Elsevier

Computers in Biology and Medicine

Volume 102, 1 November 2018, Pages 449-457
Computers in Biology and Medicine

Determinants of atrial bipolar voltage: Inter electrode distance and wavefront angle

https://doi.org/10.1016/j.compbiomed.2018.07.011Get rights and content

Highlights

  • Bipolar voltages are based on electric field measurements of the myocardium.

  • Interelectrode distance influences bipolar voltage values.

  • Wavefront angle to an electrode affects bipolar voltage values.

  • Bipolar voltage values can be scaled with electrode distance less than 4 mm.

  • Electric-field-based measurement could be an alternative to bipolar voltage.

Abstract

Background

Local bipolar electrogram (EGM) peak-to-peak voltage (Vpp) is currently used to characterise mapped myocardial substrate. However, how interelectrode distance and angle of wavefront incidence affect bipolar, Vpp values, in the current era of multi-electrode mapping is unknown.

Objectives

To elucidate the effects of tissue and electrode geometry on bipolar Vpp measurements, when mapping healthy versus diseased atrial regions.

Methods

A bidomain model of human atrial tissue was used to quantify the influence on Vpp values of various electrode configurations in healthy tissue, and tissue containing an unexcitable region. The orientation angle and interelectrode spacing of a surface bipole, and thickness and depth of the unexcitable core were serially varied. Results were validated with data obtained from isolated porcine hearts.

Results

In healthy tissue, bipolar Vpp values increased with increasing interelectrode spacing and plateaued beyond a spacing of approximately 4 mm. The bipolar Vpp values in healthy tissue were relatively less sensitive to wavefront orientation angle with large interelectrode spacing. In diseased tissue, on the contrary, with increasing interelectrode spacing, bipolar Vpp values increased linearly without a plateau and were more sensitive to orientation angle. The bipolar Vpp values decreased with increasing thickness of the scar, with larger relative decrease in small bipoles than larger ones. Bipolar Vpp values increased with a progressively intramural location of fixed-size scar and became less distinguishable from healthy tissue especially for smaller interelectrode spacings.

Conclusions

The scalable relationship established for interelectrode distances favour an electric-field-based assessment as opposed to traditional Vpp values as a tool for physiologically relevant measurement for mapping catheters with interelectrode spacing up to 4 mm. This will allow for universal assessment of myocardial health across catheters with varied spacing.

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.

References (27)

  • N.M.S. De Groot et al.

    Voltage and activation mapping: how the recording technique affects the outcome of catheter ablation procedures in patients with congenital heart disease

    Circulation

    (2003)
  • W.G. Stevenson et al.

    Recording techniques for clinical electrophysiology

    J. Cardiovasc. Electrophysiol.

    (2005)
  • M. Courtemanche et al.

    Ionic mechanisms underlying human atrial action potential properties: insights from a mathematical model

    Am. J. Physiol. Heart Circ. Physiol.

    (1998)
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