Aortic root movement correlation with the function of the left ventricle

The results of our study showed that the aortic root diastolic distance (ARDD) significantly correlated with the established and widely used left ventricular diastolic parameters, such as E/A, E/e’, e’. However, there were no significant correlations with several selected systolic parameters recorded with Doppler flow and Doppler tissue imaging (DTI), like stroke volume (SV), cardiac output (CO), and s′ medial. Additionally, another new parameter of the aortic movement, the aortic root maximal diastolic velocity (ARDV), showed weaker correlations than diastolic distance. Researching these dynamic aspects of aortic movement is especially important for the assessment of the cardiovascular system3.

Normally, in heart cycle, during systole, the aortic annulus is pulled along the left ventricle in systole and retracted in diastole. The movement of the aortic annulus towards the apex results in longitudinal stretch in the ascending aorta. Accordingly, the major systolic movement of the aortic root is downward motion. The in-plane motion and clockwise axial twist were found to be not significant for the longitudinal deformation6. What is especially important, the aortic root displacement is reduced in patients with the left ventricular dysfunction. Therefore, it can be especially useful in large population of patients assessed for LV function7. On the other hand, in some studies, it was elevated in aortic valve regurgitation due to ventricular compensation and increased stroke volume7. However, our approach looks especially promising for diastolic assessment, which is often even more difficult than systolic assessment. An assessment of the left ventricular diastolic function is an integral part of every comprehensive echocardiographic study8.

In our study, ARDD showed a positive correlation with E velocity and negative with A velocity. Among cardiac parameters, mitral peak E-wave velocity, E/A ratio, E/e′ ratio, relate best with early occurring LV diastolic pressures. The mitral E-wave reflects primarily the LA-LV pressure gradient during early diastole and is affected by preload, and LV relaxation9. The rapid pressure drop and the relaxation of the LV give the suction effect that pulls blood into the LV. Additionally, in situ, at the beginning of diastole, in normal conditions, an aortic recoil facilitates LV lengthening and early diastolic filling. This leads to higher E velocity and improved LV early feeling. However, A wave correlates with LV end-diastolic pressure. The mitral A-wave velocity reflects the LA-LV pressure gradient during late diastole, which is affected by LV compliance and LA contractile function. An aortic recoil potentially might also influence impedance to atrial emptying, decrease atrial pressure, and facilitate LA-LV pressure gradient in normal hearts. However, with increasing aortic stiffness, any beneficial contribution of aortic stretch and recoil to early diastolic filling may disappear10. The LV diastolic dysfunction is very common in patients, and it is usually the result of impaired LV relaxation with or without reduced restoring myocardial forces. Early diastolic suction and increased LV chamber stiffness can also increase cardiac filling pressures. In clinical scenario of cardiac abnormalities, the diastolic abnormalities are usually earlier than systolic abnormalities. Impaired aortic elasticity, due to aging, hypertension or diabetes, is also believed to play some independent role in the pathogenesis of LV dysfunction. Therefore, additionally to loading conditions, passive cardiac and vascular tissue properties and myocardial relaxation are affecting tissue deformation. Also, the motion of any specific part of the myocardium is influenced by overall motion (translational effects) and tethering of the heart regions. Hence, any measure of cardiac function should be interpreted carefully in the context of loading condition of the heart, wall thickness, and the shape of the ventricle.

Previously, in echocardiography, the aortic movement was mostly studied with the M-mode (motion mode, image of a single scan line over time) imaging, that is gradually disappearing from most echocardiographic guidelines1. In M-mode, the aortic walls are moving anterior in systole and posterior in diastole. One study, also based on M-mode, assessed early diastolic motion of the posterior aortic root and used the slope of early diastolic posterior aortic root motion11. However, this was limited to one direction technique, therefore providing few data about the whole aortic root. In another recent publication, the systolic movement of aorta was described as downward, anterior and lateral12. Throughout the heart cycle, it parallels the motion of the mitral annulus in the longitudinal axis of the left ventricle13. Early studies with M-mode postulated that systolic aortic root motion is a response to the action of the whole LV. Some authors believed that it should be attributed mainly to LV systolic function12. On the other hand, we found significant correlations between diastolic aortic root motion and diastolic LV parameters.

Our work adds data about the aorta complex path of motion, both in systole and in diastole, and its parameters related to the LV function. Therefore, the approach showed in our study provides potentially important information about the movement of the aortic root in healthy subjects, with currently the most often used 2D echocardiography14. When interpreting the results, it is important to keep in mind, that in our study we provide information about subjects with normal hearts, therefore, without wide variability in various factors influenced by cardiovascular diseases15.

We studied group of patients without significant risk of increased aortic stiffness, that can form additional load on the left ventricle16. Some authors proposed that alterations in both LV and aortic physiology may play a role in predisposition to heart failure, including heart failure with preserved ejection fraction (HFpEF)17. They showed that the aortic stiffening was related to global longitudinal function of the LV17. Also, impaired LV diastolic function and increased aortic stiffness have been postulated18. Diastolic recoil of the aorta, which is stretched during systole, can facilitate LV filling and ejection19.

In the future, non-invasive aortic root movement measures may identify patients at higher risk for progressive aortic enlargement and adverse clinical outcomes, potentially allowing for closer monitoring and more appropriate therapy in patients with cardiovascular diseases6,7,20. This is especially important in populations with high risk of aortic aneurysm and aortic dissection, including patients with bicuspid aortic valve (BAV) and collagen diseases, especially Marfan syndrome. Unfortunately, the aortic diameter is not a good predictor of aortic dissection and additional parameters should be studied to decrease morbidity and mortality in those patients21. Longobardo L et al. showed that impairment of elastic properties of the ascending aorta is a predictor of aortic complications in patients with bicuspid aortic valve22,23. In these studies the authors stated that the alterations of functionality often precede the anatomical changes in cardiovascular pathophysiology. Guala et al. found that the proximal aorta longitudinal strain, but not circumferential strain and distensibility, was an independent predictor of the aortic root diameter growth rate in cardiac magnetic resonance (CMR) of Marfan syndrome patients24. The axial motion of aortic root due to ventricular traction was suggested to contribute to aortic dissection by increasing its longitudinal stress. The largest aortic wall stress increase due to aortic root displacement was found approximately 20 mm above the sino-tubular junction, and that is often the place of aortic dissection tear7. However, neither axial nor in-plane motion could directly lead to aortic dissection, therefore more attributes related to aortic structure, motion and hemodynamics of aortic flow should be evaluated6.

We conclude that in healthy subjects, the aortic root motion parameters correlate significantly with established measurements of the left ventricular function. Aortic root motion parameters can be useful in patients with low ultrasound image quality, especially when there are no apical views available for routine left ventricular function assessment. New quantifiable imaging parameters that can be universally applied, like ARDD and ARDV, could be a further advance towards improving cardiovascular prevention, monitoring and therapy. In the future, to have complete information about the cardiac conditions, the aortic root motion may be included in the comprehensive analysis of the heart.

Limitations of the study

Nonetheless, our findings must be interpreted with caution and several limitations should be borne in mind. The first is the moderate number of participants included in the study and their lack of cardiovascular diseases, as healthy subjects. This might result in the obtained correlation values being different from values for the population with cardiovascular conditions. In the future, we plan to increase the number of participants by including subjects with systolic and diastolic dysfunction.

The second limitation is due to the use of the 2D images for the motion tracking. It has to be kept in mind that the aortic root motion parameters presented in this paper do not include the motion component that is perpendicular to the PLAX plane. In quest to include any movement direction, one can consider additionally using of the aortic root motion path obtained from parasternal short axis (PSAX) view, where the aortic root is clearly visible as well. The PSAX plane is perpendicular to the PLAX plane, and can therefore provide some additional information. But this approach would require an effective method for merging of two 2D motion paths obtained for different cardiac cycles into a 3D motion path, and therefore generate further technical challenges. The 3D motion information can also be obtained by tracking the aortic root directly on volumetric data available in 3D echocardiography, especially in 3D fusion echocardiography25,26.