Author + information
- Received March 13, 2015
- Revision received May 11, 2015
- Accepted June 17, 2015
- Published online October 1, 2015.
- Lilian Mantziari, MD,
- Charles Butcher, MBBS,
- Andrianos Kontogeorgis, MBBCh,
- Sandeep Panikker, MBBS,
- Karine Roy, MD,
- Vias Markides, MD and
- Tom Wong, MD∗ ()
- Heart Rhythm Centre, NIHR Cardiovascular Biomedical Research Unit, Institute of Cardiovascular Medicine and Science, the Royal Brompton and Harefield NHS Foundation Trust, Imperial College, London, United Kingdom
- ↵∗Reprint requests and correspondence:
Dr. Tom Wong, 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.
Objectives This study sought 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 its utility in humans.
Methods The first consecutive 20 cases (7 atrial tachycardia, 8 atrial fibrillation, 3 ventricular tachycardia, and 2 ventricular ectopic beat ablations) were analyzed. The system 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 to 15) min, consisting of 7,220 (3,467 to 10,947) points, 22 left atrial maps in 11 (6 to 19) min, consisting of 7,818 (4,379 to 12,262) points and 10 left ventricular maps in 37 (14 to 43) min, consisting of 8,709 (2,605 to 15,514) 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 of 62 maps. The system revealed re-entry circuits of atrial tachyarrhythmias, identified gaps on linear lesions, and 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 optimize its use in the ablation of complex arrhythmias.
- atrial fibrillation
- atrial tachycardia
- electroanatomical mapping system
- high-resolution mapping
- ventricular tachycardia
Widely available 3-dimensional electroanatomical mapping systems use point-by-point acquisition of electrograms from a roving catheter with or without multielectrode mapping capability and usually require extensive manual re-annotation (1,2). A novel mapping system (Rhythmia, Boston Scientific, Washington, DC) 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 of 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 left ventricle (LV) in humans.
We studied the first 20 consecutive electrophysiological procedures, using the Rhythmia mapping system at our institution during the first 3 months the system and catheter were clinically available. A detailed description of the cases is shown in Table 1. All patients were adults (39 to 85 years of age), 7 patients had structurally normal hearts, 9 patients had had heart failure, and 4 had adult congenital heart disease. Fourteen patients were admitted electively for procedures, and 6 patients required urgent ablation. Written informed consent was obtained in all cases according to standard practice. Patient and procedural data were prospectively collected.
All procedures were performed by 2 experienced operators. Atrial fibrillation (AF), atrial tachycardia (AT), and ventricular tachycardia (VT) ablations were performed on patients under general anesthesia and transesophageal echocardiography was performed to exclude evidence of thrombus and to guide the transseptal puncture. Two cases of ventricular ectopy (VE) ablation were performed with the patient under sedation to avoid suppression of the ectopy. AF and AT ablations were performed on patients receiving uninterrupted warfarin therapy with a therapeutic international normalized ratio on the day of the procedure. If a non–vitamin K anticoagulant was used, it was discontinued 24 to 36 h before the procedure, according to local guidelines. Antiarrhythmic medications were discontinued for 5 half-lives (excluding AF cases).
Mapping system and mini-basket multielectrode catheter
The Rhythmia mapping system is a 3-dimensional (3D) electroanatomical mapping platform that uses a hybrid location technology that combines impedance and magnetic location. The magnetic field is generated by a localization generator positioned under the catheter laboratory table and is capable of locating the magnetically tracked catheters with an accuracy of ≤1 mm. 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, multielectrode, mini-basket mapping catheter (Figure 1). Its maximum shaft diameter is 8.5-F and is advanced into cardiac chambers by using 9-F sheaths. The catheter can acquire points at variable degrees of deployment from undeployed (3 mm) to fully deployed (22 mm).
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: 1) a stable cycle length; 2) stable timing difference between 2 reference electrodes; 3) respiration gating; 4) stable catheter location; 5) stability of catheter signal compared to adjacent points; and 6) tracking quality. Mapping during AF was achieved by enabling only criteria c, d, and f. For mapping of VEs and VT, an additional criterion of correlation to a reference surface electrocardiogram (ECG) QRS interval morphology was applied.
Time and voltage maps
The setup for the mapping window was automatic. The system calculated the mean cycle length of the rhythm over 10 s 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 interval 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 at any time during or after the completion of the map by manually dragging its ends on the screen, using the pointing device (e.g., mouse), to focus on relevant parts of the cycle length, such as the diastolic part during VT, or to exclude nonrelevant electrograms such as the QRS interval during AT (Online 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 1 potential, 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 delta voltage/delta time (dV/dT) around the timing of the maximum bipolar signal. The bipolar and unipolar voltage maps were based on differences between the maximum and minimum peaks of the signal. Noise level and complete electrical silence were considered <0.03 mV, and low voltage areas were detected between 0.03 mV and 0.5 mV in the atria and 0.03 mV and 1.5 mV in the ventricles.
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 to 4 mm from the surface geometry.
Normality of distribution was tested with the Kolmogorov-Smirnov test. All variables were non-normally distributed and were reported as medians and interquartile ranges (25th to 75th percentiles). Stata version 13 software (Stata Corp., College Station, Texas) was used for statistical analysis. Data were log transformed to conform to a log normal distribution. In order to compare the time required for mapping various cardiac chambers with the number of accepted beats per type of chamber and number of electrograms, while accounting for clustering of chambers within patients, we used linear mixed models analysis. A p value of <0.05 was considered statistically significant.
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). LV maps took longer to acquire (p < 0.0001) than right atrium (RA) and left atrium (LA) maps, but there were no significant differences 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 into the atria. For RA mapping, a short 9-F sheath was used for 28 maps, and a long, fixed curve sheath was used for 2 maps in patients with a very dilated RA. To map the LA, 9-F fixed-curve long sheaths (Mullins, Cook Medical Inc., Bloomington, Indiana) were used and allowed the basket catheter to reach all areas of interest in all cases. The LV was mapped using both the transaortic and the transseptal approaches in 3 cases, by the transseptal approach alone in 1 case, and by the transaortic approach alone in 1 case with dextrocardia and surgically repaired atrial septal defect. All operators who 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 into the coronary sinus and 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.
The mini-basket catheter was meticulously flushed and inserted to the cardiac chambers after an activated clotting time of ≥300 s was achieved and maintained with boluses of intravenous heparin administration and was irrigated with a solution of heparinized normal saline (1 U/ml) at a rate of 1 ml/min 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 left ventricle, it was easily pulled back with no events of entrapment by the atrioventricular valves or their subvalvular apparati. Mapping of the LV did not affect the aortic or mitral valve function as shown on post-procedure echocardiography. 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 coronary arteries. In case 17, the patient had previously undergone a Ross procedure for bicuspid aortic valve with a pulmonary valve autograft in the place of the aortic valve. The retrograde approach and LV mapping were also uncomplicated in that case.
Accuracy of maps
The acquired maps showed highly detailed endocardial electrical activation. In most cases, manual annotation was not necessary. In only 4 of 62 maps, manual annotation was performed in 16 of 70,862 points (0.02%). The main reasons for incorrect annotations were far-field ventricular electrograms around the valve areas and artifacts; however, all points with incorrect annotation were easy to identify on the high-density map as areas of inconsistent color coding to the adjacent areas (Figure 2). In atrial voltage maps, the threshold for the scar was reduced to 0.5 to 0.05 mV, and in some cases, reduction to 0.25 mV was applied in order to facilitate the identification of gaps in linear lesions (Figure 3). In LV voltage maps, the standard cutoff value of <1.5 mV was applied, but when the lower voltage cutoff was set to 0.2 mV, isthmuses of slow conduction within scar areas were revealed. Three-dimensional basket and other catheter localization was always in keeping with the fluoroscopic findings and highly internally consistent.
Mapping of specific arrhythmias
Typical atrial flutter was used as a known arrhythmic substrate to validate the system. An example is illustrated in Figure 3 and Online Video 1. Standard pulmonary vein isolation with wide area circumferential ablation and additional activation/voltage maps of the LA before and after ablation was performed in patients with AF (n = 8) (Online Figure 2). Patients with persistent AF also had additional ablations (Table 2 shows details). Post ablation, 12 maps of the LA were acquired in 8.0 (6.2 to 14.3) min, consisting of 7,818 (4,891 to 19,351) 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 (Online 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 (Online Figure 4).
Three patients with sustained monomorphic VT were studied (cases 16, 17, and 18). The LV was mapped using the transseptal (n = 2) and transaortic (n = 3) approaches. 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 cycle length [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 (examples are shown 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-shaped re-entry VT in the inferobasal 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 to 1.5 mV to reveal additional channels of low voltage within the scar (Figure 5, Online Video 2).
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. Briefly, the system platform was user friendly and provided clear and accurate localization of catheters, geometry of cardiac chambers, and low-noise electrograms. The main advantages of the system were: 1) the high-resolution mapping of both activation timing and voltage information; 2) the short time required to acquire the maps; 3) the accurate automatic annotation; and 4) 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 (Online 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. (3) calculated the mean resolution of the maps that were automatically acquired with this system were 2.6 mm (1.8 to 4.4 mm). 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. (3) in the experimental model in canines. 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 through both the transseptal and the retrograde approaches and can reach all areas inside the LV, although manipulation was more challenging because of the ventricular myocardial trabeculations and subvalvular apparati. The longer time to acquire LV maps was mainly attributed to the low frequency of VEs in 2 cases. The automated QRS interval matching the clinical VE or VT was accurate in all cases, and the system was capable of rejecting the nonclinical ectopic beats and correctly annotating the clinical ectopic beats.
The low-noise mini-electrodes can record signals of very low voltage, and it is not clear whether this impacts the scar cutoff values. It was previously shown that endocardial areas with bipolar voltage <1.5 mV correspond to myocardial scar (8,9). Pre-clinical evaluation of this system in a swine model of ischemic scar showed that the same cut off of <1.5 mV correlated with scar on cardiac delayed-enhancement cardiac magnetic resonance imaging (CMR) (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 CMR (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 interval 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.
A small number of patients were included in this study, and a heterogeneous group of cases was 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 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 CMR 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.
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.
COMPETENCY 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.
The authors thank Dr. Kostas Dimopoulos and Mr. Winston Banya for their assistance with the statistical analysis.
This project was supported by the NIHR Cardiovascular Biomedical Research Unit of Royal Brompton and Harefield NHS Foundation Trust and Imperial College London. This report is independent research by the National Institute for Health Research Biomedical Research Unit Funding Scheme. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health. Dr. Butcher is supported by a Boston Scientific investigator lead research grant. Dr. Panikker is supported by a Boston Scientific research grant. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbreviations and Acronyms
- atrial fibrillation
- atrial tachycardia
- cycle length
- coronary sinus
- left atrium
- left ventricle
- right atrium
- right ventricle
- ventricular ectopic
- ventricular tachycardia
- Received March 13, 2015.
- Revision received May 11, 2015.
- Accepted June 17, 2015.
- American College of Cardiology Foundation
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