Unipolar voltage reduction predicts transisthmus conduction-time prolongation after cavotricuspid isthmus ablation
E Algul, Y Oz, H F Sahan, S Iscen, H Sunman, T H Efe, O OzdemirAbstract
Background
Atrial flutter (AFL) represents 5–20% of all arrhythmias and is linked with heart failure, stroke and mortality1. Cavotricuspid isthmus (CTI) ablation is the treatment of choice, with bidirectional block (BDB) as endpoint2. Complex CTI anatomy can hinder ablation success, and even when BDB is achieved, recurrence remains around 5%, often due to functional gaps or epicardial–endocardial breakthroughs from bridging fibers3. A >50% or >140 ms increase in transisthmus conduction time (TICT) is an accepted indicator of conduction block4, yet its electrophysiological predictors remain unclear.
Purpose
To assess voltage-based parameters predicting TICT prolongation after CTI ablation.
Methods
51 symptomatic AFL patients refractory to drugs were prospectively enrolled. Unipolar and bipolar voltage mapping of the CTI was obtained before ablation using a 3D system. Linear lesions were created from the tricuspid annulus to the inferior vena cava (30–35 W, ≤42 °C, contact force >5 g). TICT was measured as the interval between atrial signals at the lateral CTI and proximal coronary sinus (CSp) during flutter, or as the conduction time between these sites by sequential pacing in sinus rhythm. After ablation, measurements were repeated at identical locations in sinus rhythm. BDB was confirmed by differential pacing and, in selected patients, by high-resolution activation mapping. All post-ablation assessments were repeated following a 20-minute waiting period.
Results
Mean contact force was 15.8 ± 5.9 g, RF time 440 ± 158 s, and 24 ± 9 lesions per patient. Mean bipolar and unipolar voltages decreased from 2.68 ± 0.91 V to 1.02 ± 0.55 V (−68.8%) and 3.79 ± 1.6 V to 0.96 ± 0.38 V (−61.7%). TICT increased from 52.8 ± 12.3 ms to 144.2 ± 19.7 ms (ratio 2.84 ± 0.63) (Table 1). Unipolar voltage drop and contact force correlated with TICT prolongation, while bipolar voltage and impedance did not. Multivariate analysis confirmed unipolar voltage drop (β = 0.021, p = 0.001) and contact force (β = 0.039, p = 0.009) as independent predictors (Table 2). ROC analysis showed unipolar voltage drop ≥61.7% predicted TICT ratio >2 with 91.3% sensitivity and 100% specificity (AUC = 0.97). During 8.2 ± 2.6 months follow-up, AFL recurred in one patient (1.9%), associated with insufficient unipolar reduction (29.7%). Additional lesions achieving ≥60% reduction resulted in durable block.
Conclusions
Unipolar voltage reduction independently predicts TICT prolongation, marking effective and durable CTI lesion formation. A ≥60% reduction reliably indicates successful block, outperforming bipolar voltage and impedance. Unipolar mapping provides real-time feedback and may serve as a practical procedural endpoint when advanced monitoring is unavailable. Incorporating this parameter into workflows could enhance durability and reduce recurrence. Further multicentre studies should confirm these findings and evaluate unipolar-guided strategies in other substrates.Table 1 Table 2