TY - JOUR T1 - Metabolic Scar Assessment with<sup>18</sup>F-FDG PET: Correlation to Ischemic Ventricular Tachycardia Substrate and Successful Ablation Sites JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1591 LP - 1598 DO - 10.2967/jnumed.120.246413 VL - 62 IS - 11 AU - Yousra Ghzally AU - Hasan Imanli AU - Mark Smith AU - Jagat Mahat AU - Wengen Chen AU - Alejandro Jimenez AU - Mariem A. Sawan AU - Mohamed Aboel-Kassem F. Abdelmegid AU - Hatem Abd el Rahman Helmy AU - Salwa Demitry AU - Vincent See AU - Stephen Shorofsky AU - Vasken Dilsizian AU - Timm Dickfeld Y1 - 2021/11/01 UR - http://jnm.snmjournals.org/content/62/11/1591.abstract N2 - The functional and molecular imaging characteristics of ischemic ventricular tachycardia (VT) substrate are incompletely understood. Our objective was to compare regional 18F-FDG PET tracer uptake with detailed electroanatomic maps (EAMs) in a more extensive series of postinfarction VT patients to define the metabolic properties of VT substrate and successful ablation sites. Methods: Three-dimensional (3D) metabolic left ventricular reconstructions were created from perfusion-normalized 18F-FDG PET images in consecutive patients undergoing VT ablation. PET defects were classified as severe (defined as &lt;50% uptake) or moderate (defined as 50%–70% uptake), as referenced to the maximal 17-segment uptake. Color-coded PET scar reconstructions were coregistered with corresponding high-resolution 3D EAMs, which were classified as indicating dense scarring (defined as voltage &lt; 0.5 mV), normal myocardium (defined as voltage &gt; 1.5 mV), or border zones (defined as voltage of 0.5–1.5 mV). Results: All 56 patients had ischemic cardiomyopathy (ejection fraction, 29% ± 12%). Severe PET defects were larger than dense scarring, at 63.0 ± 48.4 cm2 versus 13.8 ± 33.1 cm2 (P &lt; 0.001). Similarly, moderate/severe PET defects (≤70%) were larger than areas with abnormal voltage (≤1.5 mV) measuring 105.1 ± 67.2 cm2 versus 56.2 ± 62.6 cm2 (P &lt; 0.001). Analysis of bipolar voltage (23,389 mapping points) showed decreased voltage among severe PET defects (n = 10,364; 0.5 ± 0.3 mV) and moderate PET defects (n = 5,243; 1.5 ± 0.9 mV, P &lt; 0.01), with normal voltage among normal PET areas (&gt;70% uptake) (n = 7,782, 3.2 ± 1.3 mV, P &lt; 0.001). Eighty-eight percent of VT channel or exit sites (n = 44) were metabolically abnormal (severe PET defect, 78%; moderate PET defect, 10%), whereas 12% (n = 6) were in PET-normal areas. Metabolic channels (n = 26) existed in 45% (n = 25) of patients, with an average length and width of 17.6 ± 12.5 mm and 10.3 ± 4.2 mm, respectively. Metabolic channels were oriented predominantly in the apex or base (86%), harboring VT channel or exit sites in 31%. Metabolic rapid-transition areas (&gt;50% change in 18F-FDG tracer uptake/15 mm) were detected in 59% of cases (n = 33), colocalizing to VT channels or exit sites (15%) or near these sites (85%, 12.8 ± 8.5 mm). Metabolism–voltage mismatches in which there was a severe PET defect but voltage indicating normal myocardium were seen in 21% of patients (n = 12), 41% of whom were harboring VT channel or exit sites. Conclusion: Abnormal 18F-FDG uptake categories could be detected using incremental 3D step-up reconstructions. They predicted decreasing bipolar voltages and VT channel or exit sites in about 90% of cases. Additionally, functional imaging allowed detection of novel molecular tissue characteristics within the ischemic VT substrate such as metabolic channels, rapid-transition areas, and metabolism–voltage mismatches demonstrating intrasubstrate heterogeneity and providing possible targets for imaging-guided ablation. ER -