter (TactiCath) that automatically measures CF and FTI every 100 milliseconds. Forty-six consecutive patients with predominantly paroxysmal (98%) AF participated in the study. The patients underwent an anatomically-guided pulmonary vein isolation procedure using the EnSite mapping system. The electrophysiologists doing the procedures followed their usual practice, but did not have access to the CF and FTI data being recorded. After a blanking period of 3 months, 40 of the patients underwent a second electrophysiologic study (similar to catheter ablation, but without necessarily creating new lesions). At this follow-up, 26 of the 40 patients (65%) showed one or more gaps. The number of gaps was found to correlate strongly with the minimum CF and the minimum FTI at the site of the gaps. The median CF for all initial ablations was 15 g and the median FTI was 479 gs.

The researchers observed that the average number of ablations per segment (the area around the PVs was divided into 8 segments for analysis purposes) was inversely correlated to isolation. This suggests that once an inadequate lesion has been produced trying to redo it only makes things worse. They make the following recommendations for increasing the probability of a successful ablation:

  1. Position the catheter carefully before ablation, preferably with a CF of 20 g, but not less than 10 g.
  2. Ensure positional stability by monitoring CF before applying RF energy.
  3. Sustain RF delivery until a minimum FTI of 400 gs is achieved before moving the catheter to a new location.

Neuzil, P, et al. Electrical reconnection after pulmonary vein isolation is contingent on contact force during initial treatment. Circulation Arrhythmia and Electrophysiology, Vol. 6, April 2013, pp. 327-33

Editor’s comment: The real-time measurement of CF and FTI during catheter ablation will no doubt prove to be of great value to EPs performing ablations, particularly less experienced ones. I suspect that the “top guns” in the ablation field have an innate capability to sense CF and, based on the thousands of ablations they have done, know exactly how long to apply RF energy in order to achieve an optimum FTI.