Probing cardiomyocyte mobility with multi-phase cardiac diffusion tensor MRI

Purpose Cardiomyocyte organization and performance underlie cardiac function, but the in vivo mobility of these cells during contraction and filling remains difficult to probe. Herein, a novel trigger delay (TD) scout sequence was used to acquire high in-plane resolution (1.6 mm) Spin-Echo (SE) cardiac diffusion tensor imaging (cDTI) at three distinct cardiac phases. The objective was to characterize cardiomyocyte organization and mobility throughout the cardiac cycle in healthy volunteers. Materials and methods Nine healthy volunteers were imaged with cDTI at three distinct cardiac phases (early systole, late systole, and diastasis). The sequence used a free-breathing Spin-Echo (SE) cDTI protocol (b-values = 350s/mm2, twelve diffusion encoding directions, eight repetitions) to acquire high-resolution images (1.6x1.6x8mm3) at 3T in ~7 minutes/cardiac phase. Helix Angle (HA), Helix Angle Range (HAR), E2 angle (E2A), Transverse Angle (TA), Mean Diffusivity (MD), diffusion tensor eigenvalues (λ1-2-3), and Fractional Anisotropy (FA) in the left ventricle (LV) were characterized. Results Images from the patient-specific TD scout sequence demonstrated that SE cDTI acquisition was possible at early systole, late systole, and diastasis in 78%, 100% and 67% of the cases, respectively. At the mid-ventricular level, mobility (reported as median [IQR]) was observed in HAR between early systole and late systole (76.9 [72.6, 80.5]° vs 96.6 [85.9, 100.3]°, p<0.001). E2A also changed significantly between early systole, late systole, and diastasis (27.7 [20.8, 35.1]° vs 45.2 [42.1, 49]° vs 20.7 [16.6, 26.4]°, p<0.001). Conclusion We demonstrate that it is possible to probe cardiomyocyte mobility using multi-phase and high resolution cDTI. In healthy volunteers, aggregate cardiomyocytes re-orient themselves more longitudinally during contraction, while cardiomyocyte sheetlets tilt radially during wall thickening. These observations provide new insights into the three-dimensional mobility of myocardial microstructure during systolic contraction.

The mechanism of mitral regurgitant jets identified by 3-dimensional transesophageal echocardiography

This study is a case report, which presents a case of severe mitral regurgitation in a 77-year-old man. Two-dimensional transesophageal echocardiography (TEE), regurgitant jets directed anteriorly in early systole and centrally to laterally in late systole were seen, while three-dimensional TEE showed a flail posterior middle scallop not only angulated centrally, but also laterally, which provided insight into the mechanism of mitral regurgitant jet direction. This case demonstrates the clinical usefulness of 3-dimensional TEE for identifying the mechanism of mitral regurgitant jets.The institution where the figures and the videos were recorded: Division of Cardiology, Mazankowski Alberta Heart Institute, University of Alberta Hospital, Edmonton, Alberta, Canada.

Abstract 15137: Vector Flow Mapping is a Novel Useful Technique in Assessing Inertia Force of Late Systolic Aortic Flow and Left Ventricular Early Diastolic Function

Background: We previously reported that the inertia force (IF) of blood flowing out of left ventricle (LV) during late-systole produces greater LV elastic recoil force and brings faster LV relaxation. Vector flow mapping (VFM TM , Hitachi-Aloka) enables us to see blood flow velocity vectors that are generated from conventional color Doppler imaging data at any phase of cardiac cycle without angle dependency. Using VFM, kinetic energy (KE) of ejecting blood flow during systole at the LV outflow tract (LVOT) can be obtained. Thus, we investigated whether the KE obtained at the LVOT during late systole (KE-ls) had any relations with the IF and invasively obtained LV function parameters. Method: Study subjects were 33 patients who underwent diagnostic cardiac catheterization and echocardiographic examination on the same day. Color Doppler images were acquired in the apical 3-chamber view. The frame rate ranged was from 40 to 51 frames per minute. Data analyses were performed offline using the commercially available software (DAS-RS1 TM, Hitachi-Aloka). A data sampling area was set at the level just below the aortic valve in the LVOT. The KE-ls was computed as the sum of KE values computed in frame by frame basis during late-systole; late-systole was defined as the latter one-third of ejecting time. LV pressure wave was obtained using a catheter-tipped micromanometer, and then, the first derivative of LV pressure (dP/dt) and a time constant τ of LV pressure decay during isovolumic relaxation were calculated. From LV pressure-dP/dt relationships (phase loop), the IF was determined. Results: A significant positive correlation was observed between the KE-ls and the IF (r=0.79, p<0.0001). The log transformed KE-ls had significant correlations with both peak negative dP/dt (r=0.53, p<0.01) and the time constant τ (r=-0.67, p<0.0001). Conclusion: VFM is a new useful technique to see blood flow in the LV chamber. Noninvasively obtained KE-ls using VFM, which may be a noninvasive surrogate for the IF, has significant correlations with the parameters of LV relaxation.

Abstract 4734: Echodynamography is a Novel Useful Technique in Assessing Inertia Force of Late Systolic Aortic Flow and Left Ventricular Early Diastolic Function

We previously reported that the inertia force (IF) of the blood flowing out of left ventricle (LV) during late systolic phase produces greater LV elastic recoil force and brings faster LV relaxation. Echodynamography (ALOKA) is a novel technique that enables us to obtain the flow velocity vector from conventional color Doppler velocity data on the range of interest at any phase of cardiac cycle without angle dependency. We investigated whether the flow velocity vector obtained at LV outflow tract (LVOT) in late systole had a relation with IF and invasively obtained LV relaxation parameters. Method: Study subjects were consecutive 26 patients who underwent diagnostic cardiac catheterization and conventional color Doppler imaging on the same day. Color Doppler image was acquired in the apical 3-chamber view. The analyses for flow velocity vector were performed offline using an echo image analyzer. The late systolic velocity of the blood flowing was obtained as an average value of the L VOT (V LVOT −late systole). LV pressure was obtained using a catheter-tipped micromanometer. From the recorded pressure waves, first derivative of LV pressure (dP/dt) and a time constant τ of LV pressure decay during isovolumic relaxation were calculated. From LV pressure-dP/dt relationships (phase loop), IF was determined. Results: A significant positive correlation was observed between the V LVOT -late systole and IF (r=0.75, p<0.0001). The V LVOT -late systole also had significant correlations both with peak negative dP/dt (r=0.49, p<0.05) and the time constant τ (r=−0.70, p<0.0001). Conclusion: This study indicates that the V LVOT -late systole, which may be a noninvasive substitute for IF, has significant correlations with the parameters of LV relaxation. Echodynamography is a new useful technique to estimate LV early diastolic function.

Direct and series transmission of left atrial pressure perturbations to the pulmonary artery: a study using wave-intensity analysis

Pressure waves are thought to travel from the left atrium (LA) to the pulmonary artery (PA) only retrogradely, via the vasculature. In seven anesthetized open-chest dogs, a balloon was placed in the LA, which was rapidly inflated and deflated during diastole, early systole, and late systole. High-fidelity pressures were measured within and around the heart. Measurements were made at low volume [LoV; left ventricular end-diastolic pressure (LVEDP) = 5–9 mmHg], high volume (HiV; LVEDP = 16–19 mmHg), and HiV with the pericardium removed. Wave-intensity analysis demonstrated that, except during late systole, balloon inflation created forward-going PA compression waves that were transmitted directly through the heart without measurable delay; backward PA compression waves were transmitted in-series through the pulmonary vasculature and arrived after delays of 90 ± 3 ms (HiV) and 103 ± 5 ms (LoV; P < 0.05). Direct transmission was greater during diastole, and both direct and series transmission increased with volume loading. Pressure waves from the LA arrive in the PA by two distinct routes: rapidly and directly through the heart and delayed and in-series through the pulmonary vasculature.

Novel method to estimate ventricular contractility using intraventricular pulse wave velocity

We developed a novel technique for estimating ventricular contractility using intraventricular pulse wave velocity (PWV). In eight isolated, cross-circulated canine hearts, we used a fast servo pump to inject a volume pulse into the base of the left ventricular chamber at late diastole and at late systole. We measured the transit time of the volume pulse wave as it traversed the distance from base to apex and calculated the intraventricular PWV. The intraventricular PWV increased from diastole (2.3 ± 0.4 m/s) to systole (11.7 ± 2.4 m/s, P < 0.0001 vs. diastole). The square of the intraventricular PWV at late systole correlated linearly with the left ventricular end-systolic elastance ( r = 0.939, P < 0.0001) and with the end-systolic Young's modulus ( r = 0.901, P < 0.0001). Moreover, the intraventricular PWV was insensitive to preload. We conclude that the intraventricular PWV at late systole reflects left ventricular end-systolic elastance reasonably well. The fact that estimation of PWV does not require volume measurement or load manipulation makes this technique an attractive means of assessing ventricular contractility.

Configuration of right ventricular pressure curves and infundibular stenosis after balloon pulmonary valvoplasty

We evaluated the clinical significance of the configuration of right ventricular pressure curves after balloon valvoplasty in 35 patients with pulmonary valvar stenosis. Right ventricular pressures were measured with a fluidfilled catheter. We divided the subjects into two groups according to the pressure curves seen after balloon valvoplasty. In eight patients, two peaks were found in the curves, with the higher peak occurring at late systole. The remaining 27 patients had a single peak observed during early to mid systole. In all patients in the group with a single peak, the ratio of ventricular pressures decreased by more than half, and no residual narrowing was seen in right ventricular outflow tract, the diameter after valvoplasty increasing by more than half over the diameter before the procedure. In contrast, in five of eight patients in the group with double peaks in the pressure curves, the ratio between ventricular pressures remained higher than 0.5, and the diameter of the right ventricular infundibulum was reduced to less than half the diameter prior to balloon valvoplasty. In three of these patients with double peaked pressure contours, to whom propranolol was administered intravenously, the pressure configuration changed to one with a single peak and the ventricular pressure ratio fell to below 0.5. The degree of obstruction of the right ventricular infundibulum also decreased. These data suggest that a high right ventricular pressure and two peaks in the pressure curve with the higher peak at late systole after balloon valvoplasty indicate, first, the presence of a significant narrowing in the right ventricular outflow tract and, second, effective balloon valvoplasty.

Normal Left Ventricular Wall Motion Measured with Two-Dimensional Myocardial Tagging

Using a myocardial tagging technique, normal left ventricular wall motion was studied in 3 true short axis views and a double oblique 4-chamber view in 14 and 11 volunteers, respectively. Three orthogonal directions of left ventricular motion were observed throughout the systole; a concentric contraction towards the center of the left ventricle, a motion of the base of the heart towards the apex, and a rotation of the left ventricle around its long axis. The direction of left ventricular rotation changed from early systole to late systole. The base and middle levels of the left ventricle rotated counterclockwise (CCW) at early systole and clockwise (CW) at late systole, whereas the apex of the heart rotated CW at early systole and CCW at late systole. The different directions of the rotation of base and apex resulted in a myocardial twisting that changed direction from early to late systole. We conclude that MR imaging with myocardial tagging is a method that can be used to study normal left ventricular wall motion, and that is promising for future use in patient groups.