THE UTILITY OF A NOVEL RAPID HIGH-RESOLUTION MAPPING SYSTEM IN THE CATHETER ABLATION OF ARRHYTHMIAS - AN

INITIAL HUMAN EXPERIENCE OF MAPPING THE ATRIA AND THE LEFT VENTRICLE

SHORT TITLE: CLINICAL UTILITY OF RAPID HIGH-RESOLUTION MAPPING

Lilian Mantziari MD PhD, Charles Butcher MRCP, Andrianos Kontogeorgis MRCP PhD, Sandeep

Panikker MBBS MRCP, Karine Roy MD, Vias Markides MD FRCP, Tom Wong MD FRCP

Royal Brompton and Harefield NHS Trust, London UK

Address for correspondence

Dr. Tom Wong, MD, FRCP

Heart Rhythm Centre, NIHR Cardiovascular Biomedical Research Unit, Institute of Cardiovascular

Medicine and Science.

The Royal Brompton and Harefield NHS Foundation Trust

Imperial College

Sydney Street, London SW3 6NP, United Kingdom

Email: tom.wong@imperial.ac.uk

Phone: +44 20 7351 8619

Fax: +44 20 7351 8629

Total word count: 4,447

Disclosures

LM, AK, KR, VM and TW none declared. CB is supported by a Boston Scientific investigator lead

research grant. SP is supported by a Boston Scientific research grant.

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Abstract

Objectives: To assess the clinical efficacy, safety and clinical utility of a novel electroanatomical mapping

system.

Background: A new mapping system, capable of rapidly acquiring detailed maps based on automatic

annotation of thousands of points was recently released for clinical use. This is the first description of it’s

utility in humans.

Methods: The first consecutive 20 cases (7 atrial tachycardia, 8 atrial fibrillation, 3 ventricular tachycardia

and 2 ventricular ectopic beat ablations) are analysed. The system (Rhythmia, Boston Scientific) uses a

bidirectional deflectable basket catheter with 64 closely spaced mini-electrodes. It automatically accepts

and annotates electrograms when a number of predefined criteria are met.

Results: Thirty right atrial maps were acquired in 11(4-15) min, consisting of 7220(3467-10947) points, 22

left atrial maps in 11(6-19) min, consisting of 7818(4379-12262) points and 10 left ventricular maps in

37(14-43) min, consisting of 8709(2605-15514) points. The mini-basket catheter could reach all areas of

interest without deflectable sheaths. No embolic events, bleeding complications or endocardial structure

damage were observed. Correction of the automatic annotation was performed in 0.02% of points in 4/62

maps. The system revealed re-entry circuits of atrial tachyarrhythmias, identified gaps on linear lesions,

identified and correctly annotated the clinical ventricular ectopic beats and channels of slow conduction

within ventricular scar.

Conclusions: The novel automatic mapping system was rapid, safe and efficacious in mapping a variety of

cardiac arrhythmias in humans. Further clinical research is needed to optimise its use in the ablation of

complex arrhythmias.

Key words: electroanatomical mapping system, high-resolution mapping, atrial tachycardia, atrial

fibrillation, ventricular tachycardia

2

Condensed abstract

This is a single centre prospective study of the initial clinical experience in mapping the atria and the left

ventricle using a novel rapid high-resolution electroanatomical mapping system and a mini-basket catheter.

A total of 62 maps were created and analysed in 20 patients. The system was found to be efficacious and

safe in mapping a variety of atrial and ventricular tachyarrhythmias in humans.

3

Abbreviations

AF=Atrial fibrillation

AT=Atrial tachycardia

CL=Cycle length

CS=Coronary sinus

LA=Left atrium/atrial

LV=Left ventricle

RA=Right atrium/atrial

RV=Right ventricle

VEs=Ventricular ectopics

VT=Ventricular tachycardia

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Introduction

The widely available 3-dimensional electroanatomical mapping systems use point-by-point acquisition of

electrograms from a roving catheter with or without multi-electrode mapping capability and usually require

extensive manual re-annotation (1,2). A novel mapping system (Rhythmia, Boston Scientific) has recently

become clinically available. This system is paired to a mini-basket array catheter with 64 mini-electrodes

(IntellaMap Orion, Boston Scientific) and is capable of acquiring and automatically annotating thousands of

points. This system has been shown to rapidly obtain high-resolution maps in canine and swine models with

no need for additional manual annotation, (3,4) however, to our knowledge, to date there is no report on the

utility of this system in humans. This paper describes the initial experience using the Rhythmia system and

the mini-basket catheter, focusing on the safety, feasibility and efficacy in mapping the atria and the LV in

humans.

Methods

Patients

We studied the first 20 consecutive electrophysiologic procedures using the Rhythmia mapping system at

our institution during the first three months of clinical availability of the system and catheter. A detailed

description of the cases is shown in table 1. All patients were adults (age 39-85), 7 patients had structurally

normal heart, 9 patients had heart failure and 4 had adult congenital heart disease. Fourteen patients were

admitted electively for procedures and 6 patients required an urgent ablation. Written informed consent

was obtained in all cases as per standard practice. Patient and procedural data were prospectively collected.

Procedures

All procedures were performed by two experienced operators. AT, AF and VT ablations were performed

under general anaesthesia and a transoesophageal echocardiogram was performed to exclude evidence of

thrombus and to guide the transseptal puncture. Two cases of ventricular ectopy (VE) ablation were

performed under sedation to avoid suppression of the ectopy. AF and AT ablations were performed on

uninterrupted warfarin with a therapeutic international normalised ratio on the day of the procedure. If a

non-vitamin K anticoagulant was used, this was discontinued 24-36 hours before the procedure according

to local guidelines. Antiarrhythmic medications were discontinued for 5 half-lives (excluding AF cases and

urgent cases).

Mapping system and mini basket multi-electrode catheter

5

The Rhythmia mapping system is a 3D electroanatomical mapping platform that uses a hybrid location

technology that combines impedance and magnetic location. The magnetic field is generated by a

localisation generator positioned under the catheter lab table and is capable of locating the magnetically

tracked catheters with an accuracy of ≤1mm. The impedance location technology is used to track catheters

that are not equipped with a magnetic sensor. The system then maps the impedance field measurements to

the magnetic location coordinates and creates an impedance field map. This map is used to enhance the

accuracy of the impedance location. The Orion catheter is a bidirectional deflectable, multi-electrode, mini-

basket mapping catheter (Figure 1). Its maximum shaft diameter is 8.5F and is advanced into cardiac

chambers via 9F sheaths. The catheter can acquire points at variable degrees of deployment from

undeployed (3mm) to fully deployed (22mm).

Map acquisition

The Orion catheter was gently manipulated inside the chamber of interest and automatically acquired

points with every accepted beat. Criteria used for beat acceptance were a) stable cycle length, b) stable

timing difference between two reference electrodes, c) respiration gating, d) stable catheter location e)

stability of catheter signal compared to adjacent points and f) tracking quality. Mapping during AF was

achieved by enabling only the criteria c, d and f. For mapping of VEs and VT, an additional criterion of

correlation to a reference surface ECG QRS morphology was applied.

Time and voltage maps

The setup of the mapping window was automatic. The system calculated the mean cycle length of the

rhythm over 10 seconds and consequently set 100% of cycle length equally before and after the timing

reference electrode (usually one of the coronary sinus (CS) electrograms, or the QRS of one of the surface

ECG leads for ventricular rhythms). The final maps showed the activation propagation rather that the

“early” and “late” points. The mapping window could be moved anytime during or after the completion of

the map by manually dragging its ends on the screen using the mouse in order to focus on relevant parts of

the cycle length, such as the diastolic part during VT or to exclude non relevant electrograms such as the

QRS during AT (supplemental Figure 1).

For the bipolar time maps, the timing of the electrodes was based on the time difference between the

maximum amplitude of the bipolar electrogram and the first reference electrode (timing reference). For

electrograms with more than one potentials, the system selected the potential that best matched the timing

of the surrounding electrograms. For unipolar time maps, the timing was based on the most negative dV/dT

around the timing of the max bipolar signal. The bipolar and unipolar voltage maps were based on the

difference between the maximum and minimum peak of the signal. Noise level and complete electrical

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silence were considered as < 0.03mV, and low voltage areas were detected between 0.03mV and 0.5mV in

the atria and 0.03mV and 1.5mV in the ventricles.

Geometry

The geometry of the cardiac chambers was gradually acquired with every accepted beat based on the

location of the outermost electrodes of the basket catheter. For all cases, the system was programmed to

select and include in the map only electrograms up to 2-4 mm from the surface geometry.

Statistical analysis

Normality of distribution was tested with the Kolmogorov Smirnov test. All variables were non-normally

distributed and were reported as median and interquartile range (25th-75th percentile). The Stata software

version 13 (Stata corp Texas, USA) was used for the statistical analysis. The data were log transformed to

conform to a log normal distribution. In order to compare the time required for mapping various cardiac

chambers, as well as the number of accepted beats per type of chamber and number of electorgrams, whilst

accounting for clustering of chambers within patients we used linear mixed models analysis. A p<0.05 was

considered statistically significant.

Results

We present data from the first 20 consecutive procedures (Table 1). Seven patients with ATs, 8 patients

undergoing ablation for AF, and 5 patients with VT or VEs ablation were studied. A total of 62 high-

resolution maps were acquired with the mini-basket mapping catheter (Table 2). The LV maps took longer

to acquire (p<0.0001) compared to the RA and LA maps but there was no significant difference in accepted

beats and electrograms acquired among the chambers mapped.

Catheter manipulation and reach

The right femoral vein was used to advance the basket catheter in the atria. For RA mapping, a short 9

French sheath was used for 28 maps and a long, fixed curve sheath used for 2 maps in patients with a very

dilated RA. To map the LA, 9 French fixed-curve long sheaths (Mullins, Cook Medical Inc., Bloomington, IN,

USA) were used and allowed the basket catheter to reach all areas of interest in all cases. The LV was

mapped via both the transaortic and transseptal approach in 3 cases, by the transseptal approach alone in 1

case and by transaortic approach alone in 1 case with dextrocardia and surgically repaired atrial septal

defect. All operators that used the catheter reported ease of manipulation in the RA and LA. There were no

areas that the catheter could not reach and it could easily be advanced in the coronary sinus and the

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pulmonary veins. Mapping of the left ventricle was also feasible in all cases. An example of a full LV map is

shown in figure 2B.

Safety

The mini-basket catheter was meticulously flushed and inserted to the cardiac chambers after an activated

clotting time≥300 sec was achieved and maintained with boluses of intravenous heparin administration and

was irrigated with heparinised normal saline solution (1U/ml) at a rate of 1ml/minute throughout the

procedure. There were no embolic complications, including stroke or systemic embolism. All catheters were

checked and found to be free from any visible thrombus at the end of the procedure. There were no bleeding

complications or pericardial effusions. When during atrial mapping the catheter inadvertently entered the

right or the left ventricle, it was easily pulled back with no events of entrapment by the atrio-ventricular

valves or their subvalvular apparatus. Mapping of the LV did not affect the aortic or mitral valve function as

shown on post procedure echocardiogram. In 4 cases we used the transaortic approach to the left ventricle

with no thromboembolic complications or evidence of damage to the aortic root, the aortic valve or the

coronary arteries. In case 17 the patient had a previous Ross procedure for bicuspid aortic valve with a

pulmonary valve autograft in the place of the aortic valve. The retrograde approach and the LV mapping

were also uncomplicated in this case.

Accuracy of maps

The acquired maps showed highly detailed endocardial electrical activation. In the majority of cases manual

annotation was not necessary. In only 4 out of 62 maps manual annotation was performed in 16 out of

70862 points (0.02%). The main reasons for incorrect annotation were far field ventricular electrograms

around the valve areas and artefacts, however all points with incorrect annotation were easy to identify on

the high density map as areas of inconsistent colour coding to the adjacent areas (Figure 2). In atrial voltage

maps the threshold for the scar was reduced to 0.5-0.05 mV and in some cases, reduction to 0.25mV was

applied in order to facilitate the identification of gaps in linear lesions (Figure 3). In LV voltage maps the

standard cut-off of <1.5mV was applied but when the lower voltage cut-off was set to 0.2 mV, isthmuses of

slow conduction within scar areas were revealed. Three-dimensional basket and other catheter localisation

was always in keeping with the fluoroscopic findings and highly internally consistent.

Mapping of specific arrhythmias

Typical atrial flutter was used as a known arrhythmia substrate to validate the system. An example is

illustrated in Figure 3 and Video 1. Standard Pulmonary vein isolation with wide area circumferential

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ablation and additional activation/voltage maps of the LA before and after ablation was performed in

patients with AF (n=8) (Supplemental Figure 2). The patients with persistent AF had also additional

ablations (see table 2 for details). Post ablation, 12 maps of the LA were acquired in 8.0 (6.2-14.3) minutes,

consisting of 7818 (4891-19351) points, in order to assess entry block into pulmonary veins, assess the

linear lesions or map an AT. Following persistent AF ablation 5 gaps on linear lesions were identified and

ablated successfully on the site indicated by the system (Figure 4,). Two cases of macro re-entrant AT in

patients with congenital heart disease were studied and gaps on previous lesions and/or atriotomy scars

were identified as the isthmuses of slow conduction (Supplemental Figure 3), followed by successful

ablation (no inducibility of tachycardias). In total 9 macro re-entry ATs were mapped. The system mapped

100% of cycle length of 8 ATs. In one case of short lasting AT the system was able to map 69% of the cycle

length.

VEs were mapped and ablated in 2 patients. In both cases the system created a template to the clinical VE

and could accurately identify the clinical VE, accept the relevant beat, and annotate the signal automatically

(Supplemental Figure 4).

Three patients with sustained monomorphic VT were studied (Cases 16, 17, 18). The LV was mapped via the

transseptal (n=2) and the transaortic (n=3) approach. Mapping during VT was performed in cases 16 and

17. The system created the maps using a mapping window equal to the full cycle length of the tachycardia.

Two macro re-entry VTs were mapped in case 17, (100% of CL mapped) and one possible macro re-entry

VT was mapped in case 16 (42% of CL was mapped). We observed that mapping the full CL of the VT could

result in errors in automatic annotation because the system annotates the largest electrogram within the

mapping window and this can be either the local diastolic electrogram or the far field systolic electrogram,

whichever is larger (see example in Figure 5A). To avoid this in case 16 we changed the mapping window in

retrospect to focus on the diastolic part of the VT. This revealed a figure-of-8 re-entry VT in the infero-basal

LV wall with corresponding diastolic potentials at the entrance and presystolic electrograms at the exit. A

substrate map of the LV was performed in sinus rhythm. The voltage threshold for scar was set to 0.2-

1.5mV, to reveal additional channels of low voltage within the scar (Figure 5, Video 2)).

Discussion

To our knowledge, this is the first description of the initial clinical experience of a novel rapid high-

resolution mapping system in a variety of arrhythmias and substrates, including patients with acquired and

congenital heart disease. In brief, the system platform was user friendly and provided clear and accurate

localisation of catheters, geometry of cardiac chambers and low noise electrograms. The main advantages

of the system were a) the high-resolution mapping of both activation timing and voltage information b) the

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short time required to acquire the maps c) the accurate automatic annotation and d) the ability to change

the mapping window in retrospect.

The mini-basket catheter does not require a balloon to be deployed or additional stiff wire and sheath in

order to be positioned as other basket catheters do (5,6). It could be easily manipulated, deployed in various

degrees from zero to maximum and advanced in cardiac chambers, including pulmonary veins

(Supplemental Figure 2) and the right and left atrial appendages (Figure 4B) with no events of cardiac

perforation, valve damage, air embolism or visible clot formation. Additionally, the mini-basket catheter

benefits from very closely spaced electrodes and acquisition of contact electrograms. The obvious

disadvantage of high-resolution regional mapping is the need for sequential data acquisition at multiple

sites.

The maps we acquired in this cohort consisted of thousands of points acquired within a few minutes.

Mapping with previously available contact multipolar catheters usually can create maps with a total of a few

hundreds of points that require manual annotation in order to be meaningful (1,2). Previously, Nakagawa et

al calculated the mean resolution of the maps that were automatically acquired with this system to be 2.6

mm (1.8-4.4 mm) (3). The detailed maps may have the potential benefit of revealing valuable information

with regard to the substrate.

We used the system in a variety of cardiac arrhythmias in order to explore its efficacy and potential future

utility. In this initial experience we observed that this system could accurately demonstrate gaps along the

linear lesions (Figures 3 and 4), verifying the results of Nakagawa et al in the experimental model in canines

(3). Limited ablation on the site of the gap shown by the system led to tachycardia termination and/or

achievement of block. The atrial voltage maps might also provide useful information for persistent AF

ablation (7). The detail that this system can record with regard to the direction and velocity of endocardial

activation may be useful to map AF in the future but this warrants further investigation.

In VT ablation, our initial experience showed that the basket catheter can be used to map the LV via both the

transseptal and retrograde approach and can reach all areas inside the LV, although manipulation was a

little more challenging because of the ventricular myocardial trabeculations and subvalvular apparatus. The

longer time to acquire the LV maps was mainly attributed to the low frequency of VEs in two cases. The

automated QRS matching to the clinical VE or VT was accurate in all cases and the system was capable of

rejecting the non-clinical ectopic beats and correctly annotating the clinical ectopics.

The low noise mini-electrodes can record signals of very low voltage and it’s not clear whether this impacts

on the scar cut off values. It was previously shown that endocardial areas with bipolar voltage <1.5mV

correspond to myocardial scar (8,9). Preclinical evaluation of this system in a swine model of ischemic scar

showed that the same cut off of <1.5mV correlated with scar on cardiac delayed-enhancement magnetic

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resonance imaging (MRI) (10). A pre-clinical study in dogs also showed that the size and location of scar

mapped on electroanatomical maps acquired with this system were highly correlated with scar observed in

cardiac MRI(11). However, looking further into scar at lower voltages may help to reveal channels of slow

conduction and facilitate the substrate mapping and ablation of VT.

One unique characteristic of this mapping system was that we could easily change the mapping window

retrospectively. By excluding the QRS and moving the window of interest on the diastolic part of the CL

during VT enabled the mapping of the local activation along the critical isthmus of the VT that occurs during

diastole (12,13). This feature requires further validation in a larger study.

The mean procedure duration and fluoroscopy time of the studies presented in this paper seems to be no

shorter than usual for our institution (14), but this is expected as we used the system to explore its potential

and future clinical use and there was a learning curve for the operators and cardiac physiologists, therefore

a direct comparison to previous standard clinical practice was not attempted.

Limitations

A small number of patients are included in this paper and a heterogeneous group of cases is described. A

comparison to other mapping systems was not attempted at this stage due to catheter/system

incompatibilities and to allow for a learning curve. The current report is a description of sequential cases

rather than being based on an experimental protocol and, on clinical grounds, there was no opportunity to

map the RV in these cases, although we would anticipate very simple manipulation in the RV and its outflow

tract based on experience in other chambers. Similarly we did not use the system to perform epicardial

mapping, where additional complexities may be encountered. We could not verify the accuracy of the

voltage maps because no scar information from cardiac MRI was available. The system uses a hybrid

magnetic and impedance location technology. Although no discrepancy was noted between the system and

the fluoroscopic location of the catheters this has not been formally validated.

Conclusions

The novel rapid automatic mapping system was used in a variety of human cardiac arrhythmias and proved

to be both safe and efficacious. We were able to acquire detailed geometry of the cardiac chambers and

high-resolution activation and voltage information based on automatic annotation. The system was capable

of mapping macro-re entry tachycardias and assessing linear lesions with detailed information on slow

conduction isthmuses, guiding the ablation for AF, creating detailed maps of the left ventricle during sinus

rhythm or VT and successfully selecting and automatically annotating the clinical ventricular ectopic beats.

Its optimal use in specific tachycardia mapping and ablation warrants further research.

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Competencies in Medical Knowledge

This novel high-resolution mapping system can rapidly acquire thousands of points and create very detailed

voltage and activation maps without the need for manual annotation. Our first clinical observations have

shown that the system is safe and efficacious in mapping the atria and the left ventricle in a variety of

arrhythmia substrates with the advantages of being automatic and rapid. In addition it offers the ability to

the operator to review the maps and change the mapping window in retrospect in order to focus on areas of

interest such as the diastolic part of the cycle length during ventricular tachycardia.

Translational Outlook

The characteristics of this novel system may improve our understanding of the mechanisms of

complex arrhythmias and enhance the ablation outcomes but this warrants further clinical research. 

Acknowledgements

We would like to thank Dr Kostas Dimopoulos and Mr Winston Banya for their assistance with the statistical

analysis.

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References

1. Weerasooriya R, Jaïs P, Wright M et al. Catheter ablation of atrial tachycardia following atrial fibrillation ablation. J Cardiovasc Electrophysiol. 2009 Jul;20(7):833–8.

2. Jones DG, McCready JW, Kaba R a, et al.. A multi-purpose spiral high-density mapping catheter: initial clinical experience in complex atrial arrhythmias. J Interv Card Electrophysiol. 2011 Sep;31(3):225–35.

3. Nakagawa H, Ikeda A, Sharma T, Lazzara R, Jackman WM. Rapid high resolution electroanatomical mapping: evaluation of a new system in a canine atrial linear lesion model. Circ Arrhythm Electrophysiol. 2012 Apr;5(2):417–24.

4. Ptaszek LM, Chalhoub F, Perna F,et al.. Rapid acquisition of high-resolution electroanatomical maps using a novel multielectrode mapping system. J Interv Card Electrophysiol. 2013 Apr;36(3):233–42.

5. Tai C-T, Liu T-Y, Lee P-C, Lin Y-J, Chang M-S, Chen S-A. Non-contact mapping to guide radiofrequency ablation of atypical right atrial flutter. J Am Coll Cardiol. 2004 Sep 1;44(5):1080–6.

6. Arentz T, von Rosenthal J, Blum T,et al. Feasibility and safety of pulmonary vein isolation using a new mapping and navigation system in patients with refractory atrial fibrillation. Circulation. 2003 Nov 18;108(20):2484–90.

7. Jadidi AS, Duncan E, Miyazaki S et al. Functional nature of electrogram fractionation demonstrated by left atrial high-density mapping. Circ Arrhythm Electrophysiol. 2012 Feb;5(1):32–42.

8. Marchlinski FE, Callans DJ, Gottlieb CD, Zado E. Linear Ablation Lesions for Control of Unmappable Ventricular Tachycardia in Patients With Ischemic and Nonischemic Cardiomyopathy. Circulation. 2000 Mar 21;101(11):1288–96.

9. Reddy VY, Wrobleski D, Houghtaling C, Josephson ME, Ruskin JN. Combined epicardial and endocardial electroanatomic mapping in a porcine model of healed myocardial infarction. Circulation. 2003 Jul 1;107(25):3236–42.

10. Tanaka Y, Genet M, Chuan Lee L, Martin AJ, Sievers R, Gerstenfeld EP. Utility of high-resolution electroanatomic mapping of the left ventricle using a multispline basket catheter in a swine model of chronic myocardial infarction. Heart Rhythm. Elsevier; 2015 Jan;12(1):144–54.

11. Cokic I, Kali A, Wang X, Yang H-J,et al. Iron deposition following chronic myocardial infarction as a substrate for cardiac electrical anomalies: initial findings in a canine model. PLoS One. 2013 Jan;8(9):e73193.

12. Stevenson WG, Soejima K. Catheter ablation for ventricular tachycardia. Circulation. 2007 May 29;115(21):2750–60.

13. Schneider HE, Schill M, Kriebel T, Paul T. Value of dynamic substrate mapping to identify the critical diastolic pathway in postoperative ventricular reentrant tachycardias after surgical repair of tetralogy of fallot. J Cardiovasc Electrophysiol. 2012 Sep;23(9):930–7.

14. Mantziari L, Suman-Horduna I, Gujic M et al. Use of asymmetric bidirectional catheters with different curvature radius for catheter ablation of cardiac arrhythmias. Pacing Clin Electrophysiol. 2013 Jun;36(6):757–63.

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Figure legends

Figure 1: The mini-basket catheter-The mini-basket catheter (IntellaMap Orion, Boston Scientific) has a

bidirectional deflectable shaft. The mini-basket consists of 8 splines with 8 closely spaced mini electrodes

on each and can be used in various degrees of deployment from undeployed (3mm) to fully deployed

(22mm).

Figure 2: Example of incorrect automatic annotation-(A) The electrogram corresponding to the blue

point (shown with red arrow) is automatically annotated on the far field V because this signal is larger than

the near field A. Note that blanking of the V (red column) was set to avoid this error however it was too

narrow to cover the late V electrograms that appear close to the tricuspid annulus. The area of incorrect

annotation (inside black box) on the RA map is easily recognised as a spot of inconsistent colour coding. On

the right panel the manual correction of the annotation is shown. This results to change of the color and the

shape of the point on the map that now appears as orange ring. (B) Area of incorrect annotation (inside

black box, magnified in the middle) shown as a spot of inconsistent colour coding on the left ventricular map

during ventricular tachycardia because of artefact mistaken as QRS complex (V).

Figure 3: Typical atrial flutter-RA maps in Left Anterior Oblique (LAO) caudal view (case 11): (A) Voltage

and activation map of the RA during typical counter-clock wise atrial flutter. (B) Voltage map after ablation

on the CTI line showing low voltage along the line but a possible isthmus of conduction. The activation mode

of the same map shows a gap on the CTI line and conduction of the activation during CS pacing. Review of

the points on the site of the gap shows fractionated signal. (C) Voltage map after further ablation on the gap

shows very low voltage along the line. The time map confirms bidirectional block with widely split double

potentials

Figure 4: Linear lesions-(A) Focused map of the LA roof seen from above (superior view of the roof)

during pacing from the left atrial appendage (LAA- the LAA is not shown on this map). The local electrogram

at the site of the gap is 39 ms earlier to the reference (CS 7-8). (B) Additional ablation on the site indicated

in (A) resulted in roof line block. (B) Activation and voltage maps of the LA roof are shown with double

potential on the roof line. (C) Focused map of the mitral isthmus area after a mitral isthmus line was

deployed. Activation map is shown during pacing from the LAA (case 13). A breakthough of activation is

seen in the middle of the mitral isthmus line with the corresponding fractionated local electrogram (EGM).

The voltage map below shows an isthmus of very low voltage on the mitral line. The voltage on the gap is

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0.068mV. (D) Re-map of the mitral isthmus area in LAA pacing after further ablation shows no endocardial

conduction in the mitral isthmus and scar along the line. However there is still epicardial conduction over

the CS. Further ablation inside the CS resulted in MVI block.

Figure 5: Left ventricular tachycardia-Maps are focused on the inferobasal LV wall. (A) Mapping of the

full tachycardia CL (262 ms) shows a possible isthmus of conduction but the right part of it is confusing

(dashed white arrow). Magnification of this area shows a lot of points with different colors resulting from

incorrect annotation, see explanation in B. (B) The system automatically annotates the largest signal within

the mapping window. When the mapping window includes the systolic activation and this happens to be

larger than the local diastolic electrogram, then the system automatically annotates the far field systolic

potential (yellow dashed line). We can manually correct this by dragging the annotation to the near field

signal (blue dashed line). A more efficient way to avoid this is to shorten the mapping window to exclude

the systolic and focus on the diastolic part of the VT. (C) This map is automatically generated after we

shortened the mapping window to 108ms focused on the diastole and it clearly shows a figure-of-8

ventricular tachycardia with early diastolic potentials at the entry site (1), mid-diastolic potentials in the

isthmus (2) and presystolic potentials at the exit site (3). (D) Substrate map of the inferobasal LV wall in SR.

The scar threshold cut-off is reduced to 0.2 mV to reveal isthmuses of low voltage within the scar area.

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Table 1: Case Description

Case #

age Clinical tachycardia

Cardiovascular history Previous ablations

Ablation endpoint duration/ fluoroscopy(minutes)

Number of Maps

Chamber mapped

complications

Follow duration/outcome

1 72 Typical atrial flutter, persistent

Normal heart - Bidirectional CTI conduction block

135/ 10.0 2 RA none 6 months/no recurrence

2 84 Paroxysmal AT Normal heart - Left ATEPS only*

111/9.0 3 RA none No ablation

3 85 Persistent AT Normal heart - Left ATEPS only*

55/4.1 1 RA none No ablation

4 48 Typical atrial flutter, paroxysmal

Normal heart - Bidirectional CTI conduction block

80/14.5 2 RA none 6 months/no recurrence

5 68 Paroxysmal AF Normal heart - PVI 177/24.1 2 LA none 5 months/No recurrence

6 39 Persistent AT ACHD(AVSD and cleft MV repair)

+Right

ATs/AF

3 right ATs were induced and ablated.

178/14.1 6 RA none 4 months/12 min of SVT

7 80 Persistent AF Normal heart - PVI, roof, MVI, endocardial CS, anterior wall CFAE ablation, endocardial CS, CTI

168/39.0 3 RALA

none 6 months/ no recurrence

8 54 VEs (LV) ACHD (Dextrocardia, ASD surgically repaired)

- Transient elimination of VEs with endocardial ablation

188/26.0 2 LV none 3 months/ NSVT

9 62 Long standing persistent AF

DCM EF 30% - PVI, roof, MVI, endocardial CS, CTI

210/10.6 2 RALA

none 5 months/ no recurrence

10 46 Persistent AF DCMEF 29%

- PVI, roof, MVI, endocardial CS lineAF organised to perimitral AT that changed to CTI dependent flutter. Termination to SR from CTI ablationGap on MVI ablated until block

320/21.6 5 RALA

none 3 months/no recurrence

11 54 Persistent atrial flutter

ACHD (VSD, Eisenmenger syndrome)

- Bidirectional CTI conduction block

69/10.4 4 RA none 4 months/no recurrence

12 75 Persistent AF Ischemic heart diseaseEF 60%

- PVI, roof, MVI, posterior line, CTIDCCV to roof dependent macro-reentrant ATAblation to SR

212/8.9 4 RALA

none 3 months/no recurrence

13 71 Persistent AF Normal heart - PVI, roof, MVI, CTI 177/23.7 5 RALA

none 5 months/ no recurrence

14 84 Paroxysmal AT DCMEF 55%

+persistent

AF

Perimitral re-entry ATMVI block

300/14.0 3 LA none 4 months/ no

16

recurrence

15 80 Persistent AF ICM- EF 40% + Typical flutter

PVI, roof, MVI, endocardial CSDCCV to SRGap on MVI- ablation until blockCTI blocked from previous procedure

276/51.0 3 RALA

none 2 months/persistent atrial flutter

16 71 VT storm ICM- EF 20% - Ablated 2 VTs in LV.No other VT inducible

265/34.4 2 LV none 4 months/ recurrence of VT as inpatient

17 54 VT and AT ACHD (Bicuspid aortic valve, Ross procedure, MI post surgery, right coronary artery to right atrial fistula)

- Ablated 2 VTs in LV.Ablated dual-loop re-entry AT (CTI and atriotomy dependent)Non inducibility of any tachycardia

298/30.7 8 LVRA

Small pseudoaneurysm of right superficial femoral artery

4 months/ no recurrence

18 85 VT storm ICM EF 27% - Poorly tolerated VT. Substrate mapping and ablation of late potentials. Clinical VT not inducible

302/61.0 1 LV none 2 months/ no recurernce

19 85 VEs ICM EF 30% - LVOT VEsElimination of VEs

134/22.1 1 LV none 3 months/ no recurrence

20 74 Persistent AF ICMEF 55%

- PVI, roof, MVI, posterior line, Left septum CFAE ablation, CTIAT- perimitral re-entry ablation to SR

330/62.0 3 RALA

none 2 months/ one episode of AF in blanking period

* Not consented for left sided procedure

CTI, Cavotricuspid isthmus;RA, right atrium;AT, atrial tachycardia;EPS, electrophysiological study;AF, atrial

fibrillation;PVI, pulmonary vein isolation;LA, left atrium;ACHD, adult congenital heart disease;AVSD,

atrioventricular septal defect;MV, mitral valve;MVI, mitral valve isthmus;CS, coronary sinus;CFAE, complex

fractionated atrial electrograms;VEs, ventricular ectopics;LV, left ventricle;ASD, atrial septal

defect;DCM,dilated cardiomyopathy;EF, ejection fraction;VSD, ventricular septal defect;DCCV, direct current

cardioversion;ICM,ischemic cardiomyopathy;VT, ventricular tachycardia;MI, myocardial infarction;LVOT,

left ventricular outflow tract

17

Table 2: Summary of maps

Right atrial maps

N=30

Left atrial maps

N=22

Left ventricular

maps n=10

P values

(LA to RA; LV

to RA)

Time, min 10.5 (4.1-15) 10.8 (5.8-19.3) 36.6 (13.6-43.2) 0.98; <0.0001

Accepted beats 540 (293-932) 758 (173-1175) 1123 (288-1732) 0.74; 0.36

Electrograms 7220 (3467-10947) 7818 (4379-12262) 8709 (2605-15514) 0.79; 0.81

18