Unraveling direction- and rate-dependent unipolar electrogram morphology using spontaneous atrial extraystoles

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: Atrial extrasystoles (AES) are notorious for triggering episodes of atrial fibrillation (AF). AES provoke conduction disorders due to (dispersion in) refractoriness and enhanced non-uniform anisotropy of atrial tissue, which are related to initiation and perpetuation of AF. However, the direction- and rate-dependency of electrophysiological tissue properties on epicardial unipolar electrogram (EGM) morphology is unknown. PURPOSE: To examine the impact of spontaneous AES on potential amplitude, -type (single-, double-, fractionated), -duration and low-voltage areas (LVA), and to correlate these differences with various degrees of prematurity and aberrancy. METHODS: Intra-operative high-resolution epicardial mapping of the right and left atrium (RA, LA), Bachmann’s Bundle (BB) and pulmonary vein area (PVA) was performed during SR in 298 patients. EGM characteristics were quantified during SR and AES, and subsequently compared. AES were categorized according their prematurity index (> 25% shortening) and degree of aberrancy (none, mild, moderate and severe). LVA were defined as the amount of unipolar voltages <1 mV. RESULTS: During 917 unique AES (495 premature; 364 mild-, 186 moderate- and 167 severe aberrant), average voltage decreased (-1.1 [-1.2, -0.9] mV, P<0.001) at all atrial regions, whereas the amount of LVA and fractionation increased (respectively +3.6 [2.9, 4.3]% and +3.2 [2.7, 3.7]%, P<0.001). Although potential voltages were mainly decreased during AES, in 910 (99.2%) AES, at least 0.8% (median 33.3 [19.0–52.1] %) of the recorded voltages was locally larger during AES compared to SR. Only weak or moderate correlations were found between each of the parameters and prematurity indices (R2<0.592, P<0.001). On the other hand, voltages decreased and the amount of fractionation increased with increasing degree of aberrancy. The effect of AES with opposite propagation direction was frequently similar as compared to severely aberrant AES. All parameters were most severely affected by either opposite or severely aberrant AES, without clear relation with degree of prematurity. CONCLUSIONS: Unipolar EGM characteristics during spontaneous AES are mainly directional-dependent and not rate-dependent. This indicates enhanced non-uniform anisotropy that is induced by spontaneous AES.