Principles of cardiovascular magnetic resonance feature tracking and echocardiographic speckle tracking for informed clinical use

Tissue tracking technology of routinely acquired cardiovascular magnetic resonance (CMR) cine acquisitions has increased the apparent ease and availability of non-invasive assessments of myocardial deformation in clinical research and practice. Its widespread availability thanks to the fact that this technology can in principle be applied on images that are part of every CMR or echocardiographic protocol. However, the two modalities are based on very different methods of image acquisition and reconstruction, each with their respective strengths and limitations. The image tracking methods applied are not necessarily directly comparable between the modalities, or with those based on dedicated CMR acquisitions for strain measurement such as tagging or displacement encoding. Here we describe the principles underlying the image tracking methods for CMR and echocardiography, and the translation of the resulting tracking estimates into parameters suited to describe myocardial mechanics. Technical limitations are presented with the objective of suggesting potential solutions that may allow informed and appropriate use in clinical applications

Analysis of the distribution and orientation of oxygenated and non-oxygenated blood in a double outlet right ventricle

Double outlet right ventricle (DORV) is a malformation of the fetal heart in utero that affects the ventricular chambers. It usually presents with a displacement of the aorta and more than half the circumference of both arterial valves in the right ventricle. A peculiar characteristic is given by an interventricular septal defect (VSD), which allows communication between the left ventricle and the right with consequent mixing of oxygenated and non-oxygenated blood inside the cavities. A crucial question in assessing the degree of severity of functional dysfunction concerns the percentage of oxygenated blood that is ejected into the primary circulation via the aorta, a result that depends on the details of the vortex flow pattern within the two ventricular chambers. This study analyzes a complete DORV case through the use of numerical simulations that allow to identify the concentrations of oxygenated and non-oxygenated blood passing through this geometry. Results show that the VSD presents a significant impact on the fluid dynamic performance of the two ventricles. The analysis of blood concentration allowed to quantify the presence of oxygenated blood ejected into the pulmonary artery and of non-oxygenated blood into the aortic artery. The analysis of this specific case aims to demonstrate how the fluid dynamics analysis of this rare malformation, properly coupled with imaging technology, can provide information that could not be obtained otherwise and that are relevant for a careful clinical management including timely therapeutic intervention

A new integrated approach to cardiac mechanics: reference values for normal left ventricle

The association between left ventricular (LV) myocardial deformation and hemodynamic forces is still mostly unexplored. The normative values and the effects of demographic and technical factors on hemodynamic forces are not known. The authors studied the association between LV myocardial deformation and hemodynamic forces in a large cohort of healthy volunteers. One-hundred seventy-six consecutive subjects (age range, 16\u201382; 51% women), with no cardiovascular risk factors or any relevant diseases, were enrolled. All subjects underwent an echo-Doppler examination. Both 2D global myocardial and endocardial longitudinal strain (GLS), circumferential strain (GCS), and the hemodynamic forces were measured with new software that enabled to calculate all these values and parameters from the three apical views. Higher LV mass index and larger LV volumes were found in males compared to females (85 \ub1 17 vs 74 \ub1 15\ua0g/m2 and 127 \ub1 28 vs 85 \ub1 18\ua0ml, p < 0.0001 respectively) while no differences of the mean values of endocardial and myocardial GLS and of myocardial GCS were found (p = ns) and higher endocardial GCS in women ( 12\ua030.6 \ub1 4.2 vs 12\ua031.8 \ub1 3.7; p = 0.05). LV longitudinal force, LV systolic longitudinal force and LV impulse were higher in men (16.2 \ub1 5.3 vs 13.2 \ub1 3.6; 25.1 \ub1 7.9 vs 19.4 \ub1 5.6 and 20.4 \ub1 7 vs 16.6 \ub1 5.2, p < 0.0001, respectively). A weak but statistically significant decline with age (p < 0.0001) was also found for these force parameters. This new integrated approach could differentiate normality from pathology by providing average deformation values and hemodynamic forces parameters, differentiated by age and gender

Combined flow-based imaging assessment of optimal cardiac resynchronization therapy pacing vector: A case report

Background: There are still many pendent issues about the effective evaluation of cardiac resynchronization therapy impact on functional mitral regurgitation. In order to reduce the intrinsic difficulties of quantification of functional mitral regurgitation itself, an automatic quantification of real-time three-dimensional full-volume color Doppler transthoracic echocardiography was proposed as a new, rapid, and accurate method for the assessment of functional mitral regurgitation severity. Recent studies suggested that images of left ventricle flow by echo-particle imaging velocimetry could be a useful marker of synchrony. Echo-particle imaging velocimetry has shown that regional anomalies of synchrony/synergy of the left ventricle are related to the alteration, reduction, or suppression of the physiological intracavitary pressure gradients. Case summary: We describe a case in which the two technologies are used in combination during acute echocardiographic optimization of left pacing vector in a 63-year-old man, Caucasian, who showed worsening heart failure symptoms a few days after an implant, and the effect of the device\u2019s optimization at 6-month follow-up. Discussion: The degree of realignment of hemodynamic forces, with quantitative analysis of the orientation of blood flow momentum (\u3c6), can represent improvement of fluid dynamics synchrony of the left ventricle, and explain, with a new deterministic parameter, the effects of cardiac resynchronization therapy on functional mitral regurgitation. Realtime three-dimensional color flow Doppler quantification is feasible and accurate for measurement of mitral inflow, left ventricular outflow stroke volumes, and functional mitral regurgitation severity. Conclusion: This clinical case offers an innovative and accurate approach for acute echocardiographic optimization of left pacing vector. It shows clinical utility of combined three-dimensional full-volume color Doppler transthoracic echocardiography/echo-particle imaging velocimetry assessment to increase response to cardiac resynchronization therapy, in terms of reduction of functional mitral regurgitation, improving fluid dynamics synchrony of the left ventricle

Richardson's pair diffusion and the stagnation point structure of turbulence

DNS and laboratory experiments show that the spatial distribution of straining stagnation points in homogeneous isotropic 3D turbulence has a fractal structure with dimension D_s = 2. In Kinematic Simulations the time exponent gamma in Richardson's law and the fractal dimension D_s are related by gamma = 6/D_s. The Richardson constant is found to be an increasing function of the number of straining stagnation points in agreement with pair duffusion occuring in bursts when pairs meet such points in the flow.Comment: 4 pages; Submitted to Phys. Rev. Let

Intraventricular flow patterns during right ventricular apical pacing

Objectives To assess differences in blood flow momentum (BFM) and kinetic energy (KE) dissipation in a model of cardiac dyssynchrony induced by electrical right ventricular apical (RVA) stimulation compared with spontaneous sinus rhythm. Methods We cross-sectionally enrolled 12 consecutive patients (mean age 74\ub18 years, 60% male, mean left ventricular ejection fraction 58%\ub16 %), within 48 hours from pacemaker (PMK) implantation. Inclusion criteria were: age>18 years, no PMK-dependency, sinus rhythm with a spontaneous narrow QRS at the ECG, preserved ejection fraction (>50%) and a low percentage of PMKstimulation (<20%). All the participants underwent a complete echocardiographic evaluation, including left ventricular strain analysis and particle image velocimetry. Results Compared with sinus rhythm, BFM shifted from 27\ub13.3 to 34\ub17.6\ub0 (p=0.016), while RVA-pacing was characterised by a 35% of increment in KE dissipation, during diastole (p=0.043) and 32% during systole (p=0.016). In the same conditions, left ventricle global longitudinal strain (LV GLS) significantly decreased from 17\ub13.3 to 11%\ub12.8% (p=0.004) during RVA-stimulation. At the multivariable analysis, BFM and diastolic KE dissipation were significantly associated with LV GLS deterioration (Beta Coeff.=0.54, 95% CI 0.07 to 1.00, p=0.034 and Beta Coeff.=0.29, 95% CI 0.02 to 0.57, p=0.049, respectively). Conclusions In RVA-stimulation, BFM impairment and KE dissipation were found to be significantly associated with LV GLS deterioration, when controlling for potential confounders. Such changes may favour the onset of cardiac remodelling and sustain heart failure