Novel Noninvasive Assessment of Pulmonary Arterial Stiffness Using Velocity Transfer Function.

Background Pulmonary artery ( PA ) stiffness is associated with increased pulmonary vascular resistance ( PVR ). PA stiffness is accurately described by invasive PA impedance because it considers pulsatile blood flow through elastic PA s. We hypothesized that PA stiffness and impedance could be evaluated noninvasively by PA velocity transfer function ( VTF ), calculated as a ratio of the frequency spectra of output/input mean velocity profiles in PA s. Methods and Results In 20 participants (55±19 years, 14 women) undergoing clinically indicated right-sided heart catheterization, comprehensive phase-contrast and cine-cardiac magnetic resonance imaging was performed to calculate PA VTF , along with right ventricular mass and function. PA impedance was measured as a ratio of frequency spectra of invasive PA pressure and echocardiographically derived PA flow waveforms. Mean PA pressure was 29.5±13.6 mm Hg, and PVR was 3.5±2.8 Wood units. A mixed-effects model showed VTF was significantly associated with PA impedance independent of elevation in pulmonary capillary wedge pressure ( P=0.005). The mean of higher frequency moduli of VTF correlated with PVR (ρ=0.63; P=0.003) and discriminated subjects with low (n=10) versus elevated PVR (≥2.5 Wood units, n=10), with an area under the curve of 0.95, similar to discrimination by impedance (area under the curve=0.93). VTF had a strong inverse association with right ventricular ejection fraction (ρ=-0.73; P<0.001) and a significant positive correlation with right ventricular mass index (ρ=0.51; P=0.02). Conclusions VTF , a novel right ventricular- PA axis coupling parameter, is a surrogate for PA impedance with the potential to assess PA stiffness and elevation in PVR noninvasively and reliably using cardiac magnetic resonance imaging.

Importance of three-dimensional geometric analysis in the assessment of the athlete's heart.

How the left ventricle remodels in response to a high-volume stimulus is important in evaluating the endurance athlete's heart. Marathoners and patients with isolated, moderate chronic compensated mitral regurgitation (MR) represent physiologic and pathologic forms of eccentric left ventricular (LV) remodeling in response to intermittent and chronic volume overload, respectively. Thus, in this study, magnetic resonance imaging with tissue tagging and 3-dimensional data analysis at rest were performed in 19 marathoners (mean age 39 ± 10 years, 47% women), 17 patients with isolated MR without coronary artery disease or medical therapy (mean age 46 ± 5 years, 53% women), and 24 controls (mean age 45 ± 8 years, 50% women). Marathoners and patients with MR had approximately 35% greater LV end-diastolic volume indexes, approximately 50% greater end-systolic volume indexes, and approximately 34% greater LV stroke volume indexes (p <0.0001) compared to controls. However, marathoners' hearts had increased long-axis length, while those of patients with MR did not differ from the hearts of controls. The hearts of patients with MR had greater LV global and apex sphericity compared to those of marathoners and controls (p <0.0001). Marathoners had normal LV mass/volume ratios and wall thicknesses, whereas these were significantly decreased in the MR group. In marathoners, the baseline LV work rate was similar to that in controls and higher in patients with MR compared to controls. In conclusion, marathoners' hearts achieve elevated stroke volume at rest with adherence to an elliptical shape defined by 3-dimensional geometry and mass/volume ratio. Thus, a comprehensive evaluation of LV geometry and mass/volume ratio may be important in the evaluation of the athlete's heart.

A dual propagation contours technique for semi-automated assessment of systolic and diastolic cardiac function by CMR.

BACKGROUND: Although cardiovascular magnetic resonance (CMR) is frequently performed to measure accurate LV volumes and ejection fractions, LV volume-time curves (VTC) derived ejection and filling rates are not routinely calculated due to lack of robust LV segmentation techniques. VTC derived peak filling rates can be used to accurately assess LV diastolic function, an important clinical parameter. We developed a novel geometry-independent dual-contour propagation technique, making use of LV endocardial contours manually drawn at end systole and end diastole, to compute VTC and measured LV ejection and filling rates in hypertensive patients and normal volunteers. METHODS: 39 normal volunteers and 49 hypertensive patients underwent CMR. LV contours were manually drawn on all time frames in 18 normal volunteers. The dual-contour propagation algorithm was used to propagate contours throughout the cardiac cycle. The results were compared to those obtained with single-contour propagation (using either end-diastolic or end-systolic contours) and commercially available software. We then used the dual-contour propagation technique to measure peak ejection rate (PER) and peak early diastolic and late diastolic filling rates (ePFR and aPFR) in all normal volunteers and hypertensive patients. RESULTS: Compared to single-contour propagation methods and the commercial method, VTC by dual-contour propagation showed significantly better agreement with manually-derived VTC. Ejection and filling rates by dual-contour propagation agreed with manual (dual-contour - manual PER: -0.12 +/- 0.08; ePFR: -0.07 +/- 0.07; aPFR: 0.06 +/- 0.03 EDV/s, all P = NS). However, the time for the manual method was approximately 4 hours per study versus approximately 7 minutes for dual-contour propagation. LV systolic function measured by LVEF and PER did not differ between normal volunteers and hypertensive patients. However, ePFR was lower in hypertensive patients vs. normal volunteers, while aPFR was higher, indicative of altered diastolic filling rates in hypertensive patients. CONCLUSION: Dual-propagated contours can accurately measure both systolic and diastolic volumetric indices that can be applied in a routine clinical CMR environment. With dual-contour propagation, the user interaction that is routinely performed to measure LVEF is leveraged to obtain additional clinically relevant parameters.

Left ventricular motion reconstruction with a prolate spheroidal B-spline model.

Tagged cardiac magnetic resonance (MR) imaging can non-invasively image deformation of the left ventricular (LV) wall. Three-dimensional (3D) analysis of tag data requires fitting a deformation model to tag lines in the image data. In this paper, we present a 3D myocardial displacement and strain reconstruction method based on a B-spline deformation model defined in prolate spheroidal coordinates, which more closely matches the shape of the LV wall than existing Cartesian or cylindrical coordinate models. The prolate spheroidal B-spline (PSB) deformation model also enforces smoothness across and can compute strain at the apex. The PSB reconstruction algorithm was evaluated on a previously published data set to allow head-to-head comparison of the PSB model with existing LV deformation reconstruction methods. We conclude that the PSB method can accurately reconstruct deformation and strain in the LV wall from tagged MR images and has several advantages relative to existing techniques.