Safety
Leshem et al demonstrated that HPSD ablation has a narrow efficacy to safety window. Small changes in ablation duration can potentially lead to non-transmural lesions in case of duration reduction or steam pops due to longer ablation duration or rapid temperature changes. Therefore, real time temperature feedback might be crucial to prevent overheating. Standard irrigated tip catheters used in the above mentioned HPSD ablation studies lack the ability to precisely measure tissue temperature in any catheter orientation due to a rather proximal temperature sensor placement in the catheter tip. It has been shown that HPSD ablation with 90 watts for 4 seconds using the QDot catheter with an enhanced thermocouple system was sensitive enough to detect small temperature changes (5;7). Adding an algorithm to scale the recorded temperature to actual tissue temperature leads to power adjustments due to temperature limit cutoffs and prevent overheating. The use of HPSD ablation with standard irrigated tip catheters in a power controlled mode is criticized by some authors irrespectively of published safety data arguing that temperature feedback is crucial (12).
Despite optimized temperature control and power adjustment, steam pops occurred in a rather high number of patients in our study (39%). None of them lead to severe complications like pericardial tamponade or clinical or neurological deficits. Not all patients with steam pops showed silent cerebral lesions detected on cMRI and the same number of patients without steam pops showed SCL (both n=2). Overall the number of SCL found in cMRI was comparable to other trials investigating cMRI findings using open-tip irrigated catheters (13).
Leshem et al reported one of the first clinical uses of the QDot catheter. In their work no steam pops were detected and the temperature controlled ablation mode with automated power reduction lead to a mean applied power of 60 watts (5). Using the same ablation mode and the same catheter we detected a mean power of 82 watts. A 20% of power increase in our group using the alleged same equipment and protocol might be an explanation of the high number of steam pops. A potential explanation for this finding is that in the first QDOT trials with 90watts/4sec the nMARQ ablation generator was used (5). During the early evaluation of the QDot catheter the use of the nGEN ablation generator was recommended by Biosense Webster. In late December 2020 Biosense Webster published a safety alert due to a higher then expected number of ”char” complaints during the external evaluation of nGEN Generator when using the 90w/4sec. At the date of publication the use of the QMODE+ using the nGEN ablation generator is stopped.