Background: Voltage thresholds for ventricular scar definition are based on historic data collected using catheters with widely spaced bipoles. Modern multipolar mapping catheters employ smaller electrodes and interelectrode spacing that theoretically allows for mapping with increased resolution and reduced far-field electrogram (EGM) component. Despite the advancement in technology, historic cutoffs of <0.5 mV for dense scar and 0.5-1.5 mV for scar borderzone continue to be used in contemporary electrophysiology. We aimed to assess the optimal voltage cutoffs for substrate characterization using the HD Grid (Abbott, Inc, USA) multipolar mapping catheter.
Methods: Three patients who underwent VT ablation for implantable cardioverter defibrillator (ICD) shocks, had substrate mapping performed using the HD Grid and pre-procedure cardiac magnetic resonance imaging (CMR). The HD Grid is a multipolar mapping catheter containing 16×1 mm electrodes in a 4×4 grid layout with equal spacing of 3 mm. Bipolar voltage maps were collected using HD wave mapping technology, whereby orthogonal bipolar wavefronts are analysed by the system and the better of the two signals is used to negate the effect of wavefront directionality. Also, the system uses the best duplicate algorithm, whereby the highest amplitude signal in a collected region is displayed on the map. Gadolinium-enhanced CMR data was analysed using the ADAS software (Galgo Medical), which segments the myocardial scar density, and was co-registered with the electroanatomical map on the Precision software platform (Abbott, Inc, USA). Voltages in CMR scar were assessed to characterize the most accurate settings for endocardial scar (Figure 1A).
Results: 1,028 voltage points in dense CMR scar were analysed. The median bipolar voltage for regions of dense CMR scar was 0.21 mV (IQR 0.11-0.33). 1,174 voltage points from ADAS scar borderzone were analysed, with a median bipolar voltage of 0.73 (IQR 0.49-1.1). The 80th centile for dense scar was 0.37 mV and for scar borderzone was 1.24 mV. ROC analysis AOC 90% suggested the optimal cutoff for endocardial dense scar was 0.45 mV, (Sensitivity 86%, Specificity 81%) (Figure 1B). ROC analysis AOC 91% suggested the optimal cutoff for endocardial scar borderzone was 1.4 mV, (Sensitivity 83%, Specificity 83%).
Conclusion: Ventricular substrate characterization with newer mapping technology, suggests that traditional voltage cutoffs may need revision for delineation of scar characteristics. This has important implications for mapping VT and characterizing channels in order to identify VT circuits. Further analysis involving more patients would help validate these values.