Measurement of left ventricular deformation using 3D echocardiography

Bakgrunn: 3D speckle tracking ekkokardiografi (STE) er en hjerteultralydmetode som gir mulighet for måling av deformasjonsparametere, som strain, rotasjon, tvist og torsjon. Den største begrensningen for 3D STE er lav tids- og romlig oppløsning. Økes den ene oppløsingen vil den andre bli redusert. I tillegg vil andre faktorer som antall flettede bilder, sektorstørrelse og dybde påvirke begge oppløsningene. Denne avhandlingen har hatt som mål å finne tilstander og opptaksinnstillinger for å optimalisere nøyaktigheten til 3D STE-parametere i et kontrollert miljø. Videre har det vært som mål å finne regional deformasjon fra 3D STE i en klinisk studie på pasienter med aortaklaffestenose (AS) ved bruk av optimaliserte innstillinger. Materiale og metode: Studie 1 og 2 utforsket nøyaktigheten til 3D STE ved bruk av et in vitro-oppsett med et fantom av venstre ventrikkel. Studie 1 sammenlignet 3D STE strain mot sonomikromertri som gullstandard i longitudinell, sirkumferensiell og radiell retning. Ved å bruke et annet fantom i studie 2 ble 3D STE tvist sammenlignet mot sonomikrometri tvist for å finne nøyaktigheten til 3D STE tvistmålinger. Studie 3 inkluderte 85 pasienter med variabel grad av AS i en tverrsnittstudie. 3D ekkokardiografi ble utført og 3D STE-parametere ble sammenlignet mellom grupper av pasienter med mild, moderat og alvorlig AS. Resultater: Studie 1 fant godt samsvar mellom 3D STE og sonomikrometri med optimalt volum rate på 36,6 volumer per sekund (VPS) ved bruk av 6 sammenflettede bilder. I studie 2 hadde 3D STE godt samsvar ved bruk av både 4 og 6 sammenflettede bilder med volum rater på henholdsvis 20,3 og 17,1 VPS. Studie 3 fant lavere global longitudinal strain i pasienter med alvorlig AS sammenlignet med mild AS. Basal og midtre longitudinal strain var også lavere i alvorlig sammenlignet med mild AS. Apikal-basal ratio var høyere for moderat i forhold til mild AS. Maks apikal-basal tvist var høyere hos pasienter med alvorlig sammenlignet med mild og moderat AS. Konklusjon: Måling av venstre ventrikkelfunksjon med 3D STE er mest nøyaktig med volum rater < 40 VPS. Høy romlig oppløsning virker å være mer viktig enn tidsoppløsning. Pasienter med alvorlig AS har lavere global, basal og midtre longitudinal strain enn pasienter med mild AS, ved bruk av 3D STE. De har også høyere tvist enn mild og moderat AS. Områder som involverer apeks, har høyere spredning av data og har antagelig lavere nøyaktighet ved bruk av 3D STE.Background: 3D speckle tracking echocardiography (STE) enables measurement of multiple parameters of deformation, such as strain, rotation, twist and torsion. The main limitation of 3D STE is low temporal and spatial resolution. Increasing resolution in time will decrease resolution in space, and vice versa. In addition, other factors such as number of stitched images, sector size and depth, influence the resolution. This thesis aimed to find conditions and acquisition settings to optimize accuracy for 3D STE parameters in a controlled in vitro environment. Secondly, it aimed to evaluate regional deformation by 3D STE in a clinical study on patients with aortic valve stenosis (AS) using optimized settings. Materials and methods: Study 1 and 2 explored the accuracy of 3D STE using an in vitro setup with a left ventricle (LV) phantom. Study 1 compared 3D STE strain to strain by sonomicrometry as the gold standard. Measurements were compared in both longitudinal, circumferential and radial direction. Using a different twisting phantom in study 2, 3D STE twist was compared to twist by sonomicrometry to evaluate the accuracy of 3D STE twist. Study 3 was a cross-sectional analysis of 85 patients with variable degree of AS in a cross-sectional study. 3D echocardiography was done, and 3D STE parameters were compared between groups of patients with mild, moderate and severe AS. Results: Study 1 found 3D STE strain to have good agreement with sonomicrometry. Optimal acquisition settings were found to be volume rate 36.6 volumes per second (VPS) obtained by 6 stitched images. Study 2 found 3D STE twist to have good agreement with sonomicrometry when using both 4 and 6 stitched images with volume rates 20.3 and 17.1 VPS, respectively. Study 3 found global longitudinal strain to be lower in patients with severe AS compared to those with mild AS. Basal and mid longitudinal strains were also lower in severe AS than in mild AS. Apical basal ratio was higher for moderate than mild AS. Peak apical-basal twist was higher in patients with severe AS than in those with mild and moderate AS. Conclusion: Assessment of LV function by 3D STE is most accurate at volume rates < 40 VPS. High spatial resolution seems to be more important than temporal resolution. Patients with severe AS have lower global, as well as lower regional basal and mid longitudinal strain compared to patients with mild AS, assessed with 3D STE. They also have higher twist than mild and moderate AS. Segments involving the apex have high dispersion and probably lower accuracy in 3D STE.Doktorgradsavhandlin

A left ventricular phantom for 3D echocardiographic twist measurements

Under embargo until: 2020-09-18Traditional two-dimensional (2D) ultrasound speckle tracking echocardiography (STE) studies have shown a wide range of twist values, also for normal hearts, which is due to the limitations of short-axis 2D ultrasound. The same limitations do not apply to three-dimensional (3D) ultrasound, and several studies have shown 3D ultrasound to be superior to 2D ultrasound, which is unreliable for measuring twist. The aim of this study was to develop a left ventricular twisting phantom and to evaluate the accuracy of 3D STE twist measurements using different acquisition methods and volume rates (VR). This phantom was not intended to simulate a heart, but to function as a medium for ultrasound deformation measurement. The phantom was made of polyvinyl alcohol (PVA) and casted using 3D printed molds. Twist was obtained by making the phantom consist of two PVA layers with different elastic properties in a spiral pattern. This gave increased apical rotation with increased stroke volume in a mock circulation. To test the accuracy of 3D STE twist, both single-beat, as well as two, four and six multi-beat acquisitions, were recorded and compared against twist from implanted sonomicrometry crystals. A custom-made software was developed to calculate twist from sonomicrometry. The phantom gave sonomicrometer twist values from 2.0° to 13.8° depending on the stroke volume. STE software tracked the phantom wall well at several combinations of temporal and spatial resolution. Agreement between the two twist methods was best for multi-beat acquisitions in the range of 14.4–30.4 volumes per second (VPS), while poorer for single-beat and higher multi-beat VRs. Smallest offset was obtained at six-beat multi-beat at 17.1 VPS and 30.4 VPS. The phantom proved to be a useful tool for simulating cardiac twist and gave different twist at different stroke volumes. Best agreement with the sonomicrometer reference method was obtained at good spatial resolution (high beam density) and a relatively low VR. 3D STE twist values showed better agreement with sonomicrometry for most multi-beat recordings compared with single-beat recordings.publishedVersio

Impact of aortic valve stenosis on myocardial deformation in different left ventricular levels: A three-dimensional speckle tracking echocardiography study

Background: Global systolic left ventricular (LV) myocardial function progressively declines as degenerative aortic valve stenosis (AS) progresses. Whether this results in uniformly distributed deformation changes from base to apex has not been investigated. Methods: Eighty-five AS patients underwent three-dimensional (3D) echocardiography in this cross-sectional study. Patients were grouped by peak jet velocity into mild (n = 32), moderate (n = 31), and severe (n = 22) AS. 3D speckle tracking derived strain, rotation, twist, and torsion were obtained to assess global LV function and myocardial function at the apical, mid, and basal levels. Results: Global longitudinal strain (GLS) was lower in patients with severe AS (-16.1 ± 2.4% in mild, -15.5 ± 2.5% in moderate, and -13.5 ± 3.0% in severe AS [all p < .01]). Peak basal and mid longitudinal strain (LS), basal rotation and twist from apical to basal level followed the same pattern, while peak apical LS was higher in moderate AS compared to severe AS (all p < .05). In multivariate analyses, lower GLS was particularly associated with male sex, higher body mass index and peak aortic jet velocity, lower basal LS with higher filling pressure (E/e’) and LV mass, lower mid LS with higher RWT and presence of AS symptoms, and lower apical LS with male sex and higher systolic blood pressure, respectively (all p < .05). Conclusion: Using 3D speckle tracking echocardiography reveals regional and global changes in LV mechanics in AS related to the severity of AS, LV remodeling and presence of cardiovascular risk factors.publishedVersio

One-year impact of bariatric surgery on left ventricular mechanics: results from the prospective FatWest study

Aims Patients with severe obesity are predisposed to left ventricular (LV) hypertrophy, increased myocardial oxygen demand, and impaired myocardial mechanics. Bariatric surgery leads to rapid weight loss and improves cardiovascular risk profile. The present prospective study assesses whether LV wall mechanics improve 1 year after bariatric surgery. Methods and results Ninety-four severely obese patients [43 ± 10 years, 71% women, body mass index (BMI) 41.8 ± 4.9 kg/m2, 57% with hypertension] underwent echocardiography before, 6 months and 1 year after gastric bypass surgery in the FatWest (Bariatric Surgery on the West Coast of Norway) study. We assessed LV mechanics by midwall shortening (MWS) and global longitudinal strain (GLS), LV power/mass as 0.222 × cardiac output × mean blood pressure (BP)/LV mass, and myocardial oxygen demand as the LV mass-wall stress-heart rate product. Surgery induced a significant reduction in BMI, heart rate, and BP (P < 0.001). Prevalence of LV hypertrophy fell from 35% to 19% 1 year after surgery (P < 0.001). The absolute value of GLS improved by—4.6% (i.e. 29% increase in GLS) while LV ejection fraction, MWS, and LV power/mass remained unchanged. In multivariate regression analyses, 1 year improvement in GLS was predicted by lower preoperative GLS, larger mean BP, and BMI reduction (all P < 0.05). Low 1-year MWS was associated with female sex, preoperative hypertension, and higher 1-year LV relative wall thickness and myocardial oxygen demand (all P < 0.001). Conclusion In severely obese patients, LV longitudinal function is largely recovered one year after bariatric surgery due to reduced afterload. LV midwall mechanics does not improve, particularly in women and patients with persistent LV geometric abnormalities.publishedVersio

Markers of Subclinical Atherosclerosis in Severe Obesity and One Year after Bariatric Surgery

Background: Aortic valve sclerosis (AVS), mitral valve sclerosis (MVS), remodeling of major arteries, and increased pericardial fat are associated with subclinical atherosclerosis. We assessed these markers of atherosclerosis in severely obese patients before and 1 year after bariatric surgery. Methods: Eighty-seven severely obese patients (43 ± 10 years, preoperative body mass index [BMI] 41.8 ± 5 kg/m2) underwent echocardiography before and 1 year after Roux-en-Y bypass surgery in the FatWest (Bariatric Surgery on the West Coast of Norway) study. We measured the end-diastolic aortic wall thickness (AWT), pericardial fat thickness at the right ventricular free wall, and AVS/MVS based on combined aortic leaflet thickness and hyperechoic valve lesions. Results: Postoperatively, patients experienced a reduction of 12.9 ± 3.9 kg/m2 in BMI, 0.5 ± 1.9 mm in AWT, 2.6 ± 2.3 mm in pericardial fat, and 45%/53% in AVS/MVS (p < 0.05). In multivariate regression analyses with adjustment for clinical and hemodynamic variables, less pericardial fat reduction was associated with male sex and higher 1-year blood pressure and BMI, and less AWT-reduction with higher age and 1-year BMI (p < 0.05). Persistent AVS and MVS were related to higher 1-year BMI and more advanced valve sclerosis preoperatively (p < 0.05). Conclusions: Markers of subclinical atherosclerosis decreases significantly 1 year after bariatric surgery, particularly in younger patients that achieve a BMI < 28 kg/m2.publishedVersio

A left ventricular phantom for 3D echocardiographic twist measurements

Traditional two-dimensional (2D) ultrasound speckle tracking echocardiography (STE) studies have shown a wide range of twist values, also for normal hearts, which is due to the limitations of short-axis 2D ultrasound. The same limitations do not apply to three-dimensional (3D) ultrasound, and several studies have shown 3D ultrasound to be superior to 2D ultrasound, which is unreliable for measuring twist. The aim of this study was to develop a left ventricular twisting phantom and to evaluate the accuracy of 3D STE twist measurements using different acquisition methods and volume rates (VR). This phantom was not intended to simulate a heart, but to function as a medium for ultrasound deformation measurement. The phantom was made of polyvinyl alcohol (PVA) and casted using 3D printed molds. Twist was obtained by making the phantom consist of two PVA layers with different elastic properties in a spiral pattern. This gave increased apical rotation with increased stroke volume in a mock circulation. To test the accuracy of 3D STE twist, both single-beat, as well as two, four and six multi-beat acquisitions, were recorded and compared against twist from implanted sonomicrometry crystals. A custom-made software was developed to calculate twist from sonomicrometry. The phantom gave sonomicrometer twist values from 2.0° to 13.8° depending on the stroke volume. STE software tracked the phantom wall well at several combinations of temporal and spatial resolution. Agreement between the two twist methods was best for multi-beat acquisitions in the range of 14.4–30.4 volumes per second (VPS), while poorer for single-beat and higher multi-beat VRs. Smallest offset was obtained at six-beat multi-beat at 17.1 VPS and 30.4 VPS. The phantom proved to be a useful tool for simulating cardiac twist and gave different twist at different stroke volumes. Best agreement with the sonomicrometer reference method was obtained at good spatial resolution (high beam density) and a relatively low VR. 3D STE twist values showed better agreement with sonomicrometry for most multi-beat recordings compared with single-beat recordings

Myocardial function in aortic stenosis - insights from radial multilayer Doppler strain

Background Left ventricular (LV) radial tissue Doppler imaging (TDI) strain increases gradually from the subepicardial to the subendocardial layer in healthy individuals. A speckle tracking echocardiography study suggested this gradient to be reduced in parallel with increasing aortic stenosis (AS) severity. Methods We used TDI strain in 84 patients with AS (mean age 73 ± 10 years, 56% hypertensive) for superior assessment of layer strain. 38 patients had non-severe and 46 severe AS by aortic valve area corrected for pressure recovery. Peak systolic radial TDI strain was measured in the subendocardial, mid-myocardial and subepicardial layers of the basal inferior LV wall, each within a region of interest of 2 × 6 mm (strain length 2 mm). Results Radial strain was lower in the subepicardial layer (33.4 ± 38.6%) compared to the mid-myocardial and subendocardial layers (50.3 ± 37.3% and 53.0 ± 40.0%, respectively, both p < 0.001 vs. subepicardial). In the subendo- and midmyocardium, radial strain was lower in patients with severe AS compared to those with non-severe AS (p < 0.05). In multivariate regression analyses including age, heart rate, inferior wall thickness, hypertension, and AS severity, radial strain in the mid-myocardium was primarily attenuated by presence of hypertension (β = −0.23) and AS severity (β = −0.26, both p < 0.05), while radial strain in the subendocardium was significantly influenced by AS severity only (β = −0.35, p < 0.01). Conclusions In AS, both the AS severity and concomitant hypertension attenuate radial TDI strain in the inferior LV wall. The subendocardial radial strain is mainly influenced by AS severity, while midmyocardial radial strain is attenuated by both hypertension and AS severity

One-year impact of bariatric surgery on left ventricular mechanics: results from the prospective FatWest study

Aims Patients with severe obesity are predisposed to left ventricular (LV) hypertrophy, increased myocardial oxygen demand, and impaired myocardial mechanics. Bariatric surgery leads to rapid weight loss and improves cardiovascular risk profile. The present prospective study assesses whether LV wall mechanics improve 1 year after bariatric surgery. Methods and results Ninety-four severely obese patients [43 ± 10 years, 71% women, body mass index (BMI) 41.8 ± 4.9 kg/m2, 57% with hypertension] underwent echocardiography before, 6 months and 1 year after gastric bypass surgery in the FatWest (Bariatric Surgery on the West Coast of Norway) study. We assessed LV mechanics by midwall shortening (MWS) and global longitudinal strain (GLS), LV power/mass as 0.222 × cardiac output × mean blood pressure (BP)/LV mass, and myocardial oxygen demand as the LV mass-wall stress-heart rate product. Surgery induced a significant reduction in BMI, heart rate, and BP (P < 0.001). Prevalence of LV hypertrophy fell from 35% to 19% 1 year after surgery (P < 0.001). The absolute value of GLS improved by—4.6% (i.e. 29% increase in GLS) while LV ejection fraction, MWS, and LV power/mass remained unchanged. In multivariate regression analyses, 1 year improvement in GLS was predicted by lower preoperative GLS, larger mean BP, and BMI reduction (all P < 0.05). Low 1-year MWS was associated with female sex, preoperative hypertension, and higher 1-year LV relative wall thickness and myocardial oxygen demand (all P < 0.001). Conclusion In severely obese patients, LV longitudinal function is largely recovered one year after bariatric surgery due to reduced afterload. LV midwall mechanics does not improve, particularly in women and patients with persistent LV geometric abnormalities