Effect of the Twisting Motion on the Nonunifornities of Transmyocardial Fiber Mechanics and Energy Demand A Theoretical Study

The contraction of the left ventricle (LV) is manifested by a distribution of strains and strain rates throughout the muscle thickness. Using a nested shell spheroidal model of the LV, which accounts for a fiber angle distribution from + 60°at the endocardium to ?60° at the epicardium, and the radial electrical activation pattern from the endocardium to the epicardium, it can be shown that endocardial layers undergo higher strains than the epicardial layers throughout the cardiac cycle, and higher length changes characterize the endocardial sarcomeres relative to the epicardial sarcomeres. However, the calculated nonuniformities in the sarcomeres' shortening are significantly moderated when the physiological twisting motion of the LV around the longitudinal axis is accounted for. Thus, the twisting motion of the heart is a basic mechanism by which the sarcomere function is maintained within its physiological range.     

Heart-sound processing by average and variance calculation--physiologic basic and clinical implications

A new statistical method for heart-sound processing was developed and tested on normal subjects and on patients suffering from various cardiac pathologies. The method is effective in decreasing noise and in separating heart sounds from murmurs, as well as in deriving new physiological parameters. The theory is based on the assumption that heart sounds can be classified into deterministic and nondeterministic sounds. The processing results in a very significant attenuation of strong murmurs, while the deterministic events, such as SI-S4, are only slightly affected. The method includes dividing the heart-sound signal into a set of repetitive signals (ensemble) according to the trigger selected to be the peak of the ECG R-wave. The variability of the time elapsed from the trigger to the evoked sound is defined as the jitter. The average and variance functions are calculated from the ensemble. Calculation of the heartsound jitter from the average and variance functions shows a jitter of 5.5 ms ±2.6 ms for Si, and 8.2 ms ±3.3 ms for S2. The jitter, which is an objective parameter of the trigger-response linkage, can be used experimentally to clarify some of the cardiac electromechanical mechanisms, and it may have diagnostic value.     

Identifying and tracking a guide wire in the coronary arteriesduring angioplasty from X-ray images

During angioplasty, a guide wire (GW) is routinely placed in the coronary artery. Balloon inflation during angioplasty causes transient occlusion of the coronary artery and regional dysfunction. Thus, it is of major importance to monitor myocardial function, which may be impaired during this period. Since the GW moves with the coronary arteries, information regarding myocardial function can potentially be extracted from the GW motion. An algorithm is suggested which is a step toward such monitoring. The algorithm presented is a semiautomatic procedure for identifying and tracking the GW using specific characteristics of the GW. This algorithm is based on working in limited active windows. A preprocessing stage which enhances the GW by the use of a modified Laplacian filter or a modified Marr-Hildreth filter is introduced. The second stage of the algorithm is the tracking of the GW, which is based on fitting a second-degree polynom to the GW using the Dough transform in each window. To further improve the results further modifications of the basic algorithms that were taken. A single set of parameters, which enabled good tracking for a large number of images taken during angioplasty, was fitted to the final algorithm     

Prospective motion correction of X-ray images for coronary interventions

A method for prospective motion correction of X-ray imaging of the heart is presented. A 3D + t coronary model is reconstructed from a biplane coronary angiogram obtained during free breathing. The deformation field is parameterized by cardiac and respiratory phase, which enables the estimation of the state of the arteries at any phase of the cardiac-respiratory cycle. The motion of the three-dimensional (3-D) coronary model is projected onto the image planes and used to compute a dewarping function for motion correcting the images. The use of a 3-D coronary model facilitates motion correction of images acquired with the X-ray system at arbitrary orientations. The performance of the algorithm was measured by tracking the motion of selected left coronary landmarks using a template matching cross-correlation. In three patients, we motion corrected the same images used to construct their 3D + t coronary model. In this best case scenario, the algorithm reduced the motion of the landmarks by 84%-85%, from mean RMS displacements of 12.8-14.6 pixels to 2.1-2.2 pixels. Prospective motion correction was tested in five patients by building the coronary model from one dataset, and correcting a second dataset. The patient's cardiac and respiratory phase are monitored and used to calculate the appropriate correction parameters. The results showed a 48%-63% reduction in the motion of the landmarks, from a mean RMS displacement of 11.5-13.6 pixels to 4.4-7.1 pixels.     

Quantitative sorting of normal and abnormal coronary flow wave formshapes

The normal phasic flow wave form in an epicardial coronary artery has a distinct characteristic shape, which reflects the interaction between the coronary tree, myocardial function and hemodynamic conditions. Since clinical measurements of phasic coronary wave forms are becoming available, determination of abnormal coronary flow wave forms is important. The authors suggest here an objective and automatic method to discriminate between normal and abnormal flow wave forms based on the Karhunen-Loeve transform (KLT), and experimentally test it. The normal flow domain was represented by the resting flow waves measured in the left anterior descending arteries in 31 anesthetized dogs. The abnormal flow conditions, imposed and tested experimentally, were varying stenosis severity and severely reduced left ventricular pressure. In addition, the effects of reactive hyperemia on the shape of the flow were examined. The sorting index was based on the mean-square error (MSE) calculated for each flow signal based on a truncated KLT expansion. The results show excellent discrimination between the normal and the abnormal groups. During reactive hyperemia, however, MSE did not change significantly. These results indicate that the shape of abnormal coronary flow wave forms can be identified and discriminated from normal wave forms     

Effects of load manipulations, heart rate, and contractility on left ventricular apical rotation. An experimental study in anesthetized dogs

BACKGROUND: Left ventricular twist or torsion has been defined as the counterclockwise rotation of the ventricular apex with respect to the base during systole. We have recently shown that since base rotation is minimal, measurement of apex rotation reflects the dynamics of left ventricular (LV) twist. Since the mechanisms by which load and contractility affect twist are controversial, we aimed to determine the relation between apex rotation and volume, contractility, and heart rate under conditions in which dimensions and pressures were accurately measured. METHODS AND RESULTS: Using our optical device coupled to the LV apex, apex rotation was recorded simultaneously with LV pressure, ECG, LV segment length, and minor-axis diameters (sonomicrometry) in 12 open-chest dogs. Using vena caval occlusion and volume loading, a linear end-diastolic (ED) relation between apex rotation and LV area index was obtained (slope, 0.61 +/- 0.06 degrees/percent change; intercept, -60.1 +/- 6.2 degrees; n = 10) that differed from the end-systolic (ES) relation (slope, 1.36 +/- 0.27 degree/percent change; intercept, -132.5 +/- 24.9 degrees; P < .005). With changes in contractility, afterload, or heart rate, for both ED and ES the apex rotation-volume points fell within the range of the relations established by changing preload, suggesting that volume is the major determinant of twist. Vena caval occlusion (preload and afterload decrease) caused an increase in amplitude of apex rotation, with maximal apex rotation occurring earlier in ejection. In contrast, acute volume loading (predominant preload increase) caused a small decrease in the amplitude of apex rotation, and twist relaxation was delayed into the isovolumic relaxation period. Likewise, with single-beat aortic occlusion (increased afterload), there was a slight decrease in the amplitude of apex rotation, and maximal apex rotation was delayed into the isovolumic relaxation period. Paired pacing (increased contractility) increased the total amplitude of apex rotation by 42% and caused a delay in untwisting until the end of the isovolumic relaxation period. An increase in heart rate over 150 beats per minute resulted in a significant decrease in the amplitude of apex rotation with a similar delay of twist relaxation into the isovolumic relaxation period. CONCLUSIONS: The effects of load, contractility, and heart rate manipulations on LV twist as measured throughout the cardiac cycle by the optical apex rotation method are manifested by changes in both the amplitude and dynamics of torsion. LV twist at ED and ES is primarily a function of volume; this relation appears to be unaltered by heart rate, afterload, and contractility. Whereas decreased load caused early untwisting, increases in preload, afterload, heart rate, and contractility caused a consistent pattern of delay in twist relaxation.     

Quantitative characterization and sorting of three-dimensional geometries: application to left ventricles in vivo

A procedure for automatic sorting of three-dimensional (3-D) shapes is proposed. The procedure is applied to sort into normal and abnormal categories, human left ventricles (LV) using in vivo data from 19 subjects (ten normal and nine abnormal LV's) studied by ultrafast tomography (Cine-CT). The procedure starts by utilizing a vector in a helical coordinate system to describe the spatial geometry of each individual LV cavity. This individual vector is then anatomically aligned and normalized to eliminate effects due to size, yielding a dimensionless vector, denoted as "geometrical cardiogram" (GCG). The GCG characterizes the instantaneous 3-D geometrical information of the individual LV. For the group of healthy subjects, the Karhunen-Loeve Transform (KLT) is then applied to compress the geometric information contained in their individuals' GCG vectors, at end diastole (ED) and end systole (ES), and yield a unique set of basis vectors. The "normal shape domain" is next defined as a truncated set of the KLT basis vectors from which a normal GCG can be reconstructed with a mean squared error (MSE) smaller than a defined threshold. The calculated MSE of any individual GCG reconstructed in this domain is then used as a criterion for sorting the 3-D shapes. Hearts which yield MSE greater than the threshold are considered abnormal. When applied to the study group of 19 subjects a significant difference (p less than 0.0001) between the MSE values obtained for the normal LV's, and those obtained for the abnormal LV's was detected, thus leading to a successful sorting of all the studied LV's. Finally, the KLT is applied to yield a compact representation of the 3-D geometry of any LV (normal or abnormal).