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.