Long-axis Strain Research Articles

Multiscale Mechanical Model of the Pacinian Corpuscle Shows Depth and Anisotropy Contribute to the Receptor's Characteristic Response to Indentation.

Cutaneous mechanoreceptors transduce different tactile stimuli into neural signals that produce distinct sensations of touch. The Pacinian corpuscle (PC), a cutaneous mechanoreceptor located deep within the dermis of the skin, detects high frequency vibrations that occur within its large receptive field. The PC is comprised of lamellae that surround the nerve fiber at its core. We hypothesized that a layered, anisotropic structure, embedded deep within the skin, would produce the nonlinear strain transmission and low spatial sensitivity characteristic of the PC. A multiscale finite-element model was used to model the equilibrium response of the PC to indentation. The first simulation considered an isolated PC with fiber networks aligned with the PC’s surface. The PC was subjected to a 10 μm indentation by a 250 μm diameter indenter. The multiscale model captured the nonlinear strain transmission through the PC, predicting decreased compressive strain with proximity to the receptor’s core, as seen experimentally by others. The second set of simulations considered a single PC embedded epidermally (shallow) or dermally (deep) to model the PC’s location within the skin. The embedded models were subjected to 10 μm indentations at a series of locations on the surface of the skin. Strain along the long axis of the PC was calculated after indentation to simulate stretch along the nerve fiber at the center of the PC. Receptive fields for the epidermis and dermis models were constructed by mapping the long-axis strain after indentation at each point on the surface of the skin mesh. The dermis model resulted in a larger receptive field, as the calculated strain showed less indenter location dependence than in the epidermis model.

Fast assessment of long axis strain with standard cardiovascular magnetic resonance: a validation study of a novel parameter with reference values.

BackgroundAssessment of longitudinal function with cardiovascular magnetic resonance (CMR) is limited to measurement of systolic excursion of the mitral annulus (MAPSE) or elaborate strain imaging modalities. The aim of this study was to develop a fast assessable parameter for the measurement of long axis strain (LAS) with CMR.Methods40 healthy volunteers and 125 patients with different forms of cardiomyopathy were retrospectively analyzed. Four different approaches for the assessment of LAS with CMR measuring the distance between the LV apex and a line connecting the origins of the mitral valve leaflets in enddiastole and endsystole were evaluated. Values for LAS were calculated according to the strain formula.ResultsLAS derived from the distance of the epicardial apical border to the midpoint of the line connecting the mitral valve insertion points (LAS-epi/mid) proved to be the most reliable parameter for the assessment of LAS among the different approaches.LAS-epi/mid displayed the highest sensitivity (81.6 %) and specificity (97.5 %), furthermore showing the best correlation with feature tracking (FTI) derived transmural longitudinal strain (r = 0.85). Moreover, LAS-epi/mid was non-inferior to FTI in discriminating controls from patients (Area under the curve (AUC) = 0.95 vs. 0.94, p = NS). The time required for analysis of LAS-epi/mid was significantly shorter than for FTI (67 ± 8 s vs. 180 ± 14 s, p < 0.0001). Additionally, LAS-epi/mid performed significantly better than MAPSE (Delta AUC = 0.09; p < 0.005) and the ejection fraction (Delta AUC = 0.11; p = 0.0002).Reference values were derived from 234 selected healthy volunteers. Mean value for LAS-epi/mid was −17.1 ± 2.3 %. Mean values for men were significantly lower compared to women (−16.5 ± 2.2 vs. -17.9 ± 2.1 %; p < 0.0001), while LAS decreased with age.ConclusionsLAS-epi/mid is a novel and fast assessable parameter for the analysis of global longitudinal function with non-inferiority compared to transmural longitudinal strain.

In active juvenile dermatomyositis, elevated eotaxin and MCP-1 and cholesterol levels in the upper normal range are associated with cardiac dysfunction.

The aim of this study was to examine the influence of chemokines and lipids on cardiac function in patients with active and inactive JDM and matched controls. Fifty-four JDM patients were clinically examined a median 16.8 years (range 2-38) after disease onset and compared with 54 sex- and age-matched controls. Inactive disease was defined by the PRINTO criteria. Serum levels of chemokines were analysed by Luminex technology. Echocardiography was performed and analysed blinded to patient information. Long-axis strain and e' were used as parameters of systolic and diastolic function, respectively. In patients, but not in controls, eotaxin and monocyte chemoattractant protein 1 (MCP-1) correlated with systolic (r = -0.65 and r = -0.45) and diastolic (r = -0.59 and r = -0.65) function, particularly in those with active disease (systolic function, r = -0.74 and r = -0.60; diastolic function, r = -0.69 and r = -0.80). Total cholesterol level was lower in patients than controls [mean 4.19 mmol/l (s.d. 0.82) vs 4.60 (0.87), P ≤ 0.01]. However, total cholesterol levels in the upper normal range were associated with systolic (r = -0.56, P < 0.01) and diastolic (r = -0.64, P < 0.001) dysfunction and with high eotaxin and MCP-1 (r = 0.56 and r = 0.50, P < 0.01) in patients with active disease, but not in those with inactive disease or in controls (all r < ±0.2). In the active disease state of JDM, eotaxin and MCP-1 were associated with cardiac dysfunction, possibly through sustained inflammation. In those with active disease and cholesterol levels in the upper normal range, eotaxin and MCP-1 might enhance susceptibility to cardiac dysfunction.

Long axis strain by MRI and echocardiography in a postmyocardial infarct population

To compare long axis strain (LAS) by magnetic resonance imaging (MRI) and echocardiography in a postinfarct patient population. Long axis left ventricle (LV) function is a sensitive index of incipient heart failure by echocardiography, but is less well established in MRI. LAS is an index of global LV function, which is easily assessed in cine loops provided by most cardiac MRI protocols. In all, 116 patients (57 ± 9 years) were studied the same day using echocardiography and MRI 7.4 ± 4.1 months after a first myocardial infarction. LV length was measured in end diastole and end systole in conventional cine images with a temporal resolution of 50 msec or less, and LAS (%) was calculated as the change in LV length, relative to end diastole. Infarct mass was assessed by contrast-enhanced MRI. LAS was progressively reduced in patients with larger infarcts, and demonstrated good correlations with infarct mass (r = 0.55, P < 0.01). There was a good agreement between LAS assessed by echocardiography and MRI (r = 0.77, P < 0.01), and between LAS by MRI and speckle tracking strain by echocardiography (r = 0.74, P < 0.01). LAS is an index that allows measurement of LV long axis function by conventional cine MRI.

In juvenile dermatomyositis, cardiac systolic dysfunction is present after long-term follow-up and is predicted by sustained early skin activity

ObjectiveTo compare systolic cardiac function in patients with juvenile dermatomyositis (JDM) with matched controls and examine associations between systolic and diastolic cardiac function and disease variables.MethodsFifty-nine patients, examined at follow-up,...

Myocardial strain in a health and disease: CMR feature tracking analysis in cardiac hypertrophy

Methods Ninety-five healthy volunteers, 45 patients with AndersonFabry disease (AFD), 48 with hypertension (HT), 65 with hypertrophic cardiomyopathy (HCM), 62 with severe aortic stenosis (AS), 85 with systemic amyloidosis (AMY) were enrolled. Longitudinal and transversal strain was calculated from 3 long-axis cine views, circumferential and radial strain from 3 short-axis cine images using a dedicated software (Tomtec Feature Tracking). Fourteen healthy volunteers were scanned twice, and inter-study, inter-observer, intra-observer intraclass correlation coefficients ranged between 0.36 and 0.77. Forty AS patients underwent a second scan six months after aortic valve replacement.

Impaired Biventricular Deformation in Marfan Syndrome: A Strain and Strain Rate Study in Adult Unoperated Patients

To investigate the presence of any regional myocardial deformation abnormalities in Marfan syndrome (MFS) and determine the benefits of using advanced echocardiography compared to conventional techniques. Myocardial dysfunction in MFS may be caused by extracellular matrix remodeling thus, resulting in uniform reduced functionality. However, increased aortic stiffness may cause segmental ventricular abnormalities. Strain rate imaging (SRI) constitutes a validated technique to assess regional deformation in various clinical conditions. With this in mind, we aimed to investigate biventricular function in MFS using SRI. Forty-four MFS patients (mean age 30 ± 12 years, 26 men) and 49 controls without valvular disease were examined using SRI. Ejection fraction (EF) was calculated by the Simpson's biplane method. Biventricular deformation was assessed by measuring strain/strain rate. Strain values were divided by left ventricular (LV) end-diastolic volume to adjust LV deformation for geometry changes providing a strain index (SI). Aortic stiffness was evaluated using the β-stiffness index. EF (%) was reduced in MFS patients (59 ± 5 vs 72 ± 4, P < 0.001), whereas β-stiffness was increased (P < 0.001). LV radial and LV and right ventricular (RV) long-axis strain values (%) were reduced in the patient group (70 ± 17 vs 93 ± 10; 19 ± 2 vs 25 ± 2; 30 ± 9 vs 36 ± 8, respectively, P < 0.001). Strain rate measurements were also reduced (P < 0.001). In a multiple regression analysis, MFS diagnosis was negatively associated with LV SI (-0.262 [-0.306, -0.219], P < 0.001). β-Stiffness was negatively associated with SI obtained from the septum, inferior and anterior walls. ROC analyses demonstrated that SRI, when compared with conventional echocardiography, had higher sensitivity and specificity in predicting biventricular dysfunction in MFS. Our study showed a uniform reduction in biventricular deformation in MFS. These findings suggest that assessment of myocardial function using advanced echocardiographic techniques could be more accurate in MFS patient evaluation than conventional echocardiography alone.

Regional myocardial long-axis strain and strain rate measured by different tissue Doppler and speckle tracking echocardiography methods: a comparison with tagged magnetic resonance imaging

Compare four different echocardiographic methods, based on tissue Doppler imaging (TDI) and speckle tracking (ST) separately or combined, for long-axis strain and strain rate (SR) measurements, using magnetic resonance imaging (MRI) tagging as a reference. In 21 subjects (10 with myocardial infarction) peak systolic strain and systolic and early diastolic SR were measured by four different echo methods: (i) two-dimensional (2D) strain (B-mode); (ii) ST (custom software) of segment end-points (B-mode); (iii) similar to (ii), but combining ST with tissue Doppler tracking; (iv) strain from tissue Doppler velocity gradients (VG). Agreement with MRI tagging was better for strain than for SR. Ninety-five per cent limits of agreement were wider for the TDI-VG method, and 2D strain showed negative bias compared with MRI tagging and the other echo methods. Reproducibility was better for 2D strain than for MRI tagging and the other echo methods. ST alone or combined with TDI seems to be suitable for automated measurements of regional myocardial deformation. The study gives important information on the strengths and weaknesses of the different methods, which is important for further development to increase accuracy and applicability.

Apical Myocardial Stunning in a Large Size Porcine Model Assessed by Strain and Strain Rate Echocardiography

Warm ischemia and subsequent reperfusion of the heart can induce a temporary dysfunction known as myocardial stunning. The aim of this study was to investigate the ability of tissue Doppler imaging (TDI) to quantify longitudinal myocardial stunning close to the apex, and perform a comparison with sonomicrometry using a well-established large size porcine model. In anesthetized pigs, postischemic myocardial stunning was induced by occluding LAD for 15 min followed by 90 min reperfusion (n = 7). Long-axis strain and strain rate was quantified by both TDI and sonomicrometry. During reperfusion, peak systolic strain measured by TDI decreased from -11.2% (+/-3.0) at baseline to -4.9% (+/-3.6), -3.4% (+/-2.9), and -4.3% (+/-5.0) at 30, 60, and 90 min, respectively (all P < 0.007). Postsystolic strain increased from -1.3% (+/-1.6) at baseline to -6.4% (+/-4.4), -4.8% (+/-4.0), and -5.2% (+/-2.7) by TDI in the reperfusion phase (all P < 0.048 except at 60 min of reperfusion (P = 0.081)). Postsystolic index increased from 0.10 (+/-0.13) at baseline to 0.56 (+/-0.24), 0.54 (+/-0.30), and 0.64 (+/-0.37) subsequently (all P < 0.012). [Correction added after online publication 30-May-2007: In the preceding sentence, the phrase 'Postsystolic index decreased from 0.10 (+/-0.13)' was changed to 'Postsystolic index increased from 0.10 (+/-0.13).'] Difference-mean and line of identity plots did not disclose any systematic error, but revealed substantial variation, indicating a mismatch between TDI and sonomicrometry. It is feasible to quantify postischemic myocardial stunning by TDI in a large size porcine model using longitudinal postsystolic shortening, and postsystolic index as indicators. TDI and sonomicrometry data reach the same end point, but the two techniques are not interchangeable when investigating myocardial stunning close to apex in reference to longitudinal strain and strain rate.

Noninvasive Myocardial Strain Measurement by Speckle Tracking Echocardiography: Validation Against Sonomicrometry and Tagged Magnetic Resonance Imaging

The aim of this study was to validate speckle tracking echocardiography (STE) as a method for angle-independent measurement of regional myocardial strain, using sonomicrometry and magnetic resonance imaging (MRI) tagging as reference methods. Tissue Doppler imaging allows non-invasive measurement of myocardial strain in the left ventricle (LV), but is limited by angle dependency. Strain measurements with STE were obtained by a custom-made program that allowed tracking of two-dimensional motion of speckle patterns in a B-mode image. In anesthetized dogs, we compared LV long- and short-axis measurements by STE to sonomicrometry during preload changes and regional myocardial ischemia. Measurements in the two orthogonal axes were obtained simultaneously in a single imaging plane. In human subjects, long-axis strain by STE and MRI tagging were compared in multiple segments of the LV. In the experimental study there was good correlation and agreement between STE and sonomicrometry for systolic strain in the long axis (r = 0.90, p < 0.001; 95% limits of agreement -4.4% to 5.0%) and systolic shortening in the short axis (r = 0.79, p < 0.001; -5.6% to 5.1%). In the clinical study, 80% of the segments could be analyzed, and correlation and agreement between STE and MRI tagging were good (r = 0.87, p < 0.001; -9.1% to 8.0%). Speckle tracking echocardiography provides accurate and angle-independent measurements of LV dimensions and strains and has potential to become a clinical bedside tool for quantifying myocardial strain.

Myocardial Strain Analysis in Acute Coronary Occlusion

This study proposes 2 new echocardiographic indices with potential application in acute coronary artery occlusion to differentiate between viable and necrotic myocardium and to identify reperfusion. We investigated whether the ratio between systolic lengthening and combined late and postsystolic shortening (L-S ratio) could identify viable myocardium and whether systolic myocardial compliance, calculated as systolic lengthening divided by systolic pressure rise, could identify necrotic myocardium. In anesthetized dogs, we measured left ventricular (LV) pressure and long-axis strain by Doppler echocardiography (SDE) and sonomicrometry. The left anterior descending coronary artery was occluded for 15 minutes with 3-hour reperfusion (n=6), for 4 hours with 3-hour reperfusion (n=6), or for 4 hours with no reperfusion (n=6). Myocardial work was quantified by pressure-segment length analysis, necrosis by triphenyltetrazolium chloride staining, and edema by water content. L-S ratio and systolic compliance were calculated by SDE. The L-S ratio ranged between 0.00 and 1.00 and was well correlated with regional myocardial work (r=0.77, P<0.0001). In entirely passive myocardium, the L-S ratio approached 1 and was similar in viable (0.88+/-0.02) and necrotic (0.81+/-0.03) myocardium. Compliance, however, was reduced in necrotic myocardium owing to edema (0.07+/-0.01%/mm Hg) but was preserved in viable myocardium (0.15+/-0.01%/mm Hg, P<0.05). Reperfusion of viable myocardium caused a reduction of the L-S ratio after 15 minutes (0.57+/-0.06, P<0.05), reflecting recovery of function. Reperfusion of necrotic myocardium caused no change in the L-S ratio, but compliance was further reduced within 15 minutes (0.03+/-0.01%/mm Hg, P<0.05). Myocardial L-S ratio and compliance by SDE identified active contraction and necrosis, respectively. These indices should be tested clinically for assessment of myocardial viability and reperfusion.

Alterations of Left Ventricular Myocardial Characteristics Associated With Obesity

Obesity is associated with heart failure, but an effect of weight, independent of comorbidities, on cardiac structure and function is not well established. We sought whether body mass index (BMI) and insulin levels were associated with subclinical myocardial disturbances. Transthoracic echocardiography, myocardial Doppler-derived systolic (sm) and early diastolic velocity (em), strain and strain rate imaging and tissue characterization with cyclic variation (CVIB), and calibrated integrated backscatter (cIB) were obtained in 109 overweight or obese subjects and 33 referents (BMI <25 kg/m2). BMI correlated with left ventricular (LV) mass and wall thickness (P<0.001). Severely obese subjects (BMI >35) had reduced LV systolic and diastolic function and increased myocardial reflectivity compared with referents, evidenced by lower average long-axis strain, sm, cIB, lower CVIB, and reduced em, whereas LV ejection fraction remained normal. Differences in regional or global strain, sm, and em were identified between the severely obese (BMI >35) and the referent patients (P<0.001). Similar but lesser degrees of reduced function by sm, em, and basal septal strain and increased reflectivity by cIB were present in overweight (BMI, 25 to 29.9) and mildly obese (BMI, 30 to 35) groups (P<0.05). Although tissue Doppler measures were not associated with duration of obesity, they did correlate with fasting insulin levels and reduced exercise capacity. BMI was independently related to average LV strain (beta=0.40, P=0.02), sm (beta=-0.36, P=0.002), and em (beta=-0.41, P<0.001). Overweight subjects without overt heart disease have subclinical changes of LV structure and function even after adjustment for mean arterial pressure, age, gender, and LV mass.

Evaluation of whole left ventricular systolic performance and local myocardial systolic function in patients with prior myocardial infarction using global long-axis myocardial strain

Left ventricular (LV) global strain along its long axis during systole, which is obtained by dividing mitral annular excursion by the distance from the mitral annulus to the LV apex at end-diastole, can be used to assess whole LV systolic performance. The evaluation of LV wall function using this parameter suggests that previous myocardial infarction (MI) causes long-axis myocardial function in remote normal LV walls, as well as in walls with MI, to deteriorate.

Influence of preload alterations on parameters of systolic left ventricular long-axis function: A doppler tissue study

The study examined the influence of preload alterations on parameters of left ventricular (LV) long-axis function during systole. Doppler tissue echocardiography was performed in 32 healthy volunteers at rest who were placed in the Trendelenburg position after administration of 0.8 mg of nitroglycerin sublingually. In a 16-segment LV model, long-axis myocardial strain and systolic velocities were assessed. Isovolumic acceleration was assessed in the lateral mitral annulus. Mean LV strain and systolic velocity were unchanged during the different load conditions. In the mitral annulus, strain was also uninfluenced by preload alterations, whereas the peak systolic velocities seemed influenced by preload reduction. The isovolumic acceleration of the mitral annulus was found to be load dependent (enhanced preload 1.38 ± 0.50 vs baseline 1.6 m/s 2 ± 0.60, P < .01; and preload reduction 2.18 ± 0.65 m/s 2, P < .01). In conclusion, LV long-axis strain and systolic velocities were not significantly influenced by load alterations, whereas myocardial systolic velocities and isovolumic acceleration in the lateral mitral annulus were significantly load dependent.