Introduction 1 2 3 4 4 5 6 5 6 7 9 7 10 11 12 13 1 2 14 17 18 Methods Between June 2004 and February 2006, patients with a known peak gradient (≥ 30 mmHg) across their native aortic valve were invited to participate in the study during their control visit to the outpatient clinic of cardiology. All patients were under control for valvular aortic stenosis. The study was in accordance with principles that have their origin in the Declaration of Helsinki, and was approved by the local review board and all patients gave their informed consent. All patients were over 18 years of age, and had to be able to lie flat and hold their breath for 20 s. Patients with congenital heart defects, renal insufficiency (serum creatinin >120 μmol/l), known contrast allergy or history of hyperthyroidism, thyroid cancer, Kahlers disease, myasthenia gravis, pheochromocytoma or mastocytosis were excluded. Patients with a body weight over 100 kg were also excluded because image quality of EBT is impaired in obese patients. Electron beam computed tomography 19 20 ® 1 1 1 1 Fig. 1 A B C  Transthoracic echocardiography 5 Statistical analysis For the measurement of the AVA by EBT, 3 manual tracings made by 1 observer (R D) were averaged. Results of continuous normally distributed variables are expressed as mean ± SD, results of continuous not normally distributed variables are expressed as median (range). The data were analyzed with the use of standard software (SPSS version 12.0.1, SPSS Institute, Chicago, IL, USA) on a PC. The Spearman’s and Pearson’s correlation coefficients (r) were used to establish the presence of linear relationships. To compare not normally distributed data, the Mann–Whitney U test was used. A Bland–Altman analysis was used to evaluate the agreement between the AVA assessed with EBT and TTE. A level of significance below 0,05 was defined as clinically significant. Results A total of 61 patients were screened for participation in the study. Nine females and 21 males (age 70.9 ± 10.0 years) were enrolled in the study. Eight patients were excluded because of renal insufficiency, 1 because of known contrast allergy, 1 because of body weight over 100 kg, and 4 patients declined to undergo an EBT. Another 17 patients were excluded because the AVA could not be assessed by TTE. In the study group, the mean peak pressure gradient across the valve was 64 ± 21 mmHg. Ten patients had symptoms according to NYHA class I, 12 patients class II and 8 patients class III. Left ventricular end-diastolic diameter was 4.9 ± 0.6 cm, interventricular septal thickness was 1.2 ± 0.3 cm and posterior wall thickness was 1.1 ± 0.1 cm. Ninety percent of the patients had signs of left ventricular hypertrophy on TTE. Twenty two patients (73%) had normal left ventricular function, 6 patients (20%) had mild and 2 patients (7%) moderate left ventricular dysfunction. Mild aortic regurgitation was present in 8 patients (27%) and moderate aortic regurgitation in 2 patients (7%). The average time between TTE and EBT was 17 ± 12 days. Aortic valve area 2 2 r P 2 2 2 2 2 P 2 2 P Fig. 2  A r P B 2  Aortic valve calcification r P 3 2 2 P Fig. 3 r P  Discussion EBT is an useful non-invasive method to evaluate aortic stenosis, both in terms of AVA and AVC. However, on average a larger AVA was measured with EBT than was assessed AVA with TTE. Indeed, this is not surprising since EBT determines the anatomical AVA, which is expected to be greater than the functional AVA assessed with TTE. Because of calcifications the valvular leaflets are less flexible, as a result the AVA will be irregularly shaped, hence the AVA becomes haemodynamically less efficient. This results in a discrepancy between the functional and anatomical AVA. 18 2  2 The results of our study are in line with those of MacMillan et al. Our study also showed that EBT measures larger AVA compared to TTE. The AVA is measured planimetrically with EBT, so it can be considered as the anatomical AVA. Our study as well as the study of MacMillan et al. compared this anatomical AVA to the functional AVA. This functional AVA is derived from haemodynamic characteristics of the aortic valve, (pressure changes and flow velocity changes) across the aortic valve. The functional AVA is supposed to yield the haemodynamic relevant AVA. However, using the continuity equation, the AVA is assumed to be circular, which does not reflect the actual morphology of the orifice of the stenotic valve, especially not in case of heavy calcification. 5 6 7 9 The larger AVA measured by EBT compared to TTE and cardiac catheterization may be related to slice orientation. In order to get an axial view of the aortic valve, the image has to be rotated in two planes by the observer. If the selected axial view is not situated perpendicular to the aortic valve, the AVA is overestimated. Moreover, from this axial view the plane with the smallest AVA has to be selected. Although the temporal resolution of EBT is high, it is possible that the smallest AVA is situated between 2 planes. Hence, the AVA can be overestimated. Nevertheless, we addressed this problem by acquiring several slices at different levels of the aortic valve. This is necessary to minimize the potential of AVA overestimation because of imprecise localization. 14 17 21 22 2 16 23 As mentioned above, the grade of AVC is a predictor of outcome in patients with aortic stenosis. Although the echocardiographic severity of aortic stenosis is correlated to AVC score, the AVA can not be predicted from the AVC score. So, to evaluate the severity of aortic valve stenosis and to indicate whether aortic valve replacement surgery is necessary it is inevitable to measure AVA. In our study, we showed a significant correlation between the AVA measured with EBT and the severity of aortic stenosis assessed with TTE. However, further research is needed to validate EBT as a technique to evaluate the AVA. 24 2 25 2 2 Conclusion EBT appears to be valuable as a non-invasive method to assess the severity of aortic valve sclerosis. EBT holds the qualifications for accurate assessment of the anatomy, morphology and physiology of the aortic valve. However, further investigations will have to be done to verify whether EBT is a suitable non-invasive imaging technique for evaluation of aortic valve disease.