The mechanism of silent steam pop during radiofrequency catheter ablation: an ex-vivo porcine heart study
Authors: Nakamura R , Suzuki S A , Usui U M , Miyazaki M S , Sasano S T 
Published: October 2024

Abstract

Background
A steam pop (SP) during radiofrequency catheter ablation(RFCA) is usually assumed as an audible one and shows obvious changes of impedance, temperature or bipolar/unipolar potential of ablation catheter. Moreover, a SP generates a void which sometime penetrate the tissue and cardiac perforation. In clinical setting, we have sometimes experienced gas explosion from an ablating site detected only by intracardiac echography (ICE) without any sound or remarkable parameter changes, so called as a ‘silent’ SP (S-SP). However, the mechanism of this phenomenon is not yet to be clarified.

Methods
We performed RFCA of porcine ventricle using Tactiflex until a SP or 120s. In the first step, the output and the contact force (CF) of RFCA were fixed for 50W and 1g, 5g, 10g or 20g. Second, an ablation catheter was moved by every second with 50W. A SP was defined as suddenly gas explosion during RFCA detected by ICE and in case of non-audible SP by 2 persons standing 50cm away from ablation site, it was provided as a S-SP. Otherwise, we defined as audible one (A-SP). We analyzed the occurrence of S-SP and ablation parameters between S-SP and A-SP.

Results
In the first stage (n=24), 4 S-SPs and 17 A-SP were observed(S-SP; 3 in 1g and 1 in 20g, A-SP; 2 in 1g, 5 in 5g, 6 in 10g and 4 in 20g, p=0.0454). The ICE images of S-SP and A-SP seemed to be similar. S-SP significantly occurred in the setting of lower CF as compared with A-SP {3.0(2.25-16.5) vs. 8.0(5.0-21.5); p=0.0290}. There were no statistical differences concerning duration of RFCA, initial/final impedance, impedance drop, initial/maximum temperature. At the timing of SP, changes of potentials were relatively smaller in S-SP {bipolar: 0.975(0.565-6.410) vs. 5.700(3.680-8.915); p=0.0648, unipolar: 1.265(0.208-3.793) vs. 8.070(5.820-8.815); p=0.0003}. Voids formation after SPs were detected in 2(50%) of S-SP and 16(94%) of A-SP(p=0.0797).
In the second beating stage (n=46), 14 S-SPs and 20 A-SPs were observed (Figure 1). Although there were no differences of average/maximum CF throughout RFCA, S-SP dominantly occurred when a catheter was pulling back against the tissue, or at the bottom of CF curve (Figure2). Whereas A-SP did when a catheter was pushing toward tissue, or at the end of ascending limb of CF curve. For ablated lesion, S-SP exhibited less void or smaller crack (Figure1).

Conclusions
S-SP was difficult to detect without ICE and occurred in the combined condition of high power (50W) and lower CF. For the setting of beating mode, just like clinical environment, S-SP was involved while an ablation catheter was moved away from the tissue. Although S-SP seemed to be safer than A-SP due to less or smaller voids, continuous RFCA after S-SP might involve a big void or perforation. Therefore, it might be better to use ICE for the detection of S-SP, especially for a site accompanied by unstable CF, like papillary muscles.Figure 1.Ablation parameters in a cathetFigure 2.The timing of steam pop