Aortic calcium scoring from computed tomography for signal localization by bone scintigraphy to predict aortic stenosis and assess prognosis in patients with transthyretin cardiac amyloidosis

Background – Transthyretin cardiomyopathy (ATTR-CM) and aortic stenosis (AS) are two frequently associated pathologies. The diagnosis of ATTR-CM can be made by performing a bone scintigraphy with tomographic acquisitions and a computed tomography (CT) scan to localize the signal if positive. Calcifications of the aortic valve can be seen on this CT scan. The aim of this study was to determine whether aortic calcifications on the CT scan performed at the time of the bone scintigraphy for the diagnosis of ATTR-CM were predictive of AS and had an impact on prognosis. Methods – Consecutive patients referred to nuclear medicine and diagnosed with ATTR-CM on bone scintigraphy after exclusion of monoclonal gammopathy were included in the study. Patients with history of aortic valve replacement were excluded. CT images performed for signal localization were reviewed for the presence of aortic calcifications. In the presence of aortic calcifications, the calcium score was calculated from axial slices based on a threshold of 130 Hounsfield units. The calcium score results were then compared with the aortic valve hemodynamic parameters by echocardiography to classify patients according to the presence of AS. A three-stage visual score has been developed to assess the significance of aortic valve calcifications (score 0, absence or spotty calcification; score 1, calcifications involving < 50 % of the annulus circumference; score 2, calcifications involving ≥ 50 % of the circumference). Receiver operating characteristic (ROC) analysis and Cox proportional hazards model were used for statistical analysis. Results – Two hundred and sixty-three patients were included. Aortic calcifications based on visual score > 0 were present in 153 (58%) patients. Among them, the median calcium score was 430 [200-1140]. A cut-off calcium score value ≥ 380 was able to predict an AS with an area under the ROC curve of 0.93, (P < 0.0001) achieving a sensitivity of 91% and a specificity of 81%. For severe AS, a threshold ≥ 1690 yielded an area under the ROC curve of 0.98 (P < 0.0001) allowing a sensitivity of 94% and a specificity of 96%. A visual score 2 predicted severe AS with 94% sensitivity and 90 % specificity. Both the aortic valve calcium score and visual score were independent predictors of all-cause mortality during follow-up. Conclusion – Aortic calcifications on CT scan of bone scintigraphy are found in almost two-thirds of patients with ATTR-CM. Assessed using both a semi-quantitative visual score and a calcium score, they are strong predictors of AS severity and mortality. A calcium score cut-off value ≥ 1690 and a visual score 2 reliably identify severe AS.