Piet Claus

Experimental Validation of a New Ultrasound Method for the Simultaneous Assessment of Radial and Longitudinal Myocardial Deformation Independent of Insonation Angle

Background— Strain and strain rate have been proposed as tools to quantify regional myocardial function. One of the major pitfalls of the current methodology is its angle dependency. To overcome this problem, we have developed a new method for the estimation of strain, independent of angle. The aim of this study was to validate this new methodology in an experimental setting using sonomicrometry. Methods and Results— In 5 open-chest sheep, ultrasound data were acquired. The new methodology was used to perform simultaneous measurements of radial and longitudinal strain in the inferolateral wall. Segment-length sonomicrometry crystals were used as the reference. After baseline acquisitions, deformation was modulated by pharmacologically changing the inotropic state of the myocardium and by inducing ischemia. Ultrasonically estimated radial and longitudinal strain were validated against sonomicrometry by means of Bland-Altman analysis and the intraclass correlation coefficient. For both strain components, good agreements were found between the ultrasound and the sonomicrometry measurements as shown by Bland-Altman statistics. The intraclass correlation coefficients were found to be 0.72 and 0.80 for the radial and longitudinal components, respectively. Conclusions— A new technique for the estimation of myocardial deformation was validated. It was shown that the current problem of angle dependency was solved and that 2 deformation components could be estimated simultaneously and accurately. Furthermore, the technique was less time-consuming, because anatomic tracking was performed automatically. This approach could potentially accelerate the clinical acceptance of ultrasound deformation imaging in cardiology.

Cardiac resynchronization therapy can reverse abnormal myocardial strain distribution in patients with heart failure and left bundle branch block.

OBJECTIVES We studied the effects of cardiac resynchronization therapy (CRT) on regional myocardial strain distribution, as determined by echocardiographic strain rate (SR) imaging. BACKGROUND Dilated hearts with left bundle branch block (LBBB) have an abnormal redistribution of myocardial fiber strain. The effects of CRT on such abnormal strain patterns are unknown. METHODS We studied 18 patients (12 males and 6 females; mean age 65 +/- 11 years [range 33 to 76 years]) with symptomatic systolic heart failure and LBBB. Doppler myocardial imaging studies were performed to acquire regional longitudinal systolic velocity (cm/s), systolic SR (s(-1)), and systolic strain (%) data from the basal and mid-segments of the septum and lateral wall before and after CRT. By convention, negative SR and strain values indicate longitudinal shortening. RESULTS Before CRT, mid-septal peak SR and peak strain were lower than in the mid-lateral wall (peak SR: -0.79 +/- 0.5 [septum] vs. -1.35 +/- 0.8 [lateral wall], p < 0.05; peak strain: -7 +/- 5 [septum] vs. -11 +/- 5 [lateral wall], p < 0.05). This relationship was reversed during CRT (peak SR: -1.35 +/- 0.8 [septum] vs. -0.93 +/- 0.6 [lateral wall], p < 0.05; peak strain: -11 +/- 6 [septum] vs. -7 +/- 6 [lateral wall], p < 0.05). Cardiac resynchronization therapy reversed the septal-lateral difference in mid-segmental peak strain from -46 +/- 94 ms (LBBB) to 17 +/- 92 ms (CRT; p < 0.05). CONCLUSIONS Left bundle branch block can lead to a significant redistribution of abnormal myocardial fiber strains. These abnormal changes in the extent and timing of septal-lateral strain relationships can be reversed by CRT. The noninvasive identification of specific abnormal but reversible strain patterns should help to improve patient selection for CRT.

Defining the Transmurality of a Chronic Myocardial Infarction by Ultrasonic Strain-Rate Imaging Implications for Identifying Intramural Viability: An Experimental Study

Background—In a correlative functional/histopathologic study, we investigated the regional deformation characteristics of both chronic nontransmural and transmural infarctions before and after a dobutamine challenge. Methods and Results—After stenosing copper-coated stent implantation to produce circumflex artery endothelial proliferation, 18 pigs were followed up for 5 weeks. Posteuthanasia histology showed 10 to have a nontransmural and 8 a transmural infarction. Eight nonstented animals served as controls. Regional radial function was monitored by measuring ultrasound-derived peak systolic strain rates (SRSYS) and systolic strains (&egr;SYS) (1) before stent implantation and (2) at 5 weeks, at baseline (bs) and during an incremental dobutamine infusion. In controls, dobutamine induced a linear increase in SRSYS (dobutamine: bs, 4.8±0.4 s−1; 20 &mgr;g · kg−1 · min−1, 9.9±0.7 s−1;P <0.0001) and an initial increase of &egr;SYS at low dose (bs, 58±5%; at 5 &mgr;g · kg−1 · min−1, 78±6%;P <0.05) but a subsequent decrease during higher infusion rates. In the nontransmural group, bs SRSYS and &egr;SYS were significantly lower than prestent values (SRSYS, 2.9±0.5 s−1 and &egr;SYS, 32±6%, P <0.05 versus prestent). During dobutamine infusion, SRSYS increased slightly at 5 &mgr;g · kg−1 · min−1 (4.7±0.6 s−1, P <0.05) but fell during higher infusion rates, whereas &egr;SYS showed no change. For nontransmural infarctions, transmural scar extension correlated closely with &egr;SYS at bs (r =0.88). For transmural infarctions, SRSYS at bs was significantly reduced and &egr;SYS was almost not measurable (SRSYS, 1.8±0.3 s−1; &egr;SYS, 3±4%). Both deformation parameters showed no further change during the incremental dobutamine infusion. Conclusions—Ultrasonic deformation values could clearly differentiate chronic nontransmural from transmural myocardial infarction. The transmural extension of the scar could be defined by the regional deformation response.

Remodeling of T-Tubules and Reduced Synchrony of Ca2+ Release in Myocytes From Chronically Ischemic Myocardium

In ventricular cardiac myocytes, T-tubule density is an important determinant of the synchrony of sarcoplasmic reticulum (SR) Ca2+ release and could be involved in the reduced SR Ca2+ release in ischemic cardiomyopathy. We therefore investigated T-tubule density and properties of SR Ca2+ release in pigs, 6 weeks after inducing severe stenosis of the circumflex coronary artery (91±3%, N=13) with myocardial infarction (8.8±2.0% of total left ventricular mass). Severe dysfunction in the infarct and adjacent myocardium was documented by magnetic resonance and Doppler myocardial velocity imaging. Myocytes isolated from the adjacent myocardium were compared with myocytes from the same region in weight-matched control pigs. T-tubule density quantified from the di-8-ANEPPS (di-8-butyl-amino-naphthyl-ethylene-pyridinium-propyl-sulfonate) sarcolemmal staining was decreased by 27±7% (P<0.05). Synchrony of SR Ca2+ release (confocal line scan images during whole-cell voltage clamp) was reduced in myocardium myocytes. Delayed release (ie, half-maximal [Ca2+]i occurring later than 20 ms) occurred at 35.5±6.4% of the scan line in myocardial infarction versus 22.7±2.5% in control pigs (P<0.05), prolonging the time to peak of the line-averaged [Ca2+]i transient (121±9 versus 102±5 ms in control pigs, P<0.05). Delayed release colocalized with regions of T-tubule rarefaction and could not be suppressed by activation of protein kinase A. The whole-cell averaged [Ca2+]i transient amplitude was reduced, whereas L-type Ca2+ current density was unchanged and SR content was increased, indicating a reduction in the gain of Ca2+-induced Ca2+ release. In conclusion, reduced T-tubule density during ischemic remodeling is associated with reduced synchrony of Ca2+ release and reduced efficiency of coupling Ca2+ influx to Ca2+ release.

Deformation imaging describes right ventricular function better than longitudinal displacement of the tricuspid ring

Aims To quantify right ventricular (RV) function in patients with chronic thromboembolic pulmonary hypertension (CTEPH) before and after pulmonary endarterectomy (PEA). Methods Out of 33 patients, 16 were evaluated clinically and with echocardiography (conventional and myocardial deformation parameters) before PEA (preop) and at 1 week, 1 month, 3 months and 6 months after PEA. RV fractional area change (RVFAC), tricuspid annular plane systolic excursion (TAPSE) as well as mid-apical and basal peak ejection strain (S) and strain rate (SR) of the RV free wall were measured. Left ventricular (LV) apical lateral wall motion was regarded as indicating changes in overall heart rocking motion (RM). Heart catheterisation was performed before, within 1 week and at 6 months after PEA. Results Clinical and haemodynamic parameters improved significantly after PEA. This correlated with the improvement in RVFAC, S and SR. TAPSE, on the other hand, showed a biphasic response (14.5 (4) mm preop, 8.5 (2.7) mm at 1 week and 11 (1.5) mm at 6 months). Changes in LV apical motion explain this finding. At baseline, TAPSE was enhanced by rocking motion of the heart as a result of the failing RV. Unloading the RV by PEA normalised the rocking motion and TAPSE decreased. Conclusions RV function of CTEPH patients improves steadily after PEA. Unlike S, SR and RVFAC, this is not reflected by TAPSE because of postoperative changes in overall heart motion. Motion independent deformation parameters (S, SR) appear superior in the accurate description of regional RV function

Quantification of regional right and left ventricular function by ultrasonic strain rate and strain indexes after surgical repair of tetralogy of fallot

The quantification of regional myocardial function in tetralogy of Fallot (TOF) by conventional M-mode and 2-dimensional echocardiography is difficult because of the complex right ventricular (RV) and altered left ventricular (LV) geometry. In 30 asymptomatic postoperative TOF patients (aged 4 to 16 years) with a low pressure in the right ventricle and with varying degrees of pulmonary regurgitation and in 30 aged-matched healthy children, the ultrasonic-derived regional deformation parameters peak systolic strain rate (SR) and systolic strain (epsilon) were acquired from ventricles and compared. In TOF RV free walls, SR, and epsilon were reduced in the basal, mid-, and apical segments and averaged -1.5 +/- 0.6 second(-1) for SR and -22 +/- 8% for epsilon, respectively (p <0.001 vs normals). Peak systolic SR of the basal RV free wall correlated significantly with the QRS duration of the electrocardiogram (r = 0.81, p <0.0001). Abnormalities in RV deformation were more marked in patients with transannular patches versus infundibular patches. In the septum there was a homogeneous reduction in SR and epsilon in the basal, mid-, and apical segments. These averaged -1.4 +/- 0.3 second(-1) for SR and -19 +/- 4% for epsilon, respectively (p <0.01 vs normals). Longitudinal SR and epsilon values of the 3 LV lateral wall segments (averaged SR = -1.6 +/- 0.4 second(-1), averaged epsilon = -20 +/- 5%; p <0.05 vs normals), and radial SR and epsilon of the LV posterior wall (SR = 3.3 +/- 0.9 second(-1); epsilon = 51 +/- 14%; p <0.05 vs normals) were significantly reduced. Thus, abnormalities in regional RV and LV systolic myocardial function in asymptomatic postoperative TOF patients were quantified by the deformation parameters SR and epsilon. RV deformation abnormalities are associated with electrical depolarization abnormalities.

Velocity and deformation imaging for the assessment of myocardial dysfunction

Recent developments in echocardiographic imaging technology and processing enabled the quantification of myocardial motion and deformation in a clinical setting. Echocardiographic strain (-rate) imaging provides a relatively easy way to study myocardial deformation. However, although (local) deformation is clearly linked to cardiac (dys-) function, it is important to understand how this information can be used in clinical practice and how specific deformation patterns should be interpreted. This review paper first discusses which issues are important to address when assessing cardiac function and how (regional) deformation and myocardial contractility are related. The use and interpretation of deformation profiles is further illustrated for some typical cardiac pathologies. The observed deformation patterns are discussed in light of the changes in regional contractility (ischemia), timing of contractile force development (LBBB and heart failure), pressure/volume overload, and assessing diastolic function.

Three-Dimensional Cardiac Strain Estimation Using Spatio–Temporal Elastic Registration of Ultrasound Images: A Feasibility Study

Current ultrasound methods for measuring myocardial strain are often limited to measurements in one or two dimensions. Cardiac motion and deformation however are truly 3-D. With the introduction of matrix transducer technology, 3-D ultrasound imaging of the heart has become feasible but suffers from low temporal and spatial resolution, making 3-D strain estimation challenging. In this paper, it is shown that automatic intensity-based spatio-temporal elastic registration of currently available 3-D volumetric ultrasound data sets can be used to measure the full 3-D strain tensor. The method was validated using simulated 3-D ultrasound data sets of the left ventricle (LV). Three types of data sets were simulated: a normal and symmetric LV with different heart rates, a more realistic asymmetric normal LV and an infarcted LV. The absolute error in the estimated displacement was between 0.47 plusmn0.23 and 1.00 plusmn0.59 mm, depending on heart rate and amount of background noise. The absolute error on the estimated strain was 9%-21% for the radial strain and 1%-4% for the longitudinal and circumferential strains. No large differences were found between the different types of data sets. The shape of the strain curves was estimated properly and the position of the infarcts could be identified correctly. Preliminary results on clinical data taken in vivo from three healthy volunteers and one patient with an apical aneurism confirmed these findings in a qualitative manner as the strain curves obtained with the proposed method have an amplitude and shape similar to what could be expected.

M 5-BRANE AND SUPERCONFORMAL (0,2) TENSOR MULTIPLET IN SIX DIMENSIONS

Abstract We present a gauge-fixed M 5-brane action: a 6-dimensional field theory of a self-interacting (0,2) tensor multiplet with 32 world-volume supersymmetries. The quadratic part of this action is shown to be invariant under rigid OSp(6,2|4) superconformal symmetry, with 16 supersymmetries and 16 special supersymmetries. We explore a deep relation between the superconformal symmetry on the world-volume of the brane and the symmetry of the near horizon anti-de Sitter infinite throat geometry of the M 5-brane in space-time.

A fast convolution-based methodology to simulate 2-Dd/3-D cardiac ultrasound images

This paper describes a fast convolution-based methodology for simulating ultrasound images in a 2-D/3-D sector format as typically used in cardiac ultrasound. The conventional convolution model is based on the assumption of a space-invariant point spread function (PSF) and typically results in linear images. These characteristics are not representative for cardiac data sets. The spatial impulse response method (IRM) has excellent accuracy in the linear domain; however, calculation time can become an issue when scatterer numbers become significant and when 3-D volumetric data sets need to be computed. As a solution to these problems, the current manuscript proposes a new convolution-based methodology in which the data sets are produced by reducing the conventional 2-D/3-D convolution model to multiple 1-D convolutions (one for each image line). As an example, simulated 2-D/3-D phantom images are presented along with their gray scale histogram statistics. In addition, the computation time is recorded and contrasted to a commonly used implementation of IRM (Field II). It is shown that COLE can produce anatomically plausible images with local Rayleigh statistics but at improved calculation time (1200 times faster than the reference method).