Myocardial necrosis can be identified with different imaging modalities. It appears as FPD with cardiac SPECT and PET MPI imaging. Dobutamine stress echocardiography has a specificity of 76% and sensitivity of 81% for the detection of viable myocardium and the contractile reserve (Garcia et al. 2020). With cardiac magnetic resonance imaging, the presence of sub-endocardial late gadolinium enhancement has a sensitivity of 95% in diagnosing non-viable myocardium (Garcia et al. 2020).
Myocardial necrosis can also be detected with CCTA as a sub-endocardial hypo-enhancement. There are few reports to have investigated the diagnostic accuracy of hypo-enhancement on dynamic CT perfusion in the diagnosis of myocardial infarction (Busch et al. 2011).
An FPD on SPECT-MPI can result in a diagnostic dilemma as to whether the defect represents hibernating myocardium/repetitive stunning or scar, possibly necessitating additional viability imaging (Dilsizian 2021) or less likely an attenuation artifact. Moreover, when an FPD accompanies a reversible defect, anatomical information with invasive coronary angiography might be required.
In this study, patients were selected with revascularization and patent stent/graft on CCTA to support the presumption that the SPECT findings represent a true FPD related to myocardial necrosis, and not hibernating myocardium. In general, CCTA is not recommended in the analysis of stents due to limited diagnostic accuracy, particularly with small stent diameters. However, when CCTA is combined with SPECT MPI in a hybrid cardiac imaging session, many of these limitations can be overcome. CCTA also has non-negligible radiation exposure in real-world practice (Andreini et al. 2020; Hossain et al. 2020). However, newer CT generations enable single heartbeat acquisition and can result extremely low radiation exposure (Kosmala et al. 2019). CZT SPECT is a flexible technology which can dramatically decrease radiation dose by 60%-70% compare to conventional cameras. Thus in the appropriate setting, the radiation dose for hybrid CCTA/MPI studies using CZT cameras is similar to, or less than MPI alone using conventional cameras (Henzlova and Duvall 2020; Schaap et al. 2013).
When indicated, CCTA with rest/stress SPECT can be complementary in the evaluation of patients with prior history of STEMI and revascularization through the detection of myocardial/subendocardial scar, assessment of coronary stents (directly with CCTA or indirectly with SPECT MPI) and non-stented coronary artery segments.
In this report, we illustrate that CCTA is a unique imaging modality, providing both anatomical and perfusion details in patients with previous revascularization. In this dataset of patients with a history of STEMI and patent stents and grafts, FPD on SPECT MPI and subendocardial hypoperfusion on CCTA were found to be largely congruent. The CCTA findings increased the specificity of the SPECT MPI findings for myocardial necrosis as opposed to attenuation artifact or hibernating/viable myocardium. The utilization of a combined hybrid cardiac assessment allowed for a more definitive and comprehensive cardiac assessment. However, our findings cannot be generalized to patients with FPDs and severe coronary artery stenosis, as the hypo-enhancement with CCTA might result from resting ischemia and hibernation. Although promising, further studies enrolling patients without previous revascularization and comparing hypo-enhancement with CCTA with other cardiac viability imaging modalities such as cardiac MRI and FDG-PET are warranted.