The Role Of Contact Force In Atrial Fibrillation Ablation

Abstract

During radiofrequency (RF) ablation, low electrode-tissue contact force (CF) is associated with ineffective RF lesion formation, whereas excessive CF may increase the risk of steam pop and perforation. Recently, ablation catheters using two technologies have been developed to measure real-time catheter-tissue CF. One catheter uses three optical fibers to measure microdeformation of a deformable body in the catheter tip. The other catheter uses a small spring connecting the ablation tip electrode to the catheter shaft with a magnetic transmitter and sensors to measure microdeflection of the spring. Pre-clinical experimental studies have shown that 1) at constant RF power and application time, RF lesion size significantly increases with increasing CF; 2) the incidence of steam pop and thrombus also increase with increasing CF; 3) modulating RF power based on CF (i.e, high RF power at low CF and lower RF power at high CF) results in a similar and predictable RF lesion size. In clinical studies in patients undergoing pulmonary vein (PV) isolation, CF during mapping in the left atrium and PVs showed a wide range of CF and transient high CF. The most common high CF site was located at the anterior/rightward left atrial roof, directly beneath the ascending aorta. There was a poor relationship between CF and previously used surrogate parameters for CF (unipolar or bipolar atrial potential amplitude and impedance). Patients who underwent PV isolation with an average CF of <10 g experienced higher AF recurrence, whereas patients with ablation using an average CF of > 20g had lower AF recurrence. AF recurred within 12 months in 6 of 8 patients (75%) who had a mean Force-Time Integral (FTI, area under the curve for contact force vs. time) < 500 gs. In contrast, AF recurred in only 4 of 13 patients (21%) with ablation using a mean FTI >1000 gs. In another study, controlling RF power based on CF prevented steam pop and impedance rise without loss of lesion effectiveness. These studies confirm that CF is a major determinant of RF lesion size and future systems combining CF, RF power and application time may provide real-time assessment of lesion formation.

Keywords: Atrial Fibrillation; Catheter Ablation; Contact Force; Electrophysiology; Mapping; Radiofrequency.

Figure 1.. Relationship between contact force and radiofrequency (RF) lesion size in the canine thigh muscle preparation. Lesion depth (A) and diameter (B) significantly increased by increasing contact force (2, 10, 20, 30 and 40 g) for both 30 Watts (left panel) and 50 Watts (right panel) RF applications (p<0.01). Modified with permission from reference.[8]

Figure 2.. Relationship between contact force and the incidence of steam pop and thrombus in the canine thigh muscle preparation. A. The incidence of steam pop increased significantly by increasing contact force at 30 Watts (left panel) and 50 Watts (right panel) RF applications (p=0.031 and p=0.0026, respectively). B. The incidence of thrombus formation also increased significantly by increasing contact force at 50 Watts allocations (right panel, p=0.0044). At 30 Watts applications (left panel), there was a trend between the incidence of thrombus and contact force (p=0.0721). Modified with permission from reference.[8]

Figure 3.. Relationship between contact force and RF lesion size in the canine beating heart. At contact 25 Watts and 60 sec RF applications in the right ventricle (RV), RF lesion size increased significantly with increasing contact force of low force (3-8, median 5.5g), moderate force (18-27, median 21.5 g) and high force (40-62, median 45.5 g, p<0.01, upper panel,). Similarly, at 40 Watts and 60 sec RF applications in the left ventricle (LV), RF lesion size increased significantly with increasing contact force (lower panel, p<0.01). Modified with permission from reference.[19]

Figure 4.. Graphs showing the incidence of steam pop as a function of contact force. The incidence of steam pop increased significantly by increasing contact force at 40 Watts applications in the left ventricle (LV). A steam pop occurred only with high contact force at 25 Watts in the right ventricle (RV). Modified with permission from reference.[19]

Figure 5.. Similar lesion depth produced by RF power modulation based on contact force in the canine right and left ventricles. A. In the right ventricle, the lesion depth is almost identical between the three group ablation: 1) median depth of 5.2 mm with low contact force (4-10g, median 8g) at 40 Watt for 60 sec; 2) median depth of 5.2 mm with the moderate contact force (15-26 g, median 20 g) at 25 watts for 60 sec, and 3) median depth of 5.0 mm with high contact force (40-57 g, median 44 g) at 10 watt for 60 sec. Four of the RV lesions were transmural, preventing measurement of the depth. Therefore, these 4 lesions are excluded for data analysis. B. In the left ventricle, there is no significant difference in lesion depth for ablation with the low contact force - 50 Watt lesions (median depth 8. 6mm), the moderate contact force - 40 Watt lesions (median depth 8.4 mm), and high contact force - 25 Watt lesions (median depth 8.0 mm). Modified with permission from reference.[19]

Figure 6.. Range of contact force for all 18 patients (5,682 sites, median 8.2 g) undergoing pulmonary vein isolation, and for operator #1 (12 patients, 3,846 sites, median 8.3 g), operator #2 (4 patients, 1,009 sites, median 7.3 g), operator #3 (2 patients, 827 sites, median 9.3 g). Box plot values are 10the percentile, 25th percentile, 50the percentile (median), 75the percentile, and 90th percentile of the range of contact force. Modified with permission from reference.[23]

Figure 7.. Contact force map in the anterior-posterior projection and contact force recording when the catheter was positioned perpendicular (angle 90°) to the anterior/rightward left atrial roof (beneath the ascending aorta) shows transient peaks (during the inspiration phase of respiration) in contact force exceeding 100 g. CF, contact force. Modified with permission from reference.[23]

Figure 8.. Computed tomography (CT) image of the aorta merged with the contact force map in the right anterior oblique (RAO) projection shows the region of very high contact force (144 g) at the anterior/rightward left atrial roof. Note that this site is located directly beneath the ascending aorta. Modified with permission from reference.[23]

Figure 9.. Poor relationship between contact force and unipolar atrial potential amplitude during sinus rhythm (A, 10 patients) and AF (B, 8 patients), bipolar atrial potential amplitude during sinus rhythm (C) and AF (D), and impedance during sinus rhythm (E) and AF (F). AF, atrial fibrillation. Modified with permission from reference.[23]