Local activation times at the high posterior wall of the left atrium during left atrial appendage pacing predict roof line block with high specificity and sensitivity.

Aims Ensuring complete block after left atrial (LA) linear lesions is important as partial block may be pro-arrhythmic. Techniques to confirm roof line block may be time consuming and challenging and have not been well described. This study investigates whether local activation times (LAT) during left atrial appendage (LAA) pacing help in the assessment of roof line block. Methods and results Forty-five patients underwent ablation for atrial fibrillation (AF) including circumferential pulmonary vein isolation, roof, and mitral isthmus lines. Local activation times were measured at pre-defined points on the posterior wall and high anterior wall during LAA pacing at the following stages: (i) baseline; (ii) incomplete roof line; (iii) roof block; and (iv) roof and mitral isthmus block. Time from pacing at high posterior wall to LAA was also recorded at each stage. Receiver operator curve analyses were performed on different parameters to assess if they could confirm roof line block. There was a stepwise increase in mean high posterior wall LAT: 83 ± 16 ms (baseline); 105 ± 20 ms (incomplete roof block); 133 ± 26 ms (roof block), and 152 ± 35 ms (roof and MI block; one way analysis of variance, P 133 ms, high posterior wall to LAA times of >125 ms and double potential >77 ms predict roof line block with high specificity and sensitivity especially if there was also mitral isthmus block. Conclusion Parameters derived from the measurement of LAT of the high posterior and anterior LA wall help guide the assessment of roof line block.