Catheter navigation by intracardiac echocardiography enables zero-fuoroscopy linear lesion formation and bidirectional cavotricuspid isthmus block in patients with typical atrial futter

Introduction

Intracardiac echocardiography (ICE) has been implemented early in catheter ablation of cardiac arrhythmias[1]. Some of the advantages of using ICE in electrophysiology (EP) procedures are the ability to safely guidetransseptal puncture for left atrial access, precise localisation of the ablation catheter tip in relation to the target substrate and important anatomical structures, earlyrecognition of complications etc. [2,3]. Te real-timevisualisation of anatomical landmarks and EP cathetersvia ICE facilitates ablation procedures both in patientswith normal anatomy, as well as in those with untreatedor corrected complex congenital heart diseases [4,5].

Another advantage of ICE technology is the potential to reduce radiation exposure in EP procedures. Asignifcant reduction in fuoroscopy time and dosagehas been reported for cryo-balloon ablation in patientswith atrial fbrillation when using ICE for balloonocclusion confrmation [6]. Furthermore, the combination of ICE with three-dimensional mapping systemsenables zero- or near-zero-fuoroscopy ablation of leftatrial or ventricular arrhythmias [7,8]. In previousstudies, we have demonstrated the feasibility and safetyof ICE-guided focal cryothermal ablation of the slowpathway in patients with atrioventricular nodal re-entrytachycardia (AVNRT) [9,10]. Compared to conventional fuoroscopic guidance, the ICE-guided real-timeechocardiographic visualisation of the ablation catheterwithin the triangle of Koch may shorten the cryo-ablation procedure in AVNRT patients, as demonstratedin our previous work [10]. Te advantage of reducingor avoiding fuoroscopy by ICE visualisation may beexpanded in other EP procedures, especially in thosewith known arrhythmogenic substrate.

In this prospective study, we aimed to investigate thefeasibility and safety of exclusively ICE-guided EP catheter navigation to create a linear lesion and bidirectionalcavotricuspid isthmus block in patients with ongoing ordocumented typical atrial futter.

Methods

In this study, we enrolled consecutive patients with electrocardiographic (ECG) documentation of atrial futter(AFL) suggesting cavotricuspid isthmus (CTI)-dependentAFL and indication for CTI ablation after giving theirinformed consent. Patients with transvenous leads, otherimplanted cardiac devices, previous cardiac surgery, ordeformations of the spinal column were excluded fromthis study. Patients with insufcient oral or intravenousanticoagulation therapy in the last three weeks underwent a transoesophageal echocardiography (TEE) priorto the EP procedure to exclude intracardiac thrombi,except for those presenting sinus rhythm.

Electrophysiological study

Three commercial sheaths (two 8F and one 7F) wereintroduced into the right femoral vein after localanaesthesia using the Seldinger technique. Zero-fluoroscopy catheter navigation via ICE was attempted inall patients. Medical staff and patients did not wearx-ray protection equipment, but fluoroscopy and leadaprons were available as a bail-out navigation strategy. ICE was performed using a steerable catheter(8F, two-dimensional; AcuNav™, Biosense Webster,Inc.) coupled to the ACUSON SC2000 Prime echocardiographic system (Siemens AG, Munich, Germany).Two common EP catheters were employed to performoverdrive stimulation, differential pacing, and radiofrequency ablation of the CTI (6F decapolar steerablediagnostic catheter, Inquiry™and 7F irrigated radiofrequency ablation catheter, Therapy™Cool Flex™;both Abbott, Eschborn, Germany). We have describedthe navigation of the AcuNav™and EP catheters indetail in our previous work [9]. The ICE-catheter wasmanoeuvered from the femoral vein to the right atriumby gentle advancement following the blood flow direction (as assessed by colour doppler) and continuousparallel adjustment of the ICE-catheter tip to the femoral, iliac, or inferior caval vein walls, (Fig. 1a). Thereal-time visualisation by ICE was used to safely guidethe two other EP catheters to specific positions in theright atrium or coronary sinus.

If AFL was present at the beginning of the procedure,overdrive pacing at CTI locations were performed toconfrm concealed entrainment and a post-pacing interval (PPI) equal or slightly longer than the AFL cyclelength (CL), (Fig. 1b and c, Additional fle 1). Tereafter,the Inquiry™catheter was placed into the coronary sinus,(Fig. 1d–f).

After confrmation of CTI- dependent AFL or inpatients presenting sinus rhythm, CTI ablation wasperformed using 50 W, open irrigated radiofrequencycurrent. Te ablation catheter was dragged from the tricuspid anulus to the inferior caval vein at the lowest position on the standard ICE-plane, as seen in Fig. 2a–d andAdditional fles2,3,4. Te inversion manoeuvre was performed if poor contact of the catheter tip with the targetsubstrate was noticed (Fig. 2e and f).

A straight ablation line was attempted by maintaining a stable echocardiographic plane and manoeuvringthe ablation catheter on that plane. After completionof the ablation line, diferential pacing was performedusing the two mentioned EP catheters. In patients withno bidirectional CTI block after completion of the ablation line, further ablations guided by local potentialswere performed. After successful ablation, pericardial  efusion was excluded by ICE visualisation and a controltransthoracic echocardiography (TTE) was performedbefore discharge from the hospital. A vascular ultrasoundexamination was performed if inspection or auscultationof the access side before discharge revealed a pathologicalresult.

Echocardiographic parameters

Diferent anatomic parameters were assessed by ICE toanalyse their correlation with the duration of diferentsteps or the entire EP procedure. CTI length was defnedas the distance between the tricuspid valve ring and theinferior vena cava, while the depth of the CTI pouch wasmeasured from the line connecting those two edges tothe deepest CTI location. Te prominence of the Eustachian ridge was measured from its highest locationto the line connecting the two CTI edges, see Fig. 3fordetails.

Statistical analysis

Categorical parameters are presented as counts andpercentages, whereas continuous variables are presented as mean values ± standard deviation. Spearman’srank correlation was used to analyse the relationship between CTI length, depth of the CTI pouch, orprominence of the Eustachian ridge and the ablation or EP procedure duration. Te t-test was used to calculate the level of signifcance; ap-value < 0.05 was considered statistically signifcant. Statistical analysis wasperformed using SPSS Version 27 (IBM, Armonk, NY,USA).

Results

Zero-fuoroscopy CTI ablation was attempted in thirtyconsecutive patients (mean age 72.9±11.4 years, 21male) with ECG recordings suggesting ongoing (n=23)or recent CTI-dependent AFL. Patients’ baseline characteristics are shown in Table 1.

All EPSs could be successfully accomplished withoutthe need for fuoroscopy, relying solely on ICE visualisation for catheter navigation. CTI-dependent AFL wasconfrmed by the entrainment manoeuvre in all patientswith ongoing AFL. Mean EPS duration, defned as thetime interval from the frst venous puncture to removalof all sheaths, was 41.4±19.9 min. Mean ablation procedure duration, defned as the time interval from the beginning of the frst RF ablation to the end of the lastone, was 20.8±17.1 min. Figure 4shows the duration ofthe diferent EPS steps in detail. RF ablation was appliedfor 6.0±3.1 min (50 W, open irrigated RF ablation in allpatients). After the last RF application, bidirectional CTIblock was confrmed by diferential pacing in all patients.Table 2shows the electrophysiological parameters of all patients.

In a series of 30 consecutive patients, who recentlyunderwent fuoroscopy guided CTI ablation in ourcentre, mean EPS duration, mean ablation procedureduration and total RF ablation time were 34.7±13.2,20.1±11.7 and 9.5±5.0 min, respectively.

Mean CTI length and depth of the CTI pouch in thestudy group were 32.4±7.2 mm and 5.5±1.5 mm, respectively. Te mean ER prominence was 5.0±1.9 mm. TeCTI pouch was shallower in patients with an ablationprocedure duration above the median (4.8±1.1 mm vs.6.4±0.9 mm,p=0.04), while CTI length or ER prominence did not correlate with EPS duration. Table 3showsthe Spearman’s rank correlation coefcients and the levelof signifcance between these echocardiographic parameters and the EPS or ablation procedure (ABL) duration.

No pericardial efusion, vascular complications, orelectrical disturbances were observed in the study population. One patient developed an intramural hematoma during ablation, but it remained asymptomaticand constant throughout the procedure (see Fig. 5andAdditional fle 5for details). At the end of the procedureor the day thereafter, the intramural hematoma couldnot be detected by TTE.

No other major or minor complications were observedin this study. All patients could be discharged from thehospital the day after the procedure after excluding procedure related pathological results in the control ECG or transthoracic echocardiography.

Discussion

In this prospective series of patients with CTI-dependent AFL, we demonstrated the feasibility of ICE-guidedcatheter navigation to achieve a successful zero-fuoroscopy ablation procedure within a reasonable time interval and with no complications related to the navigation technique.

ICE is available in most modern high- or mediumvolume EP centres, and the advantages of an excellentreal-time visualisation of the ablation catheter, targetsubstrate, or anatomical landmarks by ICE has beenpreviously reported for diferent ablation procedures[7,11,12]. Navigation of the ablation catheters or ICEcatheter itself in those studies has been mostly guidedby fuoroscopy or three-dimensional electro-anatomical mapping (3D EAM). Navigation of ICE or EP catheters relying entirely on intravascular or intracardiacechocardiographic imaging requires good anatomical knowledge and expertise in ICE-catheter control.As operators in this study had previously experiencedICE-guided zero-fuoroscopy ablation of the slow pathway in AVNRT patients [9,10], they did not face anydifculties in manoeuvring the catheters to the specifcregions in the right atrium or coronary sinus; however,the simultaneous usage of an additional catheter forcesthe operator to switch back-and-forth between the ablation and ICE catheter or requires a second operator tomaintain a stable two-dimensional echocardiographicplane. Tis hurdle could be overcome by the implementation of three-dimensional ICE catheters with broadechocardiographic volumes or ICE catheter robotic control systems with automated catheter tip repositioning,which has been successfully used in heart phantoms andanimal experiments [13].

Due to its high reputation in early recognition andreduction of potential complications during ablationprocedures, ICE has been increasingly used in EP laboratories for the last few years. Not only can the usage ofICE signifcantly reduce the risk of cardiac perforation,especially during transseptal puncture [14], it can immediately reveal intracardiac thrombus formation duringEP procedures as well [15], enabling a quick initiation ofspecifc therapeutic measures. In our study, we did notface any severe complications, such as cardiac perforation, development of pericardial efusion, or intracardiacthrombus formation, as CTI RF ablation is a relativelyshort and commonly safe procedure. However, we documented the asymptomatic development of an intramuralhematoma after an unobtrusive RF ablation on the tricuspid valve-CTI junction in one case, a complication thatmight happen more often than we assume and remainunrecognised as its diagnosis without ICE control couldbe difcult. It certainly needs to be proved in large studies if the ability of real-time visualisation of potentialcomplications outweighs the disadvantages of using anadditional vascular access side and an 8F catheter (ICE catheter).

Besides the efcacy and safety, overall ablation time,ablation procedure and EPS duration are importantaspects while introducing a novel, though simple, zerofuoroscopy ICE-guided navigation technique for CTIablation. Technical development, modern ablationcatheters, and increasing experience in electrophysiology have led to shorter ablation procedures or EPSduration in patients with CTI-dependent AFL. In mostrecent studies, the ablation time in patients who underwent RF CTI ablation with common open irrigated RFcatheters ranged from 10 to 15 min [16–18]. In a largerepresentative series of 1,051 patients, Kakehashi et al.reported a total radiofrequency time of 10.3 ± 6.6 minto achieve bidirectional CTI block [16]. Katritsis andBacillieri report similar RF delivery time across theCTI in smaller series of patients with CTI-dependent 

AFL (12.2 and 10.7 min respectively) [17,18]. Usingcontact force control and ablation- or lesion-size index(AI, LSI), as well as novel ablation strategies and catheters, such as high/very-high-power short-duration RFablation or the diamond temp ablation catheter, seemsto signifcantly shorten the RF delivery time in thesepatients, but their usage is inevitably related to highercosts [19–21]. In our series, the total radiofrequencytime was 6.0 ± 3.1 min with a mean RF applicationnumber of 13.0 ± 6.2 and, therefore, markedly shorteras in the mentioned studies and our series of patientswith fuoroscopy guided CTI ablation. Tis might beexplained by the continuous ICE-guided visualisationof the anatomy and avoidance of unnecessary and ineffective ablations in sites with poor tissue contact, asillustrated in Fig. 2e. Whether the above-mentionednovel ablation techniques or usage of contact forcecatheters could further reduce the total radiofrequencytime in the setting of ICE-guided catheter navigationin patients with CTI-dependent AFL should be investigated in further studies. Te mean ablation procedureduration and mean EPS duration in our series, with20.8 ± 17.1 and 41.4 ± 19.9 min, respectively, lie wellwithin the range of the same parameters in the mentioned studies as well. Due to the more challengingcatheter placement when relying solely on ICE visualisation, mean EPS duration in the ICE-guided groupwas slightly longer than the one in the mentionedseries of fuoroscopy guided CTI ablation in our centre(41.4 ± 19.9 vs. 34.7 ± 13.2,p< 0.05).

As with most cardiological procedures, mean fuoroscopy time during CTI ablation depends on manyfactors, such as the investigators or centre’s experience, usage of 3D EAM etc. In the study of Golian et al.mean fuoroscopy time and dose ranged from 34 ± 12to 36 ± 21 min and 728 ± 1240 to 816 ± 1011 mGycm2,whereas in our series of fuoroscopy guided CTI ablation mean fuoroscopy time and dose were 9.4 ± 6.6 minand 95.3 ± 73.4 cGycm2, respectively. In the ICE-guidedgroup fuoroscopy could be entirely avoided by the newzero-fuoroscopy catheter navigation technique.

In our study, the CTI pouch was shallower in patientswith an ablation procedure duration above the median,suggesting a more lateral ablation plane in thesepatients where the CTI musculature is stronger. It mustbe mentioned that each RF application was performedat the discretion of the operator, evaluating the localsignals derived by the ablation catheter in real time.Using AI- or LSI-guided ablation may have a diferentimpact on the ablation procedure or EPS duration.

Limitations

This new zero-fluoroscopy catheter navigation technique is limited to a relatively small number of patientswith typical atrial flutter. Catheter navigation for creation of linear lesions relying solely on real-time visualisation by ICE catheters requires some clinical expertisein intracardiac echocardiography and its broad implementation might be associated with longer proceduresor the need for additional imaging technologies, suchas fluoroscopy or three-dimensional mapping.

Conclusions

Zero-fuoroscopy CTI ablation guided solely by intracardiac echocardiography in patients with CTI-dependentAFL is feasible and safe. ICE visualisation may help tolocalise the optimal ablation plane, detect and correctpoor tissue contact of the catheter tip, and recognise earlypotential complications during the ablation procedure.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s12947-023-00312-w.

Acknowledgements

Not applicable.

Authors’ contributions

BL: Concept, Performance of the EPS, Data Collection, Statistics and Drafting,MB: Concept and Drafting, AI: Performance of the EPS, Data Collection, TR:Statistics, Artwork, SK: ICE-guidance and EPS performance, NT: Data Collection,Artwork, AS: Drafting and Critical Revision, KP: Support in EPS Performanceand Data Collection, AS: Design, Artwork and Drafting, MW: Design and CriticalRevision, RBD: Final approval, CG: Performance of the EPS, Data Collection andDrafting.

Funding

Not applicable.

Availability of data and materials

The data underlying this article will be shared on reasonable request to thecorresponding author.

DeclarationsEthics approval and consent to participate

The study was approved by the local ethics committee in accordance withthe Declaration of Helsinki and was registered within the German Clinical TrialRegister (DRKS00030421). All patients gave their informed consent for partici‑pation in this study prior to enrollment.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Author details

1Department of Cardiology and Intensive Care Medicine, Johannes WeslingUniversity Hospital Minden Ruhr-University Bochum, Hans‑Nolte‑Str. 1, Min‑den 32429, Germany.2Department of Radiology, University Hospital CenterMother Teresa, Tirana, Albania.3Department of Internal Medicine, Divisionof Cardiology and Angiology, Magdeburg University, Magdeburg, Germany.

Received: 4 June 2023 Accepted: 26 July 2023

Published online:03 August 2023