Author + information
- Duy T. Nguyen, MD∗ ( and )
- Alexis Z. Tumolo, MD
- University of Colorado, Section of Cardiac Electrophysiology, Division of Cardiology, Aurora, Colorado
- ↵∗Address for correspondence:
Dr. Duy T. Nguyen, Section of Cardiac Electrophysiology, University of Colorado, 12401 East 17th Avenue, B136, Aurora, Colorado 80045.
Multielectrode catheters are increasingly implemented during complex ablations to define underlying substrates and to inform ablation strategies. Electrogram (EGM) acquisition, especially in the myocardium bordering areas of scar, is vitally important for voltage and activation mapping to define critical substrates and circuits that maintain arrhythmias; however, there are few studies delineating how EGM signals are affected by various acquisition technology. Previously, Tung et al. (1) explored differential spacing of catheter electrodes, including bipolar 2-mm, 5-mm, and 8-mm interelectrode spacing, and unipolar acquisition on a multipolar mapping catheter (duo-decapolar LiveWire, Abbott, Minnetonka, Minnesota) to characterize regions of scar in post-infarct porcine left ventricular models through endocardial and epicardial mapping using the NAVX system (St. Jude Medical, St. Paul, Minnesota). They observed variations in EGM detected with these changes in spacing, with an increasing linear relationship between optimal voltage threshold for scar and wider spacing of the electrode bipoles. This research posits that adjustment of electrode size and spacing on multipolar mapping catheters may improve electrical characterization of myocardial tissue.
In this issue of JACC: Clinical Electrophysiology, Takigawa et al. (2) used a relatively new multipolar catheter to evaluate how interelectrode, bipolar spacing affects near and far field EGM, with reference to anatomic scar regions as defined by cardiac magnetic resonance imaging. They found that, predictably, closer interelectrode spacing could better discriminate dense scar from border zone and surviving myocardium. Increasing interelectrode spacing may miss local abnormal ventricular activities. They evaluated near- and far-field EGM characteristics based on bipolar spacing in various types of myocardial tissue (healthy, border zone, and dense scar). In general, more distant bipole spacing increased the voltage of far-field EGM signals and decreased the ratio of near- to far-field voltage.
This is an important and well-performed study that carefully analyzes the effects of bipolar spacing on both near- and far-field EGM signals in normal, border, and scar myocardium. Whereas some of these findings have been previously reported, the characterization in this study validates and expands on those findings. In this study, the investigators used and evaluated the Advisor HD Grid mapping catheter (Abbott, Chicago, Illinois), which is among several multipolar mapping catheters currently available for creation of high-resolution maps in diagnostic and ablation procedures (Figure 1); catheters with different configurations area also available from the CARTO (Biosense Webster, Irvine, California) and Rhythmia (Boston Scientific, Marlborough, Massachusetts) systems. A flexible, paddle-shaped diagnostic mapping catheter, the Abbott Advisor HD Grid has 16 electrodes positioned on 4 splines, with 3-mm interelectrode spacing along and between splines, allowing for equal voltage data collection in orthogonal directions. From the 12 pairs of perpendicular bipoles, 24 EGM are collected with each beat. The Abbott EnSite Precision AutoMap algorithm facilitates rapid collection of data with a series of filters to increase accuracy of the voltage collected. In the CARTO system, the Pentaray multipolar mapping catheter includes 20 electrodes, each 1 mm2, placed along 5 soft, flexible splines. The interelectrode spacing between the distal and proximal electrodes is 2 mm and between these pairs is 6 mm. Using EGM information collected from the electrodes, a high-resolution map is processed through the CARTO system. When compared with 3.5-mm ablation catheters for use in characterizing scar in ventricular myocardium, the Pentaray was noted to be more sensitive in identifying low-voltage, fractionated EGM (3). The Intellamap Orion high-density mapping catheter (Rhythmia mapping system) offers 64 electrodes, each 0.4 mm2 in area, with 2.5-mm interelectrode spacing, on 8 splines in a collapsible, basket arrangement. The flexibility of the splines and bidirectionality of the catheter allow for improved contact with the myocardium. Through the Rhythmia mapping system, continuous collection and annotation of EGM from these electrodes is ongoing, with automatic detection and annotation of extrasystoles. In porcine post-infarct models, the Orion catheter was more accurate than a linear catheter in identifying regions of scar that had been identified by cardiac magnetic resonance imaging (4). The current study builds on this existing published data through its delineation of near- versus far-field EGM, based on electrode spacing, in a methodical and detailed analysis; additionally, it describes a new modality to collect such data.
Nevertheless, this research largely corroborates concepts that are already understood, regarding bipolar signal acquisition, and there are several other specific limitations of this study. A limitation of the study, which the investigators note, is the impact of contact force (CF) on EGM characteristics. Whereas no multipolar catheters have CF, a CF catheter with similar bipole spacing as the 4-mm bipole pair could be used to assess the trade-off between having a larger bipole but with CF versus using a smaller 2-mm bipole without CF. This often has clinical relevance when deciding between mapping using a CF-sensing catheter versus a multipolar catheter. Vector orientation of the bipole will also have an impact on near- and far-field EGM, and this was not studied. Potentially, this issue is being addressed by the investigators in a separate study. Along the same line, for optimal signal acquisition, the Grid should be oriented in a planar fashion along the endocardium; otherwise, there may be portions of the electrodes that have insufficient contact. It is also important to ensure that electrodes are not collecting data near curvilinear structures, including the papillary muscles, cardiac valves, and trabeculations. Lastly, the study is limited to mapping of the left ventricular endocardium in partially infarcted sheep models and does not include data regarding mapping of the atrial myocardium, the epicardium, or nonischemic cardiomyopathy.
Further studies, including comparisons of the different multipolar mapping catheters (Abbott HD Grid, Biosense Webster Pentaray, and Boston Scientific Orion), will continue to inform mapping practices and ablation strategies. Moreover, the benefit of closely spaced electrodes on ablation catheters for more detailed mapping of abnormal EGM is being explored in forthcoming ablation catheters (5). Continued improvement in these technologies will facilitate appropriate treatment of arrhythmias by narrowing the field for ablation targets.
↵∗ Editorials published in JACC: Clinical Electrophysiology reflect the views of the authors and do not necessarily represent the views of JACC: Clinical Electrophysiology or the American College of Cardiology.
Dr. Nguyen has received significant research grants from Biosense Webster and CardioNXT; has received educational grants from St. Jude Medical, Boston Scientific, and Medtronic; has a provisional patent on a partially insulated focused catheter ablation; and has nonpublic equity interests/stock options in CardioNXT. Dr. Tumolo has reported that she has no relationships relevant to the contents of this paper to disclose.
All authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
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