Ventricular Tachycardia (VT) Substrate Characteristics: Insights from Multimodality Structural and Functional Imaging of the VT Substrate Using Cardiac MRI Scar, ¹²³I-Metaiodobenzylguanidine SPECT Innervation, and Bipolar Voltage

Abstract

- Post-Ischemic adaptation results in characteristic myocardial structural and functional changes of the VT(Ventricular Tachycardia) substrate. - Compare myocardial structural/functional adaptation (late gadolinium-enhancement(LGE)/abnormal innervation) with detailed VT mapping data to identify regional heterogeneities of post-ischemic changes. - Fifteen patients with ischemic cardiomyopathy and drug-refractory VT underwent LGE-Cardiac magnetic resonance imaging(CMR), 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/I-mIBG models were co-registered for further comparison. - Post-ischemic structural/functional adaptation in all three categories was similar in size (CMR scar 46.1cm[33.1-86.9cm] vs. I-mIBG-SPECT abnormal innervation 47.8cm[40.5-68.1cm] vs. low-voltage area 29.5cm[24.5-102.6cm], p>0.05). Yet, any single modality underestimated the total VT substrate area, defined as abnormal in at least one of the three modalities (76.0cm[57.9-143.2cm]; 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. - 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.

Metabolic heterogeneous zone assessed by 18FDG‐PET is predictive of postablation mortality in patients with ventricular tachycardia

“…Second, pace map matches ≥11/12 leads with the longest stim‐QRS were used to approximate the VT channel/exit 15 . Third, entrainment/activation mapping was performed to the maximum degree tolerated after the re‐induction of the VT to confirm the anatomic location of the VT channel/exit site 16,17 . Linear ablation lesions were applied as appropriate for unmappable VT 18 .…”

“…15 Third, entrainment/activation mapping was performed to the maximum degree tolerated after the re-induction of the VT to confirm the anatomic location of the VT channel/exit site. 16,17 Linear ablation lesions were applied as appropriate for unmappable VT. 18 RF ablation was performed orthogonally to the defined channel using single, overlapping RF lesions (40-50 W, the 60 s each). After the ablation, programmed electric stimulation with up to triple extra-stimuli and shortest coupling interval of 200ms from at least 2 RV (right ventricular)/LV sites was repeated, and successful ablation was defined as the inability to induce the ablated clinical VT.…”

Can the promise of radionuclide cardiac innervation imaging be fulfilled?

“…20 Finally, it will be crucial to work with other subspecialists, particularly heart failure and electrophysiology experts, to meet the needs of those on the front lines of direct patient therapeutics, demonstrated by work combining adrenergic imaging with cardiac MRI and electroanatomic mapping to improve the outcome of ventricular ablation procedures. 21 The success of radionuclide autonomic imaging will depend on its contribution to other technologies to improve the lives of people with cardiac disease.…”

40 Years Anniversary of Cardiac 123I-mIBG Imaging: State of the Heart

“…In recent years, clinical use of cardiac 123 I-mIBG imaging has also been affected by the perception that the method is outdated in comparison with other technologies. Whether it is the continued reliance on planar imaging and the rudimentary quantitation of the heart/mediastinum ratio in a field now dominated by quantitative tomographic techniques, the limited image quality of even the best 123 I-mIBG SPECT study compared with PET scans using agents such as 11 C-HED [91] or 18 F-Flubrobenguane [92], or the advancements in other imaging and invasive cardiac mapping technologies [93,94], convincing cardiologists to use cardiac 123 I-mIBG imaging is challenging. Eventual approval of a cardiac PET agent capable of quantifying sympathetic innervation will probably make this challenge even more daunting.…”