Required temporal resolution for accurate thoracic aortic pulse wave velocity measurements by phase-contrast magnetic resonance imaging and comparison with clinical standard applanation tonometry

Association of Cardiac MRI-derived Aortic Stiffness with Early Stages and Progression of Heart Failure with Preserved Ejection Fraction

Purpose To investigate if aortic stiffening as detected with cardiac MRI is an early phenomenon in the development and progression of heart failure with preserved ejection fraction (HFpEF). Materials and Methods Both clinical and preclinical studies were performed. The clinical study was a secondary analysis of the prospective HFpEF stress trial (August 2017 through September 2019) and included 48 participants (median age, 69 years [range, 65-73 years]; 33 female, 15 male) with noncardiac dyspnea (NCD, n = 21), overt HFpEF at rest (pulmonary capillary wedge pressure [PCWP] ≥ 15 mm Hg, n = 14), and masked HFpEF at rest diagnosed during exercise stress (PCWP ≥ 25 mm Hg, n = 13) according to right heart catheterization. Additionally, all participants underwent echocardiography and cardiac MRI at rest and during exercise stress. Aortic pulse wave velocity (PWV) was calculated. The mechanistic preclinical study characterized cardiac function and structure in transgenic mice with induced arterial stiffness (Runx2-smTg mice). Statistical analyses comprised nonparametric and parametric comparisons, Spearman correlations, and logistic regression models. Results Participants with HFpEF showed increased PWV (NCD vs masked HFpEF: 7.0 m/sec [IQR: 5.0-9.5 m/sec] vs 10.0 m/sec [IQR: 8.0-13.4 m/sec], P = .005; NCD vs overt HFpEF: 7.0 m/sec [IQR: 5.0-9.5 m/sec] vs 11.0 m/sec [IQR: 7.5-12.0 m/sec], P = .01). Increased PWV correlated with higher PCWP (P = .006), left atrial and left ventricular long-axis strain (all P < .02), and N-terminal pro-brain natriuretic peptide levels (P < .001). Participants with overt HFpEF had higher levels of myocardial fibrosis, as demonstrated by increased native T1 times (1199 msec [IQR: 1169-1228 msec] vs 1234 msec [IQR: 1208-1255 msec], P = .009). Aortic stiffness was independently associated with HFpEF on multivariable analyses (odds ratio, 1.31; P = .049). Runx2-smTG mice exhibited an "HFpEF" phenotype compared with wild-type controls, with preserved left ventricular fractional shortening but an early and late diastolic mitral annulus velocity less than 1 (mean, 0.67 ± 0.39 [standard error of the mean] vs 1.45 ± 0.47; P = .004), increased myocardial collagen deposition (mean, 11% ± 1 vs 2% ± 1; P < .001), and increased brain natriuretic peptide levels (mean, 171 pg/mL ± 23 vs 101 pg/mL ± 10; P < .001). Conclusion This study provides translational evidence that increased arterial stiffness might be associated with development and progression of HFpEF and may facilitate its early detection. Keywords: MR Functional Imaging, MR Imaging, Animal Studies, Cardiac, Aorta, Heart ClinicalTrials.gov identifier NCT03260621 Supplemental material is available for this article. © RSNA, 2024.

Characterization of pulmonary arterial stiffness using cardiac MRI

Pulmonary arterial stiffness (PAS) is a pathologic hallmark of all types of pulmonary hypertension (PH). Cardiac MRI (CMR), a gold-standard imaging modality for the evaluation of pulmonary flow, biventricular morphology and function has been historically reserved for the longitudinal clinical follow-up, PH phenotyping purposes, right ventricular evaluation, and research purposes. Over the last two decades, numerous indices combining invasive catheterization and non-invasive CMR have been utilized to phenotype the character and severity of PAS in different types of PH and to assess its clinically prognostic potential with encouraging results. Many recent studies have demonstrated a strong role of CMR derived PAS markers in predicting long-term clinical outcomes and improving currently gold standard risk assessment provided by the REVEAL calculator. With the utilization of a machine learning strategies, strong diagnostic and prognostic performance of CMR reported in multicenter studies, and ability to detect PH at early stages, the non-invasive assessment of PAS is on verge of routine clinical utilization. In this review, we focus on appraising important CMR studies interrogating PAS over the last 20 years, describing the benefits and limitations of different PAS indices, and their pathophysiologic relevance to pulmonary vascular remodeling. We also discuss the role of CMR and PAS in clinical surveillance and phenotyping of PH, and the long-term future goal to utilize PAS as a biomarker to aid with more targeted therapeutic management.

Characterising spinal cerebrospinal fluid flow in the pig with phase-contrast magnetic resonance imaging

BACKGROUND

Detecting changes in pulsatile cerebrospinal fluid (CSF) flow may assist clinical management decisions, but spinal CSF flow is relatively understudied. Traumatic spinal cord injuries (SCI) often cause spinal cord swelling and subarachnoid space (SAS) obstruction, potentially causing pulsatile CSF flow changes. Pigs are emerging as a favoured large animal SCI model; therefore, the aim of this study was to characterise CSF flow along the healthy pig spine.

METHODS

Phase-contrast magnetic resonance images (PC-MRI), retrospectively cardiac gated, were acquired for fourteen laterally recumbent, anaesthetised and ventilated, female domestic pigs (22-29 kg). Axial images were obtained at C2/C3, T8/T9, T11/T12 and L1/L2. Dorsal and ventral SAS regions of interest (ROI) were manually segmented. CSF flow and velocity were determined throughout a cardiac cycle. Linear mixed-effects models, with post-hoc comparisons, were used to identify differences in peak systolic/diastolic flow, and maximum velocity (cranial/caudal), across spinal levels and dorsal/ventral SAS. Velocity wave speed from C2/C3 to L1/L2 was calculated.

RESULTS

PC-MRI data were obtained for 11/14 animals. Pulsatile CSF flow was observed at all spinal levels. Peak systolic flow was greater at C2/C3 (dorsal: - 0.32 ± 0.14 mL/s, ventral: - 0.15 ± 0.13 mL/s) than T8/T9 dorsally (- 0.04 ± 0.03 mL/s; p < 0.001), but not different ventrally (- 0.08 ± 0.08 mL/s; p = 0.275), and no difference between thoracolumbar levels (p > 0.05). Peak diastolic flow was greater at C2/C3 (0.29 ± 0.08 mL/s) compared to T8/T9 (0.03 ± 0.03 mL/s, p < 0.001) dorsally, but not different ventrally (p = 1.000). Cranial and caudal maximum velocity at C2/C3 were greater than thoracolumbar levels dorsally (p < 0.001), and T8/T9 and L1/L2 ventrally (p = 0.022). Diastolic velocity wave speed was 1.41 ± 0.39 m/s dorsally and 1.22 ± 0.21 m/s ventrally, and systolic velocity wave speed was 1.02 ± 0.25 m/s dorsally and 0.91 ± 0.22 m/s ventrally.

CONCLUSIONS

In anaesthetised and ventilated domestic pigs, spinal CSF has lower pulsatile flow and slower velocity wave propagation, compared to humans. This study provides baseline CSF flow at spinal levels relevant for future SCI research in this animal model.

Higher blood pressure in adolescent boys after very preterm birth and fetal growth restriction

BACKGROUND

Although preterm birth predisposes for cardiovascular disease, recent studies in children indicate normal blood pressure and arterial stiffness. This prospective cohort study therefore assessed blood pressure and arterial stiffness in adolescents born very preterm due to verified fetal growth restriction (FGR).

METHODS

Adolescents (14 (13-17) years; 52% girls) born very preterm with FGR (preterm FGR; n = 24) and two control groups born with appropriate birth weight (AGA), one in similar gestation (preterm AGA; n = 27) and one at term (term AGA; n = 28) were included. 24-hour ambulatory blood pressure and aortic pulse wave velocity (PWV) and distensibility by magnetic resonance imaging were acquired.

RESULTS

There were no group differences in prevalence of hypertension or in arterial stiffness (all p ≥ 0.1). In boys, diastolic and mean arterial blood pressures increased from term AGA to preterm AGA to preterm FGR with higher daytime and 24-hour mean arterial blood pressures in the preterm FGR as compared to the term AGA group. In girls, no group differences were observed (all p ≥ 0.1).

CONCLUSIONS

Very preterm birth due to FGR is associated with higher, yet normal blood pressure in adolescent boys, suggesting an existing but limited impact of very preterm birth on cardiovascular risk in adolescence, enhanced by male sex and FGR.

IMPACT

Very preterm birth due to fetal growth restriction was associated with higher, yet normal blood pressure in adolescent boys. In adolescence, very preterm birth due to fetal growth restriction was not associated with increased thoracic aortic stiffness. In adolescence, very preterm birth in itself showed an existing but limited effect on blood pressure and thoracic aortic stiffness. Male sex and fetal growth restriction enhanced the effect of preterm birth on blood pressure in adolescence. Male sex and fetal growth restriction should be considered as additional risk factors to that of preterm birth in cardiovascular risk stratification.

Pulse Wave Velocity Measurements by Magnetic Resonance Imaging in Neonates and Adolescents: Methodological Aspects and Their Clinical Implications

Pulse wave velocity (PWV) by cardiovascular magnetic resonance (CMR) lacks standardization. The aim of this study was to investigate methodological aspects of PWV measurements by CMR in neonates and adolescents. A computer phantom was created to validate the temporal resolution required for accurate PWV. Fifteen neonates and 71 adolescents underwent CMR with reference standard 3D angiography and phase-contrast flow acquisitions, and in a subset coronal overview images. Velocity and flow curves, transit time methods (time-to-foot (TTF), maximum upslope, and time-to-peak (TTP)), and baseline correction methods (no correction, automatic and manual) were investigated. In neonates, required timeframes per cardiac cycle for accurate PWV was 42 for the aortic arch and 41 for the thoracic aorta. In adolescents, corresponding values were 39 and 32. Aortic length differences by overview images and 3D angiography in adolescents were - 16-18 mm (aortic arch) and - 25-30 mm (thoracic aorta). Agreement in PWV between automatic and manual baseline correction was - 0.2 ± 0.3 m/s in neonates and 0.0 ± 0.1 m/s in adolescents. Velocity and flow-derived PWV measurements did not differ in either group (all p > 0.08). In neonates, transit time methods did not differ (all p > 0.19) but in adolescents PWV was higher for TTF (3.8 ± 0.5 m/s) and maximum upslope (3.7 ± 0.6 m/s) compared to TTP (2.7 ± 1.0 m/s; p < 0.0001). This study is a step toward standardization of PWV in neonates and adolescents using CMR. It provides required temporal resolution for phase-contrast flow acquisitions for typical heartrates in neonates and adolescents, and supports 3D angiography and time-to-foot with automatic baseline correction for accurate PWV measurements.

Elevated Aortic Pulse Wave Velocity Relates to Longitudinal Gray and White Matter Changes

OBJECTIVE

To determine whether baseline aortic stiffness, measured by aortic pulse wave velocity (PWV), relates to longitudinal cerebral gray or white matter changes among older adults. Baseline cardiac magnetic resonance imaging will be used to assess aortic PWV while brain magnetic resonance imaging will be used to assess gray matter and white matter hyperintensity (WMH) volumes at baseline, 18 months, 3 years, 5 years, and 7 years. Approach and Results: Aortic PWV (m/s) was quantified from cardiac magnetic resonance. Multimodal 3T brain magnetic resonance imaging included T₁-weighted imaging for quantifying gray matter volumes and T₂-weighted fluid-attenuated inversion recovery imaging for quantifying WMHs. Mixed-effects regression models related baseline aortic PWV to longitudinal gray matter volumes (total, frontal, parietal, temporal, occipital, hippocampal, and inferior lateral ventricle) and WMH volumes (total, frontal, parietal, temporal, and occipital) adjusting for age, sex, race/ethnicity, education, cognitive diagnosis, Framingham stroke risk profile, APOE (apolipoprotein E)-ε4 carrier status, and intracranial volume. Two hundred seventy-eight participants (73±7 years, 58% male, 87% self-identified as non-Hispanic White, 159 with normal cognition, and 119 with mild cognitive impairment) from the Vanderbilt Memory & Aging Project (n=335) were followed on average for 4.9±1.6 years with PWV measurements occurring from September 2012 to November 2014 and longitudinal brain magnetic resonance imaging measurements occurring from September 2012 to June 2021. Higher baseline aortic PWV was related to greater decrease in hippocampal (β=-3.6 [mm³/y]/[m/s]; [95% CI, -7.2 to -0.02] P=0.049) and occipital lobe (β=-34.2 [mm³/y]/[m/s]; [95% CI, -67.8 to -0.55] P=0.046) gray matter volume over time. Higher baseline aortic PWV was related to greater increase in WMH volume over time in the temporal lobe (β=17.0 [mm³/y]/[m/s]; [95% CI, 7.2-26.9] P<0.001). All associations may be driven by outliers.

CONCLUSIONS

In older adults, higher baseline aortic PWV related to greater decrease in gray matter volume and greater increase in WMHs over time. Because of unmet cerebral metabolic demands and microvascular remodeling, arterial stiffening may preferentially affect certain highly active brain regions like the temporal lobes. These same regions are affected early in the course of Alzheimer disease.

Assessment of carotid stiffness by measuring carotid pulse wave velocity using a single-slice oblique-sagittal phase-contrast MRI

PURPOSE

Increased arterial stiffness has been shown to be one of the earliest markers of cerebrovascular dysfunction. As a surrogate marker of arterial stiffness, pulse wave velocity (PWV) quantifications are generally carried out on central and peripheral arteries. The purpose of this study was to develop and evaluate an MRI approach to assess carotid stiffness by measuring carotid PWV (cPWV) using a fast oblique-sagittal phase-contrast MRI sequence.

METHODS

In 29 volunteers, a single-slice oblique-sagittal phase-contrast MRI sequence with retrospective cardiac gating was used to quantify blood velocity waveforms along a vessel segment covering the common carotid artery (CCA) and the internal carotid artery (ICA). The CCA-ICA segment length was measured from a region of interest selected on the magnitude image. Phase-contrast MRI-measured velocities were also used to quantify the ICA pulsatility index along with cPWV quantification.

RESULTS

The mean value of cPWV calculated using the middle upslope area algorithm was 2.86 ± 0.71 and 3.97 ± 1.14 m/s in young and elderly subjects, respectively. Oblique-sagittal phase-contrast MRI-derived cPWV measurements showed excellent intrascan and interscan repeatability. cPWV and ICA pulsatility index were significantly greater in older subjects compared to those in the young subjects (P < .01 and P = .01, respectively). Also, increased cPWV values were associated with elevated systolic blood pressure (β = 0.05, P = .03).

CONCLUSION

This study demonstrated that oblique-sagittal phase-contrast MRI is a feasible technique for the quantification of both cPWV and ICA pulsatility index and showed their potential utility in evaluating cerebroarterial aging and age-related neurovascular disorders.

Cerebrospinal fluid pulse wave velocity measurements: In vitro and in vivo evaluation of a novel multiband cine phase-contrast MRI sequence

PURPOSE

Intracranial and intraspinal compliance are parameters of interest in the diagnosis and prediction of treatment outcome in patients with normal pressure hydrocephalus and other forms of communicating hydrocephalus. A noninvasive method to estimate the spinal cerebrospinal fluid (CSF) pulse wave velocity (PWV) as a measure of compliance was developed using a multiband cine phase-contrast MRI sequence and a foot-to-foot algorithm.

METHODS

We used computational simulations to estimate the accuracy of the MRI acquisition and transit-time algorithm. In vitro measurements were performed to investigate the reproducibility and accuracy of the measurements under controlled conditions. In vivo measurements in 20 healthy subjects and 2 patients with normal pressure hydrocephalus were acquired to show the technical feasibility in a clinical setting.

RESULTS

Simulations showed a mean deviation of the calculated CSF PWV of 3.41% ± 2.68%. In vitro results were in line with theory, showing a square-root relation between PWV and transmural pressure and a good reproducibility with SDs of repeated measurements below 5%. Mean CSF PWV over all healthy subjects was 5.83 ± 3.36 m/s. The CSF PWV measurements in the patients with normal pressure hydrocephalus were distinctly higher before CSF shunt surgery (33.80 ± 6.75 m/s and 31.31 ± 7.82 m/s), with a decrease 5 days after CSF shunt surgery (15.69 ± 3.37 m/s).

CONCLUSION

This study evaluates the feasibility of CSF PWV measurements using a multiband cine phase-contrast MRI sequence. In vitro and in vivo measurements showed that this method is a potential tool for the noninvasive estimation of intraspinal compliance.

Group delay method for MRI aortic pulse wave velocity measurements in clinical protocols with low temporal resolution: Validation in a heterogeneous cohort

BACKGROUND

MRI assessment of aortic pulse wave velocity (PWV) helps predict the risk of vascular events, but the recommended phase contrast sampling rate is faster than what is utilized in most clinical sequences. There are many existing MRI databases obtained for assessment of cardiac output using lower temporal frequency sampling where information might be obtained about aortic stiffness (PWV). In this work, we sought to evaluate whether the Group Delay (GD) method can generate a reproducible measure of stiffness and describe expected age-related stiffening of the aortic arch using lower sampling rates in standard clinical sequences.

METHODS

Phase contrast (PC) MRI was obtained on the ascending and descending aortic arch in a heterogeneous adult cohort (n = 23; 9 women) spanning over a wide range of ages (ages 24-89, mean 49.4 ± 18.4). Data was collected with standard cardiac MRI protocols for cardiac output evaluation (repetition time = 7.8 ms, views-per-segment = 4, encoding velocity = 200 cm/s). Pulse wave transit times (TT) were computed using the GD method, two other validated automated approaches (cross correlation TT Algorithm by Gaddum and Segment by Medviso), and the manual tangent method. Pressure waveforms from tonometry and flow waveforms from PC MRI were used to assess wave reflections.

RESULTS

Group Delay and TT-Algorithm showed significant and high retest reproducibility (r = 0.86 for both) as well as high PWV correlation with age (r = 0.93, P-value < 0.00005 and r = 0.96, P-value < 0.00005 respectively) and with each other (r = 0.94, P-value < 0.00001, RMSE = 0.94 m/s). Arbitrary altering of the image acquisition trigger in the GD method introduced error of 10%-13%, but the TT-algorithm error range was 11%-25%.

CONCLUSION

Group Delay enables reproducible assessment of transit time to derive PWV from low temporal resolution clinical cardiac MRI sequences that can also identify age-related stiffening.

Cardiovascular effects of severe late-onset preeclampsia are reversed within six months postpartum

OBJECTIVES

Preeclampsia (PE) is a common pregnancy-related disorder associated with cardiovascular long-term disease. Eighty percent are late-onset PE, occurring after 34 gestational weeks, and can present with severe symptoms. Magnitude and reversibility rate of maternal cardiovascular changes after severe late-onset PE have not been characterized. This study therefore evaluated longitudinal dynamics of maternal cardiovascular changes after severe late-onset PE.

STUDY DESIGN

Six previously normotensive women with severe late-onset PE and eight pregnant controls were included. Severe PE was defined as systolic blood pressure (SBP) ≥ 160 mmHg or diastolic blood pressure (DBP) ≥ 110 mmHg and proteinuria with/without evidence of end-organ dysfunction, or SBP ≥ 140 mmHg or DBP ≥ 90 mmHg with/without proteinuria and with evidence of end-organ dysfunction. Cardiovascular function was assessed by magnetic resonance imaging at 1-3 days, one week and six months postpartum.

RESULTS

Left ventricular mass at 1-3 days postpartum was higher after severe late-onset PE (57 g/m²) compared to after normal pregnancy (48 g/m²; p = 0.01). Pulse wave velocity (PWV) decreased between 1 and 3 days and six months postpartum after PE (6.1 to 5.0 m/s; p = 0.028). There was no difference in PWV 1-3 days postpartum after severe PE compared after normal pregnancy (6.1 versus 5.6 m/s; p = 0.175). Blood pressure normalized within six months in all but one patient.

CONCLUSIONS

Cardiac effects after severe late-onset PE were small and transient. This indicates that left ventricular hypertrophy after severe late-onset PE may be a secondary physiologic response to increased peripheral resistance in PE. Vascular mechanisms rather than persistent cardiac hypertrophy postpartum may be the culprit for increased long-term cardiovascular risk after PE.

The association between resting-state functional magnetic resonance imaging and aortic pulse-wave velocity in healthy adults

Resting‐state functional magnetic resonance imaging (rs‐fMRI) is frequently used to study brain function; but, it is unclear whether BOLD‐signal fluctuation amplitude and functional connectivity are associated with vascular factors, and how vascular‐health factors are reflected in rs‐fMRI metrics in the healthy population. As arterial stiffening is a known age‐related cardiovascular risk factor, we investigated the associations between aortic stiffening (as measured using pulse‐wave velocity [PWV]) and rs‐fMRI metrics. We used cardiac MRI to measure aortic PWV (an established indicator of whole‐body vascular stiffness), as well as dual‐echo pseudo‐continuous arterial‐spin labeling to measure BOLD and CBF dynamics simultaneously in a group of generally healthy adults. We found that: (1) higher aortic PWV is associated with lower variance in the resting‐state BOLD signal; (2) higher PWV is also associated with lower BOLD‐based resting‐state functional connectivity; (3) regions showing lower connectivity do not fully overlap with those showing lower BOLD variance with higher PWV; (4) CBF signal variance is a significant mediator of the above findings, only when averaged across regions‐of‐interest. Furthermore, we found no significant association between BOLD signal variance and systolic blood pressure, which is also a known predictor of vascular stiffness. Age‐related vascular stiffness, as measured by PWV, provides a unique scenario to demonstrate the extent of vascular bias in rs‐fMRI signal fluctuations and functional connectivity. These findings suggest that a substantial portion of age‐related rs‐fMRI differences may be driven by vascular effects rather than directly by brain function.

The importance of accurate measurement of aortic stiffness in patients with chronic kidney disease and end-stage renal disease

Cardiovascular (CV) disease is the leading cause of death in chronic kidney disease (CKD) and end-stage renal disease (ESRD). A key driver in this pathology is increased aortic stiffness, which is a strong, independent predictor of CV mortality in this population. Aortic stiffening is a potentially modifiable biomarker of CV dysfunction and in risk stratification for patients with CKD and ESRD. Previous work has suggested that therapeutic modification of aortic stiffness may ameliorate CV mortality. Nevertheless, future clinical implementation relies on the ability to accurately and reliably quantify stiffness in renal disease. Pulse wave velocity (PWV) is an indirect measure of stiffness and is the accepted standard for non-invasive assessment of aortic stiffness. It has typically been measured using techniques such as applanation tonometry, which is easy to use but hindered by issues such as the inability to visualize the aorta. Advances in cardiac magnetic resonance imaging now allow direct measurement of stiffness, using aortic distensibility, in addition to PWV. These techniques allow measurement of aortic stiffness locally and are obtainable as part of a comprehensive, multiparametric CV assessment. The evidence cannot yet provide a definitive answer regarding which technique or parameter can be considered superior. This review discusses the advantages and limitations of non-invasive methods that have been used to assess aortic stiffness, the key studies that have assessed aortic stiffness in patients with renal disease and why these tools should be standardized for use in clinical trial work.

Proximal aortic stiffening in Turner patients may be present before dilation can be detected: a segmental functional MRI study

BACKGROUND

To study segmental structural and functional aortic properties in Turner syndrome (TS) patients. Aortic abnormalities contribute to increased morbidity and mortality of women with Turner syndrome. Cardiovascular magnetic resonance (CMR) allows segmental study of aortic elastic properties.

METHOD

We performed Pulse Wave Velocity (PWV) and distensibility measurements using CMR of the thoracic and abdominal aorta in 55 TS-patients, aged 13-59y, and in a control population (n = 38;12-58y). We investigated the contribution of TS on aortic stiffness in our entire cohort, in bicuspid (BAV) versus tricuspid (TAV) aortic valve-morphology subgroups, and in the younger and older subgroups.

RESULTS

Differences in aortic properties were only seen at the most proximal aortic level. BAV Turner patients had significantly higher PWV, compared to TAV Turner (p = 0.014), who in turn had significantly higher PWV compared to controls (p = 0.010). BAV Turner patients had significantly larger ascending aortic (AA) luminal area and lower AA distensibility compared to both controls (all p < 0.01) and TAV Turner patients. TAV Turner had similar AA luminal areas and AA distensibility compared to Controls. Functional changes are present in younger and older Turner subjects, whereas ascending aortic dilation is prominent in older Turner patients. Clinically relevant dilatation (TAV and BAV) was associated with reduced distensibility.

CONCLUSION

Aortic stiffening and dilation in TS affects the proximal aorta, and is more pronounced, although not exclusively, in BAV TS patients. Functional abnormalities are present at an early age, suggesting an aortic wall disease inherent to the TS. Whether this increased stiffness at young age can predict later dilatation needs to be studied longitudinally.