Discussion
Prior studies investigating risk factors for the development of AF after
atrial flutter ablation have yielded inconsistent
results,1-2, 4-6,15-16 and effective risk
stratification for development of AF after AFL ablation remains an
important, unmet clinical need. Our primary findings are as follows: 1)
An overall incidence of AF after CTI AFL ablation of 40% in 114
consecutive patients at three years follow-up with routine clinical care
2) LAVI was the only independent predictor of AF after CTI AFL ablation
and 3) LAVI > 30 ml/m2 identified
patients significantly more likely to develop AF with a hazard ratio of
2.25, with similar risk of incident AF observed with LAVI 30-40
ml/m2 compared to LAVI ≥ 40 ml/m2.
While incidence of AF after typical AFL ablation in patients with no
known history of AF at three years follow-up has been reported to be up
to 82%,5 the 40% incidence observed in the present
analysis is consistent with that of several prior studies in which
incidence of AF after typical AFL ablation was observed to be 25-50% at
three years follow-up.1,6 Routine, ambulatory
arrhythmia monitoring was performed in ~40% of analyzed
patients, and monitoring intensity was similar between patients who
developed AF and those who did not develop AF.
Chen et al. investigated predictors of incident AF, including HATCH
score, in 216 patients after CTI AFL ablation and found that patients
with a HATCH score ≥ 2, and those with increased LA diameter were
significantly more likely to develop incident AF. 7The area under the receiver operator curve for HATCH score as a
predictor of incident AF after AFL ablation was 0.7. The authors
postulated that the HATCH score likely represented those patients with
enlarged and remodeled left atriums, however LAVI was not evaluated in
that study.7 The significance of the HATCH score was
subsequently investigated by Garcia-Seara et al. in 408 patients who
underwent typical AFL ablation and it was found that neither a HATCH> 2, nor a HATCH > 3 were
significant predictors of incidence of AF after typical AFL
ablation.8 They did find LA diameter to be
significantly associated with incidence of AF, with degree of
enlargement correlating with risk of incident AF, however LAVI was not
investigated in this study either. Neither HATCH score, nor any other
clinical or electrophysiologic parameter have been established as
reliable predictors of AF after AFL ablation. Our data is largely
consistent with these prior studies suggesting modest utility of HATCH
score and LA diameter as predictors of incident AF after typical AFL
ablation.
Studies investigating incidence of AF after AFL ablation have not
consistently included LAVI as a variable of interest. Limitations of LA
size assessment by LA diameter are well recognized.17Left atrial volume index is calculated via the biplane disk summation
technique, which incorporates fewer geometric assumptions than the
area-length methods and thus is perceived to be more accurate. Body
surface area is also known to largely impact left atrial size, therefore
indexing the calculated left atrial volume to body surface area also
allows for more accurate interpretation of left atrial volume
measurement. In the only prior study that we are aware of that assessed
LAVI as a predictor of AF after typical AFL ablation, Lee et al. found a
LAVI of 42.6 ml/m2 to be predictive of AF after AFL
ablation with a 69% sensitivity and 69.8%
specificity.16 The LAVI cutoff proposed by Lee, et al.
is considerably greater than our proposed cutoff of 30
ml/m2, and may have been related to greater prevalence
of structural heart disease and other comorbidities in their study.
Given the markedly higher LAVI cutoff found in Lee et al., sensitivity
analysis in our cohort comparing incidence of AF after CTI AFL ablation
in patients with LAVI 30-40 ml/m2 to that of patients
with LAVI >40 ml/m2 showed a similarly
elevated risk of incident AF in both groups.
Discordance of prognostic significance between LA diameter and LA volume
for development of AF was previously shown by Abecasis, et al. in
patients who have undergone PVI and CTI ablation for drug resistant
AF.18 In this study, LA volume derived from CT scan
was a significant predictor of arrhythmia recurrence, however
echocardiographic parameters including LA diameter did not have
significant predictive value.18 LAVI determined by
echocardiography was recently found to be significantly associated with
incidence of cardioembolic stroke and incident AF in patients with prior
cryptogenic stroke.19 Cryptogenic stroke and typical
AFL are similar conditions in that both are strongly associated with
coexistent AF, and identification of coexistent AF has significant
clinical implications including consideration of anticoagulation. The
consistency of association between elevated LAVI and incident AF across
study cohorts and disease states provides greater credibility for the
potential utility of LAVI for risk-stratification.
Three randomized clinical trials have evaluated prophylactic PVI in
patients with typical AFL and no prior history of AF, each of which has
yielded results favoring combined PVI and CTI AFL
ablation.4-6 These studies of relatively unselected
patients undergoing typical AFL ablation found that CTI plus
prophylactic PVI ablation resulted in absolute risk reductions for
incident AF of 10-28% compared to CTI ablation
alone.10 The benefit of prophylactic PVI would be
expected to be greatest in patients at greatest risk for development of
AF. The established benefit of prophylactic PVI may be substantially
greater than previously demonstrated in patients with LAVI of
>30 ml/m2, particularly with use of
improved ablation techniques for PVI.20
There were several limitations to this study. Although patients’ medical
records including all available ECG documentation were carefully
reviewed to exclude the presence of AF before ablation, minimally
symptomatic AF may have been present and undiagnosed. Similarly, the
frequency of post-ablation AF may be underestimated due to the absence
of longitudinal arrhythmia monitoring in all patients. LAVI was also
collected directly from echo reports instead of re-calculated, thus the
possibility of echocardiographer variability in measuring LAVI is
present. Additionally, this was a predominantly male patient population
and therefore these results cannot be generalized to females. Finally,
there are limitations to this study that are inherent to its
retrospective nature.