Quantification of lung water in heart failure using cardiovascular magnetic resonance imaging

Stress and Rest Pulmonary Transit Times Assessed by Cardiovascular Magnetic Resonance

Acquiring pulmonary circulation parameters as a potential marker of cardiopulmonary function is not new. Methods to obtain these parameters have been developed over time, with the latest being first-pass perfusion sequences in cardiovascular magnetic resonance (CMR). Even though more data on these parameters has been recently published, different nomenclature and acquisition methods are used across studies; some works even reported conflicting data. The most commonly used circulation parameters obtained using CMR include pulmonary transit time (PTT) and pulmonary transit beats (PTB). PTT is the time needed for a contrast agent (typically gadolinium-based) to circulate from the right ventricle (RV) to the left ventricle (LV). PTB is the number of cardiac cycles the process takes. Some authors also include corrected heart rate (HR) versions along with standard PTT. Besides other methods, CMR offers an option to assess stress circulation parameters, but data are minimal. This review aims to summarize the up-to-date findings and provide an overview of the latest progress on this promising, dynamically evolving topic.

Use of Real-Time Cine MRI to Assess the Respirophasic Variation of the Inferior Vena Cava-Proof-of-Concept and Validation Against Transthoracic Echocardiography

BACKGROUND

In clinical practice, the right heart filling status is assessed using the respirophasic variation of the inferior vena cava (IVC) assessed by transthoracic echocardiography (TTE) showing moderate correlations with the catheter-based reference standard.

PURPOSE

To develop and validate a similar approach using MRI.

STUDY TYPE

Prospective.

POPULATION

37 male elite cyclists (mean age 26 ± 4 years).

FIELD STRENGTH/SEQUENCE

Real-time balanced steady-state free-precession cine sequence at 1.5 Tesla.

ASSESSMENT

Respirophasic variation included assessment of expiratory size of the upper hepatic part of the IVC and degree of inspiratory collapse expressed as collapsibility index (CI). The IVC was studied either in long-axis direction (TTE) or using two transverse slices, separated by 30 mm (MRI) during operator-guided deep breathing. For MRI, in addition to the TTE-like diameter, IVC area and major and minor axis diameters were also assessed, together with the corresponding CIs.

STATISTICAL TESTS

Repeated measures ANOVA test with Bonferroni correction. Intraclass correlation coefficient (ICC) and Bland-Altman analysis for intrareader and inter-reader agreement. A P value <0.05 was considered statistically significant.

RESULTS

No significant differences in expiratory IVC diameter were found between TTE and MRI, i.e., 25 ± 4 mm vs. 25 ± 3 mm (P = 0.242), but MRI showed a higher CI, i.e., 76% ± 14% vs. 66% ± 14% (P < 0.05). As the IVC presented a noncircular shape, i.e., major and minor expiratory diameter of 28 ± 4 mm and 21 ± 4 mm, respectively, the CI varied according to the orientation, i.e., 63% ± 27% vs. 75% ± 16%, respectively. Alternatively, expiratory IVC area was 4.3 ± 1.1 cm2 and showed a significantly higher CI, i.e., 86% ± 14% than diameter-based CI (P < 0.05). All participants showed a CI >50% with MRI versus 35/37 (94%) with TTE. ICC values ranged 0.546-0.841 for MRI and 0.545-0.704 for TTE.

CONCLUSION

Assessment of the respirophasic IVC variation is feasible with MRI. Adding this biomarker may be of particular use in evaluating heart failure patients.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 2.

Systemic Arterial Oxygen Levels Differentiate Pre- and Post-capillary Predominant Hemodynamic Abnormalities During Exercise in Undifferentiated Dyspnea on Exertion

BACKGROUND

Whether systemic oxygen levels (SaO2) during exercise can provide a window into invasively derived exercise hemodynamic profiles in patients with undifferentiated dyspnea on exertion is unknown.

METHODS

We performed cardiopulmonary exercise testing with invasive hemodynamic monitoring and arterial blood gas sampling in individuals referred for dyspnea on exertion. Receiver operator analysis was performed to distinguish heart failure with preserved ejection fraction from pulmonary arterial hypertension.

RESULTS

Among 253 patients (mean ± SD, age 63 ± 14 years, 55% female, arterial O2 [PaO2] 87 ± 14 mmHg, SaO2 96% ± 4%, resting pulmonary capillary wedge pressure [PCWP] 18 ± 4mmHg, and pulmonary vascular resistance [PVR] 2.7 ± 1.2 Wood units), there was no exercise PCWP threshold, measured up to 49 mmHg, above which hypoxemia was consistently observed. Exercise PaO2 was not correlated with exercise PCWP (rho = 0.04; P = 0.51) but did relate to exercise PVR (rho = -0.46; P < 0.001). Exercise PaO2 and SaO2 levels distinguished left-heart-predominant dysfunction from pulmonary-vascular-predominant dysfunction with an area under the curve of 0.89 and 0.89, respectively.

CONCLUSION

Systemic O2 levels during exercise distinguish relative pre- and post-capillary pulmonary hemodynamic abnormalities in patients with undifferentiated dyspnea. Hypoxemia during upright exercise should not be attributed to isolated elevation in left heart filling pressures and should prompt consideration of pulmonary vascular dysfunction.

Noninvasive Imaging Methods for Quantification of Pulmonary Edema and Congestion: A Systematic Review

Quantification of pulmonary edema and congestion is important to guide diagnosis and risk stratification, and to objectively evaluate new therapies in heart failure. Herein, we review the validation, diagnostic performance, and clinical utility of noninvasive imaging modalities in this setting, including chest x-ray, lung ultrasound (LUS), computed tomography (CT), nuclear medicine imaging methods (positron emission tomography [PET], single photon emission CT), and magnetic resonance imaging (MRI). LUS is a clinically useful bedside modality, and fully quantitative methods (CT, MRI, PET) are likely to be important contributors to a more accurate and precise evaluation of new heart failure therapies and for clinical use in conjunction with cardiac imaging. There are only a limited number of studies evaluating pulmonary congestion during stress. Taken together, noninvasive imaging of pulmonary congestion provides utility for both clinical and research assessment, and continued refinement of methodologic accuracy, validation, and workflow has the potential to increase broader clinical adoption.

Dynamic lung water MRI during exercise stress

PURPOSE

Exercise-induced dyspnea caused by lung water is an early heart failure symptom. Dynamic lung water quantification during exercise is therefore of interest to detect early stage disease. This study developed a time-resolved 3D MRI method to quantify transient lung water dynamics during rest and exercise stress.

METHODS

The method was evaluated in 15 healthy subjects and 2 patients with heart failure imaged in transitions between rest and exercise, and in a porcine model of dynamic extravascular lung water accumulation through mitral regurgitation (n = 5). Time-resolved images were acquired at 0.55T using a continuous 3D stack-of-spirals proton density weighted sequence with 3.5 mm isotropic resolution, and derived using a motion corrected sliding-window reconstruction with 90-s temporal resolution in 20-s increments. A supine MRI-compatible pedal ergometer was used for exercise. Global and regional lung water density (LWD) and percent change in LWD (ΔLWD) were automatically quantified.

RESULTS

A ΔLWD increase of 3.3 ± 1.5% was achieved in the animals. Healthy subjects developed a ΔLWD of 7.8 ± 5.0% during moderate exercise, peaked at 16 ± 6.8% during vigorous exercise, and remained unchanged over 10 min at rest (-1.4 ± 3.5%, p = 0.18). Regional LWD were higher posteriorly compared the anterior lungs (rest: 33 ± 3.7% vs 20 ± 3.1%, p < 0.0001; peak exercise: 36 ± 5.5% vs 25 ± 4.6%, p < 0.0001). Accumulation rates were slower in patients than healthy subjects (2.0 ± 0.1%/min vs 2.6 ± 0.9%/min, respectively), whereas LWD were similar at rest (28 ± 10% and 28 ± 2.9%) and peak exercise (ΔLWD 17 ± 10% vs 16 ± 6.8%).

CONCLUSION

Lung water dynamics can be quantified during exercise using continuous 3D MRI and a sliding-window image reconstruction.

Lung water estimation on cardiac magnetic resonance imaging for predicting adverse cardiovascular outcomes in patients with heart failure

OBJECTIVES

Pulmonary congestion is a central feature of heart failure (HF) seen in acute decompensated state as well as in chronic stable disease. The present study sought to determine whether simplified cardiac magnetic resonance imaging (CMR)-derived lung water density (LWD) measurement has prognostic relevance in predicting adverse cardiovascular outcomes in patients with HF and left ventricular ejection fraction (LVEF)<50%.

METHODS

Eighty consecutive patients referred for CMR with HF and LVEF<50% along with 22 healthy age- and sex-matched controls were prospectively recruited. LWD was the lung-to-liver signal intensity ratio multiplied by 70% (estimated hepatic water density). The primary endpoint was composite of all-cause mortality or HF-related hospitalization within 6 months from CMR.

RESULTS

The mean LWD was significantly higher in HF patients compared to healthy controls (19.78 ± 6.1 vs 13.6 ± 2.3; p < 0.001). The mean LWD was significantly different among patients with NYHA class I/II and NYHA class III/IV (17.88 ± 4.8 vs 21.77 ± 1.08; p = 0.004). At 6 months, the primary endpoint was reached in 12 (15%) patients. Patients with "wet lungs" (LWD > 18.1%) had higher incidence of adverse cardiovascular outcomes compared to patients with "dry lungs". LWD was an independent predictor of adverse cardiovascular outcomes in multivariable analysis. At the optimal cut-off of LWD > 23.38%, the sensitivity and specificity were 91.67 and 91.18%, respectively, to predict adverse cardiovascular outcomes.

CONCLUSION

LWD on CMR is independently associated with increased risk of mortality and HF-related hospitalization in HF patients with LVEF<50%.

ADVANCES IN KNOWLEDGE

Non-invasive quantitative estimation of LWD on CMR can improve risk stratification and guide management in HF patients.

Visualizing diastolic failure: Non-invasive imaging-biomarkers in patients with heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction is an increasing challenge for modern day medicine and has been drawing more attention recently. Invasive right heart catheterization represents the mainstay for the diagnosis of diastolic dysfunction, however due to its attributable risk of an invasive procedure, other non-invasive clinical pathways are trying to approach this pathology in clinical practice. Diastolic failure is complex, and imaging is based on various parameters. In addition to transthoracic echocardiography, numerous novel imaging approaches, such as cardiac magnetic resonance imaging, computed tomography, positron emission (computed) tomography or single photon emission tomography techniques are being used to supplement deeper insights into causal pathology and might open targets for dedicated therapy options. This article provides insights into these sophisticated imaging techniques, their incremental value for the diagnosis of this poorly understood disease and recent promising results for an enhanced prognostication of outcome and therapy monitoring.

Clinical Phenotypes of Heart Failure across the spectrum of Ejection Fraction: A Cluster Analysis

INTRODUCTION

Heart failure (HF), and especially HF with preserved ejection fraction (HFpEF), remains a challenging condition to define. The heterogenous nature of this population may be related to a variety of underlying etiologies interacting myocardial dysfunction.

METHOD

Alberta HEART study was a prospective, observational cohort that enrolled participants along the spectrum of heart failure including: healthy controls, people at risk of HF, and patients with HF and preserved (HFpEF) or reduced ejection fraction (HFrEF). We aimed to explore phenotypes of patients with HF and at-risk of developing HF. Utilising 27 detailed clinical, echocardiographic and biomarker variables, latent class analysis with and without multiple imputation was undertaken to identify distinct clinical phenotypes.

RESULTS

Of 621 participants, 191 (30.8%) and 169 (27.2%) were adjudicated by cardiologists to have HFpEF and HFrEF respectively. In the overall cohort, latent class analysis identified four distinct phenotypes. Phenotype A (n=152, 24.5%) was a healthy and low risk group. Phenotype B (n=129, 20.8%) demonstrated increased left ventricular mass and end-diastolic volumes, with elevated natriuretic peptides and clinical features of congestion. Phenotype C (n=128, 20.6%) was primarily characterised by obesity (80%) and normal indexed cardiac chamber sizes, low natriuretic peptide levels and minimal features of congestion. Phenotype D (n=212, 34.1%) consisted of elderly patients with clinical features of congestions. Phenotypes B and D demonstrated the highest risk of mortality and hospitalization over a median follow-up of 3.7 years.

CONCLUSION

Phenotypes with congestive features demonstrated increased risk profiles. Heart failure is a heterogenous classification which requires further work to appropriately categorise patients based on the underlying etiology or mechanism of impairment.

Imaging gravity-induced lung water redistribution with automated inline processing at 0.55 T cardiovascular magnetic resonance

BACKGROUND

Quantitative assessment of dynamic lung water accumulation is of interest to unmask latent heart failure. We develop and validate a free-breathing 3D ultrashort echo time (UTE) sequence with automated inline image processing to image changes in lung water density (LWD) using high-performance 0.55 T cardiovascular magnetic resonance (CMR).

METHODS

Quantitative lung water CMR was performed on 15 healthy subjects using free-breathing 3D stack-of-spirals proton density weighted UTE at 0.55 T. Inline image reconstruction and automated image processing was performed using the Gadgetron framework. A gravity-induced redistribution of LWD was provoked by sequentially acquiring images in the supine, prone, and again supine position. Quantitative validation was performed in a phantom array of vials containing mixtures of water and deuterium oxide.

RESULTS

The phantom experiment validated the capability of the sequence in quantifying water density (bias ± SD 4.3 ± 4.8%, intraclass correlation coefficient, ICC = 0.97). The average global LWD was comparable between imaging positions (supine 24.7 ± 3.4%, prone 22.7 ± 3.1%, second supine 25.3 ± 3.6%), with small differences between imaging phases (first supine vs prone 2.0%, p < 0.001; first supine vs second supine - 0.6%, p = 0.001; prone vs second supine - 2.7%, p < 0.001). In vivo test-retest repeatability in LWD was excellent (- 0.17 ± 0.91%, ICC = 0.97). A regional LWD redistribution was observed in all subjects when repositioning, with a predominant posterior LWD accumulation when supine, and anterior accumulation when prone (difference in anterior-posterior LWD: supine - 11.6 ± 2.7%, prone 5.5 ± 2.7%, second supine - 11.4 ± 2.9%). Global LWD maps were calculated inline within 23.2 ± 0.3 s following the image reconstruction using the automated pipeline.

CONCLUSIONS

Redistribution of LWD due to gravitational forces can be depicted and quantified using a validated free-breathing 3D proton density weighted UTE sequence and inline automated image processing pipeline on a high-performance 0.55 T CMR system.

Evaluation of Dynamic Contrast-Enhanced MRI Measures of Lung Congestion and Endothelial Permeability in Heart Failure: A Prospective Method Validation Study

Background

Methods for accurate quantification of lung fluid in heart failure (HF) are needed. Dynamic contrast‐enhanced (DCE)‐MRI may be an appropriate modality.

Purpose

DCE‐MRI evaluation of fraction of fluid volume in the interstitial lung space (v_e) and vascular permeability (K^trans).

Study Type

Prospective, single‐center method validation.

Population

Seventeen evaluable healthy volunteers (HVs), 12 participants with HF, and 3 with acute decompensated HF (ADHF).

Field Strength/Sequence

T₁ mapping (spoiled gradient echo variable flip angle acquisition) followed by dynamic series (three‐dimensional spoiled gradient‐recalled echo acquisitions [constant echo time, repetition time, and flip angle at 1.5 T]).

Assessment

Three whole‐chest scans were acquired: baseline (Session 1), 1‐week later (Session 2), following exercise (Session 3). Extended Tofts model quantified v_e and K^trans (voxel‐wise basis); total lung median measures were extracted and fitted via repeat measure analysis of variance (ANOVA) model. Patient tolerability of the scanning protocol was assessed.

Statistical Tests

This was constructed as an experimental medicine study. Primary endpoints: K^trans and v_e at baseline (HV vs. HF), change in K^trans and v_e following exercise, and following lung congestion resolution (ADHF). K^trans and v_e were fitted separately using ANOVA. Secondary endpoint: repeatability, that is, within‐participant variability in v_e and K^trans between sessions (coefficient of variation estimated via mixed effects model).

Results

There was no significant difference in mean K^trans between HF and HV (P ≤ 0.17): 0.2216 minutes⁻¹ and 0.2353 minutes⁻¹ (Session 1), 0.2044 minutes⁻¹ and 0.2567 minutes⁻¹ (Session 2), 0.1841 minutes⁻¹ and 0.2108 minutes⁻¹ (Session 3), respectively. v_e was greater in the HF group (all scans, P ≤ 0.02). Results were repeatable between Sessions 1 and 2; mean values for HF and HV were 0.4946 and 0.3346 (Session 1), 0.4353 and 0.3205 (Session 2), respectively. There was minimal difference in K^trans or v_e between scans for participants with ADHF (small population precluded significance testing). Scanning was well tolerated.

Data Conclusion

While no differences were detected in K^trans, v_e was greater in chronic HF patients vs. HV, augmented beyond plasma and intracellular volume. DCE‐MRI is a valuable diagnostic and physiologic tool to evaluate changes in fluid volume in the interstitial lung space associated with symptomatic HF.

Level of Evidence

2

Technical Efficacy Stage

2

A Contemporary Review of the Effects of Exercise Training on Cardiac Structure and Function and Cardiovascular Risk Profile: Insights From Imaging

Exercise is a commonly prescribed therapy for patients with established cardiovascular disease or those at high risk for de novo disease. Exercise-based, multidisciplinary programs have been associated with improved clinical outcomes post myocardial infarction and is now recommended for patients with cancer at elevated risk for cardiovascular complications. Imaging studies have documented numerous beneficial effects of exercise on cardiac structure and function, vascular function and more recently on the cardiovascular risk profile. In this contemporary review, we will discuss the effects of exercise training on imaging-derived cardiovascular outcomes. For cardiac imaging via echocardiography or magnetic resonance, we will review the effects of exercise on left ventricular function and remodeling in patients with established or at risk for cardiac disease (myocardial infarction, heart failure, cancer survivors), and the potential utility of exercise stress to assess cardiac reserve. Exercise training also has salient effects on vascular function and health including the attenuation of age-associated arterial stiffness and thickening as assessed by Doppler ultrasound. Finally, we will review recent data on the relationship between exercise training and regional adipose tissue deposition, an emerging marker of cardiovascular risk. Imaging provides comprehensive and accurate quantification of cardiac, vascular and cardiometabolic health, and may allow refinement of risk stratification in select patient populations. Future studies are needed to evaluate the clinical utility of novel imaging metrics following exercise training.

Measuring lung water adds prognostic value in heart failure patients undergoing cardiac magnetic resonance

To assess whether a simplified cardiac magnetic resonance (CMR)–derived lung water density (LWD) quantification predicted major events in Heart Failure (HF). Single-centre retrospective study of consecutive HF patients with left ventricular ejection fraction (LVEF) < 50% who underwent CMR. All measurements were performed on HASTE sequences in a parasagittal plane at the right midclavicular line. LWD was determined by the lung-to-liver signal ratio multiplied by 0.7. A cohort of 102 controls was used to derive the LWD upper limit of normal (21.2%). The primary endpoint was a composite of time to all-cause death or HF hospitalization. Overall, 290 patients (mean age 64 ± 12 years) were included. LWD measurements took on average 35 ± 4 s, with good inter-observer reproducibility. LWD was increased in 65 (22.4%) patients, who were more symptomatic (NYHA ≥ III 29.2 vs. 1.8%; p = 0.017) and had higher NT-proBNP levels [1973 (IQR: 809–3766) vs. 802 (IQR: 355–2157 pg/mL); p < 0.001]. During a median follow-up of 21 months, 20 patients died and 40 had ≥ 1 HF hospitalization. In multivariate analysis, NYHA (III–IV vs. I–II; HR: 2.40; 95%-CI: 1.30–4.43; p = 0.005), LVEF (HR per 1%: 0.97; 95%-CI: 0.94–0.99; p = 0.031), serum creatinine (HR per 1 mg/dL: 2.51; 95%-CI: 1.36–4.61; p = 0.003) and LWD (HR per 1%: 1.07; 95%-CI: 1.02–1.12; p = 0.007) were independent predictors of the primary endpoint. These findings were mainly driven by an association between LWD and HF hospitalization (p = 0.026). A CMR-derived LWD quantification was independently associated with an increased HF hospitalization risk in HF patients with LVEF < 50%. LWD is a simple, reproducible and straightforward measurement, with prognostic value in HF.

Quantification of lung water density with UTE Yarnball MRI

PURPOSE

An efficient Yarnball ultrashort-TE k-space trajectory, in combination with an optimized pulse sequence design and automated image-processing approach, is proposed for fast and quantitative imaging of water density in the lung parenchyma.

METHODS

Three-dimensional Yarnball k-space trajectories (TE = 0.07 ms) were designed at 3 T for breath-hold and free-breathing navigator acquisitions targeting the lung parenchyma (full torso spatial coverage) with minimal T₁ and T 2 ∗ weighting. A composite of all solid tissues surrounding the lungs (muscle, liver, heart, blood pool) was used for user-independent lung water density signal referencing and B₁ -inhomogeneity correction needed for the calculation of relative lung water density images. Sponge phantom experiments were used to validate absolute water density quantification, and relative lung water density was evaluated in 10 healthy volunteers.

RESULTS

Phantom experiments showed excellent agreement between sponge wet weight and imaging-derived water density. Breath-hold (13 seconds) and free-breathing (~2 minutes) Yarnball acquisitions in volunteers (2.5-mm isotropic resolution) had negligible artifacts and good lung parenchyma SNR (>10). Whole-lung average relative lung water density values with fully automated analysis were 28.2 ± 1.9% and 28.6 ± 1.8% for breath-hold and free-breathing acquisitions, respectively, with good test-retest reproducibility (intraclass correlation coefficient = 0.86 and 0.95, respectively).

CONCLUSIONS

Quantitative lung water density imaging with an optimized Yarnball k-space acquisition approach is possible in a breath-hold or short free-breathing study with automated signal referencing and segmentation.

2020 - State of our JCMR

There were 79 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2019, including 65 original research papers, 2 reviews, 8 technical notes, 1 Society for Cardiovascular Magnetic Resonacne (SCMR) guideline, and 3 corrections. The volume was down slightly from 2018 (n = 89) with a corresponding 5.5% increase in manuscript submissions from 345 to 366. This led to a slight decrease in the acceptance rate from 25 to 22%. The quality of the submissions continues to be high. The 2019 JCMR Impact Factor (which is published in June 2020) increased from 5.07 to 5.36. The 2020 impact factor means that on average, each JCMR published in 2017 and 2018 was cited 5.36 times in 2019. Our 5 year impact factor was 5.2. We are now finishing the 13th year of JCMR as an open-access publication with BMC. As outlined in this report, the Open-Access system has dramatically increased the reading and citation of JCMR publications. I hope that our authors will continue to send their very best, high quality manuscripts for JCMR consideration and that our readers will continue to look to JCMR for the very best/state-of-the-art publications in our field. It takes a village to run a journal. JCMR is blessed to have very dedicated Associate Editors, Guest Editors, and Reviewers. I thank each of them for their efforts to ensure that the review process occurs in a timely and responsible manner. These efforts have allowed the JCMR to continue as the premier journal of our field. My role, and the entire process would not be possible without the dedication and efforts of our managing editor, Diana Gethers (who will leaving the journal in the coming months) and our assistant managing editor, Jennifer Rodriguez, who has agreed to increase her reponsibilities. Finally, I thank you for entrusting me with the editorship of the JCMR. As I begin my 5th year as your editor-in-chief, please know that I fully recognize we are not perfect in our review process. We try our best to objectively assess every submission in a timely manner, but sometimes don't get it "right." The editorial process is a tremendously fulfilling experience for me. The opportunity to review manuscripts that reflect the best in our field remains a great joy and a highlight of my week!