(A) Comparison of vagal stimulation (VS) versus baseline indicates parasympathetic responsiveness in the resting state; this was most pronounced in the pulmonary vein (PV). Comparison of propranolol (P) + atropine (ATR) versus baseline indicates resting vagal tone, which was greatest in the left atrial appendage (LAA). (B) With P + VS, more pronounced effective refractory period (ERP) shortening was noted in the PV, posterior left atrium (PLA), and LAA as compared with ERP shortening with VS alone. See text for discussion. *p < 0.05.

(A) The panel shows cumulative vagal effect as measured by the ERP difference between P + VS and P + ATR. The cumulative vagal effect is greatest in the LAA, followed by the PLA and PV (LAA > PLA PV). Panels B and C show western blots for Kir3.1 and 3.4, respectively. Each protein shows greatest expression in the LAA, followed by the PLA and PV (LAA > PLA PV). LSPV = left superior pulmonary vein; LIPV = left inferior pulmonary vein; RIPV = right inferior pulmonary vein; RSPV = right superior pulmonary vein; other abbreviations as in Figure 1.

(A) The panel shows heterogeneity of ERP shortening among individual pacing electrodes in the PV, PLA, and LAA. Interelectrode heterogeneity (Variance/N) is the greatest in the PLA and is least in the LAA. Panels B and C show examples of immunostaining (10x magnification) for Kir3.1 in the LAA and PLA, respectively. The Kir3.1 is stained red. In the LAA (B), Kir3.1 staining is very homogeneous. In contrast, staining for Kir3.1 is significantly more heterogeneous in the PLA (C). The black arrows indicate the heterogeneity of red staining in the PLA. Abbreviations as in Figure 1.

Panels A, C, and E represent baseline activation during sinus rhythm in the PV, PLA, and LAA, respectively. Panels B, D, and F represent activation in the PV, PLA, and LAA in the presence of P. (A) At baseline, earliest activation is noted on the left side of the plaque (*). (B) With P, earliest activation shifts to the opposite end of the plaque (*). No significant differences are noted in earliest activation or activation direction in the PLA (C, E) or in the LAA (E, F) in the presence of P. Each isochronal step represents 1 ms. *Earliest activation. The grid on the right shows that earliest activation is black, with later times indicated by progressively decreasing shades of gray. Abbreviations as in Figure 1.

Panels A and B represent 1 PV in the presence and absence of P, during pacing at 400 ms. (A) At baseline, earliest activation (*) is noted at the lower right (distal PV), indicating breakout in the unmapped posterior one-third of the PV. (B) With P, earliest activation (*) shifts to the opposite end (left) of the distal PV, with a resulting change in the direction of activation. Each isochronal step represents 1 ms. Abbreviations as in Figure 1.

Each panel shows X- and Y-components of conduction velocity for each region and for each intervention. (A) In the PV, VS, P, and P + VS cause a significant change in the Y-vector and the resulting X/Y relationship, indicating a change in activation direction. Panels B and C show X- and Y-vectors for the PLA and LAA, respectively. In both regions, there was no significant change in either X- or Y-component or in the X/Y relationship in response to any intervention. *p 0.05 (X vs. Y). Abbreviations as in Figure 1.