Objectives: To further characterise patients with suspected severe, but low gradient aortic stenosis (AS) by stress echocardiography and aortic valve calcium score derived by computed tomography.

Background: Severe AS is a common cardiac disease and associated with high morbidity and mortality. While in a majority of patients diagnosis can be established by conventional echocardiography alone, there is a subset of patients with low gradient AS. In these patients diagnosis of true severity remains challenging. The diagnostic approach may involve stress echocardiography and calcium score derived from computed tomography.

Methods: Retrospective analysis of a cohort of 122 consecutive patients who underwent low dose dobutamine stress echocardiography for evaluation of suspected severe, but low gradient AS on index echocardiography. Flow status was assessed based on ESC Guideline criteria (LVEF, SVi) and by calculation of transvalvular flow rate at rest and results were compared. In 90 patients results of additional computed tomography including measurement of aortic valve calcium score were available. Classification in true severe and pseudo severe AS was made based on both methods and patients with diverging results were further analysed for underlying features.

Results:  Of 122 patients studied, 72 (59%) had low flow low gradient (LFLG) AS, 17 (14%) had paradoxical low flow low gradient (PLFLG) AS and 33 (27%) had normal flow low gradient (NFLG) AS based on the ESC guideline criteria. However, only 4 of the 33 patients (12%) with normal flow situation according to ESC guideline criteria (LVEF >50% and SVi >35ml/m²BSA) had normal transvalvular flow rate at rest (>250ml/sec) by direct flow measurement in the LVOT. On the other hand, 2 patients (3%) with LFLG stenosis as defined by ESC guideline criteria had a normal transvalvular flow rate at rest. Patients with LFLG AS had the highest probability of having true severe AS (53%) compared with PLFLG AS (29%) and NFLG AS (29%). Patients classified as having true severe AS by stress echocardiography tended to have higher aortic valve calcium scores compared to patients with pseudo-severe stenosis, but the difference did not reach statistical significance (median aortic valve calcium score in men 2021 vs 1620 AU, p=0.23, and in women 1712 vs 1158, p=0.13). We used cut-off values of >2000 AU in men and >1200 AU in women (true severe aortic stenosis “likely”) to define true severe AS by aortic valve calcium score. In patients that had both conclusive stress echocardiography results and calcium score available, in 44% of cases the two methods showed diverging results. When defining the stress echocardiography as gold standard, the aortic valve calcium score had a receiver operator characteristics area under curve of 0.598 in men an 0.663 in women. Despite widespread testing for demographic, hemodynamic, and echocardiographic parameters, we were not able to identify underlying inter-group differences between patients with matching and patients with diverging results.

Conclusion: Diagnosis of true severe AS in patients with low gradient AS remains challenging. An integrative, multimodality approach is recommended and further research is required regarding the management of patients with conflicting results.