Background: During RF application using an irrigation catheter, an initial higher temperature rise may occur not on the surface but just inside the myocardium because the myocardial surface is actively cooled by irrigation saline and surrounding blood. Therefore, it is possible that excitability on the myocardial surface will be recovered following acute successful RF ablation with a shorter application time.
Objective: Experimental study (n=18) was performed to assess how the excitability on the myocardial surface and depth of unexcitable myocardium was altered after RF ablation with a shorter application time.
Methods: Two needle electrodes with an inter-electrode distance of 1-mm were inserted in a coronary perfusion wedge preparation model of beating porcine myocardium (ablation and non-ablation sites). Distribution of the pacing threshold through the myocardial wall was examined both immediately and 40 minutes after RF application (10 g contact force, 30W energy, 15 seconds application).
Results: Before RF application, distribution of the pacing threshold was homogeneous throughout the myocardial wall (1.7±1.0 V). Immediately after ablation, maximum output pacing (10V, 1 ms) failed to capture the myocardium from on the surface to a depth of 3.2±1.3 mm inside consecutively. 40 minutes after ablation, excitation on the surface myocardium was recovered in 6 of the 18 preparations (to 0.8±0.8 mm inside). Maximum depth of the uncaptured myocardium also decreased to 2.8±1.2 mm, and this length correlated to the macroscopic findings of the ablated myocardium. On the other hand, electrical threshold at the non-ablation site was stable throughout the experimental protocol.
Conclusion: Uncaptured myocardium depth created by a shorter application time could be reduced with a recovery of surface myocardial excitability. Safe and no-recurrence ablation modes may need to be studied further.<!--EndFragment-->