Echocardiographic tissue characterization demonstrates differences in the left and right sides of the ventricular septum

The Interventricular Septum Is Biomechanically Distinct from the Ventricular Free Walls

The interventricular septum contributes to the pumping function of both ventricles. However, unlike the ventricular wall, its mechanical behavior remains largely unknown. To fill the knowledge gap, this study aims to characterize the biaxial and transmural variation of the mechanical properties of the septum and compare it to the free walls of the left and right ventricles (LV/RV). Fresh hearts were obtained from healthy, adult sheep. The septal wall was sliced along the mid-line into two septal sides and compared to the epicardial layers of the LV- and RV-free walls. Biaxial tensile mechanical tests and constitutive modeling were performed to obtain the passive mechanical properties of the LV- and RV-side of the septum and ventricular walls. We found that both sides of the septum were significantly softer than the respective ventricular walls, and that the septum presented significantly less collagen than the ventricular walls. At low strains, we observed the symmetric distribution of the fiber orientations and a similar anisotropic behavior between the LV-side and RV-side of the septum, with a stiffer material property in the longitudinal direction, rather than the circumferential direction. At high strains, both sides showed isotropic behavior. Both septal sides had similar intrinsic elasticity, as evidenced by experimental data and constitutive modeling. These new findings offer important knowledge of the biomechanics of the septum wall, which may deepen the understanding of heart physiology.

Will the real ventricular architecture please stand up?

Ventricular twisting, essential for cardiac function, is attributed to the contraction of myocardial helical fibers. The exact relationship between ventricular anatomy and function remains to be determined, but one commonly used explanatory model is the helical ventricular myocardial band (HVMB) model of Torrent‐Guasp. This model has been successful in explaining many aspects of ventricular function, (Torrent‐Guasp et al. Eur. J. Cardiothorac. Surg., 25, 376, 2004; Buckberg et al. Eur. J. Cardiothorac. Surg., 47, 587, 2015; Buckberg et al. Eur. J. Cardiothorac. Surg. 47, 778, 2015) but the model ignores important aspects of ventricular anatomy and should probably be replaced. The purpose of this review is to compare the HVMB model with a different model (nested layers). A complication when interpreting experimental observations that relate anatomy to function is that, in the myocardium, shortening does not always imply activation and lengthening does not always imply inactivation.

A Comparison of the Performance of Myocardial Videodensitometry, Tissue Velocity Imaging and Tissue Tracking in Discrimination Between ST-Segment Elevation Ischemic Reperfusion Injury and Normal Reperfusion State After Non-Beating Cardiac Operation

Background:

The timely diagnosis of presence or absence of reperfusion injury after cardiac operation is critical for the patient’s outcome. Whether transesophageal echocardiography (TEE) acquisition of regional grayscale intensity (TI), velocity, and displacement (D) after cardiac operation can discriminate between patients with ST-segment elevation ischemic reperfusion injury (STEIRI) and normal reperfusion state remains unknown.

Objectives:

In this study, we investigated whether these parameters can effectively reflect the situation of ST-segment elevation ischemic reperfusion injury (STEIRI) in patients after cardiac operation and which has a higher performance of discrimination between patients with and without STEIRI.

Patients and Methods:

The maximal and minimal grayscale intensity in the cardiac cycle [TI (max), TI (min)], the difference of TI (max) and TI (min) [TI (max-min)], the cyclic variation index of TI [TI (CVI)], the systolic velocity (Vs), the early diastolic velocity (Ve), the late diastolic velocity (Va) and the peak displacement in the cardiac cycle (D) at the lateral side of the mitral annulus were measured and compared between patients with and without STEIRI. The performance of these parameters in discriminating between patients with and without STEIRI was analyzed.

Results:

Compared with the patients without STEIRI, the patients with STEIRI had significantly smaller TI (max-min), TI (CVI), Vs, Ve, Va and D (P<0.05). With the use of these parameters as the criteria to distinguish patients with STEIRI from patients without STEIRI, the areas under the receiver operating characteristic curve were 0.86 for TI (max-min), 0.99 for TI (CVI), 0.89 for Vs, 0.71 for Ve, 0.85 for Va and 0.82 for D. For the best cut-off value of TI (CVI) of less than 34.45%, the sensitivity, specificity and accuracy for the prediction of patients with STEIRI were 94.74%, 97.05%, and 96.22%, respectively.

Conclusion:

The myocardial grayscale intensity, velocity and displacement can effectively reflect the situation of STEIRI in patients after cardiac operation, and TI (CVI) has a higher performance in discriminating between patients with and without STEIRI.