Lesion efficacy during catheter-based radiofrequency (RF) ablation is known to depend on sufficient mechanical contact and electrical coupling. Real-time assessment of contact force (CF) indicates catheter stability on underlying tissue. Measurement of local impedance (LI) gained interest as LI differs between tissue substrates, while the degree of LI reduction during RF energy application reflects real-time efficacy of lesion formation. 

 

Objective:
To investigate how CF influences baseline as well as LI drop during atrial RF ablation in heterogenous atrial subtrate as combined clinical evaluation has not been performed so far.

 

In this explorative single-center series, consecutive patients presenting for re-do catheter ablation of atrial fibrillation and/or atrial tachycardia were studied. Following initial basket catheter-guided ultra-high-density mapping, ablation was performed using a novel open-irrigated single-tip ablation catheter (IntellaNav StablePoint, Boston Scientific, Marlborough, MA, USA) capable of continuously assessing CF and LI. RF deliveries were analyzed with respect to applied CF, baseline LI and force-time integral for maximum LI drop (∆LI) in atrial high (>0.5 mV), intermediate (0.1-0.5 mV) and low bipolar voltage (<0.1 mV) tissue. 

 

A total of 530 RF deliveries (left atrial n=418, right atrial n=101, coronary sinus n=11, n=10 patients, n=5 female) were analyzed. Baseline mean blood pool LI (141±13 Ω) was significantly lower compared to baseline LI within the left/right atrium (median 155 (interquartile range 147-162) / 160 (146-176) Ω, p=0.02). Maximum LI drop (∆LI) was related to baseline LI by linear regression analysis (r=0.48, p<0.001). Energy applications with >5 compared to <5 g average CF (18 (14-24) vs 14 (11-21), p=0.01) or a force-time integral >400 vs <400 gs (19 (14-26) vs 18 (13-23), p=0.02) resulted in significantly higher ∆LI. CF only displayed as a minor influence on baseline LI (r=0.28, p<0.001) with no significant impact of higher CF levels (r=0.09, p=0.13) or force-time integral increase during ablation (r=0.12, p=0.04) on ∆LI. Baseline LI as well as ∆LI were higher in regions of high vs intermediate and low voltage (p<0.001 / p=0.002). Baseline LI was a predictor for a ∆LI >20 Ω (logistic regression analysis: odds ratio 1.07 (confidence interval 1.05-1.1), p<0.001)) which has been shown to result in sufficient lesion formation, compared with the force-time integral during ablation (1.00 (1.00-1.003), p=0.02), average CF (0.99 (0.94-1.03), p=0.55) and local voltage (OR 1.11 (0.75–1.61), p=0.58). Acute procedural success was accomplished and no catheter-related periprocedural complications were observed in all patients.

 

This novel combination of CF and LI may enable enhanced beat-to-beat real-time analysis of local catheter stability, in-depth tissue characterization beyond bipolar voltage and the effect of applied RF energy on lesion formation for tailored ablation procedures. 

 

 

Figure 1. Raw tracings (Fig. A) of local impedance drop (∆LI) during ablation with simultaneous contact force (CF) registration are displayed. Higher baseline LI predicted increased LI drop during energy delivery, whereas CF beyond 5g (Fig. B) did not influence baseline LI or ∆LI.