Delineating postinfarct ventricular tachycardia substrate with dynamic voltage mapping in areas of omnipolar vector disarray

Abstract

Background: Defining postinfarct ventricular arrhythmic substrate is challenging with voltage mapping alone, though it may be improved in combination with an activation map. Omnipolar technology on the EnSite X system displays activation as vectors that can be superimposed onto a voltage map.

Objective: The study sought to optimize voltage map settings during ventricular tachycardia (VT) ablation, adjusting them dynamically using omnipolar vectors.

Methods: Consecutive patients undergoing substrate mapping were retrospectively studied. We categorized omnipolar vectors as uniform when pointing in one direction, or in disarray when pointing in multiple directions. We superimposed vectors onto voltage maps colored purple in tissue >1.5 mV, and the voltage settings were adjusted so that uniform vectors appeared within purple voltages, a process termed dynamic voltage mapping (DVM). Vectors in disarray appeared within red-blue lower voltages.

Results: A total of 17 substrate maps were studied in 14 patients (mean age 63 ± 13 years; mean left ventricular ejection fraction 35 ± 6%, median 4 [interquartile range 2-8.5] recent VT episodes). The DVM mean voltage threshold that differentiated tissue supporting uniform vectors from disarray was 0.27 mV, ranging between patients from 0.18 to 0.50 mV, with good interobserver agreement (median difference: 0.00 mV). We found that VT isthmus components, as well as sites of latest activation, isochronal crowding, and excellent pace maps colocated with tissue along the DVM border zone surrounding areas of disarray.

Conclusion: DVM, guided by areas of omnipolar vector disarray, allows for individualized postinfarct ventricular substrate characterization. Tissue bordering areas of disarray may harbor greater arrhythmogenic potential.

Keywords: 3D mapping; Ablation; Activation vector; Omnipolar electrograms; Postinfarct scar; Ventricular tachycardia.

Figure 1

A: Dynamic voltage mapping (DVM) guided by omnipolar vector disarray (see also Video 1). (Left) Right ventricular–paced omnipolar voltage map of a left ventricular (LV) inferior wall scar displayed between 0.0 and 1.50 mV scale. Omnipolar vectors have been superimposed onto the voltage map. The upper voltage limit was subsequently adjusted to 0.50 mV and a line was drawn around tissue with voltage bordering 0.50 mV. (Middle) The voltage upper limit was sequentially reduced until only those areas with vector disarray were observed below it (a zoomed-in version is depicted in panel B). This voltage cutoff, termed the DVM threshold, here is 0.20 mV. (Right, top) Monomorphic ventricular tachycardia (VT) was mapped using local activation time—while the full circuit was not contained within the endocardial surface (evident by a color timing gap), components of the VT isthmus (red color) correlated with tissue bordering the DVM threshold. (Right, bottom) Ablation set colocating within and around the border zone of the DVM. B: Omnipolar vector uniformity and disarray (see also Video 1). (Left) Vector uniformity was observed above and below 0.50 mV (white line) in purple voltage tissue until the DVM threshold. (Middle) Zoomed area demonstrating vector disarray below the DVM threshold of 0.20 mV in tissue colored nonpurple (between red-blue). (Right, top) Electrogram from tissue above 0.50 mV. (Right, middle) Electrogram from tissue below 0.50 mV but with uniform activation. (Right, bottom) Electrogram from tissue below the DVM threshold.

Figure 2

The dynamic voltage map vector disarray border zone colocates with areas of isochronal crowding (see also Video 2). (Far left) An atrial-paced voltage map of a postinfarct anteroseptal scar. The mid-anterior aspect appears uncolored, as data were not collected here owing to HD Grid instability. Omnipolar vectors have been superimposed onto the voltage map. A line was drawn around tissue with voltage <0.50 mV, and the voltage upper limit was sequentially reduced until the DVM threshold, here depicted at 0.25 mV. Orange star depicting an area of vector disarray. (Middle) Magnified view from the DVM, highlighting uniformity below 0.5 mV and disarray below the DVM threshold. The associated multicomponent late activating local electrogram from the orange star is highlighted beneath. (Right) Corresponding local activation time (LAT) map—the area of isochronal crowding coincided with the border zone of the DVM. Ablation set colocating within and around the DVM border zone.

Figure 3

The dynamic voltage map (DVM) vector disarray border zone correlates with critical ventricular tachycardia (VT) components (see also Video 3). Patient with a postinfarct inferior scar. (Left, top) Right ventricular–paced omnipolar voltage map and omnipolar vectors demonstrating a DVM threshold of 0.28 mV. (Left, middle) Clinical VT activation map (cycle length 520 ms). Region bordering DVM threshold correlated with the diastolic pathway. (Top, right) Ablation set colocating with tissue within and around the DVM border zone. (Bottom) First application of radiofrequency (RF) resulted in termination of clinical VT.

Figure 4

The dynamic voltage map (DVM) appears fixed despite changing pacing sites. (Left) Right ventricular (RV)–paced omnipolar voltage and omnipolar vector map in a patient with an inferior scar, adjusted to the DVM threshold (0.26 mV). (Center, top) Magnified area of RV-paced map to highlight vector disarray. (Right) Map from the same patient, collected in atrial pacing. The same DVM threshold (0.26 mV) was observed. (Center, bottom) Magnified area of atrial-paced map from the same location. Despite altering wavefront direction, the DVM appears generally concordant (with some minor discordance in areas of lower points density). (Far right, top) An excellent pace map morphology to the induced nonsustained ventricular tachycardia (VT) was observed in tissue near the DVM border zone (yellow star). (Far right, bottom) Ablation set colocating within and around DVM threshold.

Figure 5

Omnipolar Technology (OT) certainty threshold. The 3 panels demonstrate the same magnified image of an area of low-voltage tissue <0.30 mV. Omnipolar vectors have been superimposed. In each panel, the applied OT certainty threshold has been adjusted (left: 0.0; middle: 0.1; right: 0.3). With increasing OT certainty threshold from left to right, the number of arrows displayed can be seen to reduce. The panel on the right with OT certainty threshold of 0.3 represents the default system setting, in which the assessment of vector disarray is limited by low arrow density and hence was not favored in the study. An arrow is encircled red in the left panel. With increasing OT certainty from 0.0 to 0.1, the same arrow cannot be seen in the middle panel. The corresponding omnipolar electrogram associated with this arrow vector is displayed with peak-peak (P-P) voltage 0.12 mV. Another arrow is encircled light brown in the middle panel. With increasing OT certainty from 0.1 to 0.3, the same arrow cannot be seen in the right panel. The corresponding omnipolar electrogram associated with this arrow vector is displayed with P-P voltage 0.22 mV. Applying the default OT certainty threshold of 0.3 would remove this important multicomponent fractionated electrogram from the map. Even though some vectors with associated very low-voltage electrograms (eg, 0.12 mV) arise only at a threshold of 0.0, we chose not to include 0.0 as the study setting, as too low a value could risk the incorporation of noise; hence, we accepted the 0.1 OT certainty threshold as the study setting.