Law of Spatial Averaging During Endocardial Voltage Mapping
You Can’t Trim Out the Fat!
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See Article by Samanta et al
Since the introduction and widespread application of 3-dimensional electroanatomic mapping, voltage-based displays of the arrhythmogenic substrate have greatly facilitated the practice of scar-related ventricular tachycardia (VT) ablation. The detection of scar is predicated on a voltage threshold (<1.5 mV) used to differentiate scar from normal tissue.1 However, there has been a resurgence of interest in the fundamental principles of bipolar and unipolar voltage recordings that complicate our oversimplistic classification of low voltage on a binary system, scar or normal.2 Bipolar and unipolar amplitudes are influenced by the orientation of the recording electrode relative to the activation wavefront, which exhibits anisotropic conduction properties relative to fiber orientation and fibrosis. Recordings are necessarily made with instruments or tools, and the size, shape, and spacing of an electrode pair determine the amount of myocardium sampled by the virtual electrode.3
Voltage recordings represent an electrical biopsy, and the electrogram amplitude represents a spatial average of the relative proportion of myocardial mass to fibrosis in a given sample.4 This explains why a higher voltage threshold may be warranted to detect fibrosis in patients with hypertrophic cardiomyopathy. The number of viable myocytes that comprise an electrogram with a clinical recording tool remains unknown at present. The field of view may be much larger than the region of interest. The significance of the law of spatial averaging can be appreciated by imagining a bipolar recording with the distal electrode in contact with transmural scar and the proximal electrode in contact with normal myocardium. The resulting voltage does not reflect the exact information from either electrode. Consistent with this consideration, we …