Anders Thorstensen

Segmental and global longitudinal strain and strain rate based on echocardiography of 1266 healthy individuals: the HUNT study in Norway

AIMS To study the distribution of longitudinal systolic strain and strain rate (SR) as indicators of myocardial deformation according to age and sex in a healthy population. METHODS AND RESULTS Longitudinal strain and SR were determined in 1266 healthy individuals from three standard apical views, using a combination of speckle tracking (ST) and tissue Doppler imaging (TDI) to track regions of interest (ROIs). To test applicability of the reference values, we used a subset of the population to compare four methods of assessing myocardial deformation: (1) a combination of TDI and ST; (2) TDI with fixed ROIs; (3) TDI with tracking of ROIs; and (4) ST. Mean (SD) overall global longitudinal strain and SR were -17.4% (2.3) and -1.05 s(-1) (0.13) in women, and -15.9% (2.3) and -1.01 s(-1) (0.13) in men. Deformation indices decreased with increasing age. The combined and ST methods showed identical SR, but values were significantly lower than those obtained by TDI. Strain was overestimated by the ST method (18.4%) compared with the combined method (17.4%). CONCLUSION The reference values for global and segmental longitudinal strain and SR obtained from this population study are applicable for use in a wide clinical setting.

Reference Values and Distribution of Conventional Echocardiographic Doppler Measures and Longitudinal Tissue Doppler Velocities in a Population Free From Cardiovascular Disease

Background—This study aimed to investigate the distribution of conventional Doppler measurements, pulsed wave tissue Doppler imaging (pwTDI)- and color tissue Doppler imaging-derived velocities, by age and sex in a healthy population. Methods and Results—Longitudinal tissue Doppler velocities were determined in 1266 healthy individuals from standard apical 4- and 2-chamber views. By the pwTDI method, mean±SD systolic mitral annular velocities were 8.2±1.3 cm/s in women and 8.6±1.4 cm/s in men, and by color tissue Doppler, they were 6.6±1.1 cm/s in women and 6.9±1.3 cm/s in men. With pwTDI, diastolic early mitral annular velocities were 11.8±3.2 cm/s in women and 10.8±3.0 cm/s in men, with corresponding ratios between mitral early flow velocity and early diastolic tissue velocity of 6.7±0.8 in women and 6.4±0.8 in men. By pwTDI, tricuspid annular systolic and early diastolic velocities were 12.5±1.9 and 13.3±3.0, respectively, in women and 12.8±2.2 and 12.5±3.3, respectively, in men. There was a significant decrease in left and right ventricular function with increasing age. Conclusions—The longitudinal mitral and tricuspid annular velocities from this population study are widely applicable as reference values. Reference values for annular velocities should be specified by sex and age. The average of inferoseptal and anterolateral wall velocities may be the preferred index of left ventricular performance.

Reproducibility in echocardiographic assessment of the left ventricular global and regional function, the HUNT study

AIMS The study aimed to compare the inter-observer reproducibility of new and traditional measurements of the left ventricular (LV) global and regional function. METHODS AND RESULTS Two experienced echocardiographers performed 20 complete echo/Doppler examinations and 50 analyses on ten healthy subjects. All recordings were analysed for systolic and diastolic conventional and deformation measurements by both echocardiographers. Inter-observer mean error (absolute difference divided by the mean) was 4% and lowest (P = 0.001) for systolic M-mode annulus excursion. Mean error for the regional deformation indices was significantly higher than for all the global measurements (all P < 0.001). Mean error for analyses of the same recording was 34% (P = 0.002) lower for global systolic indices and 44% (P < 0.001) lower for global diastolic indices than inter-observer mean error for analyses made in separate recordings. CONCLUSION Systolic M-mode annulus excursion showed better inter-observer reproducibility than other traditional and newer measurements of LV systolic and diastolic function. Repeated analyses of the same recordings underestimate the more clinically relevant inter-observer reproducibility by approximately 40% for most measurements of LV function.

Cardiovascular Risk Factors and Systolic and Diastolic Cardiac Function: A Tissue Doppler and Speckle Tracking Echocardiographic Study

BACKGROUND The aim of this study was to determine whether blood pressure, body mass index (BMI), serum lipids, glucose, and renal function are associated with left ventricular (LV) and right ventricular function in a low-risk population. METHODS The associations of common risk factors with cardiac function were assessed, using multiple linear regression, in a random sample of 1,266 individuals free from hypertension, diabetes, and cardiovascular disease. A combination of conventional echocardiographic, speckle-tracking, and tissue Doppler methods was used to assess cardiac function. RESULTS Older age and higher BMI, systolic and diastolic blood pressure, and non-high-density lipoprotein (HDL) cholesterol were associated with lower LV function. Thus, LV strain was reduced by approximately 5% per 5 kg/m(2) increase in BMI and by 4% per 10 mm Hg increase in diastolic blood pressure. Corresponding reductions in peak early diastolic mitral annular velocity were 7% for both BMI and diastolic blood pressure. Higher HDL cholesterol was associated with better LV function. In women, smoking was also associated with reduced LV function. LV function was lower also at low levels of diastolic pressure and BMI. Reduced right ventricular function was related to older age, smoking, higher diastolic blood pressure and non-HDL cholesterol, and lower HDL cholesterol. CONCLUSIONS These findings suggest that conventional risk factors may predict cardiac function many years before clinical disease. The J-shaped associations related to diastolic blood pressure and BMI may suggest that in some individuals, low levels of these factors may indicate underlying but unknown disease.

Peak systolic velocity indices are more sensitive than end-systolic indices in detecting contraction changes assessed by echocardiography in young healthy humans

AIMS It remains to be proven whether left ventricular (LV) peak systolic velocity indices (peak systolic annulus tissue velocities, ejection velocity, and strain rate) are more closely related to contraction than LV end-systolic echocardiographic indices (ejection fraction, fractional shortening, systolic annulus displacement, global strain, and ejection velocity time integral). The study aimed to compare the ability of different echocardiographic methods in detecting contraction changes of the LV. METHODS AND RESULTS Thirty-three healthy volunteers (20-32 years) were examined by echocardiography at rest, during 10 μg/kg/min dobutamine (n = 20), and after injection of 15 mg metoprolol (n = 20). The effects of dobutamine and metoprolol on peak systolic velocity indices and end-systolic indices were compared. The relative increase from rest to dobutamine stress and the relative decrease after injection of metoprolol were 62 and -15% for peak systolic annulus tissue velocity, 60 and -11% for LV outflow tract (LVOT) peak velocity, 56 and -11% for peak systolic strain rate, 25 and 1% for ejection fraction, 30 and -1% for systolic mitral annulus displacement, 30 and -5% for LVOT velocity time integral, and 21 and -3% for global strain, respectively. The changes of the peak systolic indices were significantly higher (all P < 0.05) than the changes of the end-systolic indices. CONCLUSION Peak systolic velocity indices (mitral annulus tissue velocities, ejection velocities, and strain rate) exhibited greater variation than end-systolic indices during inotropic alterations from which it is assumed that they better reflected LV contraction.

Strain rate imaging combined with wall motion analysis gives incremental value in direct quantification of myocardial infarct size

BACKGROUND The study aimed to evaluate the diagnostic accuracy of a new method for direct echocardiographic quantification of the myocardial infarct size, using late enhancement magnetic resonance imaging (LE-MRI) as a reference method. METHODS AND RESULTS Echocardiography and LE-MRI were performed on average 31 days after first-time myocardial infarction in 58 patients. Echocardiography was also performed on 35 healthy controls. Direct echocardiographic quantification of the infarct size was based on automated selection and quantification of areas with hypokinesia and akinesia from colour-coded strain rate data, with manual correction based on visual wall motion analysis. The left ventricular (LV) ejection fraction, speckle-tracking-based longitudinal global strain, wall motion score index (WMSI), longitudinal systolic motion and velocity, and the ratio of early mitral inflow velocity to mitral annular early diastolic velocity were also measured by echocardiography. The area under the receiver-operating characteristic curves for the identification of the infarct size >12% by LE-MRI was 0.84, using the new method for direct echocardiographic quantification of the infarct size. The new method showed significantly a higher correlation with the infarct size by LE-MRI both at the global (r = 0.81) and segmental (r = 0.59) level compared with other indices of LV function. CONCLUSION Direct quantification of the percentage infarct size by strain rate imaging combined with wall motion analysis yields high diagnostic accuracy and better correlation to LE-MRI compared with other echocardiographic indices of global LV function. Echocardiography performed ~1 month after myocardial infarction showed ability to identify the patients with the infarct size >12%.

Fusion of 3D echocardiographic and cardiac magnetic resonance volumes

Evaluating functional and anatomical information in a side by side manner, based on 3D echocardiography (3D echo) and cardiac magnetic resonance imaging (CMR) is a complex task mainly because of inaccuracies in defining myocardial segments and spatio-temporal registration errors across different modalities. The aim of the study was to develop a method for fusing and visualizing 3D echo and CMR volumes and to demonstrate its applicability to patient data. Results: Five subjects with myocardial infarction have been selected for this study. All patients underwent 3D echo and CMR short- long-axis cine and late-gadolinium enhanced imaging the same day. The registration process was successful in all cases. The visual relationship between myocardial scar identified by LE and low end-systolic segmental strain values obtained based on 3D echo could be visually established. Conclusion: A novel method for fusing and visualizing 3D echo and CMR (cine and late-enhancement) volumes has been developed. The method provides complementary information that is not available by either modality alone, useful in the context of same day or longitudinal studies. A direct spatial relationship between tissue characterization and functional information is established which has the potential of enabling more accurate myocardial viability assessment and ischemia diagnosis.

Adaptive volume rendering of cardiac 3D ultrasound images: utilizing blood pool statistics

In this paper we introduce and investigate an adaptive direct volume rendering (DVR) method for real-time visualization of cardiac 3D ultrasound. DVR is commonly used in cardiac ultrasound to visualize interfaces between tissue and blood. However, this is particularly challenging with ultrasound images due to variability of the signal within tissue as well as variability of noise signal within the blood pool. Standard DVR involves a global mapping of sample values to opacity by an opacity transfer function (OTF). While a global OTF may represent the interface correctly in one part of the image, it may result in tissue dropouts, or even artificial interfaces within the blood pool in other parts of the image. In order to increase correctness of the rendered image, the presented method utilizes blood pool statistics to do regional adjustments of the OTF. The regional adaptive OTF was compared with a global OTF in a dataset of apical recordings from 18 subjects. For each recording, three renderings from standard views (apical 4-chamber (A4C), inverted A4C (IA4C) and mitral valve (MV)) were generated for both methods, and each rendering was tuned to the best visual appearance by a physician echocardiographer. For each rendering we measured the mean absolute error (MAE) between the rendering depth buffer and a validated left ventricular segmentation. The difference d in MAE between the global and regional method was calculated and t-test results are reported with significant improvements for the regional adaptive method (dA4C = 1.5 ± 0.3 mm, dIA4C = 2.5 ± 0.4 mm, dMV = 1.7 ± 0.2 mm, d.f. = 17, all p < 0.001). This improvement by the regional adaptive method was confirmed through qualitative visual assessment by an experienced physician echocardiographer who concluded that the regional adaptive method produced rendered images with fewer tissue dropouts and less spurious structures inside the blood pool in the vast majority of the renderings. The algorithm has been implemented on a GPU, running an average of 16 fps with a resolution of 512x512x100 samples (Nvidia GTX460).

Doo-Sabin Surface Models with Biomechanical Constraints for Kalman Filter Based Endocardial Wall Tracking in 3D+T Echocardiography.

3D+T echocardiography is a valuable tool for assessing cardiac function, as it enables real-time, non-invasive and low cost acquisition of volumetric images of the heart. The automated tracking of heart chambers in 3D+T echocardiography remains a challenging task due to reasons including speckle noise, shadowing, and the existence of intra-cavity structures [6]. Furthermore, the real-time detection of endocardial borders might be desirable for the invasive procedures and intensive care applications. State-space analysis using Kalman filtering can be employed for the detection of left ventricle (LV) structures in time-dependent recordings. Orderud et al. proposed a Kalman tracking framework for the real-time detection of LV structures in 3D+T echocardiography [5]. The study took advantage of compact Doo-Sabin model representations for rapid tracking, but it did not utilize physical properties to constrain model deformations. Liu et al. introduced a biomechanical-model constrained statespace analysis framework for the tracking of short-axis 2D+T echocardiography recordings [4]. Their study used dense Delaunay triangulated models and employed basic tri-nodal linear elements during the finite element analysis (FEA). Due to triangulated high resolution model representations, it offered a computationally expensive solution. This paper proposes an approach to combine the compact model representations with biomechanical constraints for rapid and accurate tracking. We extend the real-time Kalman tracking framework described in [5] by employing biomechanically constrained state transitions. First, FEA for the tracked Doo-Sabin surface model is performed using the isoparametric method introduced in [3]. This step enables the computation of a stiffness matrix K for a given endocardial model using shell elements without changing the model geometry. However, the computed model might lead to inaccurate deformation modes due to hypothesized model shape and FEA parameters (e.g. Young’s modulus, Poisson’s ratio). Accordingly, we improve the model shape and stiffness matrix using statistical information collected from a training data via Control Point Distribution Models (CPDM) [2]. During the improvement stage, (1) the model shape is updated to the population mean, (2) the stiffness matrix for the updated model shape is computed as K′ (see Figure 1), and (3) K′ is further modified to Kopt to produce similar modes of deformation as the statistically observed ones using Baruch and Bar-Itzhack direct matrix modifications (BBDMM) [1]. Finally, the state prediction stage of the Kalman tracking framework is formulated to perform biomechanically constrained tracking. In the results section, endocardial surface tracking quality is compared among (1) Doo-Sabin surface models with different control node resolutions, (2) biomechanically constrained and non-constrained state transitions, and (3) the systems employing statistically improved and not improved Doo-Sabin models (see Figure 2). Our analyses showed that

Relationship between infarct transmurality and regional myocardial function at different levels of the left ventricle in patients with first-time ST-elevation myocardial infarction

Introduction The relationship between regional myocardial function and the transmural extent of infarction (TEI) is complex, and there is considerable overlap in wall thickening measurements between normal and infarcted segments. Some of this overlap is caused by tethering from neighbor segments, but could possibly also be caused by errors in wall thickening measurements due to: 1)through-plane motion in basal segments, and 2)oblique orientation of the image plane relative to the left ventricular (LV) wall in apical segments.