Discussion
In this large cohort study which
ran for over 10 years, the detection of LA thrombus at repeat sessions
after initial catheter ablation for AF was very low (0.8%) in patients
who underwent TEE examination and 0.5% in the total sample of patients
who underwent repeat ablation. The use of imaging modalities at repeat
ablation was increased when performed >180 days after the
first procedure, and all patients who developed LA thrombi were
scheduled to undergo repeat ablation >180 days after the
initial ablation. No patients who did not undergo any imaging evaluation
during the repeat session developed adverse events. Repeat ablation
>180 days, non-paroxysmal atrial arrhythmia, and lower LVEF
were independent predictors of thrombi development and severe SEC at
repeat ablation in the multivariate analysis.
LA thrombi are unlikely to develop after initial catheter ablation for
AF rather than prior to the first session, given the significantly
decreased AF burden and continuous anticoagulant use after
ablation.10-12 However, little is known about the
prevalence of thrombus development and the requirements for imaging
evaluation at repeat ablation are unclear. There is only one previous
study demonstrating a 0.8% rate of thrombi detection in 263 patients
who underwent repeat TEE within 365 days.13Nonetheless, all patients were prescribed warfarin, a vitamin K
antagonist, in the previous study which was conducted over a long period
of time. In contrast, an alternative anticoagulant, DOAC, which is
mostly used in AF ablation, has the advantage of quickly promoting and
maintaining its anticoagulant effect, which could support the
suppression of thrombus development after ablation. Our study is unique
in that it evaluated outcomes of
using various imaging modalities in patients who received DOACs and
warfarin, reflecting a recent trend in clinical practice.
However, despite the presumed safety and efficacy profiles of DOAC,
three patients still developed LA thrombi at repeat ablation in our
study, which indicates that a reduced risk remains and caution is still
warranted at repeat ablation. More importantly, the thrombi developed
even in patients with grade 0 SEC in the first session, and there is no
guarantee of the absence of thrombi in reference to the examination
findings obtained during the first session. Nonetheless, all these
patients had a possible reason for the development of thrombi in our
study, such as the long period until repeat ablation, inappropriate DOAC
use, and decreased cardiac function prior to repeat ablation. In this
regard, all patients who developed thrombi were scheduled to undergo
repeat ablation >180 days after the first procedure, and
the frequency of imaging evaluation was significantly increased when the
repeat ablation was performed >180 days after the first
procedure as compared to when performed at ≤ 180 days, which suggests
that this cutoff duration value should be one of the safety parameters
when considering the need for imaging evaluation to detect thrombi
before repeat ablation. Moreover, a possible association with the risk
of thrombus development in patients with decreased LVEF and
non-paroxysmal atrial arrhythmia was mentioned in a previous
report.13 Although a sub-therapeutic dose of warfarin
should be avoided considering its significant relation to thrombus
development despite less frequent use of warfarin to date, inappropriate
DOAC dose use also increases the periprocedural risk of
thrombi.13, 14 Nonetheless, with an expandable use of
DOAC uninterruptedly during ablation, it may be possible to selectively
screen patients to identify those at low risk of developing thrombi and
those at high risk and who require TEE at repeat
ablation.15 As long as patients with a low-risk
profile continue on oral anticoagulants and undergo early repeat
ablation, any imaging modality to determine the presence of LA thrombi
may be omitted. Our results could prove useful in deciding whether
imaging should be scheduled before repeat ablation according to each
patient’s clinical profile.
In addition to TEE, contrast-enhanced CT and ICE are useful alternatives
to exclude the possibility of LA thrombi, with the hope of obviating the
need for TEE before ablation. In a meta-analysis of studies using
delayed CT imaging protocols to screen for LA thrombi, the diagnostic
accuracy for detection of LAA thrombi was reported to be nearly
100%.9 However, obtaining the CT image some time
before the planned ablation day may limit its value, as indicated for
Patient 2 in Table 4. On the other hand, previous data suggested that
ICE could be valuable in safely and effectively detecting LA thrombi,
whereas the result reflected in large part the variability seen when
performing and interpreting the ICE imaging.16-18Moreover, all patients in which thrombi were detected in the present
study had D-dimer levels within normal limits before repeat
ablation;19 therefore, any imaging modality should
still be used to screen for thrombi in patients at presumed risk of
developing thrombi and those who cannot undergo TEE imaging.