Determinants of atrial bipolar voltage: Inter electrode distance and wavefront angle
Introduction
Current era complex cardiac electrophysiological procedures rely on bipolar electrogram (EGM) peak-to-peak voltage (Vpp) values to characterise myocardial substrate. Cardiac electrophysiologists interpret the state of myocardial tissues by examining colour-coded Vpp maps of the myocardial surface. Low voltage values are usually associated with diseased areas while high voltage values represent healthy areas. Specific threshold values have been explored and defined previously [1,7]. Vpp values used in these maps are acquired from commercially available clinical catheters and systems that record bipolar EGMs. However, a wide array of different clinical catheters with varying electrode arrangements currently exist. There is also a rise in the use of high-density (HD) grid catheters (electrodes spaced 4 mm apart) which could encompass large myocardial areas for greater ease of mapping. Additionally, there is evidence presented that in human and animal tissues [1,2] as well as in simulations [3], the propagation direction of an electrical wavefront with respect to the orientation of bipolar electrode pairs greatly affect bipolar Vpp values which in turn affects bipolar voltage map profiles [4]. Specifically, if a bipolar electrode is oriented along the of a direction a wavefront a bipolar EGM with a maximum Vpp value may be obtained. However, if such an electrode pair is oriented across a wavefront Vpp values canbe minimal. The directional nature of bipolar electrodes then results in a great variance in the Vpp values [5]. There is also significant uncertainty since low bipolar Vpp values may be obsereved over healthy areas only because the bipolar electrodes are not aligned with the direction of a propagating wave suggesting this area is diseased and may become target a of unnecessary tissue ablation. This is especially important when attempting to eliminate sources of tachycardia [6].
In addition to the directional uncertainty posed, bipolar-Vpp-based substrate maps are also affected by electrode size and interelectrode spacing of the catheters used [7]. This could drastically change the interpretation of a myocardial substrate map and consequently treatment strategy. This dilemma becomes further compounded when differentiating transmural compared to partial thickness or intramural scar in the atrium. Despite these causes of variability, only a few studies have characterised bipolar EGMs with respect to electrophysiological applications [8,9] and even such studies were performed in-vivo and do not control for wave direction and catheter orientation. Because of these factors, it is important to carefully evaluate the nature of bipolar Vpp values.
In this paper, we investigate the relationship of electrode spacing, wavefront direction, and electrode orientation to bipolar Vpp values. We further hypothesized that bipolar Vpp values obtained from diseased tissues (i.e. non-transmural, transmural, and intramural scars) will be affected differently by these parameters compared to those obtained from healthy tissues. The impact of these factors was validated using data acquired from isolated porcine hearts.
Section snippets
Atrial tissue computer model
The Courtemanche human atrial action potential model [10] was used for simulations in the Cardiac Arrhythmia Research Package (CARP) software. A 3-dimensional 40 × 25 × 2 mm slab of tissue, discretized at 0.3 mm resolution, was modelled under a 6 mm deep salinebath with a conductivity of 1 S/m (Fig. 1A). A bidomain scheme, which models both intracellular and extracellular domains at the same time, was used. Fibres were oriented unidirectionally (i.e. along the x-axis of the atrial slab model).
Bipolar voltage peak-to-peak values increase as interelectrode spacing increases
As observed from our computer simulations of a healthy myocardial tissue (Fig. 4A, top panel), focusing first on bipolar electrodes at orientation angle 0°, bipolar Vpp values increased as interelectrode spacing increased, with an average slope of 0.41 ± 0.22 mV/mm. The increase in Vpp values was initially steep and then began to plateau beyond 3.6 mm interelectrode spacing. Examples of bipolar EGMs at different interelectrode spacings from healthy tissues are shown in the top panel of Fig. 4B.
Discussion
Our study demonstrates that for a fixed electrode size and a uniformly propagating planar wave, bipolar Vpp values increase with greater interelectrode spacing (1.2–6.0 mm). While there is a progressive reduction of voltage values in recorded bipolar Vpp values in healthy tissue beyond interelectrode spacings of greater than 3.6 mm, no such plateauing is observed in diseased tissue over the clinically relevant range of interelectrode spacing. These findings suggest that the bipolar EGM Vpp is
Conclusion
Understanding and compensating for wavefront direction and interelectrode spacing in bipolar EGM measurements could improve interpretation of the substrate when mapping with catheters. The relationship of bipolar voltages with interelectrode spacing and wavefront direction is linearly scalable up to approximately 4 mm. Bipolar voltage variabilities observed due to interelectrode spacing and wavefront direction favours an electric field-based assessment of the myocardium as an alternative to
Funding sources
Canadian Institutes of Health Research grant # MOP 142272. Dr. E. Vigmond received financial support from the French Government as part of the “Investments of the Future” program managed by the National Research Agency (ANR), Grant reference ANR-10-IAHU-04, and the Fondation pour la Recherche Medicale.
Disclosures
Dr K. Nanthakumar is a research consultant for Biosense Webster, Abbott Laboratories and has received speaker fees from Boston Scientific. Dr D.C. Deno is an employee of Abbott Laboratories. Dr. E. Vigmond is a co-owner of CardioSolve L.L.C. CardioSolve L.L.C. did not contribute to this research.
Conflicts of interest
None Declared.
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Cited by (21)
Quantitative evaluation of different high-density 3D mapping modes for atrial and ventricular substrate assessment of cardiac arrhythmias with the HD grid catheter
2020, Journal of ElectrocardiologyCitation Excerpt :In support of this notion, Chrispin et al. reported a correlation between wall thickness and local electrogram determination [15]. However, switching between standard and wave diagonal modes showed no difference between atria and ventricle, indicating that chamber thickness has no significant effect on the acquisition mode dependent difference of reported low voltage regions and that mere electrode spacing might be of higher relevance [16,17]. Only recently an algorithm combining unipolar and bipolar voltage acquisition modes was proposed to further qualitatively and quantitatively characterize scars and to distinguish different scar forming entities (i.e. sarcoidosis versus ARVC) [18].
To the Editor— Determinants of bipolar amplitude
2020, Heart RhythmHow, When, and Why: High-Density Mapping of Atrial Fibrillation
2020, Cardiac Electrophysiology ClinicsCitation Excerpt :Moreover, pacing could be performed at a lower output with the multielectrode catheter because of increased current density at the tissue-electrode interface.20 Similar findings regarding bipolar electrograms have been noted in an ovine ventricular infarct model focused on the effects of interelectrode spacing and a computational study examining the effect of wavefront angle and interelectrode spacing in a biodomain model of the human atrium.21,22 Another observation has been the notable and intuitive reduction in mean bipolar electrogram amplitude during AF relative to sinus rhythm, demonstrated in prior studies.23,24
Beyond High-Density Mapping: Is There a Gold Medalist?
2020, JACC: Clinical ElectrophysiologyHigh-Density Grid Catheter for Detailed Mapping of Sinus Rhythm and Scar-Related Ventricular Tachycardia: Comparison With a Linear Duodecapolar Catheter
2020, JACC: Clinical ElectrophysiologyCitation Excerpt :In the present study, the scar area identified by the grid catheter was highly correlated with that detected by the linear duodecapolar catheter, by sequential mapping in the same patient. The configuration of the grid catheter with smaller electrodes, larger interelectrode spacing, and orthogonal design in bipole pairs likely accounted for the higher voltages with subsequent smaller low-voltage areas compared with the duodecapolar catheter (14,15). The present findings validated the accuracy of the automated selection of the largest amplitude between orthogonal pairs in clinical usage, because grid (HD wave) mapping consistently yielded smaller low voltage areas compared with single orientations (grid along or across), which indicated that the orthogonal bipolar design in the grid catheter markedly affected the assessment of local voltage.
Reinserting Physiology into Cardiac Mapping Using Omnipolar Electrograms
2019, Cardiac Electrophysiology ClinicsCitation Excerpt :Optimizing bipolar Vpp measurements is challenging, especially in vivo, because it requires prior knowledge of the activation direction (AD) and complete control of catheter orientation. In addition to directionality, electrode pairs spaced widely apart, as in ablation catheters, can produce large Vpps and closely spaced electrodes, as seen in modern mapping arrays, produce small Vpps.6–8 These factors create unreliable and nonreproducible characterization of the cardiac substrate.
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M Beheshti and K Magtibay are Co-First Authors.