Cardiac mapping with irreverence to time: Replacing isochrones with omnipolar vectors

Multiple methods can be used to confirm transablation line conduction block and are routinely part of the diagnostic armamentarium and assessment of lesion monitoring in the electrophysiology laboratory. These methods include a shift in electrogram (EGM) activation when using a multipolar catheter, presence of widely spaced double potentials, and classic maneuvers including bidirectional and differential pacing. Often, these techniques require annotation of EGM local activation and assessment of timing differences around the line relative to the pacing location. Interpretation of annotation and timing differences of EGMs becomes difficult at sites with delay, conduction leak, wave collision, or epicardial bridging connections. This is especially true when trying to annotate 2 separate wavefronts, leading to confusing isochrones and the phenomenon of pseudoblock. One of the major uses of high-density mapping has been identifying pseudoblock in up to 20%–30% of linear ablations. Pseudoblock is thought to occur due to persistence of endocardial slow conduction across gaps in the ablation line or conduction through epicardial bridges that permit electrical connection to atrial endocardium. Common examples include vein of Marshall muscle bundles that are often painstakingly involved in sustaining perimitral flutters, intercaval bundles in pulmonary vein flutters, the Bachmann bundle in biatrial flutters, the septopulmonary bundle in roof-dependent left atrial flutters, and muscular sleeves in the coronary sinus ostium and middle cardiac vein in typical cavotricuspid isthmus–dependent flutters. The examples described herein highlight the limitations of mapping cardiac activation and the need for improvements to truly identify anatomic lines of block, which include improved metrics of lesion transmurality. The limitation of the reference standard is the isochrone map and its inherent limitations. As simple as it may seem, isochrone maps are produced with several assumptions that often are overlooked or ignored. These conditions have been described eloquently by Ideker et al : (1) precise electrode location; (2) assignment of a single local activation time (LAT) for each electrode; (3) presence or absence of activation that can be verified; and (4) proximity of recording electrodes providing enough density to clearly define the activation wavefront with sufficient accuracy. We would like to include a fifth condition—cycle length stability, which commonly interrupts the timing reference to align sequentially acquired EGMs.