New Aspects of Septal Function by Using 1-Dimensional Strain and Strain Rate Imaging

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.

Defining the reference range for right ventricular systolic strain by echocardiography in healthy subjects: A meta-analysis

BACKGROUND

Right ventricular (RV) systolic strain has recently demonstrated prognostic value in various cardiovascular diseases. Despite this, the reference range including the lower limit of normal (LLN) and factors associated with RV strain measurements are not well-established. This meta-analysis aimed to determine the mean and LLN of two- (2D) and three-dimensional (3D) right ventricular global (RVGLS), free wall (RVFWLS) and interventricular septal wall (IVSLS) longitudinal strains in healthy individuals and factors that affect strain measurements.

METHODS

In this meta-analysis, Pubmed, Embase and Cochrane databases were searched until 31 July 2020 for eligible studies reporting RVGLS, RVFWLS and/or IVSLS in at least 30 healthy subjects. We pooled the means and LLNs of RV strains by two- (2D) and three- (3D) dimensional echocardiography, and performed meta-regression analyses.

RESULTS

From 788 articles screened, 45 eligible studies totaling 4439 healthy subjects were eligible for analysis. Pooled means and LLNs with 95% confidence intervals for 2D- RV strains were RVGLS -23.4% (-24.2%, -22.6%) and -16.4% (-17.3%, -15.5%) in 27 studies; RVFWLS -26.9% (-28.0%, -25.9%) and -18.0% (-19.2%, -16.9%) in 32 studies; and IVSLS -20.4% (-22.0%, -18.9%) and -11.5% (-13.6%, -9.6%) in 10 studies, and similar results for 3D- RV strains. Right ventricular fractional area change and vendor software were associated with 2D-RVGLS and RVFWLS means and LLNs.

CONCLUSION

We reported the pooled means and LLNs of RV systolic strains in healthy subjects, to define thresholds for abnormal, borderline and normal strains. Important factors associated with RV systolic strains include right ventricular fractional area change and vendor software.

Peri-operative assessment of right heart function: role of echocardiography

The right heart contributes significantly to overall cardiac function. Right ventricular (RV) haemodynamics and function have been defined to be physiologically different from the left ventricle, and yet independently associated with outcomes in a spectrum of conditions. In particular, RV function has been shown to influence prognosis of patients undergoing surgery. The assessment of right heart function during the intra-operative and immediate postoperative periods plays an important role in the clinical management of patients having surgery. While a number of techniques are available for the assessment of the right heart intra-operatively, echocardiography remains the prime choice being least invasive, relatively safe, readily accessible and cost-effective. Advancements in the field of echocardiographic have improved ability to assess right heart function. This review examines the role echocardiography and advances in this imaging modality in the assessment of right heart function within the peri-operative setting.

Can myocardial strain differentiate hypertrophic from infiltrative etiology of a thickened septum?

OBJECTIVES

Radial systolic strain (ε) assessed by echocardiography has been shown to identify patterns of normal septal motion brought about by different layers, including left ventricular (LV) subendocardial (LV subendo) and mural (LV mural) layers. We aimed to use myocardial strain in assessing radial and longitudinal myocardial function in normal and thickened septum and to test if myocardial strain can differentiate hypertrophic from infiltrative cause of thickened septum.

METHODS

Forty-five patients (age 61 ± 13 years, 22 males), 13 with hypertrophic cardiomyopathy, 15 with aortic stenosis, and 17 with familial amyloid polyneuropathy, were studied and compared with 29 controls (age 61 ± 12 years, 17 males) using 1D strain and conventional echocardiography.

RESULTS

Patients had normal LV ejection fraction and stroke volume but heart rate was higher (P < 0.05) compared to controls. Septal ɛ was reduced (-7.6 ± 7.0% vs. -14.0 ± 5.5%, for LV mural and -7.9 ± 14.7% vs. -20.3 ±-7.9% for LV subendo, P < 0.001 for both layers) across LV longitudinal axis but not along its radial axis. No difference was found in any of ɛ measurements between patient groups. A decrease in strain length by 50% increased the septal strain by more than 60% in both radial and longitudinal axes.

CONCLUSION

Septal systolic strain measurements showed reduced longitudinal function but its localized nature failed to demonstrate radial disturbances in patients with pathologically thickened septum. No difference was found in systolic strain between patients according to the etiology of septal thickness. This limitation might be either technical or is explained by the maintained radial function in all patient groups.

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

The left and right ventricular function of the heart are influenced by the complex structure of the ventricular septum. The cyclic variation of ultrasonic backscatter over the cardiac cycle is known to be sensitive to both structural and functional characteristics of the myocardium. The objective of this study was to investigate differences in the measured magnitude and normalized delay of cyclic variation between the left and right sides of the ventricular septum in normal adult subjects (N = 31). The measured mean magnitudes of cyclic variation were found to be 4.9 ± 0.4 dB and 2.4 ± 0.3 dB (mean ± SE; p < 0.0001) and the corresponding normalized delay values were found to be 0.94 ± 0.05 and 1.59 ± 0.12 (mean ± SE; p < 0.0001) for the left and right sides, respectively. These results show significant differences in the measured magnitude and normalized delay of cyclic variation between the left and right sides of the ventricular septum in normal subjects that appear consistent with predictions based on previously described models of cyclic variation of backscatter and reported measurements of transmural differences in strain properties of the septum.

Non-invasive investigations of the right heart: how and why?

The importance of right ventricular (RV) function in the clinical management of patients with cardiopulmonary disorders is now well recognized. However, due to both its shape and location and to the load dependence of its ejection fraction, accurate evaluation of its function is still a challenge. Echocardiography allows morphological, hemodynamic and functional assessment of the right heart. Displacement and deformation parameters derived from new techniques are promising tools. 3D echocardiography also has a potential interest in the quantification of RV volumes and ejection fraction. Radionuclide technique allows an easy and accurate measurement of right ventricular ejection fraction. MRI remains nowadays the technique of choice for the quantification of volumes and function of the RV. All these techniques have proven their interest in various diseases affecting the right heart. RV function is an important prognostic factor in heart failure and is a major component of functional capacity in such patients. In pulmonary arterial hypertension, echocardiography is the best tool for the routine follow-up of patients. Finally, all these non-invasive techniques of investigation of the right heart enable the diagnosis of specific right ventricular damage such as myocardial infarction or arrhythmogenic right ventricular dysplasia.