Transesophageal echocardiographic strain imaging predicts aortic biomechanics: Beyond diameter

Abstract

Background: Clinical guidelines recommend resection of ascending aortic aneurysms at diameters 5.5 cm or greater to prevent rupture or dissection. However, approximately 40% of all ascending aortic dissections occur below this threshold. We propose new transesophageal echocardiography strain-imaging moduli coupled with blood pressure measurements to predict aortic dysfunction below the surgical threshold.

Methods: A total of 21 patients undergoing aortic resection were recruited to participate in this study. Transesophageal echocardiography imaging of the aortic short-axis and invasive radial blood pressure traces were taken for 3 cardiac cycles. By using EchoPAC (GE Healthcare, Madison, Wis) and postprocessing in MATLAB (MathWorks, Natick, Mass), circumferential stretch profiles were generated and combined with the blood pressure traces. From these data, 2 in vivo stiffness moduli were calculated: the Cardiac Cycle Pressure Modulus and Cardiac Cycle Stress Modulus. From the resected aortic ring, testing squares were isolated for ex vivo mechanical analysis and histopathology. Each square underwent equibiaxial tensile testing to generate stress-stretch profiles for each patient. Two ex vivo indices were calculated from these profiles (energy loss and incremental stiffness) for comparison with the Cardiac Cycle Pressure Modulus and Cardiac Cycle Stress Modulus.

Results: The echo-derived stiffness moduli demonstrate positive significant covariance with ex vivo tensile biomechanical indices: energy loss (vs Cardiac Cycle Pressure Modulus: R² = 0.5873, P < .0001; vs Cardiac Cycle Stress Modulus: R² = 0.6401, P < .0001) and apparent stiffness (vs Cardiac Cycle Pressure Modulus: R² = 0.2079, P = .0378; vs Cardiac Cycle Stress Modulus: R² = 0.3575, P = .0042). Likewise, these transesophageal echocardiography-derived moduli are highly predictive of the histopathologic composition of collagen and elastin (collagen/elastin ratio vs Cardiac Cycle Pressure Modulus: R² = 0.6165, P < .0001; vs Cardiac Cycle Stress Modulus: R² = 0.6037, P < .0001).

Conclusions: Transesophageal echocardiography-derived stiffness moduli correlate strongly with aortic wall biomechanics and histopathology, which demonstrates the added benefit of using simple echocardiography-derived biomechanics to stratify patient populations.

Keywords: aneurysm; ascending aorta; biomechanics; echocardiography; histology.