3.4.2 Analysis of outcomes with repeated procedures included
The mean follow-up for both groups was 424 ± 338 days. In the ZF group,
there were fewer patients on AAD therapy (12.9% vs 36.1 %; p< 0.001). The overall success rate was higher in the ZF group
(98.3% vs 93.5%, p < 0.004). A Kaplan-Meier curve of
arrhythmia-free survival is shown in Figure 5. This difference was
present in the ZF adult subgroup only. The overall success rate was also
higher in patients without AAD therapy (98.4% vs 90.8%, p< 0.001), a difference present in all ZF subgroups. More
specifically, there was a higher AVRT-free survival rate (99.0% vs
90.9%, p = 0.011) in the ZF group. This difference was present
only in the ZF adult subgroup. There were also more procedures per
patient in the ZF group (1.13 ± 0.356 vs 1.05 ± 0.241, p =
0.002). Detailed information is presented in the supplementary data in
Table S4.
4.0 Discussion
The results of our analysis show comparable outcomes between the ZF and
CF approaches for the treatment of SVTs with regards to efficacy and
safety. The rate of complications was low among both groups, with no
major procedural complications occurring.
The differences in the mean age and mean BMI of patients between groups
in our study can be explained by the inclusion of paediatric patients in
the ZF group only, an explanation confirmed by the ZF subgroup analysis.
The rationale behind such a decision is that the stochastic and
deterministic effects of ionising radiation are especially harmful to
paediatric patients. Due to their developing bodies and long life
expectancy post-exposure, they are more susceptible to developing cancer
[9]. As such, we referred them to ZF CA as a first choice.
Interestingly, some differences in the use of AAD therapy before and
after the CA between both groups were discovered. These differences
cannot be explained by the inclusion of paediatric patients as evidenced
by the analysis of the ZF paediatric and adult subgroups. It can be
hypothesised that, since the same physicians both referred patients for
CA procedures and performed post-procedural follow-up, there was some
degree of individual physician preference for the use of AADs.
Regarding the procedural data, we found a statistically significant
difference in procedural duration, with the mean duration being lower in
the ZF group (94.2 ± 50.4 min vs 104.0 ± 54.0 min, p = 0.002).
Our findings are in line with previous studies investigating the ZF
approach in various SVTs, which reported the mean procedural duration to
range from 50 to 129 minutes [6,10–13]. Perhaps in contrast with
the available literature, we found the procedural duration to be lower
in almost all types of arrhythmias and locations of the substrate except
in right-sided APs. We hypothesise that the features of the 3D EAM
system not present in the CF approach are the cause of the shorter
procedure times. Firstly, the ability to annotate the location of
previously effective or ineffective ablation lesions facilitates the
decision-making process during the CA procedure in almost all cases.
Secondly, the distance between the His-bundle annotation and ablation
catheter can be constantly monitored from two different views, which can
be especially helpful in AVNRT, as well as for mid-septal and
para-Hisian location of APs. Finally, local activation time mapping can
identify the location of APs or the origin of AT both more rapidly and
accurately. Additionally, our analysis of the learning curve showed that
procedure time drops significantly after the first year of experience.
Features of the 3D EAM system can perhaps explain the higher median
number of RF lesions in the ZF group (8 (4 – 17) vs 7 (4 – 13),p = 0.015). We hypothesise that the ability to localise the
successful ablation site with the 3D EAM system can prompt the operator
to add additional adjacent bonus lesions. Without the use of the 3D EAM
system, the exact location characterisation can be challenging. However,
the difference was only present in the ZF adult subgroup (11 (6 – 20)
vs 7 (4 – 13), p < 0.001). We suggest that the smaller
hearts of paediatric patients as well as the potential for important
heart structures such as the AV node and His bundle to be closer to the
successful ablation site may prevent the operator from performing
additional ablations despite the advantages of using the 3D EAM system.
There were no statistically significant differences between the two
groups regarding the overall procedural success rates. In the subgroup
analysis, the procedural success rate in patients who underwent RF
ablation for AVNRT was lower in the ZF adult subgroup (95.8% vs 99.4
%, p = 0.040). However, recurrence rates during follow-up after
index procedure in those groups were similar.
A relatively lower procedural success rate for AT in the ZF group
(70.3% vs 83.8%, p = 0.167) and a relatively higher procedural
success rate for right-sided APs in the ZF adult subgroup (100% vs
57.1%, p = 0.091) did approach but not reach statistically
significant difference. The number of patients with AT and right-sided
APs was also too low to be representative and useful for any further
statistical analysis. In addition, we found that both groups had no
major complications and no statistically significant difference in minor
complication rate (CF vs ZF; 0.4% vs 0.0%, p = 0.304).
Importantly, the reduction of radiation dose was substantial (CF; DIA:
13.9 ± 11.0 minutes; DAP: 606 ± 1003 mGym2; p< 0.001). These results are in line with the findings from
previously published studies, adding to the body of evidence on the
feasibility and safety of ZF SVT ablation [6, 10–15].
Regarding long-term outcomes, there were no statistically significant
differences between groups when only the data from the index procedure
was analysed. The overall success rate did not differ between groups (ZF
vs CF; 87.1% vs 89.2%, p = 0.422). This is also in line with
previously published studies that reported no differences between the ZF
and CF approach [10, 11, 13]. When the data on repeated procedures
was included, the overall long-term outcomes differed between the
groups, being significantly higher in the ZF group (98.3% vs 93.5%;p = 0.004). This was also true when only patients with AVRT were
analysed (99.0% vs 90.8%; p = 0.010). In the subgroup analysis
of procedures for AVRT, this difference was notable only in the ZF adult
subgroup (100% vs 90.8%, p =0.031). These differences can be
attributed to the higher number of procedures per patient in the ZF
group (1.13 ± 0.356 vs 1.05 ± 0.234; p = 0.001) improving the
overall success rate with included repeat procedures. As with the
explanation for differences in the use of AADs, these differences in
outcomes cannot be explained by the inclusion of paediatric patients, as
evidenced by the analysis of the ZF paediatric and adult groups. It can
again be hypothesised that in cases where tachycardia recurred, there
was some individual physician preference for referring patients for
repeat procedures versus the use of AADs.
An important finding that we would like to address is that CA procedures
of AVNRT performed with cryoenergy had successful long-term outcomes in
both analyses (100% after index procedure; 100% after repeated
procedures were included). This is perhaps in contrast with the
available published data. In a meta-analysis of cryoablation versus RF
ablation for AVNRT, the long-term recurrence rate was significantly
higher (9.7% vs 3.8%; p = 0.003) in patients ablated with
cryoenergy [16]. The high success rate of ZF cryoablation in our
study can, at least partially, be explained with the use of the 3D EAM
system, which enables the operator to mark the location of a possible
mechanical termination of the targeted slow pathway by the cryocatheter
[17]. With this approach, the site of the mechanical block can be
accurately ablated, in contrast to the CF approach where the exact
location of the mechanical block can be more difficult to localise. An
additional factor adding to the high success rate may be the utilisation
of cryomapping during the ongoing AVNRT with tachycardia termination
during ongoing cryoablation serving as an endpoint. This technique was
previously published by Eryazici et al. and demonstrated a high
long-term success rate [18].
Lastly, there are some limitations of the ZF approach when only a 3D EAM
system is used for guidance. One such instance is that of transseptal
punctures. To overcome the limitations of the 3D EAM system, the use of
ICE for transseptal puncture is mandatory in our institution [19].
With ICE guidance, the operator can successfully identify true
endovascular borders and anatomical structures as well as their relation
to the transseptal needle. The usefulness of ICE, however, goes beyond
guiding the transseptal puncture; with visual inspection, the presence
of possible masses in the left atrium, on the long sheath, and on the
catheter inserted into the left atrial cavity can be identified and
further appropriate actions can be taken, possibly preventing certain
potential procedural complications. It also offers precise guidance in
manipulating catheters in the heart, including supervising the stability
of the ablation catheter during lesion formation. Importantly, the
pericardial space can be readily visually inspected for early detection
of pericardial effusion.
5.0 Limitations
Our study has several limitations. Due to the nature of retrospective
studies, our results may have been influenced by selection bias. Two
factors need to be addressed here: first, the inclusion of paediatric
patients exclusively in the ZF group, which might have influenced the
study results. However, several studies showed similar procedural
outcomes compared to adult patients [20, 21]. Furthermore,
additional analysis of our ZF subgroups comparing baseline
characteristics and procedural outcomes did not show significant
differences between adult and pediatric patients. Second, cryoenergy was
used only in the ZF group. This may also have an impact on the
procedural success rate. Also, the learning curve related to the ZF
procedures might have impacted procedural parameters and outcomes in
comparison to the CF procedures. Finally, all data was collected at a
single centre; as such, the results may not be directly applicable to
experiences in other populations.
6.0 Conclusions
Our study demonstrated that the safety and efficacy of ZF CA procedures
for right and left-sided SVTs is comparable to that of the CF CA
approach. To further assess the non-inferiority of the ZF approach
compared to the CF approach, a randomised trial comparing both methods
is needed.