3.3 PMF electrophysiological characteristics
During the procedures, 32 PMF (25 clockwise and 7 counterclockwise) were detected in 28 patients (24 with AT and 4 with AF as the clinical arrhythmia). In 20 of the 32 PMF circuits (16 clockwise and 4 counterclockwise) it was possible to construct a high-density map and measure the CVs as described earlier (Figure 4 , Videos 5,6 ). The mean CL of PMFs with pseudo-block (all clockwise) did not differ significantly from the mean CL of usual PMFs (254±10 ms vs 248±13 ms, respectively; P=0.340). However, the lower CV in PMFs with pseudo-block was of significantly lower value in comparison with the lower CV in other thoroughly mapped PMF circuits (0.07±0.02 m/s vs 0.25±0.07 m/s, respectively; P<0.001). The same was true for patients with PMF who had undergone additional LA ablation beyond PVI (Figure 5 ). Conduction channels with width ≤1cm were found in 3 patients with PMF without MI pseudo-block. In these channels the mean CV was 0.34±0.08m/s (range: 0.25-0.4 m/s) (Figure 6, Video 7 ). In patients with PMF and ΜΙ pseudo-block the comparison of the ΜΙ length as well as the MI width of the ablation area showed no difference compared to patients with successful MI ablation. However, the width of the MI ablation area was significantly longer in patients with unsuccessful MI ablation (Table 2 ).