Understanding unipolar electrograms and global activation from noninvasive mapping for diagnosing arrhythmias

In the past several decades Electrocardiographic Imaging has been developed, validated, and recently commercialized for clinical use (Medtronic CardioInsight™). The technology noninvasively maps cardiac electrical potentials by combining multi-channel body surface electrocardiograms and patient specific heart-torso geometry. Unlike contact catheter mapping where bipolar electrograms are commonly used, noninvasive mapping is unipolar in nature. While bipolar electrograms reflect local activation time, noninvasive mapping reflects both local and global information. Characterizing arrhythmias using noninvasive mapping requires a different approach than what is used with bipolar mapping during electrophysiological studies. With multiple example cases, this article aims to demonstrate how in-depth analysis of noninvasive electrogram features and global activation patterns can reveal clinically important characteristics of arrhythmias, which may not be evident on the automatically generated maps. These characteristics include transmural location of the ectopic focus, differential locations within structural proximity, engagement of bundle or specific tissue, and substrate properties. The analysis approach involves applying unipolar potential fundamentals and relating electrogram features, global activation with underlying electrophysiology and cardiac anatomy to explain specific mapping phenomenon. If validated, easy-to-use diagnostic criteria or algorithms can be built and automated as product features in the commercial system to facilitate future noninvasive mapping in patients.