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Figure 4 Effect of SST on R-R slowing during PS in the CS, RPA, and SVC. Average R-R intervals during AF are plotted versus the SST. The SST significantly affected the R-R interval during AF at all three intravascular sites (p < 0.001 each, ANOVA). The mean R-R interval at each SST was also compared with the R-R interval without PS (*p < 0.05). Of note, during epicardial PS at the CS ostium, the threshold for a ventricular slowing effect during AF was considerably lower than during endovascular PS in the CS. AF = atrial fibrillation; ANOVA = analysis of variance; CS = coronary sinus; PS = parasympathetic stimulation; RPA = right pulmonary artery; R-R = ventricular rate; SST = stimulus strength.