Significant p values (<0.05) are highlighted in bold.
Despite a trend towards lower peak AI, use of a long sheath at the Mid
CTI was associated with a greater and more rapid drop in impedance.
Discussion
Our study made use of Ablation Index (AI) to examine ablation lesion
characteristics in the treatment of typical atrial flutter. We found
that using a target AI of 600Wgs across the CTI was safe, but there were
significant inconsistencies in energy delivery according to anatomical
site, with particularly notable variance seen in the Mid CTI.
Whilst mean contact force and power were similar across all CTI sites,
higher peak AI values were seen Mid CTI, which appears to be mediated
through compensatory increases in lesion duration. However, at this
site, increased peak AI values did not necessarily correlate with
greater impedance drop, and both the rate of impedance drop and the mean
lesion temperature were significantly lower at this site despite similar
catheter tip power, mean contact force and irrigation techniques,
suggestive of inferior lesion efficacy.
We propose this occurs because of significant temporal fluctuations in
contact force and catheter tip angle which are most exaggerated at the
Mid CTI (figures 3 & 4). It is accepted that changes in catheter angle
of incidence affect lesion size , and that consistent tissue contact
produces larger lesions than intermittent contact (20). The fluctuations
seen in our study are likely to indicate catheter tip instability
encountered due to established anatomical anomalies Mid CTI (13).
Consequently, whilst the relationship between AI and ID is mostly linear
(figures 1 & 2) – and hence peak AI is a reasonable surrogate for
lesion efficacy in atrial flutter – we suggest that operators should
exercise caution at the Mid CTI, where higher peak AI values do not
necessarily equate to more effective ablation.
The finding that fluctuations in contact force Mid CTI become more
pronounced at higher AI values is unexpected (figure 3); we suggest this
may relate to the accumulation of local tissue oedema as a result of
more prolonged radiofrequency applications, which may in turn further
retard impedance drop - this hypothesis could not be assessed in our
study. Importantly, the use of a long sheath appears to confer
additional stability to the catheter tip and overcome the majority of
inconsistencies in force and angle, although a significant increase in
axial plane fluctuation was noted at the ventricular margin (figure 4).
This finding may represent catheter and sheath overreach at the point of
the valve annulus into the ventricular inflow tract; a long sheath
remained effective in stabilising contact force at this site.
The optimal AI for safe and effective CTI ablation is not well
established; our target AI of 600Wgs was based on retrospective analysis
performed at our centre (18), and is in excess of that which is
generally recommended for left atrial procedures. Importantly, we did
not record any acute or long-term complications with our protocol for
CTI ablation. Our mechanistic study was not designed to assess long-term
procedural efficacy, however it is encouraging that 97.4% of patients
were in sinus rhythm after 6 months’ follow-up. Longer term clinical
review is in progress.
To our knowledge, we are the second group to analyse AI in the ablation
of atrial flutter. Zhang et al. (2019) compared AI-guided ablation
versus contact-force guided ablation of the CTI, and found higher rates
of first-pass conduction block in their AI-guided group (21). These
authors delivered ablation with AI targets of 500Wgs to the anterior two
thirds of the CTI and 400Wgs to the posterior third; these target values
were derived from studies of PVI and adjusted according to accepted
variations in CTI thickness. They found that acute reconnection of the
CTI was more common at the ventricular aspect of the CTI with AI values
of <450Wgs. In contrast to our study, the authors’ protocol
delivered higher AI values at the anterior segments and found that this
was associated with a relatively larger drop in impedance. Temporal
changes in contact force or catheter angle, and the correlation of
impedance drop with different peak AI values, were not examined. Our
study is the first to make use of precise AI-associated lesion delivery
characteristics to define the heterogeneity encountered when ablating
the CTI.
Whilst our findings may have been more sharply delineated with the
addition of peri- or -intraprocedural imaging studies, in clinical
practice outcomes for CTI ablation without these techniques are already
reasonable . Accordingly, our aim was to explore a novel utility of an
existing technology as a vehicle for incremental improvements in
procedural success and safety, which could be adopted clinically without
considerable additional resources. We have examined the correlation of
pre-specified AI targets with post hoc values of mean ID at the CTI; a
multi-centre trial (LOCALIZE) assessing the efficacy of PVI guided by
live measurements of local impedance is ongoing, and may further
contribute to our understanding of predicting lesion transmurality from
intraprocedural variables (22).
Our study has important limitations. Whilst our patient sample is
multicentre, patient numbers are small; the number of extracted lesion
data points was sufficient to permit key analyses, however meaningful
comparisons of additional potential confounders – for example catheter
curve, patient co-morbidities, or the use of general anaesthetic or of
class III anti-arrhythmic drugs – could not be performed. AI itself is
validated only for ablation catheters made by Biosense Webster; our
results may not be generalisable to equipment from other manufacturers.
Likewise, our operators did not use surround flow (STSF) catheters,
which are known to have different biophysical efficacy than their ST
equivalent and hence our findings cannot be extrapolated to this
technology . We used a measure of impedance drop as marker of ablation
efficacy; this is a widely accepted surrogate in the literature however
histological analysis is the gold standard for the assessment of lesion
quality and this was not available in our study.
Conclusions
In the ablation of CTI-dependent atrial flutter, the use of ablation
index (AI) appears safe when delivering lesions up to 600Wgs. Whilst AI
is generally a reliable marker of ablation efficacy by impedance drop,
we suggest that operators exercise caution when interpreting AI values
at the Mid CTI, where anatomical anomalies may introduce catheter
instability and hence impede energy delivery. Higher AI values are
required Mid CTI to deliver lesions comparable to the CTI margins, and
this phenomenon seems to be mediated by temporal fluctuations in contact
force and catheter angle. It appears that the use of a long sheath may
mitigate these fluctuations and restore a more linear relationship
between AI and ID. In the absence of a long sheath, an ablation strategy
which prescribes higher AI targets to the Mid CTI may improve acute
lesion efficacy and hence long-term outcomes, however this requires
prospective validation.
REFERENCES
- Thiagalingam A, D’Avila A, Foley L, Guerrero JL, Lambert H, Leo G,
Ruskin JN, Reddy VY Importance of Catheter Contact Force During
Irrigated Radiofrequency Ablation: Evaluation in a Porcine Ex Vivo
Model Using a Force‐Sensing Catheter Journal of Cardiovascular
Electrophysiology, 2010, 21 (7)
- Yokoyama K, Nakagawa H, Shah DC, Lambert H, Leo G, Aeby N, Ikeda A,
Pitha JV, Sharma T, Lazzara R, Jackman WM Contact Force Sensor
Incorporated in Irrigated Radiofrequency Ablation Catheter Predicts
Lesion Size and Incidence of Steam Pop and Thrombus. Circulation:
Arrhythmia & Electrophysiology, 2008, Vol. 1 (5).
- Reddy V, Shah D, Kautzner J, Schmidt B, Saoudi N, Herrera C, Jais P,
Hindricks G, Peichl P, Yulzari A, Lambert H, Neuzil P, Natale A, Kuck
K-H The relationship between contact force and clinical outcome
during radiofrequency catheter ablation of atrial fibrillation in the
TOCCATA study. Heart Rhythm, 2012, Vol. 9 (11).
- Nakagawa H, Ikeda A, Govari A, Papaioannou T, Constantine G, Bar-Tal
M. Prospective study to test the ability to create RF lesions at
predicted depths of 3, 5, 7 and 9 mm using a new formula incorporating
contact force, radiofrequency power and application time
(Force-Power-Time Index) in the beating canine heart. Heart Rhythm,
2013, vol. 10., S481
- Hussein A, Das M, Chaturvedi V, Asfour IK, Daryanani N, Morgan M,
Ronayne C, Shaw M, Snowdon R, Gupta D Prospective use of
Ablation Index targets improves clinical outcomes following ablation
for atrial fibrillation. Journal of Cardiovascular Electrophysiology,
2017, Vol. 28. (9)
6. Pranata R, Vania R, Huang I Ablation-index guided versus
conventional contact-force guided ablation in pulmonary vein isolation -
Systematic review and meta-analysis. Indian Pacing Electrophysiol J. ,
2019, Vol. 19. (4)
7. Santoro F, Metzner A, Brunetti ND, Heeger C-H, Mathew S, Reissman B,
Lemes C, Maurer T, Fink T, Rottner L, Inaba O, Kuck K-H, Ouyang F,
Rillig A Left atrial anterior line ablation using ablation index
and inter-lesion distance measurement. Clinical Research in Cardiology,
2019, Vol. 108. (9)
8. Phlips T, Taghji P, El Haddad M, Wolf M, Knecht S, Vandekerckhove Y,
Tavernier R, Duytschaever M. Improving procedural and one-year
outcome after contact force-guided pulmonary vein isolation: the role of
interlesion distance, ablation index, and contact force variability in
the ’CLOSE’-protocol. Europace, 2018, Vol. 1.
9. Ullah W, Hunter RJ, Finlay MC, McLean A, Dhinoja MB, Sporton S,
Earley MJ, Schilling RJ Ablation Index and Surround Flow Catheter
Irrigation: Impedance-Based Appraisal in Clinical Ablation. JACC:
Clinical Electrophysiology, 2017, Vol. 3. (10)
10. Kawaji T, Hojo S, Kushiyama A, Nakatsuma K, Kaneda K, Kato M,
Yokomatsu T, Miki S Limitations of lesion quality estimated by
ablation index: An in vitro study Journal of Cardiovascular
Electrophysiology, 2019, Vol. 30. (6)
11. Pérez FJ, Schubert CM, Parvez B, Pathak V, Ellenbogen K, Wood MALong-term outcomes after catheter ablation of cavo-tricuspid
isthmus dependent atrial flutter: a meta-analysis. Circ Arrhythm
Electrophysiol., 2009, Vol. 2. (4)
12. Brugada J, Katritsis DG, Arbelo E, Arribas F, Bax JJ,
Blomström-Lundqvist C, Calkins H, Corrado D, Deftereos SG, Diller GP,
Gomez-Doblas JJ, Gorenek B, Grace A, Ho SY, Kaski JC, Kuck KH, Lambiase
PD, Sacher F, Sarquella-Brugada G, Suwalski P, Zaza A; ESC Scientific
Document Group 2019 ESC Guidelines for the management of patients
with supraventricular tachycardia. Eur Heart J, 2019, Vol. ehz467.
13. Klimek-Piotrowska W, Hołda MK , Koziej M, Holda J, Piatek K, Tyrak
K, Bolechala F Clinical Anatomy of the Cavotricuspid Isthmus and
Terminal Crest. PLoS ONE, 2016, Vol. 11. (9)
14. García-Dora J, Pérez-Rodon J, Rodriguez-García J, Sarrias-Merce A,
Rivas-Gandara N, Roca-Luque I, Francisco-Pascual J, Santos-Ortega A,
Martin-Sanchez G, Ferreira-Gonzalez I, Rodriguez-Palomares J,
Evangelista-Masip A, Garcia-Dorado D, Moya-Mitjans A Predictors of
acute inefficacy and the radiofrequency energy time required for
cavotricuspid isthmus-dependent atrial flutter ablation. Journal of
Interventional Cardiac Electrophysiology, 2017, Vol. 49. (1)
15. Paetsch I, Sommer P, Jahnke C, Hilbert S, Loebe S, Schoene K,
Oebel S, Krueger S, Weiss S, Smink J, Lloyd T, Hindricks
G Clinical workflow and applicability of electrophysiological
cardiovascular magnetic resonance-guided radiofrequency ablation of
isthmus-dependent atrial flutter: European Heart Journal -
Cardiovascular Imaging, 2019, Vol. 20. (2)
16. Kumar S, Morton JB, Lee G, Halloran K, Kistler PM, Kalman JM.High Incidence of Low Catheter-Tissue Contact Force at the
Cavotricuspid Isthmus During Catheter Ablation of Atrial Flutter:
Implications for Achieving Isthmus Block. J Cardiovasc Electrophysiol.,
2015, Vol. 26. (8)
17. Baccillieri MS, Rizzo S, De Gaspari M, Paradiso B, Thiene G, Verlato
R, Basso C Anatomy of the cavotricuspid isthmus for radiofrequency
ablation in typical atrial flutter. Heart Rhythm, 2019, Vol. 16. (11)
18. Maclean E, Simon R, Dhillon G, Ahsan S, Hunter RJ, Behar, JMUse of ablation index to understand lesion delivery in the era of
contact force guided ablation for cavo-tricuspid isthmus dependent
atrial flutter. European Journal of Arrhythmia and Electrophysiology,
2019, Vol. 5. (Suppl. 1)
19. Reichlin T, Lane C, Nagashima K, Nof E, Chopra N, Ng J, Barbhaiya C,
Tadros T, John R, Stevenson WG, Michaud GF Feasibility, efficacy
and safety of radiofrequency ablation of atrial fibrillation guided by
monitoring of the initial impedance decrease as a surrogate of catheter
contact J Cardiovasc Electrophysiol. 2015, 26 (4), 390-396
20. Shah D, Lambert H, Nakagawa H, Langenkamp A, Aeby N, Leo G.Area Under the Real-Time Contact Force Curve (Force-Time Integral)
Predicts Radiofrequency Lesion Size in an in Vitro Contractile Model J
Cardiovasc Electrophysiol., 2010, 21 (9)
21. Zhang T, Wang Y, Han Z, Zhao H, Liang Z, Wang Y, Wu Y, Ren XCavotricuspid isthmus ablation using ablation index in typical
right atrial flutter. Journal of Cardiovascular Electrophysiology,
2019, Vol. 30. (11)
22. Retrieved from
https://clinicaltrials.gov/ct2/show/NCT03232645: Electrical
Coupling Information From The Rhythmia HDx System And DirectSense
Technology In Subjects With Paroxysmal Atrial Fibrillation (LOCALIZE)
FIGURE LEGENDS
Figure 1: Relationship between peak ablation index (Wgs) and mean
impedance drop (Ohms; mean ± SD) for all CTI lesions. Pearson’s
R2=0.89, p<0.0001.
Figure 2: Relationship between peak ablation index (Wgs) and mean
impedance drop (Ohms) per lesion according to CTI anatomical site (V CTI
R2=0.95, p<0.0001, Mid CTI
R2=0.15, p=0.21, IVC CTI R2=0.88,
p<0.0001).
Figure 3: Average temporal fluctuation in contact force (mg/s) per
ablation lesion according to peak ablation index, stratified according
to CTI anatomical site and the use of a long sheath.
Figure 4: Average temporal fluctuation in catheter angle of incidence
(degrees/s) in the lateral and axial planes for each ablation lesion,
stratified according to CTI anatomical site and the use of a long
sheath. Significant p values highlighted; other relationships
non-significant.