Non-invasive detection of coronary endothelial response to sequential handgrip exercise in coronary artery disease patients and healthy adults

The role of HIV as a risk modifier for coronary endothelial function in young adults

BACKGROUND

People living with HIV have an increased risk of cardiovascular disease (CVD). Although coronary endothelial function (CEF) is an early direct indicator of CVD, only a few studies have been able to interrogate CEF directly. Most studies have examined vascular endothelial function through indirect assessment of brachial flow-mediated dilatation (FMD). However, peripheral arteries are significantly larger and manifest atherogenesis differently from the coronary arteries, and so produce conflicting results. Additionally, none of these studies focused on young adults who acquired HIV perinatally or in early childhood.

OBJECTIVE

The present study investigates CEF in a unique population of young adults with lifelong HIV using direct magnetic resonance imaging (MRI) of coronary FMD (corFMD) with an in-house developed MRI-integrated isometric handgrip exercise system with continuous feedback and monitoring mechanisms (fmIHE).

METHODS

Young adults who acquired HIV perinatally or in early childhood (n = 23) and group-matched healthy participants (n = 12) completed corFMD-MRI with fmIHE. CorFMD was measured as the coronary cross-sectional area response to the fmIHE.

RESULTS

In univariable and multivariable regression analysis, HIV status was a significant risk modifier. CD8+ T-cell count and smoking pack-years and their interaction with HIV status were independently associated with impaired coronary artery response to fmIHE. In people living with HIV, corFMD was significantly inversely correlated with CD8+ T-cells and smoking pack-years. In a multivariable regression analysis adjusted for age and body mass index, CD8+ T-cells and smoking and their interaction with HIV status remained significant independent predictors of coronary endothelial dysfunction.

DISCUSSION

In this unique population of young adults, HIV status was a significant risk modifier, and immune activation and smoking were associated with decreased CEF, directly measured from the coronary vascular response to fmIHE.

CONCLUSIONS

Management of CVD risk factors such as smoking and developing strategies that target immune activation in people living with HIV are warranted.

Effect of Sex on Coronary Endothelial Dysfunction in People Living With HIV

Background Impaired coronary endothelial function (CEF) predicts cardiovascular events and occurs in people living with HIV (PLWH). Women compared with men living with HIV have worse cardiovascular outcomes, but prior CEF studies included few women. The authors aimed to compare CEF in women with HIV versus without HIV, investigate sex differences in CEF and PCSK9 (proprotein convertase subtilisin/kexin type 9) (a proinflammatory biomarker), and evaluate whether increased serum levels of PCSK9 are associated with CEF in PLWH. Methods and Results Magnetic resonance imaging was performed to measure CEF (as percent change in coronary cross-sectional area and coronary blood flow during isometric handgrip exercise, an endothelial-dependent stressor) and serum PCSK9 levels were measured in 106 PLWH and 76 people without HIV. CEF was significantly reduced in women with versus without HIV (cross-sectional area change -0.5%±9.7 versus 9.5%±3.2, respectively). After adjustment for age, body mass index, and menopausal status, women with HIV still had reduced CEF (percentage of cross-sectional area: ß -8.3 [-13 to -3.6], P=0.001) compared with women without HIV. PCSK9 was elevated in women living with HIV versus without (306 ng/mL [200-412 ng/mL] versus 180 ng/mL [154-223 ng/mL], P<0.001), and no sex differences in either CEF or PCSK9 were detected in PLWH. Elevated PCSK9 was associated with impaired CEF in PLWH; however, no significant sex differences in the association were detected. Conclusions Among PLWH, coronary endothelial dysfunction is present in women and comparable to men. PCSK9 is higher in women with versus without HIV and a significant inverse relationship between PCSK9 and CEF was shown. Future studies should determine whether PLWH would benefit from interventions to improve endothelial function.

Volumetric coronary endothelial function assessment: a feasibility study exploiting stack-of-stars 3D cine MRI and image-based respiratory self-gating

Abnormal coronary endothelial function (CEF), manifesting as depressed vasoreactive responses to endothelial-specific stressors, occurs early in atherosclerosis, independently predicts cardiovascular events, and responds to cardioprotective interventions. CEF is spatially heterogeneous along a coronary artery in patients with atherosclerosis, and thus recently developed and tested non-invasive 2D MRI techniques to measure CEF may not capture the extent of changes in CEF in a given coronary artery. The purpose of this study was to develop and test the first volumetric coronary 3D MRI cine method for assessing CEF along the proximal and mid-coronary arteries with isotropic spatial resolution and in free-breathing. This approach, called 3D-Stars, combines a 6 min continuous, untriggered golden-angle stack-of-stars acquisition with a novel image-based respiratory self-gating method and cardiac and respiratory motion-resolved reconstruction. The proposed respiratory self-gating method agreed well with respiratory bellows and center-of-k-space methods. In healthy subjects, 3D-Stars vessel sharpness was non-significantly different from that by conventional 2D radial in proximal segments, albeit lower in mid-portions. Importantly, 3D-Stars detected normal vasodilatation of the right coronary artery in response to endothelial-dependent isometric handgrip stress in healthy subjects. Coronary artery cross-sectional areas measured using 3D-Stars were similar to those from 2D radial MRI when similar thresholding was used. In conclusion, 3D-Stars offers good image quality and shows feasibility for non-invasively studying vasoreactivity-related lumen area changes along the proximal coronary artery in 3D during free-breathing.

Exercise Cardiovascular Magnetic Resonance: A Review

While pharmacologic stress cardiovascular magnetic resonance imaging (MRI) is a robust noninvasive tool in the diagnosis and prognostication of epicardial coronary artery disease, clinical guidelines recommend exercise-based testing in those patients who can exercise. This review describes the development of exercise cardiovascular MRI protocols, summarizes the insights across various patient populations, and highlights future research initiatives. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Quantification of myocardial oxygen extraction fraction: A proof-of-concept study

PURPOSE

To demonstrate a proof of concept for the measurement of myocardial oxygen extraction fraction (mOEF) by a cardiovascular magnetic resonance technique.

METHODS

The mOEF measurement was performed using an electrocardiogram-triggered double-echo asymmetric spin-echo sequence with EPI readout. Seven healthy volunteers (22-37 years old, 5 females) were recruited and underwent the same imaging scans at rest on 2 different days for reproducibility assessment. Another 5 subjects (23-37 years old, 4 females) underwent cardiovascular magnetic resonance studies at rest and during a handgrip isometric exercise with a 25% of maximal voluntary contraction. Both mOEF and myocardial blood volume values were obtained in septal regions from respective maps.

RESULTS

The reproducibility was excellent for the measurements of mOEF in septal myocardium (coefficient of variation: 3.37%) and moderate for myocardial blood volume (coefficient of variation: 19.7%). The average mOEF and myocardial blood volume of 7 subjects at rest were 0.61 ± 0.05 and 11.0 ± 4.3%, respectively. The mOEF agreed well with literature values that were measured by PET in healthy volunteers. In the exercise study, there was no significant change in mOEF (0.61 ± 0.06 vs 0.62 ± 0.07) or myocardial blood volume (12 ± 6% vs 13 ± 4%) from rest to exercise, as expected.

CONCLUSION

The implemented cardiovascular magnetic resonance method shows potential for the quantitative assessment of mOEF in vivo. Future technical work is needed to improve image quality and to further validate mOEF measurements.

Non-contrast coronary magnetic resonance angiography: current frontiers and future horizons

Coronary magnetic resonance angiography (coronary MRA) is advantageous in its ability to assess coronary artery morphology and function without ionizing radiation or contrast media. However, technical limitations including reduced spatial resolution, long acquisition times, and low signal-to-noise ratios prevent it from clinical routine utilization. Nonetheless, each of these limitations can be specifically addressed by a combination of novel technologies including super-resolution imaging, compressed sensing, and deep-learning reconstruction. In this paper, we first review the current clinical use and motivations for non-contrast coronary MRA, discuss currently available coronary MRA techniques, and highlight current technical developments that hold unique potential to optimize coronary MRA image acquisition and post-processing. In the final section, we examine the various research-based coronary MRA methods and metrics that can be leveraged to assess coronary stenosis severity, physiological function, and atherosclerotic plaque characterization. We specifically discuss how such technologies may contribute to the clinical translation of coronary MRA into a robust modality for routine clinical use.

Exercise cardiovascular magnetic resonance: development, current utility and future applications

Stress cardiac imaging is the current first line investigation for coronary artery disease diagnosis and decision making and an adjunctive tool in a range of non-ischaemic cardiovascular diseases. Exercise cardiovascular magnetic resonance (Ex-CMR) has developed over the past 25 years to combine the superior image qualities of CMR with the preferred method of exercise stress. Presently, numerous exercise methods exist, from performing stress on an adjacent CMR compatible treadmill to in-scanner exercise, most commonly on a supine cycle ergometer. Cardiac conditions studied by Ex-CMR are broad, commonly investigating ischaemic heart disease and congenital heart disease but extending to pulmonary hypertension and diabetic heart disease. This review presents an in-depth assessment of the various Ex-CMR stress methods and the varied pulse sequence approaches, including those specially designed for Ex-CMR. Current and future developments in image acquisition are highlighted, and will likely lead to a much greater clinical use of Ex-CMR across a range of cardiovascular conditions.

Non-invasive assessment of coronary endothelial function in children and adolescents with type 1 diabetes mellitus using isometric handgrip exercise-MRI: A feasibility study

Background

Type 1 diabetes mellitus (T1DM) in children and adolescents is associated with significant cardiovascular morbidity and mortality. Early detection of vascular dysfunction is key to patient management yet current assessment techniques are invasive and not suitable for pediatric patient populations. A novel approach using isometric handgrip exercise during magnetic resonance imaging (IHE-MRI) has recently been developed to evaluate coronary endothelial function non-invasively in adults. This project aimed to assess endothelium-dependent coronary arterial response to IHE-MRI in children with T1DM and in age matched healthy controls.

Materials and methods

Healthy volunteers and children with T1DM (>5 years) were recruited. IHE-MRI cross-sectional coronary artery area measurements were recorded at rest and under stress. Carotid intima media thickness (CIMT) and aortic pulse wave velocity (PWV) were assessed for comparison. Student’s t-tests were used to compare results between groups.

Results and discussion

Seven children with T1DM (3 female, median 14.8 years, mean 14.8 ± 1.9 years) and 16 healthy controls (7 female, median 14.8 years, mean 14.2 ± 2.4 years) participated. A significant increase in stress-induced cross-sectional coronary area was measured in controls (5.4 mm² at rest to 6.39 mm² under stress, 18.8 ± 10.7%, p = 0.0004). In contrast, mean area change in patients with T1DM was not significant (7.17 mm² at rest to 7.59 mm² under stress, 10.5% ± 28.1%, p = n.s.). There was no significant difference in the results for neither PWV nor CIMT between patients and controls, (5.3±1.5 m/s vs.4.8±0.7 m/s and 0.4±0.03mm vs.0.46 mm ± 0.03 respectively, both p = n.s.).

Conclusions

Our pilot study demonstrates the feasibility of using a totally non-invasive IHE-MRI technique in children and adolescents with and without T1DM. Preliminary results suggest a blunted endothelium-dependent coronary vasomotor function in children with T1DM (>5 years). Better knowledge and new methodologies may improve surveillance and care for T1DM patients to reduce cardiovascular morbidity and mortality.

Feasibility of coronary endothelial function assessment using arterial spin labeled CMR

Coronary endothelial dysfunction (CED) is an independent predictor of cardiovascular disease, but its assessment has been limited to invasive coronary angiography. Myocardial perfusion imaging using arterial spin labeled (ASL) cardiac magnetic resonance (CMR) may be an effective non-invasive alternative for detection of CED. Thirty-four patients were recruited: 10 healthy volunteers, 13 at high-risk for coronary artery disease (CAD), and 11 with established CAD. ASL-CMR was performed continuously in a single mid-short axis slice during rest, stress, and recovery. Stress was induced with sustained isometric handgrip exercise, an endothelial dependent stressor. Myocardial perfusion (MP) during rest, peak stress, and recovery were calculated and compared. After excluding subjects unable to complete the protocol or who exhibited poor data quality, 6 healthy, 10 high-risk, and 7 CAD patients were included in the analysis. Average MP (ml/g/min) was 1.31 ± 1.23, 1.61 ± 1.12, and 1.40 ± 0.97 at rest, and 1.64 ± 1.49, 2.31 ± 1.61, and 2.84 ± 1.77 during stress, for the CAD, high-risk and healthy group, respectively. The average MP response (MP_stress - MP_rest , ml/g/min) was 0.32 ± 1.93, 0.69 ± 1.34, and 1.44 ± 1.46 for CAD, high-risk and healthy group, respectively. MP during handgrip stress was significantly lower for both the CAD (p = 0.0005) and high-risk groups (p = 0.05) compared to the healthy volunteers. In only the healthy subjects, MP was significantly higher in stress compared to rest (p = 0.0002). Participants with CAD had significantly lower MP response compared to healthy volunteers, as detected by ASL-CMR. These findings support the feasibility of ASL-CMR for non-invasive assessment of CED.

In vitro optimization and comparison of CT angiography versus radial cardiovascular magnetic resonance for the quantification of cross-sectional areas and coronary endothelial function

BACKGROUND

Our objectives were first to determine the optimal coronary computed tomography angiography (CTA) protocol for the quantification and detection of simulated coronary artery cross-sectional area (CSA) differences in vitro, and secondly to quantitatively compare the performance of the optimized CTA protocol with a previously validated radial coronary cardiovascular magnetic resonance (CMR) technique.

METHODS

256-multidetector CTA and radial coronary CMR were used to obtain images of a custom in vitro resolution phantom simulating a range of physiological responses of coronary arteries to stress. CSAs were automatically quantified and compared with known nominal values to determine the accuracy, precision, signal-to-noise ratio (SNR), and circularity of CSA measurements, as well as the limit of detection (LOD) of CSA differences. Various iodine concentrations, radiation dose levels, tube potentials, and iterative image reconstruction algorithms (ASiR-V) were investigated to determine the optimal CTA protocol. The performance of the optimized CTA protocol was then compared with a radial coronary CMR method previously developed for endothelial function assessment under both static and moving conditions.

RESULTS

The iodine concentration, dose level, tube potential, and reconstruction algorithm all had significant effects (all p <  0.001) on the accuracy, precision, LOD, SNR, and circularity of CSA measurements with CTA. The best precision, LOD, SNR, and circularity with CTA were achieved with 6% iodine, 20 mGy, 100 kVp, and 90% ASiR-V. Compared with the optimized CTA protocol under static conditions, radial coronary CMR was less accurate (- 0.91 ± 0.13 mm2 vs. -0.35 ± 0.04 mm2, p <  0.001), but more precise (0.08 ± 0.02 mm2 vs. 0.21 ± 0.02 mm2, p <  0.001), and enabled the detection of significantly smaller CSA differences (0.16 ± 0.06 mm2 vs. 0.52 ± 0.04 mm2; p <  0.001; corresponding to CSA percentage differences of 2.3 ± 0.8% vs. 7.4 ± 0.6% for a 3-mm baseline diameter). The same results held true under moving conditions as CSA measurements with CMR were less affected by motion.

CONCLUSIONS

Radial coronary CMR was more precise and outperformed CTA for the specific task of detecting small CSA differences in vitro, and was able to reliably identify CSA changes an order of magnitude smaller than those reported for healthy physiological vasomotor responses of proximal coronary arteries. However, CTA yielded more accurate CSA measurements, which may prove useful in other clinical scenarios, such as coronary artery stenosis assessment.

Effects of Catheterization on Artery Function and Health: When Should Patients Start Exercising Following Their Coronary Intervention?

Coronary artery disease (CAD) is a leading cause of death worldwide, and percutaneous transluminal coronary angiography (PTCA) and/or percutaneous coronary intervention (PCI; angioplasty) are commonly used to diagnose and/or treat the obstructed coronaries. Exercise-based rehabilitation is recommended for all CAD patients; however, most guidelines do not specify when exercise training should commence following PTCA and/or PCI. Catheterization can result in arterial dysfunction and acute injury, and given the fact that exercise, particularly at higher intensities, is associated with elevated inflammatory and oxidative stress, endothelial dysfunction and a pro-thrombotic milieu, performing exercise post-PTCA/PCI may transiently elevate the risk of cardiac events. This review aims to summarize extant literature relating to the impacts of coronary interventions on arterial function, including the time-course of recovery and the potential deleterious and/or beneficial impacts of acute versus long-term exercise. The current literature suggests that arterial dysfunction induced by catheterization recovers 4-12 weeks following catheterization. This review proposes that a period of relative arterial vulnerability may exist and exercise during this period may contribute to elevated event susceptibility. We therefore suggest that CAD patients start an exercise training programme between 2 and 4 weeks post-PCI, recognizing that the literature suggest there is a 'grey area' for functional recovery between 2 and 12 weeks post-catheterization. The timing of exercise onset should take into consideration the individual characteristics of patients (age, severity of disease, comorbidities) and the intensity, frequency and duration of the exercise prescription.

Precision and accuracy of cross-sectional area measurements used to measure coronary endothelial function with spiral MRI

PURPOSE

Coronary endothelial function (CEF) reflects vascular health and conventional invasive CEF measures predict cardiovascular events. MRI can now noninvasively measure CEF by quantifying coronary artery cross-sectional area changes in response to isometric handgrip exercise, an endothelial-dependent stressor. Area changes (10 to 20% in healthy; 2 to -12% in impaired vessels) are only a few imaging voxels because of MRI's limited spatial resolution. Here, with numerical simulations and phantom studies, we test whether Fourier interpolation enables sub-pixel area measurement precision and determine the smallest detectable area change using spiral MRI.

METHODS

In vivo coronary SNR with the currently used CEF protocol at 3T was measured in 7 subjects for subsequent in vitro work. Area measurements of circular vessels were simulated by varying partial volume, vessel diameter, voxel size, SNR, and Fourier interpolation factor. A phantom with precision-drilled holes (diameters 3-3.42 mm) was imaged 10 times with the current CEF protocol (voxel size, Δx = 0.89 mm) and a high-resolution protocol (Δx = 0.6 mm) to determine precision, accuracy, and the smallest detectable area changes.

RESULTS

In vivo coronary SNR ranged from 30-76. Eight-fold Fourier interpolation improved area measurement precision by a factor 6.5 and 4.9 in the simulations and phantom scans, respectively. The current CEF protocol can detect mean area changes of 4-5% for SNR above 30, and 3-3.5% for SNR above 40 with a higher-resolution protocol.

CONCLUSION

Current CEF spiral MRI with in vivo SNR allows detection of a 4-5% area change and Fourier interpolation improves precision several-fold to sub-voxel dimensions.

Coronary Endothelial Dysfunction Is Associated With Elevated Serum PCSK9 Levels in People With HIV Independent of Low-Density Lipoprotein Cholesterol

Background HIV + people are at increased risk of coronary artery disease, but the responsible mechanisms are incompletely understood. Proprotein convertase subtilisin/kexin type 9 ( PCSK 9) is traditionally recognized for its importance in cholesterol metabolism; however, recent data suggest an additional, low-density lipoprotein receptor-independent adverse effect on endothelial cell inflammation and function. We tested the hypotheses that PCSK 9 levels are increased and that abnormal coronary endothelial function is related to PCSK 9 serum levels in HIV + individuals. Methods and Results Forty-eight HIV + participants receiving antiretroviral therapy with suppressed viral replication, without coronary artery disease, and 15 age- and low-density lipoprotein cholesterol-matched healthy HIV- subjects underwent magnetic resonance imaging to measure coronary endothelial function, quantified as percentage change in coronary artery cross-sectional area during isometric handgrip exercise, an endothelial-dependent stressor; and blood was obtained for serum PCSK 9 and systemic vascular biomarkers. Data are presented as mean±SD. Mean serum PCSK 9 was 65% higher in the HIV + subjects (302±146 ng/ mL ) than in the HIV - controls (183±52 ng/ mL , P<0.0001). Coronary endothelial function was significantly reduced in the HIV + versus HIV - subjects (percentage change in coronary artery cross-sectional area, 2.9±9.6% versus 11.1±3.7%; P<0.0001) and inversely related to PCSK 9 ( R=-0.51, P<0.0001). Markers of endothelial activation and injury, P-selectin and thrombomodulin, were also significantly increased in the HIV + subjects; and P-selectin was directly correlated with serum PCSK 9 ( R=0.31, P=0.0144). Conclusions Serum PCSK 9 levels are increased in treated HIV + individuals and are associated with abnormal coronary endothelial function, an established measure of vascular health.

Self-gated golden angle spiral cine MRI for coronary endothelial function assessment

PURPOSE

Depressed coronary endothelial function (CEF) is a marker for atherosclerotic disease, an independent predictor of cardiovascular events, and can be quantified non-invasively with ECG-triggered spiral cine MRI combined with isometric handgrip exercise (IHE). However, MRI-CEF measures can be hindered by faulty ECG-triggering, leading to prolonged breath-holds and degraded image quality. Here, a self-gated golden angle spiral method (SG-GA) is proposed to eliminate the need for ECG during cine MRI.

METHODS

SG-GA was tested against retrospectively ECG-gated golden angle spiral MRI (ECG-GA) and gold-standard ECG-triggered spiral cine MRI (ECG-STD) in 10 healthy volunteers. CEF data were obtained from cross-sectional images of the proximal right and left coronary arteries in a 3T scanner. Self-gating heart rates were compared to those from simultaneous ECG-gating. Coronary vessel sharpness and cross-sectional area (CSA) change with IHE were compared among the 3 methods.

RESULTS

Self-gating precision, accuracy, and correlation-coefficient were 7.7 ± 0.5 ms, 9.1 ± 0.7 ms, and 0.93 ± 0.01, respectively (mean ± standard error). Vessel sharpness by SG-GA was equal or higher than ECG-STD (rest: 63.0 ± 1.7% vs. 61.3 ± 1.3%; exercise: 62.6 ± 1.3% vs. 56.7 ± 1.6%, P < 0.05). CSA changes were in agreement among the 3 methods (ECG-STD = 8.7 ± 4.0%, ECG-GA = 9.6 ± 3.1%, SG-GA = 9.1 ± 3.5%, P = not significant).

CONCLUSION

CEF measures can be obtained with the proposed self-gated high-quality cine MRI method even when ECG is faulty or not available. Magn Reson Med 80:560-570, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

The influence of febuxostat on coronary artery endothelial dysfunction in patients with coronary artery disease: A phase 4 randomized, placebo-controlled, double-blind, crossover trial

BACKGROUND

The xanthine oxidase (XO) system is a significant source of vascular oxidative stress, which is believed to impair endothelial function, an important contributor to atherosclerotic disease. We tested whether febuxostat, a potent XO inhibitor, improves coronary endothelial function (CEF) in patients with stable coronary artery disease (CAD) in a single-center, randomized, placebo-controlled, double-blind crossover trial.

METHODS

CEF was measured using noninvasive magnetic resonance imaging (MRI) assessment of changes in 30 patients with stable CAD and baseline impaired CEF. Patients received either febuxostat or placebo for 6 weeks and then were crossed over to the alternative for an additional 6 weeks. MRI-detected changes in coronary flow and in coronary cross-sectional area from rest to isometric handgrip exercise, a known endothelial-dependent stressor, were measured at the end of each 6 week period.

RESULTS

Mean serum urate levels were lower at the end of the 6-week febuxostat period (2.9±0.8mg/dL) than at the end of the 6-week placebo period (5.9±0.04, P<.001). However, there were no significant differences in any of the CEF parameters measured at the end of the febuxostat and placebo periods.

CONCLUSIONS

In summary, although XO inhibition with febuxostat was well tolerated and lowered serum urate, it did not improve the primary end point of the study, CEF measured using MRI after 6 weeks of treatment. In conclusion, these findings suggest that short-term inhibition of XO does not significantly improve impaired CEF in patients with stable CAD.

Coronary endothelial function is better in healthy premenopausal women than in healthy older postmenopausal women and men

BACKGROUND

Premenopausal women have fewer cardiovascular disease (CVD) events than postmenopausal women and age-matched men, but the reasons are not fully understood. Coronary endothelial function (CEF), a barometer of coronary vascular health, promises important insights into age and sex differences in atherosclerotic CVD risk, but has not been well characterized in healthy individuals because of the invasive nature of conventional CEF measurements. Recently developed magnetic resonance imaging (MRI) methods were used to quantify CEF (coronary area and flow changes in response to isometric handgrip exercise (IHE), an endothelial-dependent stressor) to test the hypothesis that healthy women have better CEF compared to men particularly at a younger age.

METHODS

The study participants were 50 healthy women and men with no history of coronary artery disease (CAD) or traditional CV risk factors and Agatston coronary calcium score (on prior CT) <10 for those ≥ 50 years. Coronary cross-sectional area (CSA) measurements and flow-velocity encoded images (CBF) were obtained at baseline and during continuous IHE using 3T breath-hold cine MRI-IHE. CEF (%change in CSA and CBF with IHE) comparisons were made according to age and sex, and all women ≥50 years were post-menopausal.

RESULTS

In the overall population, there were no differences in CEF between men and women. However, when stratified by age and sex the mean changes in CSA and CBF during IHE were higher in younger premenopausal women than older postmenopausal women (%CSA: 15.2±10.6% vs. 7.0±6.8%, p = 0.03 and %CBF: 59.0±37.0% vs. 30.5±24.5% p = 0.02). CBF change was also nearly two-fold better in premenopausal women than age-matched men (59.0±37.0% vs. 33.6±12.3%, p = 0.03).

CONCLUSIONS

Premenopausal women have nearly two-fold better mean CEF compared to postmenopausal women. CEF, measured by CBF change is also better in premenopausal women than age-matched men but there are no sex differences in CEF after menopause. Fundamental age and sex differences in CEF exist and may contribute to differences in the development and clinical manifestations of atherosclerotic CVD, and guide future trials targeting sex-specific mechanisms of atherogenesis.

Local coronary wall eccentricity and endothelial function are closely related in patients with atherosclerotic coronary artery disease

BACKGROUND

Coronary endothelial function (CEF) in patients with coronary artery disease (CAD) varies among coronary segments in a given patient. Because both coronary vessel wall eccentricity and coronary endothelial dysfunction are predictors of adverse outcomes, we hypothesized that local coronary endothelial dysfunction is associated with local coronary artery eccentricity.

METHODS

We used 3 T coronary CMR to measure CEF as changes in coronary cross-sectional area (CSA) and coronary blood flow (CBF) during isometric handgrip exercise (IHE), a known endothelial-dependent stressor, in 29 patients with known CAD and 16 healthy subjects. Black-blood MRI quantified mean coronary wall thickness (CWT) and coronary eccentricity index (EI) and CEF was determined in the same segments.

RESULTS

IHE-induced changes in CSA and CBF in healthy subjects (10.6 ± 6.6% and 38.3 ± 29%, respectively) were greater than in CAD patients 1.3 ± 7.7% and 6.5 ± 19.6%, respectively, p < 0.001 vs. healthy for both measures), as expected. Mean CWT and EI in healthy subjects (1.1 ± 0.3 mm 1.9 ± 0.5, respectively) were less than those in CAD patients (1.6 ± 0.4 mm, p < 0.0001; and 2.6 ± 0.6, p = 0.006 vs. healthy). In CAD patients, we observed a significant inverse relationship between stress-induced %CSA change and both EI (r = -0.60, p = 0.0002), and CWT (r = -0.54, p = 0.001). Coronary EI was independently and significantly related to %CSA change with IHE even after controlling for mean CWT (adjusted r = -0.69, p = 0.0001). For every unit increase in EI, coronary CSA during IHE is expected to change by -6.7 ± 9.4% (95% confidence interval: -10.3 to -3.0, p = 0.001).

CONCLUSION

There is a significant inverse and independent relationship between coronary endothelial macrovascular function and the degree of local coronary wall eccentricity in CAD patients. Thus anatomic and physiologic indicators of high-risk coronary vascular pathology are closely related. The noninvasive identification of coronary eccentricity and its relationship with underlying coronary endothelial function, a marker of vascular health, may be useful in identifying high-risk patients and culprit lesions.

Coronary artery endothelial dysfunction is present in HIV-positive individuals without significant coronary artery disease

OBJECTIVE

HIV-positive (HIV+) individuals experience an increased burden of coronary artery disease (CAD) not adequately accounted for by traditional CAD risk factors. Coronary endothelial function (CEF), a barometer of vascular health, is depressed early in atherosclerosis and predict future events but has not been studied in HIV+ individuals. We tested whether CEF is impaired in HIV+ patients without CAD as compared with an HIV-negative (HIV-) population matched for cardiac risk factors.

DESIGN/METHODS

In this observational study, CEF was measured noninvasively by quantifying isometric handgrip exercise-induced changes in coronary vasoreactivity with MRI in 18 participants with HIV but no CAD (HIV+CAD-, based on prior imaging), 36 age-matched and cardiac risk factor-matched healthy participants with neither HIV nor CAD (HIV-CAD-), 41 patients with no HIV but with known CAD (HIV-CAD+), and 17 patients with both HIV and CAD (HIV+CAD+).

RESULTS

CEF was significantly depressed in HIV+CAD- patients as compared with that of risk-factor-matched HIV-CAD- patients (P < 0.0001) and was depressed to the level of that in HIV- participants with established CAD. Mean IL-6 levels were higher in HIV+ participants (P < 0.0001) and inversely related to CEF in the HIV+ patients (P = 0.007).

CONCLUSION

Marked coronary endothelial dysfunction is present in HIV+ patients without significant CAD and is as severe as that in clinical CAD patients. Furthermore, endothelial dysfunction appears inversely related to the degree of inflammation in HIV+ patients as measured by IL-6. CEF testing in HIV+ patients may be useful for assessing cardiovascular risk and testing new CAD treatment strategies, including those targeting inflammation.

Simultaneous Noninvasive Assessment of Systemic and Coronary Endothelial Function

BACKGROUND

Normal endothelial function is a measure of vascular health and dysfunction is a predictor of coronary events. Nitric oxide-mediated coronary artery endothelial function, as assessed by vasomotor reactivity during isometric handgrip exercise (IHE), was recently quantified noninvasively with magnetic resonance imaging (MRI). Because the internal mammary artery (IMA) is often visualized during coronary MRI, we propose the strategy of simultaneously assessing systemic and coronary endothelial function noninvasively by MRI during IHE.

METHODS AND RESULTS

Changes in cross-sectional area and blood flow in the right coronary artery and the IMA in 25 patients with coronary artery disease and 26 healthy subjects during IHE were assessed using 3T MRI. In 8 healthy subjects, a nitric oxide synthase inhibitor was infused to evaluate the role of nitric oxide in the IMA-IHE response. Interobserver IMA-IHE reproducibility was good for cross-sectional area (R=0.91) and blood flow (R=0.91). In healthy subjects, cross-sectional area and blood flow of the IMA increased during IHE, and these responses were significantly attenuated by monomethyl-l-arginine (P<0.01 versus placebo). In patients with coronary artery disease, the right coronary artery did not dilate with IHE, and dilation of the IMA was less than that of the healthy subjects (P=0.01). The blood flow responses of both the right coronary artery and IMA to IHE were also significantly reduced in patients with coronary artery disease.

CONCLUSIONS

MRI-detected IMA responses to IHE primarily reflect nitric oxide-dependent endothelial function and are reproducible and reduced in patients with coronary artery disease. Endothelial function in both coronary and systemic (IMA) arteries can now be measured noninvasively with the same imaging technique and promises novel insights into systemic and local factors affecting vascular health.

Isometric stress in cardiovascular magnetic resonance-a simple and easily replicable method of assessing cardiovascular differences not apparent at rest

INTRODUCTION

Isometric exercise may unmask cardiovascular disease not evident at rest, and cardiovascular magnetic resonance (CMR) imaging is proven for comprehensive resting assessment. This study devised a simple isometric exercise CMR methodology and assessed the hemodynamic response evoked by isometric exercise.

METHODS

A biceps isometric exercise technique was devised for CMR, and 75 healthy volunteers were assessed at rest, after 3-minute biceps exercise, and 5-minute of recovery using: 1) blood pressure (BP) and 2) CMR measured aortic flow and left ventricular function. Total peripheral resistance (SVR) and arterial compliance (TAC), cardiac output (CO), left ventricular volumes and function (ejection fraction, stroke volume, power output), blood pressure (BP), heart rate (HR), and rate pressure product were assessed at all time points.

RESULTS

Image quality was preserved during stress. During exercise there were increases in CO (+14.9 %), HR (+17.0 %), SVR (+9.8 %), systolic BP (+22.4 %), diastolic BP (+25.4 %) and mean BP (+23.2 %). In addition, there were decreases in TAC (-22.0 %) and left ventricular ejection fraction (-6.3 %). Age and body mass index modified the evoked response, even when resting measures were similar.

CONCLUSIONS

Isometric exercise technique evokes a significant cardiovascular response in CMR, unmasking physiological differences that are not apparent at rest.

KEY POINTS

• Isometric exercise unmasks cardiovascular differences not evident at rest. • CMR is the reference standard for non-invasive cardiovascular assessment at rest. • A new easily replicable method combines isometric exercise with CMR. • Significant haemodynamic changes occur and differences are unmasked. • The physiological, isometric CMR stressor can be easily replicated.

Coronary vasomotor responses to isometric handgrip exercise are primarily mediated by nitric oxide: a noninvasive MRI test of coronary endothelial function

Endothelial cell release of nitric oxide (NO) is a defining characteristic of nondiseased arteries, and abnormal endothelial NO release is both a marker of early atherosclerosis and a predictor of its progression and future events. Healthy coronaries respond to endothelial-dependent stressors with vasodilatation and increased coronary blood flow (CBF), but those with endothelial dysfunction respond with paradoxical vasoconstriction and reduced CBF. Recently, coronary MRI and isometric handgrip exercise (IHE) were reported to noninvasively quantify coronary endothelial function (CEF). However, it is not known whether the coronary response to IHE is actually mediated by NO and/or whether it is reproducible over weeks. To determine the contribution of NO, we studied the coronary response to IHE before and during infusion of N(G)-monomethyl-l-arginine (l-NMMA, 0.3 mg·kg(-1)·min(-1)), a NO-synthase inhibitor, in healthy volunteers. For reproducibility, we performed two MRI-IHE studies ~8 wk apart in healthy subjects and patients with coronary artery disease (CAD). Changes from rest to IHE in coronary cross-sectional area (%CSA) and diastolic CBF (%CBF) were quantified. l-NMMA completely blocked normal coronary vasodilation during IHE [%CSA, 12.9 ± 2.5 (mean ± SE, placebo) vs. -0.3 ± 1.6% (l-NMMA); P < 0.001] and significantly blunted the increase in flow [%CBF, 47.7 ± 6.4 (placebo) vs. 10.6 ± 4.6% (l-NMMA); P < 0.001]. MRI-IHE measures obtained weeks apart strongly correlated for CSA (P < 0.0001) and CBF (P < 0.01). In conclusion, the normal human coronary vasoactive response to IHE is primarily mediated by NO. This noninvasive, reproducible MRI-IHE exam of NO-mediated CEF promises to be useful for studying CAD pathogenesis in low-risk populations and for evaluating translational strategies designed to alter CAD in patients.

Multimodality Imaging in Ischemic Cardiomyopathy

Cardiac multimodality (hybrid) imaging can be obtained from a variety of techniques, such as nuclear medicine with single photon emission computed tomography (SPECT) and positron emission tomography (PET), or radiology with multislice computed tomography (CT), magnetic resonance (MR) and echography. They are typically combined in a side-by-side or fusion mode in order to provide functional and morphological data to better characterise coronary artery disease, with more proven efficacy than when used separately. The gained information is then used to guide revascularisation procedures. We present an up-to-date comprehensive overview of multimodality imaging already in clinical use, as well as a combination of techniques with promising or developing applications.