Mechanics of ventricular torsion

A displacement-based finite element formulation for incompressible and nearly-incompressible cardiac mechanics

The Lagrange Multiplier (LM) and penalty methods are commonly used to enforce incompressibility and compressibility in models of cardiac mechanics. In this paper we show how both formulations may be equivalently thought of as a weakly penalized system derived from the statically condensed Perturbed Lagrangian formulation, which may be directly discretized maintaining the simplicity of penalty formulations with the convergence characteristics of LM techniques. A modified Shamanskii-Newton-Raphson scheme is introduced to enhance the nonlinear convergence of the weakly penalized system and, exploiting its equivalence, modifications are developed for the penalty form. Focusing on accuracy, we proceed to study the convergence behavior of these approaches using different interpolation schemes for both a simple test problem and more complex models of cardiac mechanics. Our results illustrate the well-known influence of locking phenomena on the penalty approach (particularly for lower order schemes) and its effect on accuracy for whole-cycle mechanics. Additionally, we verify that direct discretization of the weakly penalized form produces similar convergence behavior to mixed formulations while avoiding the use of an additional variable. Combining a simple structure which allows the solution of computationally challenging problems with good convergence characteristics, the weakly penalized form provides an accurate and efficient alternative to incompressibility and compressibility in cardiac mechanics.

Estimating the Myocardium's Angle of Three-Dimensional Trajectory, Using the Tracking of Sequential Two-Dimensional Echocardiography Images

BACKGROUND

In this study, the angle of the myocardium's trajectory in three dimensions (ф) was estimated by simultaneous use of long-axis and short-axis views of left ventricle septum two-dimensional images. Then correlation of three-dimensional trajectory's angle with the rotation angle from the long (χ) and short (θ) axis views was estimated and compared at the three levels of base, mid and apex of the interventricular septum wall.

METHODS

Two-dimensional echocardiography images of long- and short-axis views of 19 healthy men were recorded and analyzed. Using an electrocardiogram of each individual, the images of the two views were synchronized. The interventricular septum wall motion at the three levels of base, mid and apex were estimated, using a block matching algorithm throughout three cardiac cycles. Considering the defined system of coordinates and the position vectors in long and short-axis views, the 3-dimensional angle of the trajectory was calculated.

RESULTS

Maxima of the ф, θ, and χ angles were extracted at 16.33 ± 3.01, 10.61 ± 3.38, and 15.11 ± 3.30 degrees at base level, 22.77 ± 4.95, 7.78 ± 2.96, and 16.72 ± 2.66 degrees at mid level and 14.60 ± 5.81, 10.37 ± 5.48, and 8.79 ± 3.32 degrees at apex level, respectively, of the septum wall, respectively. This study shows significant correlation between the angle of 3-dimensional trajectory (ф) with the angle in short axis view (θ) of the septum wall at the apex level; and also with the angle in long axis view (χ) of the septum wall at base and mid levels.

CONCLUSION

Due to the motion of the wall of the left ventricle in three dimensions, and the non-isotropic structure of myofibers, the angle of 3-dimensional trajectory was estimated using the speckle tracking method of 2-dimentional echocardiography images.

Effects of ventricular insertion sites on rotational motion of left ventricular segments studied by cardiac MR

OBJECTIVE

Obtaining new details for rotational motion of left ventricular (LV) segments using velocity encoding cardiac MR and correlating the regional motion patterns to LV insertion sites.

METHODS

Cardiac MR examinations were performed on 14 healthy volunteers aged between 19 and 26 years. Peak rotational velocities and circumferential velocity curves were obtained for 16 ventricular segments.

RESULTS

Reduced peak clockwise velocities of anteroseptal segments (i.e. Segments 2 and 8) and peak counterclockwise velocities of inferoseptal segments (i.e. Segments 3 and 9) were the most prominent findings. The observations can be attributed to the LV insertion sites into the right ventricle, limiting the clockwise rotation of anteroseptal LV segments and the counterclockwise rotation of inferoseptal segments as viewed from the apex. Relatively lower clockwise velocities of Segment 5 and counterclockwise velocities of Segment 6 were also noted, suggesting a cardiac fixation point between these two segments, which is in close proximity to the lateral LV wall.

CONCLUSION

Apart from showing different rotational patterns of LV base, mid ventricle and apex, the study showed significant differences in the rotational velocities of individual LV segments. Correlating regional wall motion with known orientation of myocardial aggregates has also provided new insights into the mechanisms of LV rotational motions during a cardiac cycle.

ADVANCES IN KNOWLEDGE

LV insertion into the right ventricle limits the clockwise rotation of anteroseptal LV segments and the counterclockwise rotation of inferoseptal segments adjacent to the ventricular insertion sites. The pattern should be differentiated from wall motion abnormalities in cardiac pathology.

Ventricular mechanics in patients with aortic valve disease: longitudinal, radial, and circumferential components

BACKGROUND

Reduced long-axis shortening despite enhanced global function has been reported in aortic stenosis. We sought to improve the understanding of this phenomenon using multi-dimensional strain analysis in conjunction with the evaluation of left ventricular rotation and twist - ventricular torsion - using tissue Doppler techniques.

METHODS

A total of 57 patients with variable severity of aortic stenosis, aortic regurgitation, or mixed aortic valve disease, subdivided into six groups, were studied. Ventricular morphology was assessed using long-axis/short-axis and mass/volume ratios, afterload using end-systolic meridional wall stress, and global performance using ejection fraction. The circumferential and longitudinal strain was measured from two-dimensional images, and left ventricular rotation and twist were estimated as the difference in rotation between the base and apex of the ventricle.

RESULTS

Aortic stenosis was associated with higher mass/volume, ejection fraction, circumferential strain and left ventricular rotation and twist, significantly lower end-systolic wall stress, and a trend towards lower longitudinal strain compared with normal. Myocardial mechanics in aortic regurgitation were normal despite ventricular dilation. Mixed aortic valve disease showed findings similar to aortic stenosis. Left ventricular rotation and twist correlated with midwall circumferential strain (r = 0.62 and p < 0.0001), endocardial circumferential strain (r = 0.61 and p < 0.0001), and end-systolic wall stress (r = 0.48 and p < 0.0001), but not with longitudinal strain (r = 0.18 and p > 0.05).

CONCLUSIONS

Myocardial mechanics are normal in patients with aortic regurgitation, independent of abnormalities in cardiac geometry. Conversely, in aortic stenosis and mixed aortic valve disease, significant alterations in the patterns of fibre shortening are found. The effects of stenosis on cardiac function seem to dominate the effect of ventricular remodelling.

Left ventricular torsion changes post kidney transplantation

Background

To quantify changes of left ventricular (LV) torsion in patients' pre and post kidney transplantation.

Methods

A prospective study was conducted on 48 patients who received kidney transplantation for end stage renal disease and without myocardial infarction. The rotation, twist and torsion of LV were studied pre and post kidney transplantation (6 months post transplantation) using velocity vector imaging by echocardiography. The data is expressed as mean ± standard deviation and compared by paired t-test at the p < 0.05 significance level.

Results

Six months post kidney transplantation, left ventricular ejection fraction (from 40.33 ± 11.42 to 61.00 ± 13.68%), ratio of mitral early and late diastolic filling velocity (from 1.04 ± 0.57 to 1.21 ± 0.52), rotation of basal LV (from 4.48 ± 2.66 to 5.65 ± 2.64 degree), rotation of apical LV (from 4.27 ± 3.08 to 5.50 ± 4.25 degree), LV twist (8.75 ± 4.45 to 11.14 ± 5.25 degree) and torsion (from 1.06 ± 0.54 to 1.33 ± 0.61 degree/cm) were increased significantly (p < 0.05). Interventricular septum thickness (from 11.67 ± 2.39 to 9.67 ± 0.48 mm), left ventricular mass index (from 104.00 ± 16.47 to 95.50 ± 21.44 g/m²), systolic blood pressure (from 143.50 ± 34.99 to 121.50 ± 7.09 mmHg), serum blood urea nitrogen (from 42.40 ± 7.98 to 30.43 ± 13.85 mg/dL) and creatinine (from 4.53 ± 1.96 to 2.73 ± 2.57 mg/dL) were decreased significantly (p < 0.05).

Conclusion

Kidney transplantation in end stage renal disease without myocardial infarction results in improvement in left ventricular structure, function and myocardial mechanics as detected by echocardiography and velocity vector imaging. Velocity vector imaging provided valuable information for detection and follow-up of cardiac abnormalities in patients with end stage renal disease.

Left ventricular twist during dobutamine stress echocardiography after acute myocardial infarction: association with reverse remodeling

Left ventricular (LV) twist is emerging as a marker of global LV contractility after acute myocardial infarction (AMI). This study aimed to describe stress-induced changes in LV twist during dobutamine stress echocardiography (DSE) after AMI and investigate their association with LV reverse remodeling at 6 months follow-up. In 82 consecutive first AMI patients (61 ± 12 years, 85 % male) treated with primary percutaneous coronary intervention, DSE was performed at 3 months follow-up. Two-dimensional speckle-tracking-derived apical and basal rotation and LV twist were calculated at rest, low- and peak-dose stages. LV reverse remodeling was defined as ≥10 % decrease in LV end-systolic volume between baseline and 6 months follow-up. Patterns of LV twist response on DSE consisted of either a progressive increase throughout each stage (n = 18), an increase at either low- or peak-dose (n = 53) or no significant increase (n = 11). LV reverse remodeling occurred in 28 (34 %) patients, who showed significantly higher peak-dose LV twist (8.51° vs. 6.69°, p = 0.03) and more frequently progressive LV twist increase from rest to peak-dose (39 vs. 13 %, p < 0.01) compared to patients without reverse remodeling. Furthermore, increase in LV twist from rest to peak-dose was the only independent predictor of LV reverse remodeling at 6 months follow-up (OR 1.3, 95 % CI 1.1-1.5, p = 0.005). Both the pattern of progressive increase in LV twist and the stress-induced increment in LV twist on DSE are significantly associated with LV reverse remodeling at 6 month follow-up after AMI, suggesting its potential use as a novel marker of contractile reserve.

Epicardial delivery of collagen patches with adipose-derived stem cells in rat and minipig models of chronic myocardial infarction

Although transplantation of adipose-derived stem cells (ADSC) in chronic myocardial infarction (MI) models is associated with functional improvement, its therapeutic value is limited due to poor long-term cell engraftment and survival. Thus, the objective of this study was to examine whether transplantation of collagen patches seeded with ADSC could enhance cell engraftment and improve cardiac function in models of chronic MI. With that purpose, chronically infarcted Sprague-Dawley rats (n = 58) were divided into four groups and transplanted with media, collagen scaffold (CS), rat ADSC, or CS seeded with rat ADSC (CS-rADSC). Cell engraftment, histological changes, and cardiac function were assessed 4 months after transplantation. In addition, Göttingen minipigs (n = 18) were subjected to MI and then transplanted 2 months later with CS or CS seeded with autologous minipig ADSC (CS-pADSC). Functional and histological assessments were performed 3 months post-transplantation. Transplantation of CS-rADSC was associated with increased cell engraftment, significant improvement in cardiac function, myocardial remodeling, and revascularization. Moreover, transplantation of CS-pADSC in the pre-clinical swine model improved cardiac function and was associated with decreased fibrosis and increased vasculogenesis. In summary, transplantation of CS-ADSC resulted in enhanced cell engraftment and was associated with a significant improvement in cardiac function and myocardial remodeling.

Off-pump epicardial ventricular reconstruction restores left ventricular twist and reverses remodeling in an ovine anteroapical aneurysm model

OBJECTIVE

The loss of normal apical rotation is associated with left ventricular (LV) remodeling and systolic dysfunction in patients with congestive heart failure after myocardial infarction. The objective of the present study was to evaluate the effect of epicardial ventricular reconstruction, an off-pump, less-invasive surgical reshaping technique, on myocardial strain, LV twist, and the potential alteration of myocardial fiber orientation in an ovine model of LV anteroapical aneurysm.

METHODS

LV anteroapical myocardial infarction was induced by coil embolization of the left anterior descending artery. Eight weeks after occlusion, epicardial ventricular reconstruction was performed using left thoracotomy under fluoroscopic guidance in 8 sheep to completely exclude the scar. The peak systolic longitudinal/circumferential strains and LV twist were evaluated using speckle tracking echocardiography before (baseline), after device implantation, and at 6 weeks of follow-up.

RESULTS

Epicardial ventricular reconstruction was completed in all sheep without any complications. Immediately after device implantation, LV twist significantly increased (4.18 ± 1.40 vs baseline 1.97 ± 1.92; P = .02). The ejection fraction had increased 17% and LV end-systolic volume had decreased 40%. The global longitudinal strain increased from -5.3% to -9.1% (P < .05). Circumferential strain increased in both middle and apical LV segments, with the greatest improvement in the inferior lateral wall (from -11.4% to -20.6%, P < .001). These effects were maintained ≥6 weeks after device implantation without redilation.

CONCLUSIONS

Less invasive than alternative therapies, epicardial ventricular reconstruction on the off-pump beating heart can restore LV twist and systolic strain and reverse LV remodeling in an ovine anteroapical aneurysm model.

Feasibility and reproducibility of left ventricular rotation by speckle tracking echocardiography in elderly individuals and the impact of different software

BACKGROUND

Changes in ventricular rotation measured by two-dimensional speckle tracking echocardiography (2DSTE) are early indicators of cardiac disease. Data on the clinical feasibility of this important measure are scarce and there is no information on the comparability of different software versions. We assessed the feasibility, reproducibility and within patient temporal variability of 2DSTE in a large community based sample of older adults. We additionally compared 2DSTE results to those generated by 3DSTE.

METHODS AND RESULTS

1408 participants underwent transthoracic echocardiography. Using Philips Qlab 8.1 peak LV rotation at either the base or the apex was analysable in 432 (31%) participants. Peak twist measurements were achieved in 274 (20%) participants. 66 participants were randomly selected for the reproducibility study. 20 additional participants had scans 4-6 weeks apart for temporal variability and 3D echocardiography to assess the agreement between 2DSTE and 3DSTE. Reproducibility was evaluated using the intraclass coefficient of correlation (ICC). Better reproducibility for rotation and twist were obtained when measured at the endocardium, and when using more recent software versions, Peak twist and rotation were significantly different using two versions of the same software. Agreement with 3DSTE was better using newer software.

CONCLUSION

Feasibility of 2DSTE is low in this cohort of elderly individuals severely limiting its utility in clinical settings. However if high quality images can be acquired assessment of ventricular rotation by 2DSTE is reproducible. Caution should be taken when comparing measurements of ventricular rotation by software from different vendors or different versions of software from the same vendor.

Preparation and characterization of collagen-based ADSC-carrier sheets for cardiovascular application

The use of scaffolds composed of natural biodegradable matrices represents an attractive strategy to circumvent the lack of cell engraftment, a major limitation of stem cell therapy in cardiovascular diseases. Bovine-derived non-porous collagen scaffolds with different degrees of cross-linking (C0, C2, C5 and C10) were produced and tested for their mechanical behavior, in vitro biocompatibility with adipose-derived stem cells (ADSCs) and tissue adhesion and inflammatory reaction. Uniaxial tensile tests revealed an anisotropic behavior of collagen scaffolds (2×0.5cm) and statistically significant differences in the mechanical behavior between cross-linked and non-cross-linked scaffolds (n=5). In vitro, ADSCs adhered homogenously and showed a similar degree of proliferation on all four types of scaffolds (cells×10(3)cm(-2) at day 7: C0: 94.7±37.1; C2: 91.7±25.6; C5: 88.2±6.8; C10: 72.8±10.7; P=n.s.; n=3). In order to test the in vivo biocompatibility, a chronic myocardial infarction model was performed in rats and 1.2×1.2cm size collagen scaffolds implanted onto the heart 1month post-infarction. Six animals per group were killed 2, 7 and 30days after transplant. Complete and long-lasting adhesion to the heart was only observed with the non-cross-linked scaffolds with almost total degradation 1month post-transplantation. After 7 and 30days post-implantation, the degree of inflammation was significantly lower in the hearts treated with non-cross-linked scaffolds (day 7: C0: 10.2±2.1%; C2: 16.3±2.9%; C5: 15.9±4.8%; C10: 17.4±4.1%; P<0.05 vs. C0; day 30: C0: 1.3±1.3%; C2: 9.4±3.0%; C5: 7.0±2.1%; C10: 9.8±2.5%; P<0.01 vs. C0). In view of the results, the non-cross-linked scaffold (C0) was chosen as an ADSC-carrier sheet and tested in vivo. One week post-implantation, 25.3±7.0% of the cells transplanted were detected in those animals receiving the cell-carrier sheet whereas no cells were found in animals receiving cells alone (n=3 animals/group). We conclude that the biocompatibility and mechanical properties of the non-cross-linked collagen scaffolds make them a useful cell carrier that greatly favors tissue cell engraftment and may be exploited for cell transplantation in models of cardiac disease.

Assessment of subendocardial contractile function in aortic stenosis: a study using speckle tracking echocardiography

BACKGROUND

Angina and an electrocardiographic strain pattern are potential manifestations of subendocardial ischemia in aortic stenosis (AS). Left ventricular (LV) twist is known to increase proportionally to the severity of AS, which may be a result of loss of the inhibiting effect of the subendocardial fibers due to subendocardial dysfunction. It has also been shown that the ratio of LV twist to circumferential shortening of the endocardium (twist-to-shortening ratio [TSR]) is a reliable parameter of subendocardial dysfunction. The aim of this study was to investigate whether these markers are increased in AS patients with angina and/or electrocardiographic strain.

METHODS

The study comprised 60 AS patients with an aortic valve area <2.0 cm(2) and LV ejection fraction >50%, and 30 healthy-for age and gender matched-control subjects. LV rotation parameters were determined by speckle tracking echocardiography.

RESULTS

Comparison of patients without angina and strain (n = 22), with either angina or strain (n = 28), and with both angina and strain (n = 8), showed highest peak systolic LV apical rotation, peak systolic LV twist, and TSR, in patients with more signs of subendocardial ischemia. In a multivariate linear regression model, only severity of AS and the presence of angina and/or strain could be identified as independent predictors of peak systolic LV twist and TSR.

CONCLUSIONS

Peak systolic LV twist and TSR are increased in AS patients and related to the severity of AS and symptoms (angina) or electrocardiographic signs (strain) compatible with subendocardial ischemia.

Evaluation of left ventricular torsion by cardiovascular magnetic resonance

Recently there has been considerable interest in LV torsion and its relationship with symptomatic and pre-symptomatic disease processes. Torsion gives useful additional information about myocardial tissue performance in both systolic and diastolic function. CMR assessment of LV torsion is simply and efficiently performed. However, there is currently a wide variation in the reporting of torsional motion and the procedures used for its calculation. For example, torsion has been presented as twist (degrees), twist per length (degrees/mm), shear angle (degrees), and shear strain (dimensionless). This paper reviews current clinical applications and shows how torsion can give insights into LV mechanics and the influence of LV geometry and myocyte fiber architecture on cardiac function. Finally, it provides recommendations for CMR measurement protocols, attempts to stimulate standardization of torsion calculation, and suggests areas of useful future research.

Orthotropic active strain models for the numerical simulation of cardiac biomechanics

A model for the active deformation of cardiac tissue considering orthotropic constitutive laws is introduced and studied. In particular, the passive mechanical properties of the myocardium are described by the Holzapfel-Ogden relation, whereas the activation model is based on the concept of active strain. There, an incompatible intermediate configuration is considered, which entails a multiplicative decomposition between active and passive deformation gradients. The underlying Euler-Lagrange equations for minimizing the total energy are written in terms of these deformation factors, where the active part is assumed to depend, at the cell level, on the electrodynamics and on the specific orientation of the cardiomyocytes. The active strain formulation is compared with the classical active stress model from both numerical and modeling perspectives. The well-posedness of the linear system derived from a generic Newton iteration of the original problem is analyzed, and different mechanical activation functions are considered. Taylor-Hood and MINI finite elements are used in the discretization of the overall mechanical problem. The results of several numerical experiments show that the proposed formulation is mathematically consistent and is able to represent the main features of the phenomenon, while allowing savings in computational costs.

Left ventricular dyssynchrony using three-dimensional speckle-tracking imaging as a determinant of torsional mechanics in patients with idiopathic dilated cardiomyopathy

The aim of this study was to use 3-dimensional (3D) speckle-tracking echocardiography to test the hypothesis that left ventricular (LV) dyssynchrony may negatively affect LV torsional mechanics in patients with idiopathic dilated cardiomyopathy (IDC) and that LV torsion may improve after cardiac resynchronization therapy. This study included 65 subjects; 20 with IDC with ejection fractions ≤35% and wide QRS complexes (≥120 ms), 20 with IDC with ejection fractions ≤35% and narrow QRS complexes (<120 ms), and 25 controls. LV dyssynchrony index was determined as the SD of time to peak 3D speckle-tracking radial strain and regional heterogeneity of LV rotation (rotational dispersion index) as the SD of 3D speckle-tracking time to peak rotation. All rotational indexes were significantly impaired in patients with IDC, while LV torsion in patients with IDC with wide QRS complexes was significantly smaller than that in patients with IDC with narrow QRS complexes and controls. Conversely, LV dyssynchrony index (127.3 ± 24.0 ms [p <0.01 vs controls and vs patients with narrow QRS complexes] vs 88.8 ± 22.5 ms [p <0.01 versus controls] vs 30.9 ± 10.0 ms) and rotational dispersion index (115.1 ± 27.5 ms [p <0.01 vs controls and vs patients with narrow QRS complexes] vs 96.0 ± 23.4 ms [p <0.01 versus controls] vs 45.0 ± 13.7 ms) were significantly higher in patients with IDC with wide QRS complexes. Multivariate analysis showed that the LV ejection fraction (β = 0.688, p <0.001) and rotational dispersion index (β = -0.249, p <0.01) were independent determinants of LV torsion. Moreover, LV torsion in patients with IDC with wide QRS complexes improved after cardiac resynchronization therapy (p <0.05), along with reductions in LV dyssynchrony and rotational dispersion indexes. In conclusion, these findings obtained with a novel 3D speckle-tracking system feature a novel aspect of LV torsional mechanics and demonstrate its association with LV dyssynchrony.

Load independence of two-dimensional speckle-tracking-derived left ventricular twist and apex-to-base rotation delay in nonischemic dilated cardiomyopathy: implications for left ventricular dyssynchrony assessment

BACKGROUND

Left ventricular (LV) twist mechanics are a promising, sensitive tool for assessing pathophysiologic changes in patients with systolic heart failure. Although LV twist is known to be load dependent in healthy volunteers, this has not been examined in patients with "long-standing" dilated cardiomyopathy (DCM). The aim of this study was to determine whether LV twist remains load dependent in the setting of long-standing, nonischemic DCM.

METHODS

Thirty-four patients with DCM with baseline LV ejection fractions (LVEFs) < 40% and 13 subjects with preserved LVEFs (≥50%) were enrolled. After baseline measurements, pneumatic compression of the lower extremities (Pcom) was used to increase LV afterload. Subsequently, sublingual nitroglycerin (SL-NG) was administered to modify preload. Conventional echocardiographic parameters, LV end-systolic wall stress, net LV twist angle, and apex-to-base-rotation delay (ABRD) were assessed under each condition.

RESULTS

In patients with DCM, although LV end-systolic wall stress significantly increased under Pcom (196.9 ± 64.9 g/m(2) at baseline vs 231.8 ± 78.9 g/m(2) under Pcom, P < .017) and decreased after SL-NG application (231.8 ± 78.9 g/m(2) under Pcom vs 197.4 ± 67.4 g/m(2) after SL-NG, P < .017), net LV twist angle and ABRD showed no significant changes depending on LV loading condition (for LV twist, 7.63 ± 4.47° at baseline vs 7.03 ± 4.13° under Pcom vs 7.35 ± 4.36° after SL-NG, P = 0.65; for ABRD, 16.56 ± 13.81% at baseline vs 17.19 ± 14.81% under Pcom vs 15.95 ± 13.27% after SL-NG, P = .53). Careful examination of individual patient data revealed that LV twist was load independent when patients had LV twist < 12°. ABRD was also found to be load independent, but only in patients with LVEFs < 34%. In contrast, LV twist and ABRD were load dependent in patients with preserved LVEFs.

CONCLUSIONS

LV twist and its component, ABRD, had relatively load insensitive properties in patients with long-standing DCM and can be used in future clinical trials as load-independent indexes of LV dyssynchrony.

Left ventricular mechanics in humans with high aerobic fitness: adaptation independent of structural remodelling, arterial haemodynamics and heart rate

Individuals with high aerobic fitness have lower systolic left ventricular strain, rotation and twist (‘left ventricular (LV) mechanics’) at rest, suggesting a beneficial reduction in LV myofibre stress and more efficient systolic function. However, the mechanisms responsible for this functional adaptation are not known and the influence of aerobic fitness on LV mechanics during dynamic exercise has never been studied. We assessed LV mechanics, LV wall thickness and dimensions, central augmentation index (AIx), aortic pulse wave velocity (aPWV), blood pressure and heart rate in 28 males (age: 21±2 years SD) with a consistent physical activity level (no change>6 months). Individuals were examined at rest and during exercise (40% peak exercise capacity) and separated post hoc into a moderate and high aerobic fitness group (˙V(O2peak): 49 ± 5 and 63 ± 7ml kg−1 min−1, respectively, P <0.0001). At rest and during exercise, there were no significant differences in gross LVstructure, AIx, blood pressure or heart rate (P >0.05).However, for the same AIx, the high ˙V(O2peak) group had significantly lower LV apical rotation (P =0.002) and LV twist (P =0.003) while basal rotation and strain indices did not differ between groups (P >0.05).We conclude that young males with high aerobic fitness have lower LVapical rotation at rest and during submaximal exercise that can occur without changes in gross LV structure, arterial haemodynamics or heart rate. The findings suggest a previously unknown type of physiological adaptation of the left ventricle that may have important implications for exercise training in older individuals and patient populations in which exercise training has previously failed to show clear benefits for LV function.

Exercise response in hypertrophic cardiomyopathy: blunted left ventricular deformational and twisting reserve with altered systolic-diastolic coupling

BACKGROUND

Abnormal left ventricular (LV) deformational mechanics have been demonstrated in patients with hypertrophic cardiomyopathy (HCM) at rest, but there is a lack of information on their adaptation to exercise. The aim of this study was to assess the adaptability of LV strains and torsional mechanics during exercise in HCM patients.

METHODS AND RESULTS

Twenty nonobstructive HCM patients (age, 48.3±12.3 years; 14 men) and 20 control subjects underwent speckle-tracking echocardiographic measurement of longitudinal, radial, and circumferential strains, systolic twist, and diastolic untwisting rate (UTR) at rest and submaximal exercise. HCM patients showed lower resting longitudinal (-15.7±5.0% versus -19.4±2.6%, P<0.001) and radial (38.1±11.3% versus 44.7±14.4%, P<0.05) strains but higher circumferential strain (-21.9±4.0% versus -18.8±2.3%, P<0.05) and twist (15.7±3.6° versus 9.3±2.6°, P<0.0001) than control subjects. Exercise induced an increase in all strains in control subjects but only a moderate increase in longitudinal strain (to -18.4±5.0%), without significant changes in radial and circumferential strains or twist in HCM patients. Exercise peak UTR was lower (-119.0±31.5°/s versus -137.3±41.1°/s) and occurred later (137±18% versus 125±11% systolic time, P<0.05) in HCM than in control subjects. A significant relationship between twist and UTR was obtained in control subjects (ß=-0.0807, P<0.001) but not in HCM patients (ß=-0.0051, P=0.68).

CONCLUSIONS

HCM patients had severely limited strain adaptability and no LV twisting reserve at exercise. They had reduced and delayed UTR with reduced systolic-diastolic coupling efficiency by twist-untwist mechanics.

Cardiac assist with a twist: apical torsion as a means to improve failing heart function

Changes in muscle fiber orientation across the wall of the left ventricle (LV) cause the apex of the heart to turn 10-15 deg in opposition to its base during systole and are believed to increase stroke volume and lower wall stress in healthy hearts. Studies show that cardiac torsion is sensitive to various disease states, which suggests that it may be an important aspect of cardiac function. Modern imaging techniques have sparked renewed interest in cardiac torsion dynamics, but no work has been done to determine whether mechanically augmented apical torsion can be used to restore function to failing hearts. In this report, we discuss the potential advantages of this approach and present evidence that turning the cardiac apex by mechanical means can displace a clinically significant volume of blood from failing hearts. Computational models of normal and reduced-function LVs were created to predict the effects of applied apical torsion on ventricular stroke work and wall stress. These same conditions were reproduced in anesthetized pigs with drug-induced heart failure using a custom apical torsion device programmed to rotate over various angles during cardiac systole. Simulations of applied 90 deg torsion in a prolate spheroidal computational model of a reduced-function pig heart produced significant increases in stroke work (25%) and stroke volume with reduced fiber stress in the epicardial region. These calculations were in substantial agreement with corresponding in vivo measurements. Specifically, the computer model predicted torsion-induced stroke volume increases from 13.1 to 14.4 mL (9.9%) while actual stroke volume in a pig heart of similar size and degree of dysfunction increased from 11.1 to 13.0 mL (17.1%). Likewise, peak LV pressures in the computer model rose from 85 to 95 mm Hg (11.7%) with torsion while maximum ventricular pressures in vivo increased in similar proportion, from 55 to 61 mm Hg (10.9%). These data suggest that: (a) the computer model of apical torsion developed for this work is a fair and accurate predictor of experimental outcomes, and (b) supra-physiologic apical torsion may be a viable means to boost cardiac output while avoiding blood contact that occurs with other assist methods.

An active strain electromechanical model for cardiac tissue

We propose a finite element approximation of a system of partial differential equations describing the coupling between the propagation of electrical potential and large deformations of the cardiac tissue. The underlying mathematical model is based on the active strain assumption, in which it is assumed that there is a multiplicative decomposition of the deformation tensor into a passive and active part holds, the latter carrying the information of the electrical potential propagation and anisotropy of the cardiac tissue into the equations of either incompressible or compressible nonlinear elasticity, governing the mechanical response of the biological material. In addition, by changing from a Eulerian to a Lagrangian configuration, the bidomain or monodomain equations modeling the evolution of the electrical propagation exhibit a nonlinear diffusion term. Piecewise quadratic finite elements are employed to approximate the displacements field, whereas for pressure, electrical potentials and ionic variables are approximated by piecewise linear elements. Various numerical tests performed with a parallel finite element code illustrate that the proposed model can capture some important features of the electromechanical coupling and show that our numerical scheme is efficient and accurate.

Cardiac myosin binding protein C insufficiency leads to early onset of mechanical dysfunction

BACKGROUND

Decreased expression of cardiac myosin binding protein C (cMyBPC) as a result of genetic mutations may contribute to the development of hypertrophic cardiomyopathy (HCM); however, the mechanisms that link cMyBPC expression and HCM development, especially contractile dysfunction, remain unclear.

METHODS AND RESULTS

We evaluated cardiac mechanical function in vitro and in vivo in young mice (8-10 weeks of age) carrying no functional cMyBPC alleles (cMyBPC(-/-)) or 1 functional cMyBPC allele (cMyBPC(±)). Skinned myocardium isolated from cMyBPC(-/-) hearts displayed significant accelerations in stretch activation cross-bridge kinetics. Cardiac MRI studies revealed severely depressed in vivo left ventricular (LV) magnitude and rates of LV wall strain and torsion compared with wild-type (WT) mice. Heterozygous cMyBPC(±) hearts expressed 23±5% less cMyBPC than WT hearts but did not display overt hypertrophy. Skinned myocardium isolated from cMyBPC(±) hearts displayed small accelerations in the rate of stretch induced cross-bridge recruitment. MRI measurements revealed reductions in LV torsion and circumferential strain, as well reduced circumferential strain rates in early systole and diastole.

CONCLUSIONS

Modest decreases in cMyBPC expression in the mouse heart result in early-onset subtle changes in cross-bridge kinetics and in vivo LV mechanical function, which could contribute to the development of HCM later in life.

Quantitative comparison of myocardial fiber structure between mice, rabbit, and sheep using diffusion tensor cardiovascular magnetic resonance

BACKGROUND

Accurate interpretations of cardiac functions require precise structural models of the myocardium, but the latter is not available always and for all species. Although scaling or substitution of myocardial fiber information from alternate species has been used in cardiac functional modeling, the validity of such practice has not been tested.

METHODS

Fixed mouse (n = 10), rabbit (n = 6), and sheep (n = 5) hearts underwent diffusion tensor imaging (DTI). The myocardial structures in terms of the left ventricular fiber orientation helix angle index were quantitatively compared between the mouse rabbit and sheep hearts.

RESULTS

The results show that significant fiber structural differences exist between any two of the three species. Specifically, the subepicardial fiber orientation, and the transmural range and linearity of fiber helix angles are significantly different between the mouse and either rabbit or sheep. Additionally, a significant difference was found between the transmural helix angle range between the rabbit and sheep. Across different circumferential regions of the heart, the fiber orientation was not found to be significantly different.

CONCLUSIONS

The current study indicates that myocardial structural differences exist between different size hearts. An immediate implication of the present findings for myocardial structural or functional modeling studies is that caution must be exercised when extrapolating myocardial structures from one species to another.

[Assessment of left ventricular twist mechanics by two-dimensional strain in severe aortic stenosis with preserved ejection fraction]

Left ventricular (LV) twist is increased in aortic stenosis (AS) and the hypothesis of a compensatory mechanism is suggested but not established. Our aim was to assess LV twist mechanics in severe AS (<1cm(2) or 0.6cm(2)/m(2)) with preserved LV ejection fraction (LVEF>50%), and to analyze its relationship with LV systolic longitudinal function, early impaired in this setting, LV diastolic function, and symptomatic status.

METHODS

Forty-five consecutive patients with severe AS and preserved LVEF (mean age 73±11 years, 47% female, LVEF 68±11%, 67% symptomatic) underwent a transthoracic echocardiography including a bidimensional strain analysis by speckle tracking method, and were compared to a control group matched for age and sex (n=15). Global longitudinal strain (GLS) was measured using the four, two, and three apical views, and LV twist mechanics from the basal and apical short axis views. LV twist was defined as the net difference between apical and basal rotation, and LV twisting and untwisting rate (in°/s) were derived from twist curves.

RESULTS

Peak apical rotation, LV twist (25±8° vs 20±6), as well as peak systolic and diastolic apical rotation rate, and peak LV twisting rate were significantly higher in patients with AS when compared to controls (all, P<0.05), whereas, the other parameters of LV twist mechanics including basal rotation, were not significantly different between groups. By contrast, the GLS was significantly lower in patients with AS when compared to controls (-17.9±4 vs -20.5±2%, P<0.01). In addition, the GLS was significantly correlated to LV torsion (r=-0.42, P<0.01). Moreover, LV twist progressively impaired with the worsening of diastolic dysfunction and with symptoms onset.

CONCLUSION

LV twist is increased in severe AS with preserved LVEF, compensating the impairment of systolic longitudinal function. However, above a certain threshold LV twist deteriorates, attesting the failure of the compensatory mechanisms, leading to advanced diastolic dysfunction and symptom onset.

Effects of mechanical limitation of apical rotation on left ventricular relaxation and end-diastolic pressure

Left ventricular (LV) twist is thought to play an important role in cardiac function. However, how twist affects systolic or diastolic function is not understood in detail. We acquired apical and basal short-axis images of dogs undergoing open-chest procedures ( n = 15) using a GE Vivid 7 at baseline and during the use of an apical suction device (Starfish) to limit apical rotation. We measured LV pressure and stroke volume using a micromanometer-tipped catheter and an ultrasonic flow probe, respectively. Peak radial strain, peak rotation, peak twist, peak systolic twisting rate (TR), peak untwisting rate during isovolumic relaxation period (URIVR), and peak early diastolic untwisting rate after mitral valve opening (URE) were determined using speckle tracking echocardiography. Immobilizing the apex with gentle suction significantly decreased apical rotation (−50 ± 27%) and slightly increased basal rotation, resulting in a significant decrease in twist. The time constant of LV relaxation (τ) was prolonged, and LV end-diastolic pressure increased. TR and URIVR decreased. LV systolic pressure, peak positive and negative first derivative of LV pressure (±dP/d t), stroke volume, radial strain, and URE were not changed. The correlation between τ and URIVR ( r = 0.63, P = 0.0006) was stronger than that between peak +dP/d t and TR ( r = 0.46, P = 0.01). Diastolic function was impaired with reduced apical rotation and URIVR when the apex of the heart was immobilized using an apical suction device.

Computational finite element model of cardiac torsion

PURPOSE

A novel finite-element model of ventricular torsion for the analysis of the twisting behavior of the left human ventricle was developed, in order to investigate the influence of various biomechanical parameters on cardiac kinematics.

METHODS

The ventricle was simulated as a thick-walled ellipsoid composed of nine concentric layers. Arrays of reinforcement bars were embedded in each layer to mimic physiological myocardial anisotropy. The reinforcement bars were activated through an artificial combination of thermal and mechanical effects in order to obtain a contractile behavior which is similar to that of myocardial fibers. The presence of an incompressible fluid inside the ventricular cavity was also simulated and the ventricle was combined with simple lumped-parameter hydraulic circuits reproducing preload and afterload. Changes to a number of cardiac parameters, such as preload, afterload and fiber angle orientation were introduced, in order to study the effects of these changes on cardiac torsion.

RESULTS

The model is able to reproduce a similar torsional behavior to that of a physiological heart. The results of the simulations showed that there was sound correspondence between the model outcomes and available data from the literature. Results confirmed the importance of symmetric transmural patterns for fiber orientation.

CONCLUSIONS

This model represents an important step on the path towards unveiling the complexity of cardiac torsion. It proves to be a practical and versatile tool which could assist clinicians and researchers by providing them with easily-accessible, detailed data on cardiac kinematics for future diagnostic and surgical purposes.

Transmural heterogeneity of left ventricular myocardium remodeling in postinfarct porcine model revealed by MR diffusion tensor imaging

PURPOSE

To investigate the transmural heterogeneity of left ventricular myocardium structural remodeling.

MATERIALS AND METHODS

Ex vivo diffusion tensor imaging (DTI) was performed in six adult porcine heart samples with apical septum infarction collected 13 weeks after permanent left anterior descending coronary artery ligation and six age-matched intact controls. Alterations in diffusion indices and myocardial fiber orientation, including fractional anisotropy (FA), mean apparent diffusion coefficient (mean ADC), axial diffusivity (λ(∥) ), radial diffusivity (λ(⟂) ), and fiber helix angle were investigated at five transmural zones across myocardium wall in regions adjacent and remote to the infarct.

RESULTS

In both adjacent and remote regions of infarcted hearts, FA showed no significant alteration across transmural zones compared to controls. However, mean ADC, λ(∥) , and λ(⟂) exhibited significant decreases at endocardium zones but not epicardium zones. Moreover, myocardial fiber helix angle shifted towards left-handed orientation at all transmural zones, especially in regions adjacent to the infarct, becoming more aligned with the epicardium fiber orientation.

CONCLUSION

These experimental DTI findings indicate that the endocardium was more vulnerable to infarction, leading to more pronounced microstructural changes during remodeling. The current DTI approach reveals additional information in delineating postinfarct remodeling process, which may provide insights into cardiac mechanics and clinical assessment of cardiac diseases.

Torsional mechanics of the left ventricle in patients after surgical repair of tetralogy of Fallot

BACKGROUND

This study aimed to test the hypothesis that alteration of left ventricular (LV) torsional mechanics occurs in patients after repair of tetralogy of Fallot (TOF) and is associated with right ventricular (RV) volume overload and changes in LV configuration.

METHODS AND RESULTS

Fifty-five TOF patients aged 19.0 ± 8.1 years and 27 age-matched healthy controls were studied. The LV and RV volumes were measured using 3-dimensional echocardiography while LV geometry was quantified by the diastolic eccentricity index (EI). The LV peak systolic torsion and systolic twisting and diastolic untwisting velocities were determined by speckle tracking. Compared with controls, patients had significantly greater RV end-systolic (P < 0.001) and diastolic (P < 0.001) volumes and LV diastolic EI (P < 0.001). In contrast, LV peak apical rotation (P < 0.001), systolic torsion (P = 0.004), systolic twisting velocity (P = 0.001), and diastolic untwisting velocity (P = 0.001) were lower in patients than in controls. For the whole cohort, RV EDV and LV diastolic EI correlated negatively with peak systolic torsion, systolic twisting velocity, and diastolic untwisting velocity (all P ≤ 0.001). Systolic torsion correlated strongly with diastolic untwisting velocity (r = 0.72, P < 0.001), while systolic twisting velocity correlated with LV ejection fraction (r = 0.3, P = 0.005).

CONCLUSIONS

LV torsional mechanics is impaired and is negatively related to RV volume overload and LV eccentricity in patients after TOF repair.

Differences in left ventricular twist related to age: speckle tracking echocardiographic data for healthy volunteers from neonate to age 70 years

OBJECTIVE

To determine normal left ventricular (LV) twist characteristics in different age groups and assess changes between neonates and the elderly.

METHODS

Short-axis left ventricle images at basal and apical levels were acquired in 274 healthy volunteers (aged 15 days to 72 years) by two-dimensional echocardiography, and were analyzed off-line using Speckle tracking echocardiography (STE) software to obtain LV twist measurements. The peak apical rotation (PAr), peak basal rotation (PBr), peak LV twist (Ptw), peak LV twist normalized by LV length (PtwN), peak untwisting velocity (PutwV), and isovolumic untwisting% (Iutw%) were measured.

RESULTS

LV twist values vary with age. Ptw was higher in older volunteers. PtwN varied inconsistently with age. PutwV and Iutw% were lower in the young and old with a peak in mid-age ranges.

CONCLUSIONS

STE is an effective noninvasive method to assess LV twist. Age-related differences in LV twist may reflect maturation and adaptive modulation of LV torsional biomechanics from neonate to the elderly.

Left ventricular mechanics in asymptomatic normotensive and hypertensive patients with aortic regurgitation

BACKGROUND

The aims of this study were to detect subclinical left ventricular (LV) dysfunction and to determine the impact of arterial hypertension on LV systolic function using speckle-tracking echocardiography in patients with chronic aortic regurgitation (AR).

METHODS

Sixty-eight patients with AR and 47 healthy controls were included in the study. LV rotation and longitudinal, radial, and circumferential strain were measured using speckle-tracking imaging.

RESULTS

Longitudinal axis dysfunction was found in patients with moderate AR with hypertension but was not present in patients with moderate AR without hypertension. Radial strain in patients with moderate AR was unchanged, but reduced levels were noted at the apical level in patients with severe AR without hypertension and preserved in those with severe hypertensive AR. LV basal rotation was reduced in patients with severe AR, whereas apical rotation was increased in those with moderate AR. LV torsion was reduced in patients with severe AR.

CONCLUSIONS

Patients with asymptomatic AR show subclinical LV longitudinal axis dysfunction, with more attenuation demonstrated in hypertensive than in normotensive patients.

Effects of graded heat stress on global left ventricular function and twist mechanics at rest and during exercise in healthy humans

Increased left ventricular (LV) twist and untwisting (LV twist mechanics) contribute to the maintenance of stroke volume during passive heat stress. However, it remains unknown whether changes in LV twist mechanics are related to the magnitude of heat stress and whether performing exercise during heat stress alters this response. We examined global LV function and LV twist mechanics in 10 healthy men at baseline and three progressive levels of heat stress, at rest and during knee-extensor exercise. At rest, heat stress increased cardiac output and reduced end-diastolic volume and end-systolic volume, whilst stroke volume and mean arterial pressure (MAP) were maintained. Left ventricular twist and untwisting velocity also increased from baseline to severe heat stress (from 10.6 ± 3.3 to 15.1 ± 5.2 deg and from -123 ± 55 to -210 ± 49 deg s(-1), respectively, both P < 0.01) and correlated significantly with body temperature, heart rate and LV volumes (P < 0.05). Similar to resting conditions, progressive heat stress during exercise increased cardiac output and reduced end-diastolic volume and end-systolic volume with a maintained stroke volume. However, MAP declined (P < 0.01) and there was no significant change in LV twist and untwisting velocity, resulting in non-significant relationships between twist mechanics and systemic responses. In conclusion, LV twist mechanics increase proportionally with the magnitude of heat stress at rest. However, there is no increase in LV twist and untwisting velocity from control exercise to severe heat stress during exercise despite a significant increase in body temperatures and cardiac output. We, therefore, suggest that the maintenance of stroke volume in the combined conditions of heat stress and small muscle mass exercise may be further facilitated by other peripheral factors, such as the continuous decline in MAP.

Kinetics of Left Ventricular Strains and Torsion During Incremental Exercise in Healthy Subjects

Background—

The dynamics of systolic and diastolic strains and torsional mechanics of the left ventricle (LV) and their relation to diastolic filling never have been evaluated at various exercise intensities.

Methods and Results—

Speckle tracking echocardiography was performed in 20 healthy sedentary subjects at rest and during a progressive submaximal exercise test at 20%, 30%, and 40% of maximal aerobic power. LV twist increased progressively with exercise intensity (10.5±3.2 to 15.8±4.5°; P <0.001), whereas longitudinal strain remained unchanged after the first workload, underlining the key role of torsional reserve in systolic-diastolic coupling during exercise. The increase in diastolic untwisting (−88.7±34.2 to −182.9±53.5 deg · s −1 ; P <0.01) was correlated to enhanced systolic twist ( R =0.61; P <0.001), and its magnitude of increase was significantly higher compared to diastolic longitudinal and circumferential strain rates (119±64% versus 65±44% and 57±24%, respectively), emphasizing its contribution to diastolic filling. The timing of peak untwisting and the chronology of diastolic mechanical events were unchanged during effort. Untwisting was driven mainly by apical rotation and determined mitral opening and isovolumic relaxation time ( R =0.47 and 0.61, respectively; P <0.001), whereas basal rotation and longitudinal and circumferential diastolic strain rates were major determinants of increased early diastolic filling ( R =0.64, 0.79, and 0.81, respectively; P <0.001).

Conclusions—

The use of speckle tracking echocardiography gives new insights into physiological adaptive LV mechanics during incremental exercise in healthy subjects, underlining the key role of torsional mechanics. It might be useful to better understand the mechanisms of diastolic dysfunction and exercise intolerance in various pathological conditions.

Effect of cardiac resynchronization therapy on subendo- and subepicardial left ventricular twist mechanics and relation to favorable outcome

The analysis of left ventricular (LV) mechanics provides novel insights into the effects of cardiac resynchronization therapy (CRT) on LV performance. Currently, advances in speckle-tracking echocardiographic analysis have permitted the characterization of subendocardial and subepicardial LV twist. The aim of this study was to investigate the role of the acute changes in subendocardial and subepicardial LV twist for the prediction of midterm beneficial effects of CRT. A total of 84 patients with heart failure scheduled for CRT were recruited. All patients underwent echocardiography before and <48 hours after CRT implantation and at 6-month follow-up. The assessment of LV volumes, ejection fractions, and mechanical dyssynchrony (systolic dyssynchrony index) was performed with real-time 3-dimensional echocardiography. The assessment of subendocardial and subepicardial LV twist was performed with 2-dimensional speckle-tracking echocardiography. A favorable outcome was defined as the occurrence of a reduction > or =15% in LV end-systolic volume associated with an improvement of > or =1 New York Heart Association functional class at 6-month follow-up. At 6-month follow-up, 53% of the patients showed favorable outcomes. Ischemic cause of heart failure, baseline systolic dyssynchrony index, immediate improvement in the LV ejection fraction, immediate improvement in systolic dyssynchrony index, and immediate improvement in subendocardial and subepicardial LV twist were significantly related to favorable outcomes. However, in multivariate logistic regression analysis, only the immediate improvement of subepicardial LV twist was independently related to favorable outcomes (odds ratio 2.31, 95% confidence interval 1.29 to 4.15, p = 0.005). Furthermore, the immediate improvement of subepicardial LV twist had incremental value over established parameters. In conclusion, the immediate improvement of subepicardial LV twist (but not subendocardial LV twist) is independently related to favorable outcomes after CRT.

Altered in vivo left ventricular torsion and principal strains in hypothyroid rats

The twisting and untwisting motions of the left ventricle (LV) lead to efficient ejection of blood during systole and filling of the ventricle during diastole. Global LV mechanical performance is dependent on the contractile properties of cardiac myocytes; however, it is not known how changes in contractile protein expression affect the pattern and timing of LV rotation. At the myofilament level, contractile performance is largely dependent on the isoforms of myosin heavy chain (MHC) that are expressed. Therefore, in this study, we used MRI to examine the in vivo mechanical consequences of altered MHC isoform expression by comparing the contractile properties of hypothyroid rats, which expressed only the slow β-MHC isoform, and euthyroid rats, which predominantly expressed the fast α-MHC isoform. Unloaded shortening velocity (V(o)) and apparent rate constants of force development (k(tr)) were measured in the skinned ventricular myocardium isolated from euthyroid and hypothyroid hearts. Increased expression of β-MHC reduced LV torsion and fiber strain and delayed the development of peak torsion and strain during systole. Depressed in vivo mechanical performance in hypothyroid rats was related to slowed cross-bridge performance, as indicated by significantly slower V(o) and k(tr), compared with euthyroid rats. Dobutamine infusion in hypothyroid hearts produced smaller increases in torsion and strain and aberrant transmural torsion patterns, suggesting that the myocardial response to β-adrenergic stress is compromised. Thus, increased expression of β-MHC alters the pattern and decreases the magnitude of LV rotation, contributing to reduced mechanical performance during systole, especially in conditions of increased workload.

Longitudinally and circumferentially directed movements of the left ventricle studied by cardiovascular magnetic resonance phase contrast velocity mapping

OBJECTIVE

Using high resolution cardiovascular magnetic resonance (CMR), we aimed to detect new details of left ventricular (LV) systolic and diastolic function, to explain the twisting and longitudinal movements of the left ventricle.

METHODS

Using CMR phase contrast velocity mapping (also called Tissue Phase Mapping) regional wall motion patterns and longitudinally and circumferentially directed movements of the left ventricle were studied using a high temporal resolution technique in healthy male subjects (n = 14, age 23 +/- 3 years).

RESULTS

Previously undescribed systolic and diastolic motion patterns were obtained for left ventricular segments (based on the AHA segmental) and for basal, mid and apical segments. The summation of segmental motion results in a complex pattern of ventricular twisting and longitudinal motion in the normal human heart which underlies systolic and diastolic function. As viewed from the apex, the entire LV initially rotates in a counter-clockwise direction at the beginning of ventricular systole, followed by opposing clockwise rotation of the base and counter-clockwise rotation at the apex, resulting in ventricular torsion. Simultaneously, as the entire LV moves in an apical direction during systole, the base and apex move towards each other, with little net apical displacement. The reverse of these motion patterns occur in diastole.

CONCLUSION

Left ventricular function may be a consequence of the relative orientations and moments of torque of the sub-epicardial relative to the sub-endocardial myocyte layers, with influence from tethering of the heart to adjacent structures and the directional forces associated with blood flow. Understanding the complex mechanics of the left ventricle is vital to enable these techniques to be used for the evaluation of cardiac pathology.

MR investigation of the coupling between myocardial fiber architecture and cardiac contraction

Left ventricular structure has proved to be related with cardiac function; however the relation of myocardial fiber distribution with regional wall motion remains to be elucidated. In this study, both in vivo tagging and ex vivo DTI studies were performed in adult rats. LV circumferential strain, myocardium twist and myocardial fiber architecture were investigated. Results show that myocardial fiber distribution has direct relation with LV myocardium magnitude of circumferential strain and twist angle. Such integrated functional and structural analysis may provide more information for understanding the fundamental cardiac mechanics and assessment of pathological changes.