Usefulness of a new automatic boundary detection system (acoustic quantification) for assessing stiffness of the descending thoracic aorta by transesophageal echocardiography

Abstract

Increasing attention has been concentrated on the noninvasive assessment of aortic wall stiffness. 1 Aortic stiffness was found to correlate with age, hypercholesterolemia, arterial hypertension and degree of atherosclerosis. 1,2 It has been proposed that aortic stiffness may identify patients at risk for rapid progression of coronary artery disease. 2 Aortic stiffness is usually measured in terms of Young's modulus or the β index. 3 Both parameters are calculated from the relation between systemic blood pressure and arterial diameter. Arterial diameter may be measured by angiography 4,5 or transcutaneous ultrasonic systems. 2,3,5 The latter technique appears to be more practicable than angiography, but analysis based on this technique is strongly dependent on sufficient image quality. Furthermore, measurement of systolic-diastolic changes of arterial diameter by ultrasonography at 1 given point of the aortic circumference may not be representative for the distensibility of the entire arterial wall. In the present study, stiffness of the descending thoracic aorta was assessed by transesophageal echocardiography (TEE) in patients with various cardiac diseases. Ultrasonic assessment of the descending thoracic aorta from the esophagus provides optimal image quality in virtually all patients. In contrast to previous studies, systolic-diastolic changes of aortic areas were measured, rather than changes in aortic diameters, using a new, commercially available automatic boundary detection system (acoustic quantification [AQ]). AQ permits online tracking of borders between endocardium and blood based on integrated backscatter analysis. 6 These automatically detected borders are displayed in real-time on the 2-dimensional echocardiogram. Furthermore, AQ software enables continuous analysis of areas on a beatby-beat basis.