Left Ventricle Mechanics Research Articles

Instantaneous Decrease in Left Ventricular Afterload during Transcatheter Aortic Valve Implantation Results in Immediate Changes in Left Ventricular Strain.

Severe aortic stenosis causes chronic increased afterload on the left ventricle (LV) resulting in myocardial hypertrophy and ultimately dysfunction if left untreated. Transcatheter aortic valve implantation (TAVI) immediately decreases the afterload on the LV by reducing the pressure gradient through the aortic valve. In our study, we aim to evaluate immediate changes in LV mechanics using intra-procedural transesophageal echocardiography (TEE) to assess circumferential and radial strain via speckle tracking. Intra-operative TEE was performed during TAVI for 53 patients (mean age 84 ± 8 years). Two-dimensional images in the transgastric view were acquired at the level of the papillary muscle. Circumferential and radial strain was calculated using speckle tracking with Philips Qlab software. Global LV afterload was measured by calculating valvulo-arterial impedance (Zva). Immediately post-TAVI, there was a change in both radial strain rate (Pre: 0.73 ± 0.04 vs. Post: 0.88 ± 0.04 per second, P < 0.001) and circumferential strain rate (-0.53 ± 0.04 (pre) vs. -0.74 ± 0.04 (post) per second, P < 0.001). There was also an immediate improvement in circumferential global strain parameters (-14.5 ± 5% (pre) vs. -16.0 ± 4.7% (post), P < 0.05), whereas there was no significant change seen in global radial strain (15.6 ± 0.8% (pre) vs. 15.2 ± 0.9% (post), P = 0.69). No significant change was seen in LV ejection fraction (51.5 ± 14.2% (pre) vs. 52.1 ± 14.0% (post), P = 0.77). Speckle tracking using TEE images is feasible and identifies significant improvements in LV strain and strain rate immediately following TAVI that is not detected by conventional measure of LV function.

Abstract 19564: Short Term Improvement in Subtle Cardiac Dysfunction in Severely Obese Patients After Bariatric Surgery is Not Associated With Changes in Nt-pro-bnp: A Speckle Tracking Study

Background and objective: The impact of bariatric surgery on sub-clinical alteration of cardiac function assessed using speckle-tracking strain and its relationship with metabolic changes is unknown. We assessed in obese patients with normal left ventricle (LV) systolic function who underwent the biliopancreatic diversion with duodenal switch (BPD-DS); 1) prevalence of subclinical cardiac dysfunction and dyssynchrony in comparison with gender-matched subjects and, 2) the impact of bariatric surgery on myocardial function and its association with changes in NT-proBNP levels and insulin sensitivity. Methods: Prospective, observational study of the effect of BPD-DS after six months on strain, strain rate (SR) and displacement curves using a repeated measures mixed linear regression model analysis. Changes in systolic (LV end-systolic dimension, longitudinal strain) and diastolic (E/A, ESr) parameters were correlated with changes in body mass index (BMI), HOMA and NT-proBNP. Results: Thirty-eight severely obese patients (BMI 48.4±7.4 Kg/m 2 ) had decreased longitudinal strain (-17.0±2.5%) in comparison with 20 patients without obesity (-19.7±1.5%) (p&lt;0.001), which was comparable to controls after surgery (19.3±1.8%) at a mean BMI of 35.7±6 mg/m 2 . Eighteen patients (47%) had a global longitudinal strain considered clinically abnormal. Following surgery, 94% of these patients improved their LV mechanics, with normalization of their global longitudinal strain (p&lt;0.001). Changes in longitudinal strain were not related with changes in NT-proBNP or improvement in insulin sensitivity. Conclusions: There is significant subclinical cardiac dysfunction in patients with severe obesity with normal systolic function. Improvement in longitudinal strain after surgery was not explained by improved insulin sensitivity or changes in NT-proBNP.

Different responses of the myocardial contractility by layer following acute pressure unloading in severe aortic stenosis patients

The present study evaluated change in left ventricle (LV) biomechanics, layer-by-layer, following acute pressure unloading in patients with severe aortic stenosis (AS). In twenty-eight consecutive patients with severe AS who underwent transcatheter aortic valve replacement (TAVR), LV peak global longitudinal and circumferential strains of the endo-, midmyo- and epicardium were evaluated using multilayer speckle tracking echocardiography before, 1 week after, and 1 month after TAVR. Longitudinal and circumferential strains were significantly highest in the endocardium and lowest in the epicardium at baseline. At 1 month following TAVR, longitudinal strain significantly improved in all layers compared with the baseline [endocardium (%) -16.7 ± 3.8 vs. -18.6 ± 3.3, P = 0.01; mid-myocardium -14.4 ± 3.2 vs. -16.2 ± 3.5, P < 0.01; epicardium -12.4 ± 2.8 vs. -13.6 ± 2.6, P = 0.01], whereas LV ejection fraction and circumferential strain remained unchanged. Importantly, only those with LV hypertrophy demonstrated improved longitudinal strain [endocardium (%) -15.7 ± 3.0 vs. -18.7 ± 2.9, P < 0.01; mid-myocardium -13.6 ± 2.7 vs. -16.0 ± 2.5, P < 0.01; epicardium -11.8 ± 2.4 vs. -13.7 ± 2.3, P < 0.01]. The improvement in longitudinal strain was more prominent in the endocardium, which was evident even at an early time point (1 week) after TAVR. Longitudinal strain significantly improved in all three layers following acute pressure unloading, the most prominent of which was observed in the endocardium. Evaluation of multilayer strain may provide new insights into the LV mechanics in the future.

Ventricular Function Before and After Surgery for Isolated and Combined Regurgitation in the Young

Chronic mitral and aortic regurgitation (MR and AR) are associated with progressive contractile dysfunction. In the young, the risk of left ventricle (LV) dysfunction after operation for isolated and combined AR and MR is poorly defined. We aimed to compare LV mechanics in children and young adults with isolated and combined AR and MR, and identify risk factors for LV dysfunction after valve surgery. Echocardiograms from children and young adults undergoing surgery for isolated severe AR (group I, n= 14), MR (group II, n= 21), or combined AR and MR (group III, n= 13), before and up to 18 months after surgery were compared with a normal population (n= 89). Normalized measures of LV geometry and mechanics were expressed as z scores. Before surgery all groups had LV dilatation, while groups I and III had afterload elevation and LV dysfunction. After operation LV dysfunction was more common in group III than in groups I and II (11 [84.5%] vs 5 [35.7%] vs 12 [57.1%], p= 0.04). The preoperative end-systolic volume z score predicted LV dysfunction after surgery in group I and II patients (p= 0.047, area under the curve = 0.75) but not in group III, where moderate LV dysfunction was related to the preoperative stress velocity index (-2.6 with vs -1.1 without, p= 0.04). Left ventricular mechanics in combined AR and MR closely resemble those of AR. End-systolic volume predicts postoperative LV dysfunction in patients with isolated valve regurgitation, while those with combined disease were at high risk of postoperative LV dysfunction.

Evaluation of Left Ventricular Function and its Relationship With Multidimensional Grading System (BODE Index) in Patients With COPD

Cardiovascular disease (CVD) is one of the main causes of morbidity and mortality in chronic obstructive pulmonary disease (COPD) patients however data regarding left ventricle (LV) function in COPD is limited. We, in this study, aimed to evaluate the LV systolic function and its relation to BODE index in COPD patients with the utility of two-dimensional speckle tracking echocardiography (2D-STE). The study involved 125 COPD patients and 30 control subjects. All patients underwent 2D-echocardiography, pulmonary function tests and -minute walk tests. The patients were divided into four quartiles according to BODE index score. COPD patients had lower mitral annulus systolic velocity (Sm), average global longitudinal strain (GLS), average global longitudinal strain rate systolic (GLSRs), average GLSR early diastolic (GLSRe), average GLSR late diastolic (GLSRa), tricuspid annular plane systolic excursion (TAPSE) and peak systolic myocardial velocity (Sm-RV) (p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001 and p = 0.002 respectively) than control subjects. There were significant differences between BODE index quartiles in terms of Sm, average GLS and average GLSRs. Patients were divided into two groups according to median value of GLS (> –18.6 and ≤ –18.6). BODE index quartiles were found to be independent predictors of decreased GLS in multivariate logistic regression analysis (p = 0.030). Increased BODE index was associated with impaired LV mechanics in patients with COPD.

Effect of fibre orientation on diastolic mechanics of human ventricle.

Fibre orientation of myocardial wall plays a significant role in ventricular wall stress, which is assumed to be responsible for many cardiac mechanics, including ventricular remodelling, associated with heart failure. Previous studies, conducted to identify the effects of fibre orientation on left -ventricle (LV) diastolic mechanics, used only animal's myocardium properties (no human data) and therefore, may not apply for predicting human cardiac mechanics. In the present study, computational modelling of LV diastole was carried out to investigate the effects of fibre orientation on LV end diastolic pressure volume relation (EDPVR) and wall stress distribution using subject-specific in vivo passive properties of human myocardium for two human hearts. Results indicated that LV inflation increased when fibres were aligned more towards LV longitudinal axis and the effect was more notable when the fibre angle was higher in endocardium than epicardium wall. Changes in fibre angle distribution considerably altered fibre stress distribution of LV wall and the changes were significant in anterior and lateral regions of equatorial and apical locations. Furthermore, the regions of high fibre stress from midwall to endocardium were gradually confined towards endocardium with the decrease in fibre angle. Such information will be useful for future studies/diagnoses of LV mechanics in normal and pathological conditions.

Computational modelling of left-ventricular diastolic mechanics: Effect of fibre orientation and right-ventricle topology

Majority of heart failure patients who suffer from diastolic dysfunction retain normal systolic pump action. The dysfunction remodels the myocardial fibre structure of left-ventricle (LV), changing its regular diastolic behaviour. Existing LV diastolic models ignored the effects of right-ventricular (RV) deformation, resulting in inaccurate strain analysis of LV wall during diastole. This paper, for the first time, proposes a numerical approach to investigate the effect of fibre-angle distribution and RV deformation on LV diastolic mechanics. A finite element modelling of LV passive inflation was carried out, using structure-based orthotropic constitutive law. Rule-based fibre architecture was assigned on a bi-ventricular (BV) geometry constructed from non-invasive imaging of human heart. The effect of RV deformation on LV diastolic mechanics was investigated by comparing the results predicted by BV and single LV model constructed from the same image data. Results indicated an important influence of RV deformation which led to additional LV passive inflation and increase of average fibre and sheet stress–strain in LV wall during diastole. Sensitivity of LV passive mechanics to the changes in the fibre distribution was also examined. The study revealed that LV diastolic volume increased when fibres were aligned more towards LV longitudinal axis. Changes in fibre angle distribution significantly altered fibre stress–strain distribution of LV wall. The simulation results strongly suggest that patient-specific fibre structure and RV deformation play very important roles in LV diastolic mechanics and should be accounted for in computational modelling for improved understanding of the LV mechanics under normal and pathological conditions.

A Low-Order Parametric Description of Left Ventricular Kinematics

An approximate description for the deformation of the left ventricle (LV) throughout the cardiac cycle is developed in terms of three time-dependent parameters. The reference configuration, corresponding to end-diastole, is represented as a thick-walled prolate spheroid. By using prolate spheroidal coordinates, a three-parameter family of mappings is defined to represent the deformed shapes of the LV wall, while identically conserving wall volume. The three parameters represent lengthening with constant internal volume, contraction with reduction of internal volume, and torsion. Feasibility is illustrated using echocardiography data from a healthy subject. The reference configuration was defined by fitting observed points on LV endocardial and epicardial surfaces in long-axis images at end diastole. Time-courses of parameters defining LV kinematics were obtained for best fit to longitudinal strains, circumferential strains and rotations (LS, CS and R) obtained from speckle tracking echocardiography at 36 LV regions. Fitted versus echocardiography-measured CS, LS and R were compared at the LV base, mid-wall and apex at the endocardium and epicardium. The RMS deviation between fitted and measured peak strains was 0.06 (LS) and 0.08 (CS). Fitted and measured LV volume changes during contraction agreed closely. Circumferential variations in strain, which may be significant in normal and pathological hearts, are not represented here. The results demonstrate feasibility of a low-order description of the deformation field in the LV myocardium, based on echocardiographic imaging data. Such a description provides a basis for low-order models of LV mechanics and eventual real-time patient-specific analysis of LV mechanical parameters.

Mixed Aortic Valve Disease in the Young: Initial Observations

The short-term surgical results for mixed aortic valve disease (MAVD) and the long-term effects on the left ventricle (LV) are unknown. Retrospective review identified patients with at least both moderate aortic stenosis (AS) and aortic regurgitation (AR) before surgical intervention. A one-to-one comparison cohort of patients with MAVD not referred for surgical intervention was identified. The 45 patients in this study underwent surgical management for MAVD. A control group of 45 medically managed patients with MAVD also was identified. Both groups had elevated LV end-diastolic volume (EDV), elevated LV mass, a normal LV mass:volume ratio (MVR), and a normal ejection fraction. Both groups had diastolic dysfunction shown by early diastolic pulsed-Doppler mitral inflow/early diastolic tissue Doppler velocity z-score. The LV end-diastolic pressure (EDP) was correlated with age (R = 0.4; p = 0.03) and LV MVR (R = 0.4; p = 0.03) but not with AS, AR, or the score combining gradient and LV size. As shown by 6- to 12-month postoperative echocardiograms, aortic valve gradients and AR significantly improved (gradient 65 ± 17 to 28 ± 18 mmHg, p = 0.01; median regurgitation grade moderate to mild; p < 0.01), LV EDV normalized, and LV mass significantly improved (p < 0.01). Diastolic dysfunction was unchanged. Symptoms did not correlate with any measured parameter, but the preoperative symptoms resolved. In conclusion, despite diastolic dysfunction, systolic function is invariably preserved, and symptoms are not correlated with aortic valve function or LV EDP. Current surgical practice preserves LV mechanics and results in short-term improvement in valve function and symptoms.

Echocardiographic Assessment of Left Ventricular Twisting and Untwisting Rate in Normal Subjects by Tissue Doppler and Velocity Vector Imaging: Comparison of Two Methods

Background: The torsional parameters of the left ventricle (LV) are sensitive indicators of the cardiac performance. The torsion/twist of the LV is the wringing motion of the heart around its long axis created by oppositely directed apical and basal rotations and is determined by contracting myofibers in the LV wall which are arranged in opposite directions between the subendocardial and subepicardial layers. This motion is essential for regulating the LV systolic and diastolic functions. Objectives: Recent advances in echocardiography techniques have allowed for quantification of LV mechanics. The aim of the present study was to compare various LV twisting and untwisting parameters in healthy human subjects determined by velocity vector imaging (VVI) and tissue Doppler imaging (TDI) at rest. Patients and Methods: All volunteers (47 healthy subjects in two groups: 24 subjects in VVI group and 23 subjects in TDI group) underwent complete echocardiographic study, and LV torsional parameters were assessed by VVI or TDI methods. In addition, LV torsion and LV twisting/untwisting rate profiles were calculated throughout cardiac cycle. Results: Twist degree was significantly lower in the VVI group than in the TDI group (P = 0.008, r = 0.56). LV torsion was lower in the VVI group but was not significant. (P = 0.13, r = 0.38). Twisting rate (P = 0.004, r = 0.66) and untwisting rate (P = 0.0001, r = 0.61) were lower in the VVI group, but when timing of untwisting rate was normalized by systolic duration, there was no significant difference between the two groups (P = 0.41, r = 0.59). Similarly, when peak untwisting rate was normalized by LV length, there was a significant decline in normalized peak untwisting rate in the VVI group (P = 0.004, r = 0.62), but not in peak twisting rate normalized by LV length (P = 0.12, r = 0.42). Peak untwisting rate normalized by LV torsion was not statistically different between the two groups (P = 0.05, r = 0.53). Conclusions: Results suggest that these methods cannot be interchanged, and VVI showed significantly lower LV peak twist, peak twisting rate and peak untwisting rate. However, when LV twist and LV twisting rates were normalized to LV length, values were comparable for both imaging techniques.

Influence of myocardial fiber/sheet orientations on left ventricular mechanical contraction

At any point in space the material properties of the myocardium are characterized as orthotropic, that is, there are three mutually orthogonal axes along which both electrical and mechanical parameters differ. To investigate the role of spatial structural heterogeneity in an orthotropic material, electro-mechanically coupled models of the left ventricle (LV) were used. The implemented models differed in their arrangement of fibers and sheets in the myocardium, but were identical otherwise: (i) a generic homogeneous model, where a rule-based method was applied to assign fiber and sheet orientations, and (ii) a heterogeneous model, where the assignment of the orthotropic tissue structure was based on experimentally obtained fiber/sheet orientations. While both models resulted in pressure–volume loops and metrics of global mechanical function that were qualitatively and quantitatively similar and matched well with experimental data, the predicted deformations were strikingly different between these models, particularly with regard to torsion. Thus, the simulation results strongly suggest that heterogeneous structure properties play an important nonnegligible role in LV mechanics and, consequently, should be accounted for in computational models.

Why SIT Works: Normal Function Despite Typical Myofiber Pattern in Situs Inversus Totalis (SIT) Hearts Derived by Shear-induced Myofiber Reorientation

The left ventricle (LV) of mammals with Situs Solitus (SS, normal organ arrangement) displays hardly any interindividual variation in myofiber pattern and experimentally determined torsion. SS LV myofiber pattern has been suggested to result from adaptive myofiber reorientation, in turn leading to efficient pump and myofiber function. Limited data from the Situs Inversus Totalis (SIT, a complete mirror image of organ anatomy and position) LV demonstrated an essential different myofiber pattern, being normal at the apex but mirrored at the base. Considerable differences in torsion patterns in between human SIT LVs even suggest variation in myofiber pattern among SIT LVs themselves. We addressed whether different myofiber patterns in the SIT LV can be predicted by adaptive myofiber reorientation and whether they yield similar pump and myofiber function as in the SS LV. With a mathematical model of LV mechanics including shear induced myofiber reorientation, we predicted myofiber patterns of one SS and three different SIT LVs. Initial conditions for SIT were based on scarce information on the helix angle. The transverse angle was set to zero. During reorientation, a non-zero transverse angle developed, pump function increased, and myofiber function increased and became more homogeneous. Three continuous SIT structures emerged with a different location of transition between normal and mirrored myofiber orientation pattern. Predicted SIT torsion patterns matched experimentally determined ones. Pump and myofiber function in SIT and SS LVs are similar, despite essential differences in myocardial structure. SS and SIT LV structure and function may originate from same processes of adaptive myofiber reorientation.

Basic Science of Cardiac Resynchronization Therapy

Electromechanical dyssynchrony can markedly worsen heart failure (HF) morbidity and mortality, independent of traditional risk factors.1–4 Depending on the metric used, current estimates of the prevalence of dyssynchrony vary from 25–30% in patients with HF (based on QRS widening) up to 60%, based on tissue Doppler or MRI measures of dyssynchronous contraction of the left ventricle (LV).5,6 Cardiac resynchronization therapy (CRT) or biventricular pacing has emerged as a promising option to treat patients with HF and dyssynchronous contraction.7–9 The past few decades have seen the rise of pharmacotherapy, primarily through agents that antagonize the effect of excessive concentrations of circulating neurohormones, yet, HF-related morbidity and mortality remain high.3–6 Biventricular stimulation has been demonstrated to improve contractile performance in patients with mechanical dyssynchrony acutely and chronically while also prolonging long-term survival—something not yet achieved by drug therapy.10 Although the clinical and mechanical effectiveness of CRT are well described, 30% of patients do not benefit from CRT and clinical criteria to identify CRT nonresponders remain elusive8,11,12 Currently, the most widely used predictor of reverse remodeling is the presence of marked mechanical dyssynchrony before CRT, as indexed by the width of the QRS.13 Mechanical dyssynchrony seems important, yet imaging-based measures have not predicted response well14 and even improvement in dyssynchrony after initiation of CRT only weakly predicts chronic response.15 Limited understanding of the molecular mechanisms underlying reverse cardiac remodeling induced by CRT has hampered the selection of potential responders. In this review, we focus on the electrophysiological aspects and molecular networks underlying the benefits of CRT. We will review how CRT homogenizes regional differences in stress kinase signaling and electric remodeling and then review its global effect on myocyte function and its …

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 &lt;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 &lt;0.01) was correlated to enhanced systolic twist ( R =0.61; P &lt;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 &lt;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 &lt;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.

Doppler-derived deformation imaging in unsedated healthy adult dogs

Objectives To evaluate feasibility, repeatability and reproducibility (R&R) of Doppler-derived deformation imaging (DI) in healthy adult dogs. Animals, materials and methods Forty-nine dogs underwent physical examination, ECG, blood pressure measurement and echocardiography. Doppler-derived DI parameters obtained from six selected Regions of Interest (ROI) within the left ventricle (LV) were: strain (S), systolic strain rate (SSR), strain rate E wave (SRE), and strain rate A wave (SRA). The averages of the six ROIs were calculated and labeled avS, avSSR, avSRE, and avSRA. Randomly selected dogs underwent two echocardiographic studies to evaluate intraoperator ( n = 14) and interoperator ( n = 17) variability. Results DI data were obtained in 87.2% of dogs and 77.2% of ROIs. Compared to controls, avSSR was significantly reduced in Doberman Pinchers (DP) and it was increased in dogs <30 kg, compared to dogs >30 kg. The intraoperator Coefficient of Variability (CV) for some ROIs was greater than 15% but for averaged measurements it was ≤ 5.0%. Interoperator CV varied widely but were all <15% for avSSR, avS, and avSRA. Conclusions The CV for Doppler-derived DI varied widely. Averaging values from multiple ROIs improved R&R. DI may help elucidate differences in LV mechanics between canine breeds.

Direction of Preoperative Ventricular Shunting Affects Ventricular Mechanics After Tetralogy of Fallot Repair

Tetralogy of Fallot (TOF) typically results in clinical cyanosis or volume overload of the left ventricle (LV), depending on the direction and magnitude of shunting across the ventricular septal defect (VSD). The present study examines the effects of surgical TOF repair on LV mechanics and compares these changes between patients with VSD shunts that are predominantly right-to-left (R-L; "blue TOF") and those with VSD shunts that are predominantly left-to-right (L-R; "pink TOF"). Eleven patients (6 R-L and 5 L-R) 4.3 to 18.4 months old (median 7.1 months old) were studied. LV end-diastolic area (EDA) was calculated from transesophageal echocardiograms obtained during initiation and weaning of cardiopulmonary bypass. LV end-diastolic pressure was measured by micromanometer. Compliance was assessed by end-diastolic pressure-area curves. Contractility was assessed from preload recruitable stroke work by the stroke work-versus-LV EDA relation. VSD shunt direction was determined by preoperative Doppler echocardiography. Changes in LV function at the conclusion of cardiopulmonary bypass included decreased stroke area (from 6.6 +/- 0.9 to 4.1 +/- 0.4 cm(2)/m(2), P=0.012) and ejection fraction (from 55 +/- 2% to 41 +/- 3%, P<0.001). LV EDA at a common pressure in 8 patients decreased (from 10.4 +/- 1.4 to 7.6 +/- 1.2 cm(2)/m(2), P=0.003), which suggests a decrease in ventricular compliance. Additionally, the end-diastolic pressure-area curves shifted to the left in all patients. Preload recruitable stroke work decreased (from 34.8 +/- 2.4 to 21.8 +/- 2.6 mm Hg, P=0.007), which demonstrates a decrease in ventricular contractility. When separated by preoperative shunt direction, LV EDA increased in R-L patients by 0.9+/-0.5 cm(2)/m(2) postoperatively but decreased in L-R patients by 4.3 +/- 0.8 cm(2)/m(2) (P<0.001). Area ejection fraction decreased in all patients independent of shunting or change in LV EDA. LV diastolic and systolic function are depressed after TOF repair. Mechanical effects of the VSD patch and myocardial depressant effects of ischemia and reperfusion during surgery probably contribute to the observed changes in LV mechanics. Different effects of surgical repair on LV preload in pink and blue TOF also contribute to the spectrum of clinical results observed after surgery.

Disparate Patterns of Left Ventricular Mechanics Differentiate Constrictive Pericarditis From Restrictive Cardiomyopathy

The purpose of this study was to compare the longitudinal, circumferential, and radial mechanics of the left ventricle (LV) in patients with constrictive pericarditis (CP) and restrictive cardiomyopathy (RCM). Diastolic dysfunction in CP is related to epicardial tethering and pericardial constraint, whereas in RCM it is predominantly characterized by subendocardial dysfunction. Assessment of variations in longitudinal and circumferential deformation of LV might be useful to distinguish these 2 conditions. Longitudinal, radial, and circumferential mechanics of the LV were quantified by 2-dimensional speckle tracking of B-mode cardiac ultrasound images in 26 patients with CP, 19 patients with RCM, and 21 control subjects. In comparison with control subjects, patients with CP had significantly reduced circumferential strain (base; -16 +/- 6% vs. -9 +/- 6%; p < 0.016), torsion (3 +/- 1 degrees /cm vs. 1 +/- 1 degrees /cm; p < 0.016), and early diastolic apical untwisting velocities (E(r); 116 +/- 62 degrees /s vs. -36 +/- 50 degrees /s; p < 0.016), whereas longitudinal strains, displacement, and early diastolic velocities at the LV base (E(m)) were similar to control subjects. In contrast, patients with RCM showed significantly reduced longitudinal displacement (base; 14.7 +/- 2.5 cm vs. 9.8 +/- 2.8 cm; p < 0.016) and E(m) (-8.7 +/- 1.3 cm/s vs. -4.4 +/- 1.1 cm/s; p < 0.016), whereas circumferential strain and E(r) were similar to those of control subjects. For differentiation of CP from RCM, the area under the curve was significantly higher for E(m) in comparison with E(r) (0.97 vs. 0.76, respectively; p = 0.01). After pericardiectomy, there was a significant decrease in longitudinal early diastolic LV basal myocardial velocities (7.4 cm/s vs. 6.8 cm/s; p = 0.023). Circumferential strain, torsion, and E(r), however, remained unchanged. Deformation of the LV is constrained in the circumferential direction in CP and in the longitudinal direction in RCM. Subsequent early diastolic recoil of LV is also attenuated in each of the 2 directions, respectively, uniquely differentiating the abnormal diastolic restoration mechanics of the LV seen in CP and RCM.

LEFT VENTRICULAR MECHANICS IN PATIENTS WITH SYSTOLIC HEART FAILURE

The end systolic stress–strain relationship (mean end‐systolic fiber stress (MESFS) and the logarithm ln(h0/h) [h0 = wall thickness extrapolated to a “cero” ventricular volume; h = end‐systolic wall thickness]), evaluates the mechanics of the left ventricle (LV) independently of its mass and geometry. Objectives: To compare the LV mechanics in patients without and with compensated systolic heart failure (HF) using the MESFS–ln(h0/h) relationship. Methods: We perform echo Doppler studies in 37 patients with compensated HF (11 women) 65±15 years old (18–85) and 162 patients without HF (102 women) 50±16 years old (18–83). MESFS and ln(h0/h) were calculated and compared between the groups, and the resulting curve was plotted. Results. (o) without HF; with HF. Conclusion: Patients with compensated HF have higher‐end systolic MESFS and ln(h0/h). Consequently, they show a rightward shift in the end‐systolic MESFS‐ ln(h0/h) curve.

Timing of depolarization and contraction in the paced canine left ventricle: model and experiment.

For efficient pump function, contraction of the heart should be as synchronous as possible. Ventricular pacing induces asynchrony of depolarization and contraction. The degree of asynchrony depends on the position of the pacing electrode. The aim of this study was to extend an existing numerical model of electromechanics in the left ventricle (LV) to the application of ventricular pacing. With the model, the relation between pacing site and patterns of depolarization and contraction was investigated. The LV was approximated by a thick-walled ellipsoid with a realistic myofiber orientation. Propagation of the depolarization wave was described by the eikonal-diffusion equation, in which five parameters play a role: myocardial and subendocardial velocity of wave propagation along the myofiber cm and ce; myocardial and subendocardial anisotropy am and ae; and parameter k, describing the influence of wave curvature on wave velocity. Parameters cm, ae, and k were taken from literature. Parameters am and ce were estimated by fitting the model to experimental data, obtained by pacing the canine left ventricular free wall (LVFW). The best fit was found with cm = 0.75 m/s, ce = 1.3 m/s, am = 2.5, ae = 1.5, and k = 2.1 x 10(-4) m2/s. With these parameter settings, for right ventricular apex (RVA) pacing, the depolarization times were realistically simulated as also shown by the wavefronts and the time needed to activate the LVFW. The moment of depolarization was used to initiate myofiber contraction in a model of LV mechanics. For both pacing situations, mid-wall circumferential strains and onset of myofiber shortening were obtained. With a relatively simple model setup, simulated depolarization timing patterns agreed with measurements for pacing at the LVFW and RVA in an LV. Myocardial cross-fiber wave velocity is estimated to be 0.40 times the velocity along the myofiber direction (0.75 m/s). Subendocardial wave velocity is about 1.7 times faster than in the rest of the myocardium, but about 3 times slower than as found in Purkinje fibers. Furthermore, model and experiment agreed in the following respects. (1) Ventricular pacing decreased both systolic pressure and ejection fraction relative to natural sinus rhythm. (2) In early depolarized regions, early shortening was observed in the isovolumic contraction phase; in late depolarized regions, myofibers were stretched in this phase. Maps showing timing of onset of shortening were similar to previously measured maps in which wave velocity of contraction appeared similar to that of depolarization.

Torsion of the left ventricle during the ejection phase in the intact dog.

Torsion of the left ventricle (LV) is associated with rotation of the apex with respect to the base around the long axis of the LV. A mathematical model of LV mechanics, which relates torsion to transmural distribution of fibre shortening, was evaluated with two-dimensional echocardiography in nine anaesthetised closed-chest dogs. Torsion was calculated as the difference between the angles of rotation (radians) of echo-derived transverse cross-section projections of the LV obtained at the mitral valve and low papillary level, divided by the axial distance between these projections measured in a long-axis cross-section, and multiplied by the outer radius in a mid-papillary transverse projection of the LV. A shortening to torsion ratio (STR) was defined as the ratio of inner wall shortening to torsion occurring during ejection. In a series of 11 measurements, each based on frame-to-frame analysis of 15 cardiac cycles, STR was found to be 2.31 +/- 0.23 rad-1 (mean +/- SD), whereas the mathematical model predicted a STR value of 2.4 rad-1 over a wide range of preload, afterload and contractility levels. We conclude that two-dimensional echocardiography validates the presence of torsion in the normal canine left ventricle, as predicted by the model of left ventricular mechanics.