Multielectrode Unipolar Voltage Mapping and Electrogram Morphology to Identify Post-Infarct Scar Geometry: Validation by Histology.

OBJECTIVES: This study sought to evaluate the ability of uni- and bipolar electrograms collected with a multielectrode catheter with smaller electrodes to: 1) delineate scar; and 2) determine local scar complexity. BACKGROUND: Early reperfusion results in variable endocardial scar, often overlaid with surviving viable myocardium. Although bipolar voltage (BV) mapping is considered the pillar of substrate-based ablation, the role of unipolar voltage (UV) mapping has not been sufficiently explored. It has been suggested that bipolar electrograms collected with small electrode catheters can better identify complex scar geometries. METHODS: Twelve swine with early reperfusion infarctions were mapped with the 48-electrode OctaRay catheter and a conventional catheter during sinus rhythm. BV electrograms with double components were identified. Transmural (n = 933) biopsy specimens corresponding to mapping points were obtained, histologically assessed, and classified by scar geometry. RESULTS: OctaRay UV (UVOcta) and BV (BVOcta) amplitude were associated with the amount of viable myocardium at a given location, with a stronger association for UVOcta (R2 = 0.767 vs 0.473). Cutoff values of 3.7 mV and 1.0 mV could delineate scar (area under the curve: 0.803 and 0.728 for UVOcta and BVOcta, respectively). The morphology of bipolar electrograms collected with the OctaRay catheter more frequently identified areas with 2 layers of surviving myocardium than electrograms collected with the conventional catheter (84% vs 71%). CONCLUSIONS: UV mapping can generate a map to delineate the area of interest when using a multielectrode catheter. Within this area of interest, the morphology of bipolar electrograms can identify areas in which a surviving epicardial layer may overlay a poorly coupled, potentially arrhythmogenic, endocardium.

Mini-, Micro-, and Conventional Electrodes: An in Vivo Electrophysiology and Ex Vivo Histology Head-to-Head Comparison.

OBJECTIVES: This study sought to assess the relative effect of catheter, tissue, and catheter-tissue parameters, on the ability to determine the amount of viable myocardium in vivo. BACKGROUND: Although multiple variables impact bipolar voltages (BVs), electrode size, interelectrode spacing, and directional dependency are of particular interest with the development of catheters incorporating mini and microelectrodes. METHODS: Nine swine with early reperfusion myocardial infarctions were mapped using the QDot catheter and then remapped using a Pentaray catheter. All QDot points were matched with Pentaray points within 5 mm. The swine were sacrificed, and mapping data projected onto the heart. Transmural biopsies corresponding to mapping points were obtained, allowing a comparison of electrograms recorded by mini, micro-, and conventional electrodes with histology. RESULTS: The conventional BV of 2,322 QDot points was 1.9 ± 1.3 mV. The largest of the 3 microelectrode BVs (BVµMax) average 4.8 ± 3.1 mV. The difference between the largest (BVµMax) and smallest (BVµMin) at a given location was 53.7 ± 18.1%. The relationships between both BVµMax and BVµMin and between the conventional BV and BVµMax were positively related but with a significant spread in data, which was more pronounced for the latter. Pentaray points positively related to the BVµMax with poor fit. On histology, increasing viable myocardium increased voltage, but both the slope coefficient and fit were best for BVµMax. CONCLUSIONS: Using histology, we could demonstrate that BVµMax is superior to identify viable myocardium compared with BVC and BV using the Pentaray catheter. The ability to simultaneously record 3 BVµs with different orientations, for the same beat, with controllable contact and selecting BVµMax for local BV may partially compensate for wave front direction.

Multisize Electrodes for Substrate Identification in Ischemic Cardiomyopathy: Validation by Integration of Whole Heart Histology.

OBJECTIVES: This study sought to evaluate the value of combined electrogram (EGM) information provided by simultaneous mapping using micro- and conventional electrodes in the identification of post-myocardial infarction ventricular tachycardia substrate. BACKGROUND: Ventricular tachycardias after myocardial infarction are related to scars with complex geometry. Scar delineation and ventricular tachycardia substrate identification relies on bipolar voltages (BV) and EGM characteristics. Early reperfusion therapy results in small, nontransmural scars, the details of which may not be delineated using 3.5 mm tip catheters. METHODS: Nine swine with early reperfusion myocardial infarction were mapped using Biosense Webster's QDOT Micro catheter, incorporating 3 microelectrodes at the tip of the standard 3.5 mm electrode. Analysis of EGM during sinus rhythm, right ventricular pacing, and short-coupled right ventricular extrastimuli was performed. The swine were sacrificed and mapping data were projected onto the heart. Transmural biopsies (n = 196) corresponding to mapping points were obtained, allowing a head-to-head comparison of EGM recorded by micro- and conventional electrodes with histology. RESULTS: To identify scar areas using standard electrodes, unique cutoff values of unipolar voltage <5.44 mV, BV <1.27 mV (conventional), and BV <2.84 mV (microelectrode) were identified. Combining the information provided by unipolar voltage and BV mapping, the sensitivity of scar identification was increased to 93%. Micro-EGM were better able to distinguish small near-fields corresponding to a layer of viable subendocardium than conventional EGM were. CONCLUSIONS: The combined information provided by multisize electrode mapping increases the sensitivity with which areas of scar are identified. EGM from microelectrodes, with narrower spacing, allow identification of near-fields arising from thin subendocardial layer and layers activated with short delay obscured in EGM from conventional mapping catheter.