Pulmonary artery distensibility and blood flow patterns: a magnetic resonance study of normal subjects and of patients with pulmonary arterial hypertension

MRI evaluation of right heart functions in children with mild cystic fibrosis

BACKGROUND

This study aimed to assess the ventricular anatomy, function of the right ventricle, and the haemodynamic findings of pulmonary artery in children with cystic fibrosis using cardiac MRI.

PATIENTS

This prospective study consisted of 32 children with mild cystic fibrosis and 30 age-matched healthy control participants.

METHODS

Cardiac MRI was used to assess right ventricular volumes, anatomy, and function and to assessment of haemodynamic findings of pulmonary artery in the control and study groups. Haemodynamic findings of pulmonary arteries were determined using pulmonary arteries peak velocity (cm/s), and pulmonary arteries time-to-peak velocity (ms) and pulmonary artery systolic pressure. All data of children with mild cystic fibrosis were compared with those of 30 age-matched healthy control group participants.

RESULTS

Our patients and their age-matched controls were aged from 6 to 17 years and from 7 to 15 years, respectively. We found that ejection fraction (%), cardiac output (L/ml), cardiac output (L/ml/m2), and systolic volume (ml/m2) were significantly lower in children with cystic fibrosis (p < 0.01). Right ventricular anterior wall thickness (mm) was significantly higher in children with cystic fibrosis (p = 0.01). No significant difference was observed between the haemodynamic parameters of pulmonary artery in the patient group.

CONCLUSION

In our study, cardiac MRI was used to investigate whether the right ventricle was affected functionally and anatomically in children with mild cystic fibrosis. We detected a significant decrease in right ventricular systolic functions and notable alterations in the right ventricular geometry of children with mild cystic fibrosis. These alterations usually manifest themselves as hypertrophy of the right ventricle. Our study's results demonstrate no relationship between the development of pulmonary hypertension in mild cystic fibrosis children.

Quantitative Imaging Metrics for the Assessment of Pulmonary Pathophysiology: An Official American Thoracic Society and Fleischner Society Joint Workshop Report

Multiple thoracic imaging modalities have been developed to link structure to function in the diagnosis and monitoring of lung disease. Volumetric computed tomography (CT) renders three-dimensional maps of lung structures and may be combined with positron emission tomography (PET) to obtain dynamic physiological data. Magnetic resonance imaging (MRI) using ultrashort-echo time (UTE) sequences has improved signal detection from lung parenchyma; contrast agents are used to deduce airway function, ventilation-perfusion-diffusion, and mechanics. Proton MRI can measure regional ventilation-perfusion ratio. Quantitative imaging (QI)-derived endpoints have been developed to identify structure-function phenotypes, including air-blood-tissue volume partition, bronchovascular remodeling, emphysema, fibrosis, and textural patterns indicating architectural alteration. Coregistered landmarks on paired images obtained at different lung volumes are used to infer airway caliber, air trapping, gas and blood transport, compliance, and deformation. This document summarizes fundamental "good practice" stereological principles in QI study design and analysis; evaluates technical capabilities and limitations of common imaging modalities; and assesses major QI endpoints regarding underlying assumptions and limitations, ability to detect and stratify heterogeneous, overlapping pathophysiology, and monitor disease progression and therapeutic response, correlated with and complementary to, functional indices. The goal is to promote unbiased quantification and interpretation of in vivo imaging data, compare metrics obtained using different QI modalities to ensure accurate and reproducible metric derivation, and avoid misrepresentation of inferred physiological processes. The role of imaging-based computational modeling in advancing these goals is emphasized. Fundamental principles outlined herein are critical for all forms of QI irrespective of acquisition modality or disease entity.

Right Pulmonary Artery Distensibility Index in Heartworm Infected Dogs: Are the Different Methods Leading to Same Results?

Canine Heartworm Disease (HWD) is mainly a pulmonary vascular disease. The reduction of the Pulmonary Artery Distensibility (PAD) is an early index of pulmonary vascular disease. Echocardiographic evaluation of the Right Pulmonary Artery Distensibility index (RPADi) is calculated as the percentage change in diameter of the right pulmonary artery (RPA) between systole and diastole. Historically, two main methods have been used for RPADi calculation: The Venco method and Visser method; however, different hybrid methods have also been used by other authors. Therefore, it could be difficult for a clinician to decide which method to apply and how to interpret the results based on the reference values reported. The aim of this study was to compare the RPADi obtained by five different techniques (Venco classic, Venco modified, Visser classic, Visser modified 1, and Visser modified 2). The study design was a retrospective, single center, observational study. Forty-seven client-owned dogs were included. The measurements were performed off-line as an average of three consecutive cardiac cycles by a single investigator blinded to the dogs' diagnosis. The RPADi was satisfactorily obtained by all methods in all dogs. Intra-observer measurement variability was clinically acceptable both for systolic and diastolic measurements. Although the Bland-Altman test showed a statistical agreement between the various methods used to calculate the RPADi, these methods cannot be used interchangeably in a clinical setting. Instead, the measurement method and reference values should always be specified.

A Clinical Approach to Multimodality Imaging in Pulmonary Hypertension

Pulmonary hypertension (PH) is a clinical condition characterized by progressive elevations in mean pulmonary artery pressures and right ventricular dysfunction, associated with significant morbidity and mortality. For resting PH to develop, ~50-70% of the pulmonary vasculature must be affected, suggesting that even mild hemodynamic abnormalities are representative of advanced pulmonary vascular disease. The definitive diagnosis of PH is based upon hemodynamics measured by right heart catheterization; however this is an invasive and resource intense study. Early identification of pulmonary vascular disease offers the opportunity to improve outcomes by instituting therapies that slow, reverse, or potentially prevent this devastating disease. Multimodality imaging, including non-invasive modalities such as echocardiography, computed tomography, ventilation perfusion scans, and cardiac magnetic resonance imaging, has emerged as an integral tool for screening, classifying, prognosticating, and monitoring response to therapy in PH. Additionally, novel imaging modalities such as echocardiographic strain imaging, 3D echocardiography, dual energy CT, FDG-PET, and 4D flow MRI are actively being investigated to assess the severity of right ventricular dysfunction in PH. In this review, we will describe the utility and clinical application of multimodality imaging techniques across PH subtypes as it pertains to screening and monitoring of PH.

Effect of pulsatile stretch on unfolded protein response in a new model of the pulmonary hypertensive vascular wall

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by hypoxemia and arterial remodeling. Dynamic stretch and recoil of the arterial wall during pulsation (in normal conduit arteries, stretch 20% above diastolic diameter) maintains homeostasis; a static arterial wall is associated with remodeling. PPHN is diagnosed by echocardiography as decreased pulmonary artery wall displacement during systole, causing decreased pulmonary arterial pressure acceleration time in a stiff artery. We hypothesized that a 'normal' amplitude of pulsatile stretch is protective against ER stress, while the loss of stretch is a trigger for hypoxia-induced stress responses. Using a novel in vitro model of pulmonary arterial myocytes subject to repetitive stretch-relaxation cycles within a normoxic or hypoxic environment, we examined the relative impact of hypoxia (pulmonary circuit during unresolved PPHN) and cyclic mechanical stretch (diminished in PPHN) on myocyte homeostasis, specifically on signaling proteins for autophagy and endoplasmic reticulum (ER) stress. Stretch induced autophagosome abundance under electron microscopy. Hypoxia, in presence or absence of pulsatile stretch, decreased unfolded protein response (UPR) hallmark BIP (GRP78) in contractile phenotype pulmonary arterial myocytes. Inositol requiring enzyme-1 α (IRE1α) was not activated; but hypoxia induced eif2α phosphorylation, increasing expression of ATF4 (activating transcription factor-4). This was sensitive to inhibition by autophagy inhibitor bafilomycin A1. We conclude that in the pulmonary circuit, hypoxia induces one arm of the UPR pathway and causes ER stress. Pulsatile stretch ameliorates the hypoxic UPR response, and while increasing presence of autophagosomes, does not activate canonical autophagy signaling pathways. We propose that simultaneous application of hypoxia and graded levels of cyclic stretch can be used to distinguish myocyte signaling in the deformable pulmonary artery of early PPHN, versus the inflexible late stage PPHN artery.

Cardiac Magnetic Resonance Imaging in Pulmonary Arterial Hypertension: Ready for Clinical Practice and Guidelines?

Purpose of Review

Pulmonary arterial hypertension (PAH) is a progressive disease with high mortality. A greater understanding of the physiology and function of the cardiovascular system in PAH will help improve survival. This review covers the latest advances within cardiovascular magnetic resonance imaging (CMR) regarding diagnosis, evaluation of treatment, and prognostication of patients with PAH.

Recent Findings

New CMR measures that have been proven relevant in PAH include measures of ventricular and atrial volumes and function, tissue characterization, pulmonary artery velocities, and arterio-ventricular coupling.

Summary

CMR markers carry prognostic information relevant for clinical care such as treatment response and thereby can affect survival. Future research should investigate if CMR, as a non-invasive method, can improve existing measures or even provide new and better measures in the diagnosis, evaluation of treatment, and determination of prognosis of PAH.

Aging influences pulmonary artery flow and stiffness in healthy individuals: non-invasive assessment using cardiac MRI

AIM

To investigate age-related changes of the pulmonary artery (PA) using cardiac magnetic resonance imaging (cMRI) in healthy subjects.

MATERIALS AND METHODS

A cross-sectional observational study was conducted on apparently healthy subjects who underwent PA velocity-encoded cMRI. cMRI was used to determine PA stiffness parameters such as PA elasticity, relative area change (PA-RAC) and pulse-wave velocity (PA-PWV), and PA flow parameters by subtracting simultaneous forward flow (FF) and backward flow (BF) velocity across the PA cross-section. Data were presented in five age and sex matched groups.

RESULTS

One hundred and fifty subjects (20-70 years, 75 men) met the enrolment criteria. PA elasticity and PA-RAC significantly decreased with age (p<0.001), while PA-PWV, regurgitant volume (V_reg) and backward flow volume (V_BF) increased in the elderly (p<0.001). Linear regression analysis indicated that PA elasticity (r=-0.441, p<0.0001) and PA-RAC (r=-0.484, p<0.0001) were indirectly and negatively associated with advancing age, whereas PA_min (r=0.331, p<0.0001), PA-PWV (r=0.490, p<0.0001), V_Reg (r=0.335, p<0.0001) and V_BF (r=0.349, p<0.0001) were directly associated with age. Multivariate analysis indicated that age was independently associated with V_reg and V_BF, and the addition of PA_min and PA-PWV marginally increased its predictive capacity.

CONCLUSION

Aging significantly increases cMRI-based PA flow and stiffness parameters. These could become relevant markers of subclinical changes of the PA geometry in healthy subjects.

Transthoracic M-mode echocardiographic assessment of pulmonary vein-to-pulmonary artery ratio in healthy horses

Equine cardiovascular structures and function are routinely assessed by transthoracic echocardiography. Recently, investigators have described the echocardiographic visualization of equine pulmonary vein ostia. In companion animals, the right pulmonary vein (RPV) to right pulmonary artery (RPA) ratio has been used as an index to estimate the severity of cardiac diseases resulting in left ventricular volume overload. We sought to assess the feasibility of measuring RPV and RPA dimensions, and sought to provide various previously examined RPV and RPA variables in clinically healthy horses that could be used to assess cardiopulmonary disease status. Echocardiographic examination was prospectively performed in 70 healthy horses. The RPV and RPA were visualized using a modified right parasternal long-axis view and maximum and minimum diameters of both vessels were measured from 2D guided M-mode traces. The aortic diameter (Ao) was measured from the right parasternal short-axis view in early diastole. These measurements were then used to produce various ratio indices. RPV and RPA were imaged in all 70 horses. Median of the minimum and maximum RPV/RPA was 0.51 and 0.60, respectively. Median fractional dimensional change of vessels was 33% for RPV and 22% for RPA. The medians of the minimum and maximum RPV/Ao and RPA/Ao were 0.18, 0.28, 0.35 and 0.46, respectively. No relationships between either bodyweight or heart rate and any of the vein or artery variables were identified (maximum r2 = 0.04). Inter- and intra-observer measurement variability was very good for all RPV and RPA measurements. Measuring of RPV and RPA diameters using M-mode transthoracic echocardiography is feasible in healthy horses. Further studies of these variables in horses with cardiac diseases are needed to determine the clinical applicability and utility.

Influence of coupled hemodynamics-arterial wall interaction on compliance in a realistic pulmonary artery with variable intravascular wall properties

Pulmonary hypertension is characterized by elevation of pulmonary artery (PA) pressure (p) and structural remodeling of the PA wall, leading to reduction in arterial compliance (c). As a step towards improving diagnosis of pulmonary disease, we use the PA branch geometry (main pulmonary artery (MPA) branching into left (LPA) and right (RPA) pulmonary arteries) obtained from MRI in conjunction with an inverse algorithm to obtain the pre-stress level in the artery walls. Next, a coupled blood-wall interaction (BWI) calculation provides hemodynamic information as well as compliance of the PA walls. We show that the computed load-free geometry from the inverse algorithm exhibits a 27.8% lower inner diameter (d) and 18.5% lower outer d compared to the in vivo geometry from MRI. Further, the mean p computed from the BWI computation in the main PA (p_MPA-n) is within 4% of the mean p_MPA-e (n-numerical; e-experimental). Also, the mean Q computed in the left PA (Q_LPA-n) is within 10% of the mean Q_LPA-e. Finally, the compliance c_MPA-n is computed to be 27% lower than c_MPA-e, while the c_LPA-n is computed to be 20.4% lower than c_LPA-e. Importantly, the PA shows significant intra-vascular variation in compliance, with the MPA showing higher overall compliance compared to the LPA (3.5-4 times).

A preliminary study for the assessment of hypertension using static and dynamic IR thermograms

Structural changes in blood vessels occur due to prolonged hypertension. Early detection of blood pressure (mm Hg) is essential for disease prevention. The aim of this work is to propose a computer-aided diagnostic (CADx) model for the diagnosis of hypertension using variables derived from non-contact static and dynamic thermal imaging in comparison with the pulse wave velocity (PWV)-derived parameters. Static and dynamic infrared (IR) thermograms of selected skin areas of the body from known hypertensive (n=14) and age- and sex-matched normal subjects were captured. The average skin surface temperature [SST (°C)] of selected skin areas of the body was calculated from a static IR thermogram. After denoising the dynamic IR thermogram using wavelets, the statistical variables power, mean, standard deviation (SD), variance, skewness and kurtosis were calculated. The variables derived from both static and dynamic thermograms were used to develop the CADx model. The performance of the CAD model was also tested by feature selection using principal component analysis (PCA). An accuracy of 75% (sensitivity=78.6%, specificity=71.4%) could be achieved with the average SST (°C) of the static IR thermogram alone. The statistical variables derived from the dynamic IR thermogram alone gave an accuracy of 82% (and 85% after feature selection by PCA), whereas the accuracy using standard methods like variables derived from PWV was only 71.4% (with and without feature selection). The highest accuracy of 89% could be achieved by combining variables like average SST (°C) measured from static and dynamic IR thermograms and PWV-derived variables.

Impaired cardiac output during exercise in adults operated for ventricular septal defect in childhood: a hitherto unrecognised pathophysiological response

BACKGROUND

Recent studies have demonstrated that surgical ventricular septal defect closure in childhood is associated with reduced functional capacity and disruption of the right ventricular force-frequency relationship during exercise. To further describe long-term cardiac function, we performed a non-invasive assessment of cardiac index during exercise in adults having undergone surgery for ventricular septal defect in early childhood.

METHODS

A total of 20 patients (surgical age 2.1±1.4 years, age at examination 22.1±2.2 years) and 20 healthy, matched controls (23.4±2.1 years at examination) underwent continuous supine bicycle ergometry during MRI. Their blood flow was recorded in the ascending aorta and the pulmonary trunk at increasing exercise levels. Cardiac index, retrograde flow, and vessel diameters were determined by blinded, post hoc analyses.

RESULTS

The patient group had normal cardiac index at rest (2.9±0.7 L/minute/m2), which was comparable with that of the controls (3.0±0.6 L/minute/m2); however, they had a lower increase in cardiac index during exercise (reaching 7.3±1.3 L/minute/m2 at submaximal exercise) compared with controls (8.2±1.2 L/minute/m2), p<0.05. Patients had a significantly higher ascending aorta retrograde flow than controls at rest and throughout exercise. In the pulmonary artery, the retrograde flow was minimal at rest in both groups, but increased significantly in patients during exercise compared with controls.

CONCLUSIONS

Young adults with a surgically closed ventricular septal defect have a reduced cardiac index during exercise compared with healthy, young adults. The impaired cardiac index appears to be related to an increasing retrograde flow in the pulmonary artery with progressive exertion.

Pulmonary Vascular Distensibility Predicts Pulmonary Hypertension Severity, Exercise Capacity, and Survival in Heart Failure

BACKGROUND

Pulmonary vascular (PV) distensibility, defined as the percent increase in pulmonary vessel diameter per mm Hg increase in pressure, permits the pulmonary vessels to increase in size to accommodate increased blood flow. We hypothesized that PV distensibility is abnormally low in patients with heart failure (HF) and serves as an important determinant of right ventricular performance and exercise capacity.

METHODS AND RESULTS

Patients with HF with preserved ejection fraction (n=48), HF with reduced ejection fraction (n=55), pulmonary arterial hypertension without left heart failure (n=18), and control subjects (n=30) underwent cardiopulmonary exercise testing with invasive hemodynamic monitoring and first-pass radionuclide ventriculography. PV distensibility was derived from 1257 matched measurements (mean±SD, 8.3±2.8 per subject) of pulmonary arterial pressure, pulmonary arterial wedge pressure and cardiac output. PV distensibility was lowest in the pulmonary arterial hypertension group (0.40±0.24% per mm Hg) and intermediate in the HF with preserved ejection fraction and HF with reduced ejection fraction groups (0.92±0.39 and 0.84±0.33% per mm Hg, respectively) compared to the control group (1.39±0.32% per mm Hg, P<0.0001 for all three). PV distensibility was associated with change in right ventricular ejection fraction (RVEF, ρ=0.39, P<0.0001) with exercise and was an independent predictor of peak VO2. PV distensibility also predicted cardiovascular mortality independent of peak VO2 in HF patients (n=103; Cox hazard ratio, 0.30; 95% confidence interval, 0.10-0.93; P=0.036). In a subset of patients with HF with reduced ejection fraction (n=26), 12 weeks of treatment with the pulmonary vasodilator sildenafil or placebo led to a 24.6% increase in PV distensibility (P=0.015) in the sildenafil group only.

CONCLUSIONS

PV distensibility is reduced in patients with HF and pulmonary arterial hypertension and is closely related to RV systolic function during exercise, maximal exercise capacity, and survival. Furthermore, PV distensibility is modifiable with selective pulmonary vasodilator therapy and may represent an important target for therapy in selected HF patients with pulmonary hypertension.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00309790.

Breath-hold and free-breathing 2D phase-contrast MRI for quantification of oxygen-induced changes of pulmonary circulation dynamics in healthy volunteers

PURPOSE

To evaluate the effect of inhaled 100% oxygen on pulmonary circulation dynamics in healthy volunteers using 2D phase-contrast magnetic resonance imaging (2D PC MRI).

MATERIALS AND METHODS

Twenty-one healthy volunteers were examined at 1.5T. Through-plane 2D PC MRI measurements were performed in the main pulmonary artery during free-breathing and breath-hold. Acceleration time and volume, maximum and minimum area, area change, average and maximum mean velocity, forward volume, heart rate, as well as blood pressure were determined. At baseline, subjects breathed room air. After application of a closed-fit full face mask, three further measurements were conducted: at room air (control), directly after starting 15 L/min 100% oxygen (wash-in), and after 5 minutes during continuous oxygen supply (saturation). Data were analyzed with a mixed linear model. Skewed distributed variables were rank-transformed. Tukey contrasts with family-wise adjusted P-values were applied for pairwise comparisons.

RESULTS

Inhaled oxygen affected several hemodynamic parameters. Average mean velocity (P < 0.01: breath-hold during wash-in and saturation, P = 0.03: free-breathing during saturation) and maximum mean velocity (P < 0.01: breath-hold and free-breathing during saturation) decreased. When obtained during free-breathing, acceleration volume (P = 0.02: saturation), area change (P = 0.02: saturation), and maximum area (P = 0.02: wash-in, P = 0.03: saturation) increased, while minimum area and forward volume did not change.

CONCLUSION

Oxygen alters pulmonary circulation dynamics in the main pulmonary artery of healthy volunteers, which can be reliably detected using 2D phase-contrast MRI.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1698-1706.

Evaluation of Hemodynamics in a Prestressed and Compliant Tapered Femoral Artery Using an Optimization-Based Inverse Algorithm

The important factors that affect the arterial wall compliance are the tissue properties of the arterial wall, the in vivo pulsatile pressure, and the prestressed condition of the artery. It is necessary to obtain the load-free geometry for determining the physiological level of prestress in the arterial wall. The previously developed optimization-based inverse algorithm was improved to obtain the load-free geometry and the wall prestress of an idealized tapered femoral artery of a dog under varying arterial wall properties. The compliance of the artery was also evaluated over a range of systemic pressures (72.5–140.7 mmHg), associated blood flows, and artery wall properties using the prestressed arterial geometry. The results showed that the computed load-free outer diameter at the inlet of the tapered artery was 6.7%, 9.0%, and 12% smaller than the corresponding in vivo diameter for the 25% softer, baseline, and 25% stiffer arterial wall properties, respectively. In contrast, the variations in the prestressed geometry and circumferential wall prestress were less than 2% for variable arterial wall properties. The computed compliance at the inlet of the prestressed artery for the baseline arterial wall property was 0.34%, 0.19%, and 0.13% diameter change/mmHg for time-averaged pressures of 72.5, 104.1, and 140.7 mmHg, respectively. However, the variation in compliance due to the change in arterial wall property was less than 6%. The load-free and prestressed geometries of the idealized tapered femoral artery were accurately (error within 1.2% of the in vivo geometry) computed under variable arterial wall properties using the modified inverse algorithm. Based on the blood-arterial wall interaction results, the arterial wall compliance was influenced significantly by the change in average pressure. In contrast, the change in arterial wall property did not influence the arterial wall compliance.

Canine pulmonary vein-to-pulmonary artery ratio: echocardiographic technique and reference intervals

OBJECTIVES

The size of the pulmonary veins (PVs) and pulmonary arteries (PAs) changes in response to hemodynamic alterations caused by physiological events and disease. We sought to create standardized echocardiographic methods for imaging the right ostium of the pulmonary veins (RPVs) and the right pulmonary artery (RPA) using specific landmarks and timing to quantify vessel diameters and phasic changes during the cardiac cycle.

ANIMALS

Fifty client-owned healthy dogs prospectively recruited.

METHODS

M-mode and 2-dimensional images were obtained from modified right parasternal long and short axis views. Right ostium of the pulmonary veins and RPA measurements were timed with electrical [peak of the QRS complex (RPV_QRS and RPA_QRS) and end of T wave (RPV_T and RPA_T)] or mechanical events [RPV and RPA vessels at their respective maximal (RPV_MAX; RPA_MAX) and minimal (RPV_MIN; RPA_MIN) diameters]. Right ostium of the pulmonary veins and RPA measurements were also indexed to the aorta.

RESULTS

In normal dogs regardless of the echocardiographic view or time in the cardiac cycle, the RPV/RPA ratio approximated 1.0. Mechanically timed fractional changes (distensibility indices) in RPV and RPA diameters did not differ (p=0.99; 36.9% and 36.8%, respectively). ECG-timed fractional changes (distensibility indices) in RPV and RPA diameter were at least 50% smaller than mechanically timed changes (p<0.05). RPV:Ao and RPA:Ao ranged between 0.3 and 0.6, with lower values obtained in diastole and larger values in systole (p<0.0001). Multiple positive and negative deflections were identified on the RPV and RPA M-mode tracings.

CONCLUSION

This study provides detailed methodology and 2D and M-mode reference intervals for the RPV and RPA dimensions and the phasic changes during the cardiac cycle of the dog using echocardiography.

Vicious circle between progressive right ventricular dilatation and pulmonary regurgitation in patients after tetralogy of Fallot repair? Right heart enlargement promotes flow reversal in the left pulmonary artery

BACKGROUND

The left pulmonary artery (LPA) contributes more than the right (RPA) to total pulmonary regurgitation (PR) in patients after tetralogy of Fallot (TOF) repair, but the mechanism of this difference is not well understood. This study aimed to analyze the interplay between heart and lung size, mediastinal geometry, and differential PR.

METHODS

Forty-eight Cardiovascular Magnetic Resonance (CMR) studies in patients after TOF repair were analyzed. In addition to the routine blood flow and ventricular volume quantification cardiac angle between the thoracic anterior-posterior line and the interventricular septum, right and left lung areas as well as right and left hemithorax areas were measured on an axial image. Statistical analysis was performed to compare flow parameters between RPA and LPA and to assess correlation among right ventricular volume, pulmonary blood flow parameters and lung area.

RESULTS

There was no difference between LPA and RPA diameters. The LPA showed significantly less total forward flow (2.49 ± 0.87 L/min/m(2) vs 2.86 ± 0.89 L/min/m(2); p = 0.02), smaller net forward flow (1.40 ± 0.51 vs 1.89 ± 0.60 mL/min/m(2); p = <0.001), and greater regurgitant fraction (RF) (34 ± 10 % vs 43 ± 12 %; p = 0.001) than the RPA. There was no difference in regurgitant flow volume between RPA and LPA (p = 0.29). Indexed right ventricular end-diastolic volume (RVEDVi) correlated with LPA RF (R = 0.48, p < 0.001), but not with RPA RF (p = 0.09). Larger RVEDVi correlated with a more leftward cardiac axis (R = 0.46, p < 0.001) and with smaller left lung area (R = -0.58, p < 0.001). LPA RF, but not RPA RF, correlated inversely with left lung area (R = -0.34, p = 0.02). The follow-up CMRs in 20 patients showed a correlation of the rate of RV enlargement with the rates of LPA RF worsening (R = 0.50, p = 0.03), and of increasing left lung compression (R = -0.55, p = 0.012).

CONCLUSION

An enlarged and levorotated heart is associated with left lung compression and impaired flow into the left lung.

MR and CT Imaging for the Evaluation of Pulmonary Hypertension

Imaging plays a central role in the diagnosis and management of all forms of pulmonary hypertension (PH). Although Doppler echocardiography is essential for the evaluation of PH, its ability to optimally evaluate the right ventricle and pulmonary vasculature is limited by its 2-dimensional planar capabilities. Magnetic resonance and computed tomography are capable of determining the etiology and pathophysiology of PH, and can be very useful in the management of these patients. Exciting new techniques such as right ventricle tissue characterization with T1 mapping, 4-dimensional flow of the right ventricle and pulmonary arteries, and computed tomography lung perfusion imaging are paving the way for a new era of imaging in PH. These imaging modalities complement echocardiography and invasive hemodynamic testing and may be useful as surrogate endpoints for early phase PH clinical trials. Here we discuss the role of magnetic resonance imaging and computed tomography in the diagnosis and management of PH, including current uses and novel research applications, and we discuss the role of value-based imaging in PH.

Pulmonary artery diameters, cross sectional areas and area changes measured by cine cardiovascular magnetic resonance in healthy volunteers

BACKGROUND

We measured by cine cardiovascular magnetic resonance (CMR) main and branch pulmonary artery diameters and cross sectional areas in diastole and systole in order to establish normal ranges and the effects on them of age, gender and body surface area (BSA). Documentation of normal ranges provides a reference for research and clinical investigation in the fields of congenital heart disease, pulmonary hypertension and connective tissue disorders.

METHODS

We recruited 120 healthy volunteers: ten males (M) and ten females (F) in each decile between 20 and 79 years, imaging them in a 1.5 Tesla CMR system. Scout acquisitions guided the placement of steady state free precession cine acquisitions transecting the main, right and left pulmonary arteries (MPA, RPA and LPA). Cross sections were rarely quite circular.

RESULTS

From all subjects, the means of the greater and lesser orthogonal diastolic diameters in mm were: MPA, 22.9 ± 2.4 (M) and 21.2 ± 2.1 (F), RPA 16.6 ± 2.8 (M) and 14.7 ± 2.2 (F), and LPA 17.3 ± 2.5 (M) and 15.9 ± 2.0 (F), p < 0.0001 between genders in each case. The diastolic diameters increased with BSA and age, and plots are provided for reference. From measurements of minimum diastolic and maximum systolic cross sectional areas, the % systolic distensions were: MPA 42.7 ± 17.2 (M) and 41.8 ± 15.7 (F), RPA 50.6 ± 16.9 (M) and 48.2 ± 14.5 (F), LPA 35.6 ± 10.1 (M) and 35.2 ± 10.3 (F), and there was a decrease in distension with age (p < 0.0001 for the MPA).

CONCLUSIONS

Measurements of MPA, RPA and LPA by cine CMR are provided for reference, with documentation of their changes with age and BSA.

Low WSS and High OSI Measured by 3D Cine PC MRI Reflect High Pulmonary Artery Pressures in Suspected Secondary Pulmonary Arterial Hypertension

Purpose:

Institutional Review Board (IRB)-approved prospective study was conducted to test whether objective and quantitative hemodynamic markers wall shear stress (WSS) and oscillatory shear index (OSI) measured by three-dimensional (3D) cine phase-contrast (PC) can reflect pulmonary arterial hypertension (PAH).

Patients and Methods:

Seventeen consecutive patients of suspected secondary PAH were examined for pulmonary artery pressures (PAPs) with right heart catheterization (RHC) and three-dimensional (3D) cine PC MR. Based on the RHC data, patients were subdivided into two groups of 12 non-PAH (median age of 74.5 years) and 5 PAH (median age of 77 years) patients. Based on 3D cine PC magnetic resonance (MR), hemodynamic parameters including spatially averaged systolic WSS (sWSS), diastolic WSS (dWSS), mean WSS (mWSS), OSI and blood vessel section area (BVSA) at the pulmonary arterial trunk were calculated. Streamline images in the pulmonary arteries were also assessed. All the parameters were compared between non-PAH and PAH groups.

Results:

sWSS (N/m²) and mWSS (N/m²) of PAH group was lower than that of non-PAH group (0.594 ± 0.067 vs. 0.961 ± 0.590, P = 0.001), (0.365 ± 0.035 vs. 0.489 ± 0.132, P = 0.027). OSI of PAH group was higher than that of non-PAH (0.214 ± 0.026 vs. 0.130 ± 0.046, P = 0.001). sWSS, mWSS, and dWSS were inversely correlated and OSI was positively correlated to mean PAP or systolic PAP with r values of –0.638 (P = 0.005), –0.643 (P = 0.005), –0.485 (P = 0.049), and 0.625 (P = 0.007); or –0.622 (P = 0.008), –0.629 (P = 0.007), –0.484 (P = 0.049), and 0.594 (P = 0.012), respectively. sWSS was also inversely correlated to BVSA with r value of –0.488 (P = 0.049), and OSI was correlated to BVSA with r value of 0.574 (P = 0.016). Vortex or helical flows were observed more frequently in PAH patients.

Conclusions:

The low sWSS and mWSS as well as high OSI measured with 3D cine PC MR could be potential hemodynamic markers for the increased PAP in suspected secondary PAH patients.

The role of pulmonary arterial stiffness in COPD

COPD is the second most common cause of pulmonary hypertension, and is a common complication of severe COPD with significant implications for both quality of life and mortality. However, the use of a rigid diagnostic threshold of a mean pulmonary arterial pressure (mPAP) of ≥25mHg when considering the impact of the pulmonary vasculature on symptoms and disease is misleading. Even minimal exertion causes oxygen desaturation and elevations in mPAP, with right ventricular hypertrophy and dilatation present in patients with mild to moderate COPD with pressures below the threshold for diagnosis of pulmonary hypertension. This has significant implications, with right ventricular dysfunction associated with poorer exercise capability and increased mortality independent of pulmonary function tests.

The compliance of the pulmonary artery (PA) is a key component in decoupling the right ventricle from the pulmonary bed, allowing the right ventricle to work at maximum efficiency and protecting the microcirculation from large pressure gradients. PA stiffness increases with the severity of COPD, and correlates well with the presence of exercise induced pulmonary hypertension. A curvilinear relationship exists between PA distensibility and mPAP and pulmonary vascular resistance (PVR) with marked loss of distensibility before a rapid rise in mPAP and PVR occurs with resultant right ventricular failure. This combination of features suggests PA stiffness as a promising biomarker for early detection of pulmonary vascular disease, and to play a role in right ventricular failure in COPD. Early detection would open this up as a potential therapeutic target before end stage arterial remodelling occurs.

•

Pulmonary hypertension is common in COPD.

•

Right ventricular remodeling occurs at pressures below the diagnostic threshold of PH.

•

Pulmonary arterial stiffening occurs early in the development of PH.

•

Non-invasive measurement of pulmonary stiffness may serve as an early biomarker of PH.

[Study of scan parameters using three-dimensional cine phase contrast imaging for pulmonary artery velocity measurement]

Pulmonary artery flow velocity, flow volume and their derived biomarkers, such as acceleration time (AT), acceleration volume (AV) and peak velocity (PV), vary depending on the severity and type of pulmonary disease. Therefore, accurate measurements of pulmonary artery velocity are very important for assessing the severity of pulmonary disease. The purpose of this study was to optimize the imaging parameters for pulmonary artery flow velocity using 3D cine PC MR, and to evaluate AT, AV, and PV for pulmonary hypertension. We changed the flip angle (FA) and view per segment (VPS). FA influenced the signal intensity, which was calculated from the magnitude images. Smaller VPS improved the accuracy of PV. Consequently, optimal setting of FA and VPS was important for hemodynamic analysis. We established the optimal FA and VPS for use in the hemodynamic analysis. AV and PV at the right pulmonary artery differed significantly between healthy volunteers and patients with pulmonary hypertension. Hemodynamic analysis of 3D cine PC MR imaging was considered promising for the evaluation of pulmonary disease.

Electrocardiogram-gated 320-slice multidetector computed tomography for the measurement of pulmonary arterial distensibility in chronic thromboembolic pulmonary hypertension

Background

We aimed to study whether pulmonary arterial distensibility (PAD) correlates with hemodynamic parameters in chronic thromboembolic pulmonary hypertension (CTEPH) using electrocardiogram (ECG)-gated 320-slice multidetector computed tomography (MDCT).

Methods and Findings

ECG-gated 320-slice MDCT and right heart catheterization (RHC) was performed in 53 subjects (60.6±11.4 years old; 37 females) with CTEPH. We retrospectively measured the minimum and maximum values of the cross sectional area (CSA) of the main pulmonary artery (mainPA), right pulmonary artery (rtPA), and left pulmonary artery (ltPA) during one heartbeat. PAD was calculated using the following formula: PAD = [(CSAmaximum−CSAminimum)/CSAmaximum]×100(%). The correlation between hemodynamic parameters and PAD was assessed. Mean pulmonary arterial pressure (mPAP) and pulmonary vascular resistance (PVR) were 40.8±8.7 mmHg and 8.3±3.0 wood units, respectively. PAD values were as follows: mainPA (14.0±5.0%), rtPA (12.8±5.6%), and ltPA (9.7±4.6%). Good correlations existed between mainPAD, with mPAP (r = −0.594, p<0.001) and PVR (r = −0.659, p<0.001). The correlation coefficients between rtPAD and ltPAD with pulmonary hemodynamics were all lower or equal than for mainPAD.

Conclusions

PAD measured using ECG-gated 320-slice MDCT correlates with pulmonary hemodynamics in subjects with CTEPH. The mainPA is suitable for PAD measurement.

Right Pulmonary Artery Distensibility Index (RPAD Index). A field study of an echocardiographic method to detect early development of pulmonary hypertension and its severity even in the absence of regurgitant jets for Doppler evaluation in heartworm-infected dogs

Despite the term "heartworm disease" Dirofilaria immitis infection in dogs should be considered a pulmonary arterial disease that might only involve the right heart structures in its late stage. Chronic infection by adult heartworms in dogs results in proliferative endoarteritis leading to progressively increasing pulmonary artery pressure due to reduced elasticity. Elasticity allows the pulmonary arteries to stretch in response to each pulse and helps maintain a relatively constant pressure in the arteries despite the pulsating nature of the blood flow. Pulmonary artery distensibility for both acute and chronic pulmonary hypertension has been investigated in humans using MRI and has been correlated with the severity of hypertension and its outcome and treatment response. The aim of the present study was to investigate whether echocardiographic measurement of the percentage change in diameter of the right pulmonary artery in systole and diastole (distensibility) may be of value in assessing the presence and severity of pulmonary hypertension in heartworm-infected dogs. The Right Pulmonary Artery Distensibility Index (RPAD Index) (which is calculated as the difference in diameter of the right pulmonary artery in systole and diastole) was calculated in healthy and naturally infected heartworm-positive dogs. The right pulmonary artery was chosen because it is usually affected earlier and to a greater degree. Data were obtained from healthy heartworm-free dogs without any clinical, radiographic, or echocardiographic signs of pulmonary hypertension; naturally infected heartworm-positive dogs in different stages of the disease in which pulmonary pressure could be measured by Doppler echocardiography (using tricuspid and or pulmonary regurgitation velocity and pressure gradient); and naturally infected heartworm-positive dogs in different stages of the disease (with or without tricuspid and or pulmonary regurgitation) in which the pulmonary pressure was measured invasively and noninvasively if possible. Results of these evaluations indicated that RPAD Index is a valuable method for early detection of the presence and severity of pulmonary hypertension in heartworm-infected dogs even in the absence of regurgitant jets for Doppler evaluation and that there is a strong correlation between the RPAD Index and the level of pulmonary hypertension.

Magnetic resonance imaging for pulmonary hypertension: methods, applications, and outcomes

Pulmonary hypertension (PH) is a potentially life-threatening disease. Clinical classification of PH has undergone multiple modifications and was last updated in 2008. Initial detection and classification rely on a combination of invasive and noninvasive tests, among which the most important are echocardiography, right-sided heart catheterization, and computed tomography. Treatment response assessment and monitoring are focused on the functional evaluation of the right ventricle, and magnetic resonance imaging is the noninvasive test of choice as its accuracy and reproducibility are superior to echocardiography. In this article, we discuss our PH evaluation magnetic resonance imaging protocol, which has been customized to provide clinicians with the information needed to assess right-sided heart functional status and determine response to treatment or disease progression.

Cardiac MRI as a diagnostic tool in pulmonary hypertension

ABSTRACT: Pulmonary hypertension is characterized by alterations in the viscoelastic properties of the pulmonary arteries, leading to increased pulmonary arterial stiffness and elevated pressures. Early detection and accurate quantification of pulmonary hypertension are limitations to conventional noninvasive imaging and may have therapeutic implications. Cardiac MRI provides important information that can aid the clinician, particularly relating to morphologic right ventricular alterations and quantification of stiffness, as well as providing a novel prognostic framework.

[Evaluation of pulmonary artery stiffness using routine clinical imaging methods]

Recently, there has been much debate about pulmonary hypertension due to modern therapeutic options available. Arterial hypertension is frequently associated with stiffening of a given artery. The aim of the present review is to present clinical imaging methods for the evaluation of the function and stiffness of the pulmonary artery.

Intraoperative cardiac ultrasound examination using vector flow imaging

Conventional ultrasound (US) methods for blood velocity estimation only provide one-dimensional and angle-dependent velocity estimates; thus, the complexity of cardiac flow has been difficult to measure. To circumvent these limitations, the Transverse Oscillation (TO) vector flow method has been proposed. The vector flow method implemented on a commercial scanner provided real-time, angle-independent estimates of cardiac blood flow. Epicardiac and epiaortic, intraoperative US examinations were performed on three patients with stenosed coronary arteries scheduled for bypass surgery. Repeating cyclic beat-to-beat flow patterns were seen in the ascending aorta and pulmonary artery of each patient, but these patterns varied between patients. Early systolic retrograde flow filling the aortic sinuses was seen in the ascending aorta as well as early systolic retrograde flow in the pulmonary artery. In diastole, stable vortices in aortic sinuses of the ascending aorta created central antegrade flow. A stable vortex in the right atrium was seen during the entire heart cycle. The measurements were compared with estimates obtained intraoperatively with conventional spectral Doppler US using a transesophageal and an epiaortic approach. Mean differences in peak systole velocity of 11% and 26% were observed when TO was compared with transesophageal echocardiography and epiaortic US, respectively. In one patient, the cardiac output derived from vector velocities was compared with pulmonary artery catheter thermodilution technique and showed a difference of 16%. Vector flow provides real-time, angle-independent vector velocities of cardiac blood flow. The technique can potentially reveal new information of cardiovascular physiology and give insight into blood flow dynamics.

Wall shear stress measured by phase contrast cardiovascular magnetic resonance in children and adolescents with pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a devastating disease with significant morbidity and mortality. At the macroscopic level, disease progression is observed as a complex interplay between mean pulmonary artery pressure, pulmonary vascular resistance, pulmonary vascular stiffness, arterial size, and flow. Wall shear stress (WSS) is known to mediate or be dependent on a number of these factors. Given that WSS is known to promote architectural vessel remodeling, it is imperative that the changes of this factor be quantified in the presence of PAH.

METHODS

In this study, we analyzed phase contrast imaging of the right pulmonary artery derived from cardiovascular magnetic resonance to quantify the local, temporal and circumferentially averaged WSS of a PAH population and a pediatric control population. In addition, information about flow and relative area change were derived.

RESULTS

Although the normotensive and PAH shear waveform exhibited a WSS profile which is uniform in magnitude and direction along the vessel circumference at systole, time-averaged WSS (2.2 ± 1.6 vs. 6.6 ± 3.4 dynes/cm(2), P = 0.018) and systolic WSS (8.2 ± 5.0 v. 20.0 ± 9.1 dynes/cm(2), P = 0.018) was significantly depressed in the PAH population as compared to the controls. BSA-indexed PA diameter was significantly larger in the PAH population (1.5 ± 0.4 vs. 0.7 ± 0.1 cm/m(2), P = 0.003).

CONCLUSIONS

In the presence of preserved flow rates through a large PAH pulmonary artery, WSS is significantly decreased. This may have implications for proximal pulmonary artery remodeling and cellular function in the progression of PAH.

Noninvasive monitoring of serial changes in pulmonary vascular resistance and acute vasodilator testing using cardiac magnetic resonance

OBJECTIVES

The study sought to evaluate the ability of cardiac magnetic resonance (CMR) to monitor acute and long-term changes in pulmonary vascular resistance (PVR) noninvasively.

BACKGROUND

PVR monitoring during the follow-up of patients with pulmonary hypertension (PH) and the response to vasodilator testing require invasive right heart catheterization.

METHODS

An experimental study in pigs was designed to evaluate the ability of CMR to monitor: 1) an acute increase in PVR generated by acute pulmonary embolization (n = 10); 2) serial changes in PVR in chronic PH (n = 22); and 3) changes in PVR during vasodilator testing in chronic PH (n = 10). CMR studies were performed with simultaneous hemodynamic assessment using a CMR-compatible Swan-Ganz catheter. Average flow velocity in the main pulmonary artery (PA) was quantified with phase contrast imaging. Pearson correlation and mixed model analysis were used to correlate changes in PVR with changes in CMR-quantified PA velocity. Additionally, PVR was estimated from CMR data (PA velocity and right ventricular ejection fraction) using a formula previously validated.

RESULTS

Changes in PA velocity strongly and inversely correlated with acute increases in PVR induced by pulmonary embolization (r = -0.92), serial PVR fluctuations in chronic PH (r = -0.89), and acute reductions during vasodilator testing (r = -0.89, p ≤ 0.01 for all). CMR-estimated PVR showed adequate agreement with invasive PVR (mean bias -1.1 Wood units,; 95% confidence interval: -5.9 to 3.7) and changes in both indices correlated strongly (r = 0.86, p < 0.01).

CONCLUSIONS

CMR allows for noninvasive monitoring of acute and chronic changes in PVR in PH. This capability may be valuable in the evaluation and follow-up of patients with PH.

Effects of pulmonary regurgitation on distensibility and flow of the branch pulmonary arteries in tetralogy of Fallot

Significant pulmonary regurgitation (PR) after repair of tetralogy of Fallot (TOF) may affect flow in the pulmonary artery (PA) side branches. We sought to assess flow changes and distensibility of the PA side branches in vivo and test correlation with the degree of PR and right-ventricular (RV) dilatation. Thirty patients after TOF repair and 16 controls underwent cardiovascular magnetic resonance for quantification of RV volumes and measurement of flow in the PA side branches. RV volumes and function, blood flow volumes, and cross-sectional area of the main, left (LPA), and right (RPA) PA were measured and regurgitant volumes and distensibility calculated. Results were compared between the LPA and the RPA and between patients and controls. Median regurgitation fraction of PR was 41 % (range 22-60 %). Regurgitant fraction was greater in the LPA (40 %) than in the RPA (29 %), resulting in lower net flow into the LPA (p < 0.001). LPA area was significantly greater than that of the RPA (303.9 vs. 232.7 mm(2)/m(2)) (p < 0.0001). The LPA showed lower distensibility than the RPA (39 vs. 44 %). PA side branch distensibility correlated with MPA regurgitant volume (p = 0.001), MPA regurgitant fraction (p = 0.001), and RV end-diastolic volume (p = 0.03). PA side branches have greater distensibility in patients with PR than in normal subjects. Significant PR leads to changes in flow profile and distensibility of the PA side branches. The LPA shows greater regurgitant volume and greater area but lower distensibility than the RPA.

Pulmonary artery and right ventricle assessment in pulmonary hypertension: correlation between functional parameters of ECG-gated CT and right-side heart catheterization

BACKGROUND

Right ventricular function predicts outcome in patients with pulmonary hypertension (PH). Therefore accurate assessment of right ventricular function is essential to graduate severity, assess follow-up, and response to therapy.

PURPOSE

To evaluate whether PH severity could be assessed using electrocardiography-gated CT (ECG-gated CT) functional parameters. A further objective was to evaluate cardiac output (CO) using two ECG-gated CT methods: the reference Simpson technique and the fully automatic technique generated by commercially available cardiac software.

MATERIAL AND METHODS

Our institutional review board approved this study; patient consent was not required. Twenty-seven patients who had undergone ECG-gated CT and right heart catheterization (RHC) were included. Two independent observers measured pulmonary artery (PA) diameter, PA distensibility, aorta diameter, right ventricular cardiac output (CT-RVCO) and right ventricular ejection fraction (CT-RVEF) with automatic and Simpson techniques on ECG-gated CT. RHC-CO and mean pulmonary arterial pressure (mPAP) were measured on RHC. Relationship between ECG-gated CT and RHC measurements was tested with linear regression analysis.

RESULTS

Inter-observer agreement was good for all measurements (r > 0.7) except for CT-RVCO calculated with Simpson's technique (r = 0.63). Pulmonary artery (PA) distensibility was significantly correlated to mPAP (r = -0.426, P = 0.027). CT-RVEF was correlated with mPAP only when issued from Simpson technique (r = -0.417, P = 0.034). CT-RVEF was not significantly correlated to RHC-CO (P > 0.2). CT-RVCO measured with Simpson technique (r = 0.487, P = 0.010) and automatic segmentation (r = 0.549, P = 0.005) correlated equally with RHC-CO.

CONCLUSION

CT-RVEF and CT-RVCO measured on ECG-gated CT are significantly correlated, respectively, to mPAP and RHC-CO in this population with severe reduction of the right ventricular ejection fraction and could be useful for evaluating and following patients with PH.

Right heart on multidetector CT

Right ventricular function plays an integral role in the pathogenesis and outcome of many cardiovascular diseases. Imaging the right ventricle has long been a challenge because of its complex geometry. In recent years there has been a tremendous expansion in multidetector row CT (MDCT) and its cardiac applications. By judicious modification of contrast medium protocol, it is possible to achieve good opacification of the right-sided cardiac chambers, thereby paving the way for exploring the overshadowed right heart. This article will describe the key features of right heart anatomy, review MDCT acquisition techniques, elaborate the various morphological and functional information that can be obtained, and illustrate some important clinical conditions associated with an abnormal right heart.

Pulmonary arterial hypertension: an imaging review comparing MR pulmonary angiography and perfusion with multidetector CT angiography

Pulmonary hypertension (PH) is a progressive disease that leads to substantial morbidity and eventual death. Pulmonary multidetector CT angiography (MDCTA), pulmonary MR angiography (MRA) and MR-derived pulmonary perfusion (MRPP) imaging are non-invasive imaging techniques for the differential diagnosis of PH. MDCTA is considered the gold standard for the diagnosis of pulmonary embolism, one of the most common causes of PH. MRA and MRPP are promising techniques that do not require the use of ionising radiation or iodinated contrast material, and can be useful for patients for whom such material cannot be used. This review compares the imaging aspects of pulmonary MRA and 64-row MDCTA in patients with chronic thromboembolic or idiopathic PH.

Assessment of normal flow patterns in the pulmonary circulation by using 4D magnetic resonance velocity mapping

OBJECTIVE

The purpose of this study was to analyze flow patterns in the pulmonary circulation of healthy volunteers by using 4D flow magnetic resonance imaging.

MATERIALS AND METHODS

The study was approved by the local ethics committee and all subjects gave written informed consent. Eighteen volunteers underwent a 4D flow scan of the whole-heart. Two patients with congenital heart disease were also included to detect possible patterns of flow abnormalities (Patient 1: corrected transposition of great arteries (TGA); Patient 2: partial anomalous pulmonary venous return and atrial septal defect). To analyze flow patterns, 2D planes were placed on the main pulmonary artery (PA), left and right PA. Flow patterns were assessed manually by two independent viewers using vector fields, streamlines and particle traces, and semi-automatically by vorticity quantification.

RESULTS

Two counter-rotating helices were found in the main PA of volunteers. Right-handed helical flow was detected in the right PA of 15 volunteers. Analysis of the helical flow by particles traces revealed that both helices contributed mainly to the flow in the right PA. In the patient with corrected TGA helical flow was not detected. Abnormal vortical flow was visualized in the main PA of patient 2, suggesting elevated mean PA pressure.

CONCLUSIONS

Helical flow is normally present in the main PA and right PA. 4D flow is an excellent tool to evaluate noninvasively complex blood flow patterns in the pulmonary circulation. Knowledge of normal and abnormal flow patterns might help to evaluate patients with congenital heart disease adding functional information undetectable with other imaging modalities.

[Multidetector computed tomography assessment of cardiac comorbidity in patients with chronic obstructive pulmonary disease]

Cardiac comorbidity is one of the most important prognostic factors in lung disease, especially in chronic obstructive pulmonary disease (COPD). The imaging techniques available for the study of this systemic manifestation concomitant with COPD include heart catheterization, transthoracic echocardiography, and magnetic resonance imaging. Multidetector computed tomography (MDCT) represents a significant advance in this field because it enables the acquisition of simultaneous studies of the cardiopulmonary anatomy that go beyond anatomic and morphologic analysis to include a functional approach to this condition. In this article, we review the practical aspects necessary to evaluate cardiac comorbidity in patients with COPD, both from the point of view of pulmonary hypertension and of the analysis of ventricular dysfunction and coronary heart disease.

The role and potential of imaging in COPD

Chronic obstructive pulmonary disease is a heterogeneous condition of the lungs and body. Techniques in chest imaging and quantitative image analysis provide novel in vivo insight into the disease and potentially examine divergent responses to therapy. This article reviews the strengths and limitations of the leading imaging techniques: computed tomography, magnetic resonance imaging, positron emission tomography, and optical coherence tomography. Following an explanation of the technique, each section details some of the useful information obtained with these examinations. Future clinical care and investigation will likely include some combination of these imaging modalities and more standard assessments of disease severity.

Abnormal pulmonary artery stiffness in pulmonary arterial hypertension: in vivo study with intravascular ultrasound

Background

There is increasing recognition that pulmonary artery stiffness is an important determinant of right ventricular (RV) afterload in pulmonary arterial hypertension (PAH). We used intravascular ultrasound (IVUS) to evaluate the mechanical properties of the elastic pulmonary arteries (PA) in subjects with PAH, and assessed the effects of PAH-specific therapy on indices of arterial stiffness.

Method

Using IVUS and simultaneous right heart catheterisation, 20 pulmonary segments in 8 PAH subjects and 12 pulmonary segments in 8 controls were studied to determine their compliance, distensibility, elastic modulus and stiffness index β. PAH subjects underwent repeat IVUS examinations after 6-months of bosentan therapy.

Results

At baseline, PAH subjects demonstrated greater stiffness in all measured indices compared to controls: compliance (1.50±0.11×10^–2 mm^2/mmHg vs 4.49±0.43×10^–2 mm^2/mmHg, p<0.0001), distensibility (0.32±0.03%/mmHg vs 1.18±0.13%/mmHg, p<0.0001), elastic modulus (720±64 mmHg vs 198±19 mmHg, p<0.0001), and stiffness index β (15.0±1.4 vs 11.0±0.7, p = 0.046). Strong inverse exponential associations existed between mean pulmonary artery pressure and compliance (r² = 0.82, p<0.0001), and also between mean PAP and distensibility (r² = 0.79, p = 0.002). Bosentan therapy, for 6-months, was not associated with any significant changes in all indices of PA stiffness.

Conclusion

Increased stiffness occurs in the proximal elastic PA in patients with PAH and contributes to the pathogenesis RV failure. Bosentan therapy may not be effective at improving PA stiffness.

Cardiovascular magnetic resonance in pulmonary hypertension

Pulmonary hypertension represents a group of conditions characterized by higher than normal pulmonary artery pressures. Despite improved treatments, outcomes in many instances remain poor. In recent years, there has been growing interest in the use of cardiovascular magnetic resonance (CMR) in patients with pulmonary hypertension. This technique offers certain advantages over other imaging modalities since it is well suited to the assessment of the right ventricle and the proximal pulmonary arteries. Reflecting the relatively sparse evidence supporting its use, CMR is not routinely recommended for patients with pulmonary hypertension. However, it is particularly useful in patient with pulmonary arterial hypertension associated with congenital heart disease. Furthermore, it has proven informative in a number of ways; illustrating how right ventricular remodeling is favorably reversed by drug therapies and providing explicit confirmation of the importance of the right ventricle to clinical outcome. This review will discuss these aspects and practical considerations before speculating on future applications.

Assessment of pulmonary artery stiffness using velocity-encoding magnetic resonance imaging: evaluation of techniques

The loss of pulmonary artery (PA) compliance has significant pathophysiological effect on the right ventricle. Noninvasive and reliable assessment of PA wall stiffness would be an essential determiner of right heart load and a clinically useful factor to assess cardiovascular risk. Two MRI techniques have been proposed for assessing PA stiffness by measuring pulse wave velocity (PWV): transit time (TT) and flow area (QA). However, no data are available that compares the two techniques and evaluates their performance, especially over a wide range of PWV values or at 3.0-T, which is the purpose of the present study. Thirty-three patients with different heart conditions were imaged using optimized high-temporal resolution and high-spatial resolution velocity-encoding MRI sequences. Statistical analysis was conducted to study intermethod, interobserver and intraobserver variabilities. The PWV measurements using TT and QA techniques showed good agreement (P>0.1). The Bland-Altman analysis showed negligible differences between the two methods (mean±S.D.=0.11±0.35 m/s, correlation coefficient r=0.94). The repeated measurements showed low interobserver and intraobserver variabilities, although the S.D. of the differences was larger in the QA technique. The mean±S.D. of the TT/QA measurement differences were -0.05±0.2/0.0±0.36 m/s and 0.02±0.26/0.02±0.39 m/s for the interobserver and intraobserver differences, respectively. In conclusion, each technique has its own advantages and disadvantages. The two techniques result in similar measurements, although the QA method is more subjective due to its dependency on operator intervention.

New index α improves detection of pulmonary hypertension in comparison with other cardiac magnetic resonance indices

BACKGROUND

Cardiovascular magnetic resonance (CMR) has been proposed for the evaluation of patients with pulmonary hypertension (PH). However, there is no consensus on the optimal method for PH diagnosis using CMR.

OBJECTIVE

To compare the diagnostic ability of multiple CMR-derived indices for the detection of PH as determined by right heart catheterization (RHC).

METHODS

A total of 185 patients with known or suspected chronic PH who underwent cardiac CMR and RHC in ≤15 days were included. PH was defined as a mean pulmonary artery (PA) pressure ≥25 mmHg. Right ventricular (RV) volumes, RV ejection fraction (RVEF), PA areas, and PA average blood flow velocity were quantified with CMR. A novel index α was defined as the ratio between minimal PA area and RVEF.

RESULTS

According to the RHC, PH was present in 152 patients. All CMR-derived parameters correlated with the degree of mean PA pressure, with α having the highest correlation coefficient (r=0.61, p<0.001). Correlations were also highest for α in the patients with pulmonary arterial hypertension (PAH; r=0.55, p<0.001) and non-PAH subgroup (r=0.61, p<0.001). Diagnostic accuracy for the detection of PH, based on receiver operating curve analysis, was best for α (area under the curve=0.95). A cutoff value of 7.2 demonstrated a sensitivity of 90% and a specificity of 88%.

CONCLUSIONS

An easily-obtainable and novel CMR index α that combines geometrical and functional information of the PA and the RV allows for the noninvasive diagnosis of PH with high accuracy, above other common CMR-derived parameters.