VT Substrate Characteristics: Insights from Multi-modality Structural and Functional Imaging of the VT Substrate Using CMR Scar, 123 I-mIBG-SPECT Innervation and Bipolar Voltage.

Background - Post-Ischemic adaptation results in characteristic myocardial structural and functional changes of the VT(Ventricular Tachycardia) substrate. Objective - Compare myocardial structural/functional adaptation (late gadolinium-enhancement(LGE)/abnormal innervation) with detailed VT mapping data to identify regional heterogeneities of post-ischemic changes. Methods - Fifteen patients with ischemic cardiomyopathy and drug-refractory VT underwent LGE-Cardiac magnetic resonance imaging(CMR), 123 I-mIBG-SPECT and high-resolution bipolar voltage mapping to assess fibrosis(>3SD), abnormal innervation(<50% tracer uptake) and low-voltage areas(<1.5mV), respectively. 3D-reconstructed CMR/123 I-mIBG models were co-registered for further comparison. Results - Post-ischemic structural/functional adaptation in all three categories was similar in size (CMR scar 46.1cm2 [33.1-86.9cm2 ] vs. 123 I-mIBG-SPECT abnormal innervation 47.8cm2 [40.5-68.1cm2 ] vs. low-voltage area 29.5cm2 [24.5-102.6cm2 ], p>0.05). Yet, any single modality underestimated the total VT substrate area, defined as abnormal in at least one of the three modalities (76.0cm2 [57.9-143.2cm2 ]; p<0.001). Within the total VT substrate area, regions abnormal in all 3 modalities were most common (25.2%). However, significant parts of the VT substrate had undergone heterogeneous adaptation (abnormal in <3 modalities); most common categories were 'abnormal innervation only'(18.2%), 'CMR scar+abnormal innervation only'(14.9%) and 'CMR scar only'(14.6%). All 14 VT channel/exit sites(0.88±0.74mV) localized to myocardium demonstrating CMR scar AND abnormal innervation. This specific tissue category accounted for 68.3% of the CMR scar and 31.2% of the total abnormal post-ischemic VT substrate. Conclusion - Structural/functional imaging demonstrates regional heterogeneities of the post-ischemic VT substrate not appreciated by any single modality alone. Co-existence of abnormal innervation and CMR scar may identify a state of particularly proarrhythmic adaptation and represent a potential novel target for VT ablation.