Magnetic resonance tissue phase mapping of myocardial motion: new insight in age and gender

Cold ischaemic time and time after transplantation alter segmental myocardial velocities after heart transplantation

OBJECTIVES

The aim of this study was to investigate changes in segmental, three-directional left ventricular (LV) velocities in patients after heart transplantation (Tx).

METHODS

Magnetic resonance tissue phase mapping was used to assess myocardial velocities in patients after Tx (n = 27) with normal LV ejection fraction (63 ± 5%) and those without signs of rejection. Regional wall motion and dyssynchrony were analysed in relation to cold ischaemic time (150 ± 57 min, median = 154 min), age of the donor heart (35 ± 13 years, median = 29 years), time after transplantation (32 ± 26 months, median = 31 months) and global LV morphology and function.

RESULTS

Segmental myocardial velocities were significantly altered in patients with cold ischaemic times >155 min resulting in an increase in peak systolic radial velocities (2 of 16 segments, P = 0.03-0.04) and reduced segmental diastolic long-axis velocities (5 of 16 segments, P = 0.01-0.04). Time after transplantation (n = 8 patients <12 months after Tx vs n = 19 >12 months) had a significant influence on systolic radial velocities (increased in 2 of 16 segments, P = 0.01-0.04) and diastolic long-axis velocities (reduced in 5 of 16 segments, P = 0.02-0.04). Correlation analysis and multiple regression revealed significant relationships of cold ischaemic time (R = -0.384, P = 0.048), the donor heart's age (β= 0.9, P = 0.01) and time from transplantation (β= -0.36, P = 0.03) with long-axis diastolic dyssynchrony.

CONCLUSIONS

Time after transplantation and cold ischaemic time strongly affect segmental systolic and diastolic motion in patients after Tx. The understanding of alterations in regional LV motion in the transplanted heart under stable conditions is essential in order to utilize this methodology in the future as a potentially non-invasive means of diagnosing transplant rejection.

Spatial correlation of action potential duration and diastolic dysfunction in transgenic and drug-induced LQT2 rabbits

BACKGROUND

Enhanced dispersion of action potential duration (APD) is a major contributor to long QT syndrome (LQTS)-related arrhythmias.

OBJECTIVE

To investigate spatial correlations of regional heterogeneities in cardiac repolarization and mechanical function in LQTS.

METHODS

Female transgenic LQTS type 2 (LQT2; n = 11) and wild-type littermate control (LMC) rabbits (n = 9 without E4031 and n = 10 with E4031) were subjected to phase contrast magnetic resonance imaging to assess regional myocardial velocities. In the same rabbits' hearts, monophasic APDs were assessed in corresponding segments.

RESULTS

In LQT2 and E4031-treated rabbits, APD was longer in all left ventricular segments (P < .01) and APD dispersion was greater than that in LMC rabbits (P < .01). In diastole, peak radial velocities (Vr) were reduced in LQT2 and E4031-treated compared to LMC rabbits in LV base and mid (LQT2: -3.36 ± 0.4 cm/s, P < .01; E4031-treated: -3.24 ± 0.6 cm/s, P < .0001; LMC: -4.42 ± 0.5 cm/s), indicating an impaired diastolic function. Regionally heterogeneous diastolic Vr correlated with APD (LQT2: correlation coefficient [CC] 0.38, P = .01; E4031-treated: CC 0.42, P < .05). Time-to-diastolic peak Vr were prolonged in LQT2 rabbits (LQT2: 196.8 ± 2.9 ms, P < .001; E4031-treated: 199.5 ± 2.2 ms, P < .0001, LMC 183.1 ± 1.5), indicating a prolonged contraction duration. Moreover, in transgenic LQT2 rabbits, diastolic time-to-diastolic peak Vr correlated with APD (CC 0.47, P = .001). In systole, peak Vr were reduced in LQT2 and E4031-treated rabbits (P < .01) but longitudinal velocities or ejection fraction did not differ. Finally, random forest machine learning algorithms enabled a differentiation between LQT2, E4031-treated, and LMC rabbits solely based on "mechanical" magnetic resonance imaging data.

CONCLUSIONS

The prolongation of APD led to impaired diastolic and systolic function in transgenic and drug-induced LQT2 rabbits. APD correlated with regional diastolic dysfunction, indicating that LQTS is not purely an electrical but an electromechanical disorder.

Efficient and reproducible high resolution spiral myocardial phase velocity mapping of the entire cardiac cycle

BACKGROUND

Three-directional phase velocity mapping (PVM) is capable of measuring longitudinal, radial and circumferential regional myocardial velocities. Current techniques use Cartesian k-space coverage and navigator-gated high spatial and high temporal resolution acquisitions are long. In addition, prospective ECG-gating means that analysis of the full cardiac cycle is not possible. The aim of this study is to develop a high temporal and high spatial resolution PVM technique using efficient spiral k-space coverage and retrospective ECG-gating. Detailed analysis of regional motion over the entire cardiac cycle, including atrial systole for the first time using MR, is presented in 10 healthy volunteers together with a comprehensive assessment of reproducibility.

METHODS

A navigator-gated high temporal (21 ms) and spatial (1.4 × 1.4 mm) resolution spiral PVM sequence was developed, acquiring three-directional velocities in 53 heartbeats (100% respiratory-gating efficiency). Basal, mid and apical short-axis slices were acquired in 10 healthy volunteers on two occasions. Regional and transmural early systolic, early diastolic and atrial systolic peak longitudinal, radial and circumferential velocities were measured, together with the times to those peaks (TTPs). Reproducibilities were determined as mean ± SD of the signed differences between measurements made from acquisitions performed on the two days.

RESULTS

All slices were acquired in all volunteers on both occasions with good image quality. The high temporal resolution allowed consistent detection of fine features of motion, while the high spatial resolution allowed the detection of statistically significant regional and transmural differences in motion. Colour plots showing the regional variations in velocity over the entire cardiac cycle enable rapid interpretation of the regional motion within any given slice. The reproducibility of peak velocities was high with the reproducibility of early systolic, early diastolic and atrial systolic peak radial velocities in the mid slice (for example) being -0.01 ± 0.36, 0.20 ± 0.56 and 0.14 ± 0.42 cm/s respectively. Reproducibility of the corresponding TTP values, when normalised to a fixed systolic and diastolic length, was also high (-13.8 ± 27.4, 1.3 ± 21.3 and 3.0 ± 10.9 ms for early systolic, early diastolic and atrial systolic respectively).

CONCLUSIONS

Retrospectively gated spiral PVM is an efficient and reproducible method of acquiring 3-directional, high resolution velocity data throughout the entire cardiac cycle, including atrial systole.

Variability and homogeneity of cardiovascular magnetic resonance myocardial T2-mapping in volunteers compared to patients with edema

BACKGROUND

The aim of the study was to test the reproducibility and variability of myocardial T2 mapping in relation to sequence type and spatial orientation in a large group of healthy volunteers. For control T2 mapping was also applied in patients with true edema. Cardiovascular magnetic resonance (CMR) T2-mapping has potential for the detection and quantification of myocardial edema. Clinical experience is limited so far. The variability and potential pitfalls in broad application are unknown.

METHODS

Healthy volunteers (n = 73, 35 ± 13 years) and patients with edema (n = 28, 55 ± 17 years) underwent CMR at 1.5 T. Steady state free precession (SSFP) cine loops and T2-weighted spin echo images were obtained. In patients, additionally late gadolinium enhancement images were acquired. We obtained T2 maps in midventricular short axis (SAX) and four-chamber view (4CV) based on images with T2 preparation times of 0, 24, 55 ms and compared fast low angle shot (FLASH) and SSFP readout. 10 volunteers were scanned twice on separate days. Two observers analysed segmental and global T2 per slice.

RESULTS

In volunteers global myocardial T2 systematically differed depending on image orientation and sequence (FLASH 52 ± 5 vs. SSFP 55 ± 5 ms in SAX and 57 ± 6 vs. 59 ± 6 ms in 4CV; p < 0.0001 for both). Anteroseptal and apical segments had higher T2 than inferior and basal segments (SAX: 59 ± 6 vs. 48 ± 5 ms for FLASH and 59 ± 7 vs. 52 ± 4 ms for SSFP; p < 0.0001 for both). 14 volunteers had segments with T2 ≥ 70 ms. Mean intraobserver variability was 1.07 ± 1.03 ms (r = 0.94); interobserver variability was 1.6 ± 1.5 ms (r = 0.87). The coefficient of variation for repeated scans was 7.6% for SAX and 6.6% for 4CV. Mapping revealed focally increased T2 (73 ± 9 vs. 51 ± 3 ms in remote myocardium; p < 0.0001) in all patients with edema.

CONCLUSIONS

Myocardial T2 mapping is technically feasible and highly reproducible. It can detect focal edema and differentiate it from normal myocardium. Increased T2 was found in some volunteers most likely due to partial volume and residual motion.

Sex differences in cardiac autonomic regulation and in repolarisation electrocardiography

The review summarises the present knowledge on the sex differences in cardiac autonomic regulations and in related aspects of electrocardiography with particular attention to myocardial repolarisation. Although some of the sex differences are far from fully established, multitude of observations show consistent differences between women and men. Despite more pronounced parasympathetic cardiac regulation, women have higher resting heart rate and lower baroreflex sensitivity. Of the electrocardiographic phenomena, women have longer QT interval duration, repolarisation sequence more synchronised with the inverse of the depolarisation sequence, and likely increased regional heterogeneity of myocardial repolarisation. Studies investigating the relationship of these sex disparities to hormonal differences led frequently to conflicting results. Although sex hormones seem to play a key role by influencing both autonomic tone and electrophysiological properties at the cellular level, neither the truly relevant hormones nor their detailed actions are known. Physiologic usefulness of the described sex differences is also unknown. The review suggests that new studies are needed to advance the understanding of the physiologic mechanisms responsible for these inequalities between women and men and provides key methodological suggestions that need to be followed in future research.

Global and regional left ventricular myocardial deformation measures by magnetic resonance feature tracking in healthy volunteers: comparison with tagging and relevance of gender

BACKGROUND

Feature tracking software offers measurements of myocardial strain, velocities and displacement from cine cardiovascular magnetic resonance (CMR) images. We used it to record deformation parameters in healthy adults and compared values to those obtained by tagging.

METHODS

We used TomTec 2D Cardiac Performance Analysis software to derive global, regional and segmental myocardial deformation parameters in 145 healthy volunteers who had steady state free precession (SSFP) cine left ventricular short (basal, mid and apical levels) and long axis views (horizontal long axis, vertical long axis and left ventricular out flow tract) obtained on a 1.5 T Siemens Sonata scanner. 20 subjects also had tagged acquisitions and we compared global and regional deformation values obtained from these with those from Feature Tracking.

RESULTS

For globally averaged measurements of strain, only those measured circumferentially in short axis slices showed reasonably good levels of agreement between FT and tagging (limits of agreement -0.06 to 0.04). Longitudinal strain showed wide limits of agreement (-0.16 to 0.03) with evidence of overestimation of strain by FT relative to tagging as the mean of both measures increased. Radial strain was systematically overestimated by FT relative to tagging with very wide limits of agreement extending to as much as 100% of the mean value (-0.01 to 0.23). Reproducibility showed similar relative trends with acceptable global inter-observer variability for circumferential measures (coefficient of variation 4.9%) but poor reproducibility in the radial direction (coefficient of variation 32.3%). Ranges for deformation parameters varied between basal, mid and apical LV levels with higher levels at base compared to apex, and between genders by both FT and tagging.

CONCLUSIONS

FT measurements of circumferential but not longitudinally or radially directed global strain showed reasonable agreement with tagging and acceptable inter-observer reproducibility. We record provisional ranges of FT deformation parameters at global, regional and segmental levels. They show evidence of variation with gender and myocardial region in the volunteers studied, but have yet to be compared with tagging measurements at the segmental level.

Global and regional left ventricular myocardial deformation measures by magnetic resonance feature tracking in healthy volunteers: comparison with tagging and relevance of gender

BACKGROUND

Feature tracking software offers measurements of myocardial strain, velocities and displacement from cine cardiovascular magnetic resonance (CMR) images. We used it to record deformation parameters in healthy adults and compared values to those obtained by tagging.

METHODS

We used TomTec 2D Cardiac Performance Analysis software to derive global, regional and segmental myocardial deformation parameters in 145 healthy volunteers who had steady state free precession (SSFP) cine left ventricular short (basal, mid and apical levels) and long axis views (horizontal long axis, vertical long axis and left ventricular out flow tract) obtained on a 1.5 T Siemens Sonata scanner. 20 subjects also had tagged acquisitions and we compared global and regional deformation values obtained from these with those from Feature Tracking.

RESULTS

For globally averaged measurements of strain, only those measured circumferentially in short axis slices showed reasonably good levels of agreement between FT and tagging (limits of agreement -0.06 to 0.04). Longitudinal strain showed wide limits of agreement (-0.16 to 0.03) with evidence of overestimation of strain by FT relative to tagging as the mean of both measures increased. Radial strain was systematically overestimated by FT relative to tagging with very wide limits of agreement extending to as much as 100% of the mean value (-0.01 to 0.23). Reproducibility showed similar relative trends with acceptable global inter-observer variability for circumferential measures (coefficient of variation 4.9%) but poor reproducibility in the radial direction (coefficient of variation 32.3%). Ranges for deformation parameters varied between basal, mid and apical LV levels with higher levels at base compared to apex, and between genders by both FT and tagging.

CONCLUSIONS

FT measurements of circumferential but not longitudinally or radially directed global strain showed reasonable agreement with tagging and acceptable inter-observer reproducibility. We record provisional ranges of FT deformation parameters at global, regional and segmental levels. They show evidence of variation with gender and myocardial region in the volunteers studied, but have yet to be compared with tagging measurements at the segmental level.

Hemodynamic responses to rapid saline loading: the impact of age, sex, and heart failure

BACKGROUND

Hemodynamic assessment after volume challenge has been proposed as a way to identify heart failure with preserved ejection fraction. However, the normal hemodynamic response to a volume challenge and how age and sex affect this relationship remain unknown.

METHODS AND RESULTS

Sixty healthy subjects underwent right heart catheterization to measure age- and sex-related normative responses of pulmonary capillary wedge pressure and mean pulmonary arterial pressure to volume loading with rapid saline infusion (100-200 mL/min). Hemodynamic responses to saline infusion in heart failure with preserved ejection fraction (n=11) were then compared with those of healthy young (<50 years of age) and older (≥50 years of age) subjects. In healthy subjects, pulmonary capillary wedge pressure increased from 10±2 to 16±3 mm Hg after ~1 L and to 20±3 mm Hg after ~2 L of saline infusion. Older women displayed a steeper increase in pulmonary capillary wedge pressure relative to volume infused (16±4 mm Hg·L(-1)·m(2)) than the other 3 groups (P≤0.019). Saline infusion resulted in a greater increase in mean pulmonary arterial pressure relative to cardiac output in women compared with men regardless of age. Subjects with heart failure with preserved ejection fraction exhibited a steeper increase in pulmonary capillary wedge pressure relative to infused volume (25±12 mm Hg·L(-1)·m(2)) than healthy young and older subjects (P≤0.005).

CONCLUSIONS

Filling pressures rise significantly with volume loading, even in healthy volunteers. Older women and patients with heart failure with preserved ejection fraction exhibit the largest increases in pulmonary capillary wedge pressure and mean pulmonary arterial pressure.

A quantitative comparison of regional myocardial motion in mice, rabbits and humans using in-vivo phase contrast CMR

BACKGROUND

Genetically manipulated animals like mice or rabbits play an important role in the exploration of human cardiovascular diseases. It is therefore important to identify animal models that closely mimic physiological and pathological human cardiac function.

METHODS

In-vivo phase contrast cardiovascular magnetic resonance (CMR) was used to measure regional three-directional left ventricular myocardial motion with high temporal resolution in mice (N=18), rabbits (N=8), and humans (N=20). Radial, long-axis, and rotational myocardial velocities were acquired in left ventricular basal, mid-ventricular, and apical short-axis locations.

RESULTS

Regional analysis revealed different patterns of motion: 1) In humans and rabbits, the apex showed slower radial velocities compared to the base. 2) Significant differences within species were seen in the pattern of long-axis motion. Long-axis velocities during systole were fairly homogeneously distributed in mice, whereas humans showed a dominant component in the lateral wall and rabbits in the base. 3) Rotational velocities and twist showed the most distinct patterns in both temporal evolution and relative contribution of base, mid-ventricle and apex, respectively. Interestingly, a marked difference in rotational behavior during early-systole was found in mice, which exhibited clockwise rotation in all slice locations compared to counter-clockwise rotation in rabbits and humans.

CONCLUSIONS

Phase contrast CMR revealed subtle, but significantly different regional myocardial motion patterns in mice, rabbits and humans. This finding has to be considered when investigating myocardial motion pattern in small animal models of heart disease.

Age, gender, blood pressure, and ventricular geometry influence normal 3D blood flow characteristics in the left heart

AIMS

The aim of this study was to assess the effect of age, gender, physiological, and global cardiac function parameters on differences in normal 3D blood flow in the left ventricle (LV) and atrium (LA) using 4D flow magnetic resonance imaging (MRI).

METHODS AND RESULTS

Four-dimensional flow MRI was acquired in healthy volunteers of two age and gender groups: <30 years (6 women, n = 12) and >50 years (6 women, n = 12). Systolic and early to mid-diastolic vortex flow (number of vortices, duration, area, peak velocity inside the vortex) in the LA and LV was assessed using intra-cardiac flow visualization based on 3D particle traces and velocity vector fields. A larger number of vortices in the LA were found in young compared with older individuals (number of diastolic vortices: 1.6 ± 0.8 vs. 0.7 ± 0.7, P = 0.01) with higher velocities (54 ± 12 cm/s vs. 41 ± 11 cm/s in systole, 47 ± 13 vs. 31 ± 8 cm/s in diastole, P < 0.05). Vortices in the LV base were smaller in women compared with men (369 ± 133 vs. 543 ± 176 mm(2), P = 0.009), while vortex size was increased in mid-ventricular locations (maximum area: 546 ± 321 vs. 293 ± 174 mm(2), P < 0.05). Correlation analysis revealed significant relationships (P = 0.005-0.048, correlation coefficients = 0.44-0.84) between LA and LV vortex characteristics (number, size, vortex velocities) and blood pressure as well as end-diastolic volume, LV length, and ejection fraction.

CONCLUSIONS

Flow patterns in the left heart demonstrated differences related to age, gender, blood pressure, and ventricular geometry. The findings constitute a prerequisite for the understanding of the impact of cardiac disease on intra-cardiac haemodynamics.

Improved MR phase-contrast velocimetry using a novel nine-point balanced motion-encoding scheme with increased robustness to eddy current effects

Phase-contrast MRI (PC-MRI) velocimetry is a noninvasive, high-resolution motion assessment tool. However, high motion sensitivity requires strong motion-encoding magnetic gradients, making phase-contrast-MRI prone to baseline shift artifacts due to the generation of eddy currents. In this study, we propose a novel nine-point balanced velocity-encoding strategy, designed to be more accurate in the presence of strong and rapidly changing gradients. The proposed method was validated using a rotating phantom, and its robustness and precision were explored and compared with established approaches through computer simulations and in vivo experiments. Computer simulations yielded a 39-57% improvement in velocity-noise ratio (corresponding to a 27-33% reduction in measurement error), depending on which method was used for comparison. Moreover, in vivo experiments confirmed this by demonstrating a 26-53% reduction in accumulated velocity error over the R-R interval. The nine-point balanced phase-contrast-MRI-encoding strategy is likely useful for settings where high spatial and temporal resolution and/or high motion sensitivity is required, such as in high-resolution rodent myocardial tissue phase mapping.

Effect of ageing on left ventricular compliance and distensibility in healthy sedentary humans

Healthy, but sedentary ageing leads to marked atrophy and stiffening of the heart, with substantially reduced cardiac compliance; but the time course of when this process occurs during normal ageing is unknown. Seventy healthy sedentary subjects (39 female; 21–77 years) were recruited from the Dallas Heart Study, a population-based, random community sample and enriched by a second random sample from employees of Texas Health Resources. Subjects were highly screened for co-morbidities and stratified into four groups according to age: G(21−34): 21–34 years, G(35−49): 35–49 years, G5(0−64): 50–64 years, G(≥65): ≥65 years. All subjects underwent invasive haemodynamic measurements with right heart catheterization to define Starling and left ventricular (LV) pressure–volume curves. LV end-diastolic volumes (EDV) were measured by echocardiography at baseline, −15 and −30 mmHg lower-body negative pressure, and 15 and 30 ml kg(−1) saline infusion with simultaneous measurements of pulmonary capillary wedge pressure. There were no differences in heart rate or blood pressures among the four groups at baseline. Baseline EDV index was smaller in G(≥65) than other groups. LV diastolic pressure–volume curves confirmed a substantially greater LV compliance in G(21−34) compared with G(50−64) and G(≥65), resulting in greater LV volume changes with preload manipulations. Although LV chamber compliance in G(50−64) and G(≥65) appeared identical, pressure–volume curves were shifted leftward, toward a decreased distensibility, with increasing age. These results suggest that LV stiffening in healthy ageing occurs during the transition between youth and middle-age and becomes manifest between the ages of 50 to 64. Thereafter, this LV stiffening is followed by LV volume contraction and remodelling after the age of 65.

Modeling radial viscoelastic behavior of left ventricle based on MRI tissue phase mapping

The viscoelastic behavior of myocardial tissue is a measure that has recently found to be a deterministic factor in quality of contraction. Parameters imposing the viscoelastic behavior of the heart are influenced in part by sarcomere function and myocardial composition. Despite the overall agreement on significance of cardiac viscoelasticity, a practical model that can measure and characterize the viscoelastic behavior of the myocardial segments does not yet exist. Pressure-Volume (P-V) curves are currently the only measure for stiffness/compliance of the left ventricle. However, obtaining P-V curves requires invasive cardiac catheterization, and only provides qualitative information on how pressure and volume change with respect to each other. For accurate assessment of myocardial mechanical behavior, it is required to obtain quantitative measures for viscoelasticity. In this work, we have devised a model that yields myocardial elastic and viscous damping coefficient functions through the cardiac cycle. The required inputs for this model are kinematic information with respect to changes in LV short axes that were obtained by Magnetic Resonance Imaging (MRI) using a tissue phase mapping (TPM) pulse sequence. We evaluated viscoelastic coefficients of LV myocardium in two different age groups of 20-40 and greater than 60. We found that the magnitude of stiffness coefficients is noticeably greater in the older subjects. Additionally, we found that slope of viscous damping functions follow similar patterns for each individual age group. This method may shed light on dynamics of contraction through MRI in conditions where composition of myocardium is changed such as in aging, adverse remodeling, and cardiomyopathies.

Multi-modality imaging of diastolic function

Non-invasive evaluation of diastolic function continues to play a critical role in furthering our understanding of diastole, improving the diagnosis of diastolic dysfunction, evaluating left ventricular filling pressures, and providing important prognostic information for patients with heart failure. Echocardiography, cardiovascular magnetic resonance, and nuclear cardiology each provide important tools for evaluating diastolic performance. This review will focus on the techniques from multiple cardiovascular imaging modalities which have been used for the clinical assessment of diastolic function.