Clinical and experimental evaluation of averaged impedance drop during radiofrequency catheter ablation

BACKGROUND: Real-time monitoring of myocardial tissue response during radiofrequency applications using a mesh-shaped flexible irrigation tip ablation catheter (TactiFlex) remains challenging. This study assessed the dynamics of averaged impedance drop percentage (AID%), a novel ablation parameter, and its association with conduction gaps and lesion characteristics. METHODS: We retrospectively analyzed 1,423 radiofrequency applications in 30 patients undergoing initial pulmonary vein isolation using TactiFlex to examine the relationship between AID% and radiofrequency applications within conduction gap segments. Mechanistic validation was performed using an ex-vivo porcine myocardial model (152 lesions). RESULTS: Among 1,423 radiofrequency applications, 138 were located within conduction gap segments. AID% was lower in radiofrequency applications in conduction gap segments than in non-conduction gap segments, although the difference was modest (10.2 [8.3-12.2] % vs. 10.9 [9.0-13.1] %, p = 0.002). The overall discriminative performance was limited (area under the curve, 0.58; 95% confidence interval, 0.53-0.63). In mixed-effects logistic regression accounting for within-patient clustering, AID% <10% was not significantly associated with radiofrequency applications in conduction gap segments (odds ratio, 1.560; 95% confidence interval, 0.970-2.500; p = 0.065), whereas average radiofrequency power was significant. In the ex vivo study, lesion characteristics varied according to radiofrequency power, contact force, and duration, even under fixed target AID% conditions. CONCLUSIONS: AID% reflects a composite impedance-based tissue response to radiofrequency delivery that is influenced by multiple ablation parameters. Its limited ability to discriminate conduction-gap segments, together with the variability in lesion characteristics across radiofrequency delivery conditions, suggests that AID% should be interpreted as a marker of tissue response rather than as a stand-alone lesion-quality metric. The averaged impedance drop percentage (AID%) reflects a composite impedance-based tissue response to radiofrequency delivery that is influenced by multiple ablation parameters. Its limited ability to discriminate conduction gap segments, together with the variability in lesion characteristics across radiofrequency delivery conditions, suggests that AID% should be interpreted as a marker of tissue response rather than as a stand-alone lesion-quality metric.