Age-Dependence of Flow Homeostasis in the Left Ventricle

Abstract

Background: Intracardiac flow homeostasis requires avoiding blood stasis and platelet activation during its transit through the cardiac chambers. However, the foundations of intraventricular blood washout and its exposure to shear stresses have been poorly addressed. We aimed to characterize and quantify these features in a wide population of healthy subjects and assess the relationships of these indices with age. Methods: We used color-Doppler echocardiography and custom post-processing methods to study 149 healthy volunteers from 26 days to 80 years old. From the intraventricular flow-velocity fields we obtained personalized maps of (1) the residence time of blood in the LV, and (2) the shear index, a metric accounting for the strongest occurrence of shear stresses inside the chamber. From these maps we derived quantitative indices of the overall intraventricular blood washout and shear exposure. We addressed the age-dependence of these indices and analyzed their relationship with age-related changes in filling-flow. Results: The entire intraventricular blood pool was replaced before 8 cycles. Average residence time of blood inside the LV was <3 cycles in all subjects and followed an inverse U-shape relationship with age, increasing from median (IQR) of 1.0 (0.7 to 1.2) cycles in the 1st year of life to 1.8 (1.4–2.2) cycles in young adults (17–30 years old), becoming shorter again thereafter. Shear index showed no relation with age and was bounded around 20 dyn·s/cm 2 . Regions with the longest residence time and highest shear index were identified near the apex. Differences in the degree of apical penetration of the filling waves and the duration of the late-filling phase explained the age-dependence of residence time ( = 0.48, p < 0.001). Conclusions: In average, blood spends 1 to 3 beats inside the LV with very low shear stress rates. The apical region is the most prone to blood stasis, particularly in mid-aged adults. The washout of blood in the normal LV is age-dependent due to physiological changes in the degree of apical penetration of the filling waves.

Non-Newtonian Blood Rheology Impacts Left Atrial Stasis in Patient-Specific Simulations

“…Our observations in the LAA contrast with the finding that considering the kinetics of rouleaux formation notably decreased shear-thinning effects in abdominal aortic and intracranial aneurysms [23]. We attribute this difference to the fact that blood residence time inside the LAA seems to be considerably longer than in aneurysms [23,59] [61], and these features are exacerbated after acute myocardial infarction [12]. Overall, the existing data suggest that non-Newtonian effects in the LV might be appreciable in some pathological conditions.…”

“…In the LV, clinical observation of echocardiographic "smoke" suggest RBC aggregates can form in this chamber [81,82] [84], and these features are exacerbated after acute myocardial infarction [13]. Thus, the existing data suggest that non-Newtonian effects in the LV should not be discarded altogether.…”

“…We attribute this difference to the fact that blood residence time inside the LAA seems to be considerably longer than in aneurysms [37,80]. [84], and these features are exacerbated after acute myocardial infarction [13]. Overall, the existing data suggest that non-Newtonian effects in the LV might be appreciable in some pathological conditions.…”

The prevalence of left ventricular thrombus among patients with low ejection fraction by trans-thoracic echocardiography

“…19 The apical site of thrombi was explained by Benito who reported that the apex of the ventricle is the most prone to blood stasis. 20 In this study, 80% of the patients with low EF were khat chewers and 80% of LV thrombus were in IHD. This result is consistent with Al-Motarreb et al, who reported that khat chewing is a risk factor for acute MI by causing coronary spasm.…”

Optimization of Microbubble Concentration and Acoustic Pressure for Left Ventricular High-Frame-Rate EchoPIV in Patients

“…Acquiring a full-field Eulerian velocity field allows for calculation of many relevant parameters, such as vorticity [22], [34], [39], [40], kinetic energy (dissipation) [7], and relative pressure gradients [41]. It is also possible to perform particle displacement analyses using these flow fields to simulate parameters such as particle residence time and washout period [42], [43]. The potential of using echoPIV for assessment of these parameters should be studied and validated in future work.…”