The Prognostic Value of 18F-FDG Uptake Ratio Between the Right and Left Ventricles in Idiopathic Pulmonary Arterial Hypertension

Refining Prognostication and Therapeutic Guidance Through Advances in Right Heart Imaging Approaches

There is growing consensus on the importance of accurately assessing right heart size and function because of its critical relationship with cardiac outcomes across a wide range of cardiovascular diseases. The right heart plays a central role in maintaining cardiac performance, making its assessment essential for diagnosis, management, and prognostication. The need for precise and reliable assessment tools has led to substantial advancements in imaging technology, which have been used to successfully address many of the challenges posed by the unique and complex anatomy of the right heart chambers. In this review we underscore the evolving role of multimodality imaging in risk stratification, therapeutic guidance, and outcome prediction. Further advancements in technology and clinical integration are essential to optimizing care and improving outcomes for patients with cardiovascular disease. We will delve into the strengths and limitations of multimodality techniques and their applicability in different clinical scenarios to equip clinicians with insights into selecting the most appropriate modality for specific cardiac conditions. Additionally, we underscore the practical implications of these imaging modalities in guiding clinical decisions and improving patient outcomes.

Guidelines for the Echocardiographic Assessment of the Right Heart in Adults and Special Considerations in Pulmonary Hypertension: Recommendations from the American Society of Echocardiography

Right heart adaptation to pulmonary hypertension (PH) is a critical determinant of clinical outcomes, morbidity, and mortality in patients with or at risk for cardiopulmonary disease. The World Symposium on Pulmonary Hypertension recently redefined PH as a mean pulmonary arterial pressure >20 mm Hg, based on a wealth of epidemiologic evidence underscoring the significant impact of even mildly elevated mean pulmonary artery pressures on major adverse clinical events. The lowered diagnostic threshold for PH has renewed interest in echocardiography and its critical role in early detection and screening, refined hemodynamic evaluation, and longitudinal monitoring. However, the systematic assessment of the right heart remains inconsistent, largely due to the predominant focus on left heart evaluation, limited familiarity with right heart ultrasound techniques, and a paucity of reference data defining normal right heart size and function. A systematic, comprehensive ultrasound-based assessment of the right heart offers valuable diagnostic insights for in screening at-risk populations, PH classification, risk stratification, monitoring therapeutic response, and informing prognostication, thereby improving clinical outcomes.

Association of the Right Ventricle Cardiac Power Index with Glucose Metabolism and Prognosis in Pulmonary Arterial Hypertension Patients-PET/MRI Study

Background: In pulmonary arterial hypertension (PAH), there is still a need for new prognostic markers to precisely identify patients before clinical deterioration. We investigated the right ventricle cardiac power index (RV CPI) as a tool to assess RV function. We also hypothesized that hemodynamic changes occurring in PAH assessed with the RV CPI are related with cardiac metabolism alterations in PET imaging, which affects prognosis. Methods: Twenty-eight stable PAH patients (51.4 ± 15.9 years old) had PET/CMR and heart catheterization performed at baseline and after 24 months. The PET-derived SUV RV/LV ratio was used to estimate cardiac glucose uptake. Clinical endpoints (CEPs-death or clinical deterioration) were assessed between visits. The RV CPI was defined as cardiac index × mean pulmonary artery pressure × 2.22 × 10-3. Results: The baseline RV CPI was 0.28 ± 0.09 W/m2 and correlated significantly with the SUV RV/LV ratio (r = 0.55, p = 0.002), confirming a relationship between RV hemodynamics and glucose metabolism. After 24 months of PAH-specific therapy, we observed significant improvement in the follow-up RV CPI-0.23 ± 0.04 W/m2 (p = 0.04). During 2-year observations, 16 patients (57%) experienced CEPs (including four deaths). Patients with CEPs had a higher baseline CPI than stable patients (0.32 ± 0.09 vs. 0.21 ± 0.05, p = 0.0006). The cut-off value of the RV CPI to predict worse prognosis was 0.24 W/m2 (log-rank test, p = 0.003). Conclusions: To sum up, the indexed cardiac power output parameter may reflect RV efficiency and is related to its glucose metabolism alterations in PAH. Its low value may help to identify stable patients at higher risk of death or clinical deterioration in long-term prognosis.

PET/CT Imaging of the Right Heart Perfusion and Glucose Metabolism Depending on a Risk Status in Patients With Idiopathic Pulmonary Arterial Hypertension

Right ventricular heart failure (RV HF) is the leading cause of death in pulmonary arterial hypertension (PAH). Relevance of the low-risk status assessment using available diagnostic tools requires a reliable confirmation. The study aimed to evaluate right ventricular perfusion and glucose metabolism using positron emission tomography (PET)/computed tomography (CT) with [13N]-ammonia and [18F]-fluorodeoxyglucose ([18F]-FDG) in 30 IPAH patients (33.8 ± 9.4 years) according to ESC/ERS 2022 risk status. The ratio of SUVmaxRV/LV metabolism and SUVmaxRV/LV perfusion showed significant positive correlation with pulmonary artery pressure, right heart dilatation, NT-proBNP level and negative correlation with the RV ejection fraction. The SUVmaxRV/LV perfusion and SUVmaxRV/LV metabolism ratios differed significantly according to risk status. Low risk patients had a SUVmaxRV/LV metabolism comparable to the controls without PH. The SUVmaxRV/LV perfusion ratio was elevated in low-risk IPAH patients compared with controls. Increased SUVmaxRV/LV perfusion may be an early marker of coronary flow adaptation to RV pressure overload in low-risk IPAH patients and requires further evaluation. Further long-term studies are needed to determine the clinical relevance and cut-off values for the RV/LV PET/CT with [13N]-ammonia and [18F]-fluorodeoxyglucose ([18F]-FDG) uptake in different IPAH risk groups.

Cardiac PET/MRI: Recent Developments and Future Aspects

Positron emission tomography/magnetic resonance (PET/MRI) hybrid imaging is now available for over a decade and although the quantity of installed systems is rather low, the number of emerging applications for cardiovascular diseases is still growing. PET/MRI provides integrated images of high quality anatomical and functional assessment obtained by MRI with the possibilities of PET for quantification of molecular parameters such as metabolism, inflammation, and perfusion. In recent years, sequential co-registration of myocardial tissue characterization with its molecular data had become an increasingly helpful tool in clinical practice and an integrated device simplifies this task. This review summarizes recent developments and future possibilities in the use of the PET/MRI in the diagnosis and treatment of cardiovascular disorders.

Mitochondrial Integrity Is Critical in Right Heart Failure Development

Molecular processes underlying right ventricular (RV) dysfunction (RVD) and right heart failure (RHF) need to be understood to develop tailored therapies for the abatement of mortality of a growing patient population. Today, the armament to combat RHF is poor, despite the advancing identification of pathomechanistic processes. Mitochondrial dysfunction implying diminished energy yield, the enhanced release of reactive oxygen species, and inefficient substrate metabolism emerges as a potentially significant cardiomyocyte subcellular protagonist in RHF development. Dependent on the course of the disease, mitochondrial biogenesis, substrate utilization, redox balance, and oxidative phosphorylation are affected. The objective of this review is to comprehensively analyze the current knowledge on mitochondrial dysregulation in preclinical and clinical RVD and RHF and to decipher the relationship between mitochondrial processes and the functional aspects of the right ventricle (RV).

Multimodality Imaging of Right Heart Function: JACC Scientific Statement

Right ventricular (RV) size and function assessed by multimodality imaging are associated with outcomes in a variety of cardiovascular diseases. Understanding RV anatomy and physiology is essential in appreciating the strengths and weaknesses of current imaging methods and gives these measurements greater context. The adaptation of the right ventricle to different types and severity of stress, particularly over time, is specific to the cardiovascular disease process. Multimodality imaging parameters, which determine outcomes, reflect the ability to image the initial and longitudinal RV response to stress. This paper will review the standard and novel imaging methods for assessing RV function and the impact of these parameters on outcomes in specific disease states.

The impact of specific pulmonary arterial hypertension therapy on cardiac fluorodeoxyglucose distribution in PET/MRI hybrid imaging-follow-up study

BACKGROUND

PET/MRI hybrid imaging in pulmonary arterial hypertension (PAH) provides important prognostic information identifying patients who might benefit from early therapy escalation, as right ventricle (RV) metabolic alterations are linked with hemodynamics and might precede clinical deterioration. Now, we hypothesize that adequate PAH therapy escalation may result in reversal of unfavourable increased glucose uptake of RV, which is associated with improved prognosis.

METHODS

Out of twenty-six initially clinically stable PAH patients who had baseline PET/MRI scans, twenty (49.9 ± 14.9 years) had second PET/MRI after 24 months. SUV_RV/SUV_LV ratio was used to estimate and compare cardiac glucose uptake. Occurrences of clinical endpoints (CEP), defined as death or clinical deterioration, were assessed during 48-month follow-up from baseline.

RESULTS

In first 24 months of observation, sixteen patients had CEP and needed PAH therapy escalation. At follow-up visits, we observed significant improvement of RV ejection fraction (45.1 ± 9.6% to 52.4 ± 12.9%, p = 0.01), mean pulmonary artery pressure (50.5 ± 18.3 to 42.8 ± 18.6 mmHg, p = 0.03), and SUV_RV/SUV_LV, which tended to decrease (mean change -0.20 ± 0.74). Patients with baseline SUV_RV/SUV_LV value higher than 0.54 had worse prognosis in 48 months observation (log-rank test, p = 0.0007); follow up SUV_RV/SUV_LV > 1 predicted CEP in the following 24 months, regardless of previously escalated treatment.

CONCLUSIONS

PAH therapy escalation may influence RV glucose metabolism, what seems to be related with patients' prognosis. PET/MRI assessment may predict clinical deterioration regardless of previous clinical course, however its clinical significance in PAH requires further studies. Importantly, even mild alterations of RV glucose metabolism predict clinical deterioration in long follow-up. Clinical Trial Registration ClinicalTrials.gov, NCT03688698, 05/01/2016, https://clinicaltrials.gov/ct2/show/study/NCT03688698?term=NCT03688698&draw=2&rank=1.

Multimodal assessment of right ventricle overload-metabolic and clinical consequences in pulmonary arterial hypertension

BACKGROUND

In pulmonary arterial hypertension (PAH) increased afterload leads to adaptive processes of the right ventricle (RV) that help to maintain arterio-ventricular coupling of RV and preserve cardiac output, but with time the adaptive mechanisms fail. In this study, we propose a multimodal approach which allows to estimate prognostic value of RV coupling parameters in PAH patients.

METHODS

Twenty-seven stable PAH patients (49.5 ± 15.5 years) and 12 controls underwent cardiovascular magnetic resonance (CMR). CMR feature tracking analysis was performed for RV global longitudinal strain assessment (RV GLS). RV-arterial coupling was evaluated by combination of RV GLS and three proposed surrogates of RV afterload-pulmonary artery systolic pressure (PASP), pulmonary vascular resistance (PVR) and pulmonary artery compliance (PAC). 18-FDG positron emission tomography (PET) analysis was used to assess RV glucose uptake presented as SUVRV/LV. Follow-up time of this study was 25 months and the clinical end-point was defined as death or clinical deterioration.

RESULTS

Coupling parameters (RV GLS/PASP, RV GLS/PVR and RV GLS*PAC) significantly correlated with RV function and standardized uptake value (SUVRV/LV). Patients who experienced a clinical end-point (n = 18) had a significantly worse coupling parameters at the baseline visit. RV GLS/PASP had the highest area under curve in predicting a clinical end-point and patients with a value higher than (-)0.29%/mmHg had significantly worse prognosis. It was also a statistically significant predictor of clinical end-point in multivariate analysis (adjusted R2 = 0.68; p < 0.001).

CONCLUSIONS

Coupling parameters are linked with RV hemodynamics and glucose metabolism in PAH. Combining CMR and hemodynamic measurements offers more comprehensive assessment of RV function required for prognostication of PAH patients.

TRIAL REGISTRATION

NCT03688698, 09/26/2018, retrospectively registered; Protocol ID: 2017/25/N/NZ5/02689.

Suppression of Myocardial Hypoxia-Inducible Factor-1α Compromises Metabolic Adaptation and Impairs Cardiac Function in Patients With Cyanotic Congenital Heart Disease During Puberty

BACKGROUND

Cyanotic congenital heart disease (CCHD) is a complex pathophysiological condition involving systemic chronic hypoxia (CH). Some patients with CCHD are unoperated for various reasons and remain chronically hypoxic throughout their lives, which heightens the risk of heart failure as they age. Hypoxia activates cellular metabolic adaptation to balance energy demands by accumulating hypoxia-inducible factor 1-α (HIF-1α). This study aims to determine the effect of CH on cardiac metabolism and function in patients with CCHD and its association with age. The role of HIF-1α in this process was investigated, and potential therapeutic targets were explored.

METHODS

Patients with CCHD (n=25) were evaluated for cardiac metabolism and function with positron emission tomography/computed tomography and magnetic resonance imaging. Heart tissue samples were subjected to metabolomic and protein analyses. CH rodent models were generated to enable continuous observation of changes in cardiac metabolism and function. The role of HIF-1α in cardiac metabolic adaptation to CH was investigated with genetically modified animals and isotope-labeled metabolomic pathway tracing studies.

RESULTS

Prepubertal patients with CCHD had glucose-dominant cardiac metabolism and normal cardiac function. In comparison, among patients who had entered puberty, the levels of myocardial glucose uptake and glycolytic intermediates were significantly decreased, but fatty acids were significantly increased, along with decreased left ventricular ejection fraction. These clinical phenotypes were replicated in CH rodent models. In patients with CCHD and animals exposed to CH, myocardial HIF-1α was upregulated before puberty but was significantly downregulated during puberty. In cardiomyocyte-specific Hif-1α-knockout mice, CH failed to initiate the switch of myocardial substrates from fatty acids to glucose, thereby inhibiting ATP production and impairing cardiac function. Increased insulin resistance during puberty suppressed myocardial HIF-1α and was responsible for cardiac metabolic maladaptation in animals exposed to CH. Pioglitazone significantly reduced myocardial insulin resistance, restored glucose metabolism, and improved cardiac function in pubertal CH animals.

CONCLUSIONS

In patients with CCHD, maladaptation of cardiac metabolism occurred during puberty, along with impaired cardiac function. HIF-1α was identified as the key regulator of cardiac metabolic adaptation in animals exposed to CH, and pubertal insulin resistance could suppress its expression. Pioglitazone administration during puberty might help improve cardiac function in patients with CCHD.

Prognostic role of PET/MRI hybrid imaging in patients with pulmonary arterial hypertension

OBJECTIVE

Right ventricular (RV) function is a major determinant of survival in patients with pulmonary arterial hypertension (PAH). Metabolic alterations may precede haemodynamic and clinical deterioration. Increased RV fluorodeoxyglucose (FDG) uptake in positron emission tomography (PET) was recently associated with progressive RV dysfunction in MRI, but the prognostic value of their combination has not been established.

METHODS

Twenty-six clinically stable patients with PAH (49.9±15.2 years) and 12 healthy subjects (control group, 44.7±13.5 years) had simultaneous PET/MRI scans. FDG uptake was quantified as mean standardised uptake value (SUV) for both left ventricle (LV) and RV. Mean follow-up time of this study was 14.2±7.3 months and the clinical end point was defined as death or clinical deterioration.

RESULTS

Median SUV_RV/SUV_LV ratio was 1.02 (IQR 0.42-1.21) in PAH group and 0.16 (0.13-0.25) in controls, p<0.001. In PAH group, SUV_RV/SUV_LV significantly correlated with RV haemodynamic deterioration. In comparison to the stable ones, 12 patients who experienced clinical end point had significantly higher baseline SUV_RV/SUV_LV ratio (1.21 (IQR 0.87-1.95) vs 0.53 (0.24-1.08), p=0.01) and lower RV ejection fraction (RVEF) (37.9±5.2 vs 46.8±5.7, p=0.03). Cox regression revealed that SUV_RV/SUV_LV ratio was significantly associated with the time to clinical end point. Kaplan-Meier analysis showed that combination of RVEF from MRI and SUV_RV/SUV_LV assessment may help to predict prognosis.

CONCLUSIONS

Increased RV glucose uptake in PET and decreased RVEF identify patients with PAH with worse prognosis. Combining parameters from PET and MRI may help to identify patients at higher risk who potentially benefit from therapy escalation, but this hypothesis requires prospective validation.

Metabolic Remodeling in the Pressure-Loaded Right Ventricle: Shifts in Glucose and Fatty Acid Metabolism-A Systematic Review and Meta-Analysis

Background

Right ventricular (RV) failure because of chronic pressure load is an important determinant of outcome in pulmonary hypertension. Progression towards RV failure is characterized by diastolic dysfunction, fibrosis and metabolic dysregulation. Metabolic modulation has been suggested as therapeutic option, yet, metabolic dysregulation may have various faces in different experimental models and disease severity. In this systematic review and meta‐analysis, we aimed to identify metabolic changes in the pressure loaded RV and formulate recommendations required to optimize translation between animal models and human disease.

Methods and Results

Medline and EMBASE were searched to identify original studies describing cardiac metabolic variables in the pressure loaded RV. We identified mostly rat‐models, inducing pressure load by hypoxia, Sugen‐hypoxia, monocrotaline (MCT), pulmonary artery banding (PAB) or strain (fawn hooded rats, FHR), and human studies. Meta‐analysis revealed increased Hedges’ g (effect size) of the gene expression of GLUT1 and HK1 and glycolytic flux. The expression of MCAD was uniformly decreased. Mitochondrial respiratory capacity and fatty acid uptake varied considerably between studies, yet there was a model effect in carbohydrate respiratory capacity in MCT‐rats.

Conclusions

This systematic review and meta‐analysis on metabolic remodeling in the pressure‐loaded RV showed a consistent increase in glucose uptake and glycolysis, strongly suggest a downregulation of beta‐oxidation, and showed divergent and model‐specific changes regarding fatty acid uptake and oxidative metabolism. To translate metabolic results from animal models to human disease, more extensive characterization, including function, and uniformity in methodology and studied variables, will be required.

Current Knowledge and Recent Advances of Right Ventricular Molecular Biology and Metabolism from Congenital Heart Disease to Chronic Pulmonary Hypertension

Studies about pulmonary hypertension and congenital heart diseases have introduced the concept of right ventricular remodeling leading these pathologies to a similar outcome: right ventricular failure. However right ventricular remodeling is also a physiological process that enables the normal fetal right ventricle to adapt at birth and gain its adult phenotype. The healthy mature right ventricle is exposed to low pulmonary vascular resistances and is compliant. However, in the setting of chronic pressure overload, as in pulmonary hypertension, or volume overload, as in congenital heart diseases, the right ventricle reverts back to a fetal phenotype to sustain its function. Mechanisms include angiogenic changes and concomitant increased metabolic activity to maintain energy production. Eventually, the remodeled right ventricle cannot resist the increased afterload, leading to right ventricular failure. After comparing the fetal and adult healthy right ventricles, we sought to review the main metabolic and cellular changes occurring in the setting of PH and CHD. Their association with RV function and potential impact on clinical practice will also be discussed.

Pulmonary Hypertension and Indicators of Right Ventricular Function

Pulmonary hypertension (PH) is a rare disease, whose underlying mechanisms are not fully understood. It is characterized by pulmonary arterial vasoconstriction and vessels wall thickening, mainly intimal and medial layers. Several molecular pathways have been studied, but their respective roles remain unknown. Cardiac repercussions of PH are hypertrophy, dilation, and progressive right ventricular dysfunction. Multiple echocardiographic parameters are being used, in order to assess anatomy and cardiac function, but there are no guidelines edited about their usefulness. Thus, it is now recommended to associate the best-known parameters, such as atrial and ventricular diameters or tricuspid annular plane systolic excursion. Cardiac catheterization remains necessary to establish the diagnosis of PH and to assess pulmonary hemodynamic state. Concerning energetic metabolism, free fatty acids, normally used to provide energy for myocardial contraction, are replaced by glucose uptake. These abnormalities are illustrated by increased (18)F-fluorodeoxyglucose ((18)F-FDG) uptake on positron emission tomography/computed tomography, which seems to be correlated with echocardiographic and hemodynamic parameters.