Diagnostic impact of hybrid cardiac SPECT/CT imaging on confirming causative diseases for patients with decompensated heart failure

Introduction: Confirming causative diseases, coronary artery disease (CAD) in particular, is essential to manage patients with decompensated heart failure (DHF). While cardiac perfusion and fatty-acid metabolism SPECT are conventionally used to confirm the causative diseases of DHF, the diagnostic performance of SPECT-only imaging is limited due to the lack of coronary artery distribution information. The aim of this study was to evaluate the diagnostic performance of hybrid cardiac SPECT/CT imaging for patients with DHF of unknown cause. Materials and methods: Thirty consecutive patients (22 men and 8 women; 66 ± 10 years), who were hospitalized due to new onset of DHF, were included in this study. All participants underwent cardiac perfusion SPECT using ^99mTc-methoxy-isobutyl-isonitrile (MIBI), cardiac fatty-acid metabolism SPECT using ¹²³I-beta-methyl-P-iodophenyl-pentadecanoic acid (BMIPP), cardiac CT (CCT), and hybrid cardiac SPECT/CT imaging. On the SPECT images, MIBI and BMIPP defects were quantified using a 17-segment model with a 5-point grading system. A summed MIBI defect score (SMDS), summed BMIPP defect score (SBDS), and summed mismatch score (SMS) were then calculated. In addition, the presence or absence of significant coronary artery stenosis (≥ 70% in diameter) was observed in the CCT images. Definitive diagnoses were confirmed in all patients based on electrocardiography, echocardiography, and coronary angiography findings as well as various clinical parameters. The cardiac SPECT and CCT findings were compared between the CAD and non-CAD groups, and the diagnostic performances of SPECT-only imaging and hybrid SPECT/CT imaging were compared as well. For all patients, the diagnoses of both SPECT-only and SPECT/CT imaging were categorized as CAD: SPECT accumulation defects coinciding with coronary artery territories, equivocal: unclear relationship of accumulation defects and coronary artery territories, or non-CAD: accumulation defects not coinciding with coronary artery territories. Results: Out of a total of 30 participants, the CAD and non-CAD groups consisted of 18 and 12 participants, respectively. While SMDS and SBDS were significantly higher for patients with CAD than those with non-CAD [SMDS: 20 (11-27) vs. 4 (2-16), p = 0.021; SBDS: 24 (19-31) vs. 10 (5-21), p = 0.036], SMS did not significantly differ between the groups [SMS: 4 (2-9) vs. 5 (2-9), p = 0.838]. In the CCT images, significant stenoses were detected in 17 of 18 patients in the CAD group (94%) and 6 of 12 patients in the non-CAD group (50%). Compared with SPECT-only imaging (sensitivity: 80% and specificity: 73%), hybrid SPECT/CT imaging showed a higher accuracy (sensitivity: 89% and specificity: 100%) for the diagnosis of CAD or non-CAD. Conclusions: Hybrid cardiac SPECT/CT imaging likely has superior diagnostic performance when compared with SPECT-only imaging in confirming causative diseases for DHF patients.