Determinants of left atrial local impedance: relationships with contact force, atrial fibrosis and rhythm

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Private company. Main funding source(s): Boston Scientific BACKGROUND: The relationships between baseline tissue local impedance (LI), contact force (CF), atrial fibrosis and atrial rhythm are uninvestigated in a clinical setting. OBJECTIVES: To compare the relationship of LI and CF between atrial fibrillation (AF) and sinus rhythm (SR). Establish the effects of atrial fibrosis as assessed by bipolar voltage and LI. METHODS: Patients undergoing persistent AF ablation were recruited. The ablation catheter was placed against the left atrial wall and CF levels varied from 1-40g. LI was recorded concurrent to changes in CF at these locations, with data collected at the same locations in AF and SR following DC cardioversion. LI values were referenced to patient blood pool, (LIr). RESULTS: 20 patients were recruited. 109 locations were sampled obtaining 1903 datapoints (SR: 966, AF: 937). CF correlated strongly with LI (repeated measures correlation = 0.64). The relationship between CF and LIr was logarithmic. Rhythm and CF had a significant main (both p < 0.0005) and interaction effect (p = 0.022) on tissue LI: AF demonstrated higher LIr values than SR for similar CF (Figure 1). Furthermore, AF modelled a more predictable relationship between CF and LI than SR (R2 = 0.21 vs 0.13). Bipolar voltage had no effect on the relationship of CF to LIr in either rhythm when using conventional cut-offs to determine scar (0.05mV and 0.5mV). Cut-offs for assessing scar using LIr used values of 0.5Ω and 10.5Ω based on concurrent work. Through assessing fibrosis using these values, LIr showed an interaction effect with CF for LIr in SR and AF, (SR: p <0.0005, AF: p = 0.01), with more fibrosis demonstrating shallower CF-LIr curves than healthier tissue, (Figure 2). CONCLUSIONS: CF and rhythm significantly affect the measured LIr of LA myocardium. Optimal catheter-tissue coupling may be better achieved with higher levels of CF and in AF rather than SR. Atrial fibrosis as assessed by bipolar voltage did not affect the CF-LI relationship, but was when assessed by LIr. [Figure: see text] [Figure: see text]