Britta Lind

Ultrasonographic strain imaging is superior to conventional non-invasive measures of vascular stiffness in the detection of age-dependent differences in the mechanical properties of the common carotid artery

AIMS Elastic properties of large arteries have been shown to deteriorate with age and in the presence of atherosclerotic vascular disease. In this study, the performance of ultrasonographic strain measurements was compared with conventional measures of vascular stiffness in the detection of age-dependent differences in the elastic properties of the common carotid artery (CCA). METHODS AND RESULTS In 10 younger (25-28 years, four women) and 10 older (50-59 years, four women) healthy individuals, global and regional circumferential, and radial strain variables were measured in the short-axis view of the right CCA using ultrasonographic two-dimensional (2D) strain imaging with recently introduced speckle tracking technique. Conventional elasticity variables, elastic modulus (E(p)), and beta stiffness index, were calculated using M-mode sonography and non-invasive blood pressure measurements. Global and regional circumferential systolic strain and strain rate values were significantly higher (P < 0.01 for regional late systolic strain rate, P < 0.001 otherwise) in the younger individuals, whereas the values of conventional stiffness variables in the same group were lower (P < 0.05). Among all strain and conventional stiffness variables, principal component analysis and its regression extension identified only circumferential systolic strain variables as contributing significantly to the observed discrimination between the younger and older age groups. CONCLUSION Ultrasonographic 2D-strain imaging is a sensitive method for the assessment of elastic properties in the CCA, being in this respect superior to the conventional measures of vascular stiffness. The method has potential to become a valuable non-invasive tool in the detection of early atherosclerotic vascular changes.

Wave intensity wall analysis: a novel noninvasive method to measure wave intensity

Wave intensity analysis is a concept providing information about the interaction of the heart and the vascular system. Originally, the technique was invasive. Since then new noninvasive methods have been developed. A recently developed ultrasound technique to estimate tissue motion and deformation is speckle-tracking echocardiography. Speckle tracking-based techniques allow for accurate measurement of movement and deformation variables in the arterial wall in both the radial and the longitudinal direction. The aim of this study was to test if speckle tracking-derived deformation data could be used as input for wave intensity calculations. The new concept was to approximate changes of flow and pressure by deformation changes of the arterial wall in longitudinal and radial directions. Flow changes (dU/dt) were approximated by strain rate (sr, 1/s) of the arterial wall in the longitudinal direction, whereas pressure changes (dP/dt) were approximated by sign reversed strain rate (1/s) in the arterial wall in the radial direction. To validate the new concept, a comparison between the newly developed Wave Intensity Wall Analysis (WIWA) algorithm and a commonly used and validated wave intensity system (SSD-5500, Aloka, Tokyo, Japan) was performed. The studied population consisted of ten healthy individuals (three women, seven men) and ten patients (all men) with coronary artery disease. The present validation study indicates that the mechanical properties of the arterial wall, as measured by a speckle tracking-based technique are a possible input for wave intensity calculations. The study demonstrates good visual agreement between the two systems and the time interval between the two positive peaks (W1–W2) measured by the Aloka system and the WIWA system correlated for the total group (r = 0.595, P < 0.001). The correlation for the diseased subgroup was r = 0.797, P < 0.001 and for the healthy subgroup no significant correlation was found (P > 0.05). The results of the study indicate that the mechanical properties of the arterial wall could be used as input for wave intensity calculations. The WIWA concept is a promising new method that potentially provides several advantages over earlier wave intensity methods, but it still has limitations and needs further refinement and larger studies to find the optimal clinical use.

Temporal frequency requirements for tissue velocity imaging of the fetal heart

The high velocity and short duration of myocardial motion requires a high sampling rate to obtain adequate temporal resolution; this issue becomes even more important when taking into consideration the high fetal heart rate. In this study we have established optimal sampling requirements for assessing the duration of various cardiac cycle events and myocardial velocities of the fetal heart using color‐coded tissue velocity imaging (TVI).

Left ventricular mechanical dyssynchrony in patients with different stages of chronic kidney disease and the effects of hemodialysis

Left ventricular (LV) dyssynchrony is a known cause of mortality in patients with heart failure and may possibly play a similar role in patients with chronic kidney disease (CKD) in whom sudden death is one of the most common and as yet not fully explained cause of death. LV synchronicity and its relationship with increased volume load and various biomarkers was analyzed in 145 patients including 53 patients with CKD stages 3 and 4 and in 92 CKD stage 5 patients undergoing hemodialysis (HD) or peritoneal dialysis (PD) using color tissue Doppler imaging and tissue synchronization imaging. The HD patients were evaluated both before and after a single HD session. LV dyssynchrony was defined as a regional difference in time to peak systolic myocardial velocity, between 12 LV segments > 105 milliseconds. LV dyssynchrony was present in 54% of the patients with no difference between CKD 3 and 4 (58%), HD (48%), and PD (51%). LV dyssynchrony was independently associated with LV mass index and increased estimation of LV end‐diastolic pressure. A single HD session resulted in significant changes in LV synchronicity variables—with improvement in 50% of the patients—especially in patients with higher myocardial systolic velocities and lower LV mass index. Abnormalities in LV synchronicity are highly prevalent in CKD patients already prior to dialysis treatment and are associated with LV hypertrophy, LV dysfunction and load conditions, underlining the importance of volume status for LV synchronicity in CKD patients.

Differences in myocardial velocities during supine and upright exercise stress echocardiography in healthy adults

Background:  Tissue Velocity Imaging (TVI) is a method for quantitative analysis of longitudinal myocardial velocities, which can be used during exercise and pharmacological stress echocardiography. It is of interest to evaluate cardiac response to different types of stress tests and the differences between upright and supine bicycle exercise tests have not been fully investigated. Therefore, the aim of this study was to compare cardiac response during supine and upright exercise stress tests.

Fetal cardiac muscle contractility decreases with gestational age: a color-coded tissue velocity imaging study

BackgroundPresent data regarding how the fetal heart works and develops throughout gestation is limited. However, the possibility to analyze the myocardial velocity profile provides new possibilities to gain further knowledge in this area. Thus, the objective of this study was to evaluate human fetal myocardial characteristics and deformation properties using color-coded tissue velocity imaging (TVI).MethodsTVI recordings from 55 healthy fetuses, at 18 to 42 weeks of gestation, were acquired at a frame rate of 201–273 frames/s for offline analysis using software enabling retrieval of the myocardial velocity curve and 2D anatomical information. The measurements were taken from an apical four-chamber view, and the acquired data was correlated using regression analysis.ResultsLeft ventricular length and width increased uniformly with gestational age. Atrioventricular plane displacement and the E’/A’ ratio also increased with gestational age, while a longitudinal shortening was demonstrated.ConclusionsFetal cardiac muscle contractility decreases with gestational age. As numerous fetal- and pregnancy-associated conditions directly influence the pumping function of the fetal heart, we believe that this new insight into the physiology of the human fetal cardiovascular system could contribute to make diagnosis and risk assessment easier and more accurate.

The Cardiac State Diagram as a Novel Approach for the Evaluation of Pre- and Post-ejection Phases of the Cardiac Cycle in Asphyxiated Fetal Lambs

The aim of this study was to investigate myocardial wall motion using echocardiography and color-coded tissue velocity imaging and to generate a cardiac state diagram for evaluation of the duration of the pre- and post-ejection phases in asphyxiated fetal lambs. Six near-term lambs were partly exteriorized and brought to cardiac arrest through asphyxia. Echocardiography measurements were recorded simultaneously with arterial blood sampling for lactate and blood gases. All fetal lambs exhibited prolongation of the pre- and post-ejection phases at the time when the most pronounced changes in lactate concentration and pH occurred. The mean change in duration of the pre- and post-ejection phases for all fetal lambs was 36 ± 7 ms (p < 0.002) and 77 ± 17 ms (p < 0.019), respectively, and the percentage change was 50% (p < 0.001) and 38% (p < 0.049), respectively. As asphyxia progressed in fetal lambs, the duration of the pre- and post-ejection phases increased. The cardiac state diagram has the potential to be a comprehensible tool for detecting fetal asphyxia.

In-vivo assessment of radial and longitudinal strain in the carotid artery using speckle tracking

Ultrasound-based algorithms are commonly used to assess mechanical properties of arterial walls in studies of arterial stiffness and atherosclerosis. Speckle tracking based techniques used for estimation of myocardial strain can be applied on vessels to estimate strain of the arterial wall. Previous elastography studies in vessels have mainly focused on radial strain measurements, whereas the longitudinal strain has been more or less ignored. However, recently we showed the feasibility of speckle tracking to assess longitudinal strain of the carotid artery in-silico. The aim of this study was to test this methodology in-vivo. Ultrasound images were obtained in seven healthy subjects with no known cardiovascular disease (39 ± 14 years old) and in seven patients with coronary artery disease (CAD), (69 ± 4 years old). Speckle tracking was performed on the envelope detected data using our previous developed algorithm. Radial and longitudinal strains were estimated throughout two cardiac cycles in a region of interest (ROI) positioned in the posterior vessel wall. The mean peak systolic radial and longitudinal strain values from the two heart cycles were compared between the groups using a students t-test. The mean peak radial strain was −39.1 ± 15.1% for the healthy group and −20.4 ± 7.5% for the diseased group (p = 0.01), whereas the mean peak longitudinal strain was 4.8 ± 1.1% and 3.2 ± 1.6% (p = 0.05) for the healthy and diseased group, respectively. Both peak radial and longitudinal strain values were thus significantly reduced in the CAD patient group. This study shows the feasibility to estimate radial and longitudinal strain in-vivo using speckle tracking and indicates that the method can detect differences between groups of healthy and diseased (CAD) subjects.

OC18.02: The cardiac state diagram as a novel approach for evaluation of re- and post ejection phases of the cardiac cycle in asphyxiated fetal lambs

Objectives: To investigate whether levels of cell free fetal DNA (cffDNA) assessed at 25 weeks gestation when determining fetal RHD status and PAPP-A from the combined first trimester risk assessment for trisomy 21 can identify women at risk of developing pre-eclampsia and SGA neonates. Methods: A population of 964 singleton pregnant RhD negative women with an RHD positive fetus who participated in the antenatal RHD screening programme in the Capital Region of Denmark. All women had a first trimester nuchal translucency scan and a 20 week malformation scan. Gestational age was based on CRL measurement at first trimester screening, PAPP-A was measured at 8–14 weeks. SGA was calculated using the regression equation constructed by Marsál and co-workers. We used a standard dilution curve to calculate the amounts of cffDNA. Results: A total of 38 women developed pre-eclampsia (3.9%), 15 cases of severe and 23 cases of mild pre-eclampsia. The number of neonates born SGA was 51 (5.3 %). The OR of developing mild pre-eclampsia given a cffDNA level below the 5th centile was 4.1 (95% CI: 1.2–13.2) and the OR of developing severe pre-eclampsia given a cffDNA level above the 90th centile was 10.2 (95% CI: 3.4–30.4). SGA was significantly associated with fetal DNA levels above the 90th centile (P = 0.009). Amongst women diagnosed with pre-eclampsia 46% in the group with cffDNA levels above the 90th centile delivered an SGA neonate compared to 7% in the group with cffDNA levels below the 90th centile. Amongst women not developing pre-eclampsia the numbers were 7.1% versus 4.5%. PAPP-A levels below the 5th centile were associated with mild pre-eclampsia, but not with SGA. Conclusions: Cell free fetal DNA is a marker for pre-eclampsia. High levels were associated with severe pre-eclampsia, low levels with mild pre-eclampsia, thus indicating different placental pathologic mechanisms. High levels of cffDNA is a poor marker of SGA independently of pre-eclampsia.

Velocity tracking — A novel method for quantitative analysis of longitudinal myocardial function

Doppler tissue imaging is a method for quantitative analysis of longitudinal myocardial velocity. Commercially available ultrasound systems can only present velocity information using a color Doppler-based overlapping continuous color scale. The analysis is time-consuming and does not allow for simultaneous analysis in different projections. We have developed a new method, velocity tracking, using a stepwise color coding of the regional longitudinal myocardial velocity. The velocity data from 3 apical projections are presented as static and dynamic bulls-eye plots to give a 3-dimensional understanding of the function of the left ventricle. The static bulls-eye plot can display peak systolic velocity, late diastolic tissue velocity, or the sum of peak systolic velocity and early diastolic tissue velocity. Conversely, the dynamic bulls-eye plot displays how the myocardial velocities change over one heart cycle. Velocity tracking allows for a fast, simple, and intuitive visual analysis of the regional longitudinal contraction pattern of the left ventricle with a great potential to identify characteristic pathologic patterns.