It is well-established that pulmonary vein (PV) ectopic activity is the trigger for paroxysmal atrial fibrillation (AF). However, the role of electrophysiological and structural heterogeneity in the genesis and maintenance of AF following PV ectopy are still relatively unknown.

In this preliminary study, we report on an optical mapping study to determine the structure-function relationship and electrophysiolopgical heterogeneity in left atrial vs PV tissue. Optical mapping experiments were performed in circumflex artery-perfused left atrial preparations from sheep. The atria were paced on the endocardial surface (n=5) between 0.5 to 6Hz. Action potential duration (APD) was measured from four different regions of interest (ROI): LAAEN (left atrial appendage), LAREN (left atrial roof) and PVEN (pulmonary veins ostium) on endocardial surface and from LAAEP (left atrial appendage) on epicardial surface.

During pacing of the endocardium, no significant APD differences were observed between the four ROIs, except at a basic cycle length of 400msec where the pulmonary vein region displays shorter action potentials than the (LAAEN: 209.58±17.04msec and PVEN: 184.23±14.19msec, P<0.05). In addition, preliminary results also show that AP forms are heterogenic. The action potential upstroke is is slower in PVEN rather than in LAAEN.

In conclusion, our results indicate electrophysiological heterogeneity in the intact sheep left atrium which may contribute to the mechanisms underlying the genesis and maintenance of AF.