Title : Diagnostic odyssey of microvascular abnormalities in INOCA: 13N-ammonia and gadolinium synchronous dual-perfusion PET/MR approach
Abstract:
Background: Ischemia with no obstructive coronary arteries (INOCA), a chronic disorder with a poor prognosis, remains diagnostically challenging. Positron emission tomography (PET) has been established as the non-invasive reference benchmark for quantifying myocardial blood flow (MBF). The innovative hybrid PET-MR technology enables the concurrent procurement of PET and magnetic resonance (MR) data under precisely the same experimental and physiological circumstances. This study aimed to utilize hybrid PET/MR to simultaneously obtain PET and magnetic resonance data of patients, aiming to identify potential predictive factors for the reduction of coronary flow reserve (CFR).
Methods: We prospectively enrolled 16 patients (8 females and 8 males) with typical angina pectoris and no obvious coronary stenoses shown by angiography. Under resting conditions and stress states induced by regadenoson, these patients simultaneously received injections of gadolinium contrast agent and 13N - Ammonia on a PET/MR scanner, followed by MR imaging and PET myocardial perfusion imaging examinations. According to the guidelines of the European Society of Cardiology, INOCA was characterized as typical angina in the absence of coronary stenosis (INOCA n = 8, no INOCA n = 8). CFR was defined as the ratio of hyperemic MBF (after regadenoson) to resting MBF. Microvascular dysfunction was determined by a CFR below 2.Then it was correlated with the parameters obtained from MR as well as clinical parameters respectively. The receiver operating characteristic (ROC) curves and diagnostic cutoff values were analyzed to evaluate the predictive value of factors significantly influencing the diagnosis of INOCA. Subsequently, the statistically significant predictive factors were aggregated into the number of risk factors (NRF).
Results: Global CFR (1.47 ? 0.55 vs. 4.04 ? 1.69; P < 0.001) was significantly lower in patients with INOCA than in those with no INOCA. ROC curve analysis was performed and the Youden Index was calculated to determine the best cut-off value with the highest sensitivity and specificity. ROC analysis identified the following continuous variables significant for INOCA diagnosis: global radial strain [AUC = 0.938, 95% confidence interval (CI): 0.81 - 1.00, P = 0.003] with a cut-off value of 57.35%; triglycerides (AUC = 0.945, 95% CI: 0.84 - 1.00, P = 0.003), cut-off 1.2 mmol/L; very - low - density lipoprotein (VLDL) (AUC = 0.797, 95% CI: 0.56 - 1.00, P = 0.046), cut-off 0.72 mmol/L; and rest T1 (AUC = 0.984, 95% CI: 0.94 - 1.00, P = 0.001), cut-off 1243.5 ms. The categorical variable with statistical significance is late gadolinium enhancement (LGE) [AUC = 0.813 (95% CI: 0.59 - 1.00), P = 0.036]. Based on the aforementioned factors, the NRF for each patient was calculated cumulatively and subsequently input into the ROC curve analysis. The findings revealed that our NRF exhibited excellent diagnostic efficacy for INOCA. Notably, the optimal cut-off value for NRF was determined to be 3.5 [AUC = 0.945 (95% CI: 0.84 - 1.00), P = 0.003].
Conclusion: Accumulated risk factors negatively impact CFR. Calculating the NRF in patients with suspected INOCA can effectively predict the probability of microvascular dysfunction among these patients. We propose that patients with NRF greater than 3.5 should have their CFR measured via PET.
