THE IMPACT OF ANTERIOR MITRAL BLOCK ON LEFT ATRIAL APPENDAGE ACTIVATION TIME

Introduction: Left anterior ablation line (LAL), which can be used for the management of perimitral reentrant atrial tachycardia, is almost invariantly associated with the change in activation of the left atrial appendage (LAA) during sinus rhythm (SR). This study investigated magnitude of this change in the setting of hypothetical block at the LAL. Methods: We utilized the electronatomic data from left atrial (LA) mapping in 68 pts (46 men, 59±10 y) who underwent catheter ablation for paroxysmal (75%) or persistent atrial fibrillation. The LA activation maps in SR were carefully edited to localize the lateral perimitral collision zone (Figure). The electrical distance between the base of LAA and this collision zone was used to estimate the relative delay in LAA activation if virtual block at the LAL is achieved. Results: In SR, the activation time of LAA base was -76±40 ms before the onset of QRS complex. The activation time at the collision zone was -52±41ms. In the setting of hypothetical LAL block, LAA activation time would be delayed by 64±35 (range 4–156)ms resulting in the reduction of LAA activation prematurity relative to the QRS onset (-21±32; range -97–68ms). In 14 (21%) patients, LAA activation would start after the QRS onset. Only 10 (15%) patients would have LAA activated earlier than 50 ms prior to the QRS onset. Out of those 10 patients, 6 (60%) have PR interval longer than 200ms, which is significantly higher proportion than in rest of cohort (21%), p=0.01. Conclusions: The experimental model helped to demonstrate that the block at the LAL is associated with significant delay of LAA activation. Consequently, the anterior mitral block may adversely influence the benefit from SR restoration because of worsening of LAA function. Prolonged PR interval seems to be protective from delayed LAA activation after completing of LAL.