Effects of catecholamine stress on diastolic function and myocardial energetics in obesity

Hyperpolarized 13C and 31P MRS detects differences in cardiac energetics, metabolism, and function in obesity, and responses following treatment

Obesity is associated with important changes in cardiac energetics and function, and an increased risk of adverse cardiovascular outcomes. Multi-nuclear MRS and MRI techniques have the potential to provide a comprehensive non-invasive assessment of cardiac metabolic perturbation in obesity. A rat model of obesity was created by high-fat diet feeding. This model was characterized using in vivo hyperpolarized [1-13C]pyruvate and [2-13C]pyruvate MRS, echocardiography and perfused heart 31P MRS. Two groups of obese rats were subsequently treated with either caloric restriction or the glucagon-like peptide-1 analogue/agonist liraglutide, prior to reassessment. The model recapitulated cardiovascular consequences of human obesity, including mild left ventricular hypertrophy, and diastolic, but not systolic, dysfunction. Hyperpolarized 13C and 31P MRS demonstrated that obesity was associated with reduced myocardial pyruvate dehydrogenase flux, altered cardiac tricarboxylic acid (TCA) cycle metabolism, and impaired myocardial energetic status (lower phosphocreatine to adenosine triphosphate ratio and impaired cardiac ΔG~ATP). Both caloric restriction and liraglutide treatment were associated with normalization of metabolic changes, alongside improvement in cardiac diastolic function. In this model of obesity, hyperpolarized 13C and 31P MRS demonstrated abnormalities in cardiac metabolism at multiple levels, including myocardial substrate selection, TCA cycle, and high-energy phosphorus metabolism. Metabolic changes were linked with impairment of diastolic function and were reversed in concert following either caloric restriction or liraglutide treatment. With hyperpolarized 13C and 31P techniques now available for human use, the findings support a role for multi-nuclear MRS in the development of new therapies for obesity.

Human cardiac metabolism

The heart is the most metabolically active organ in the human body, and cardiac metabolism has been studied for decades. However, the bulk of studies have focused on animal models. The objective of this review is to summarize specifically what is known about cardiac metabolism in humans. Techniques available to study human cardiac metabolism are first discussed, followed by a review of human cardiac metabolism in health and in heart failure. Mechanistic insights, where available, are reviewed, and the evidence for the contribution of metabolic insufficiency to heart failure, as well as past and current attempts at metabolism-based therapies, is also discussed.

Supporting patients' workload through wearable devices and mobile health applications, a systematic literature review

Patients face a challenging workload in their course of care. In this study, we investigate the impact of using mobile health technologies in supporting this workload and identify the system challenges of its application through a systematic review of the literature published in the last two decades following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Reviews and Meta-Analysis guidelines PRISMA guidelines. Twenty-two studies that satisfied the inclusion criteria were included. The review revealed various mobile health and wearable devices used to support mental demand, physical demand, frustration, and performance. Better outcomes were related to mobile health use in healthcare for patients in different settings. There were no applications of health that supported the temporal demand of patients. Some populations, such as cancer patients, need more than only physical demand. Mhealth devices are important in supporting the patients' workload in their daily activities and clinical settings.Practitioner summary: This review study shows the importance of mHealth and wearables in supporting patients' workload (physical, mental, emotional) but not the temporal load.

Noninvasive Pressure-Volume Loops Predict Major Adverse Cardiac Events in Heart Failure With Reduced Ejection Fraction

Background

Heart failure with reduced ejection fraction (HFrEF) is characterized by ventricular remodeling and impaired myocardial energetics. Left ventricular pressure-volume (PV) loop analysis can be performed noninvasively using cardiovascular magnetic resonance (CMR) imaging to assess cardiac thermodynamic efficiency.

Objectives

The aim of the study was to investigate whether noninvasive PV loop parameters, derived from CMR, could predict major adverse cardiac events (MACE) in HFrEF patients.

Methods

PV loop parameters (stroke work, ventricular efficiency, external power, contractility, and energy per ejected volume) were computed from CMR cine images and brachial blood pressure. The primary end point was MACE (cardiovascular death, heart failure (HF) hospitalization, myocardial infarction, revascularization, ventricular tachycardia/fibrillation, heart transplantation, or left ventricular assist device implantation within 5 years). Associations between PV loop parameters and MACE were evaluated using multivariable Cox regression.

Results

One hundred and sixty-four HFrEF patients (left ventricular ejection fraction ≤40%, age 63 [IQR: 55-70] years, 79% male) who underwent clinical CMR examination between 2004 and 2014 were included. Eighty-eight patients (54%) experienced at least one MACE after an average of 2.8 years. Unadjusted models demonstrated a significant association between MACE and all PV loop parameters (P < 0.05 for all), HF etiology (P < 0.001), left ventricular ejection fraction (P = 0.003), global longitudinal strain (P < 0.001), and N-terminal prohormone of brain natriuretic peptide level (P = 0.001). In the multivariable Cox regression analysis adjusted for age, sex, hypertension, diabetes, and HF etiology, ventricular efficiency was associated with MACE (HR: 1.04 (95% CI: 1.01-1.08) per-% decrease, P = 0.01).

Conclusions

Ventricular efficiency, derived from noninvasive PV loop analysis from standard CMR scans, is associated with MACE in patients with HFrEF.

3D ultra-short echo time 31P-MRSI with rosette k-space pattern: Feasibility and comparison with conventional weighted CSI

Phosphorus-31 magnetic resonance spectroscopic imaging (31P-MRSI) provides valuable non-invasive in vivo information on tissue metabolism but is burdened by poor sensitivity and prolonged scan duration. Ultra-short echo time (UTE) acquisitions minimize signal loss when probing signals with relatively short spin-spin relaxation time (T2), while also preventing first-order dephasing. Here, a three-dimensional (3D) UTE sequence with a rosette k-space trajectory is applied to 31P-MRSI at 3T. Conventional chemical shift imaging (CSI) employs highly regular Cartesian k-space sampling, susceptible to substantial artifacts when accelerated via undersampling. In contrast, this novel sequence's "petal-like" pattern offers incoherent sampling more suitable for compressed sensing (CS). These results showcase the competitive performance of UTE rosette 31P-MRSI against conventional weighted CSI with simulation, phantom, and in vivo leg muscle comparisons.

Myocardial Metabolism in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is increasingly prevalent and now accounts for half of all heart failure cases. This rise is largely attributed to growing rates of obesity, hypertension, and diabetes. Despite its prevalence, the pathophysiological mechanisms of HFpEF are not fully understood. The heart, being the most energy-demanding organ, appears to have a compromised bioenergetic capacity in heart failure, affecting all phenotypes and aetiologies. While metabolic disturbances in heart failure with reduced ejection fraction (HFrEF) have been extensively studied, similar insights into HFpEF are limited. This review collates evidence from both animal and human studies, highlighting metabolic dysregulations associated with HFpEF and its risk factors, such as obesity, hypertension, and diabetes. We discuss how changes in substrate utilisation, oxidative phosphorylation, and energy transport contribute to HFpEF. By delving into these pathological shifts in myocardial energy production, we aim to reveal novel therapeutic opportunities. Potential strategies include modulating energy substrates, improving metabolic efficiency, and enhancing critical metabolic pathways. Understanding these aspects could be key to developing more effective treatments for HFpEF.

Left ventricular strain-volume loops and diastolic dysfunction in suspected heart failure with preserved ejection fraction

BACKGROUND

Presence of left ventricular diastolic dysfunction (DD) is key in the pathogenesis of heart failure with preserved ejection fraction (HFpEF). However, non-invasive assessment of diastolic function is complex, cumbersome, and largely based on consensus recommendations. Novel imaging techniques may help detecting DD. Therefore, we compared left ventricular strain-volume loop (SVL) characteristics and diastolic (dys-)function in suspected HFpEF patients.

METHOD AND RESULTS

257 suspected HFpEF patients with sinus rhythm during echocardiography were prospectively included. 211 patients with quality-controlled images and strain and volume analysis were classified according to the 2016 ASE/EACVI recommendations. Patients with indeterminate diastolic function were excluded, resulting in two groups: normal diastolic function (control; n = 65) and DD (n = 91). Patients with DD were older (74.8 ± 6.9 vs. 68.5 ± 9.4 years, p < 0.001), more often female (88% vs 72%, p = 0.021), and more often had a history of atrial fibrillation (42% vs. 23%, p = 0.024) and hypertension (91% vs. 71%, p = 0.001) compared to normal diastolic function. SVL analysis showed a larger uncoupling i.e., a different longitudinal strain contribution to volume change, in DD compared to controls (0.556 ± 1.10% vs. -0.051 ± 1.14%, respectively, P < 0.001). This observation suggests different deformational properties during the cardiac cycle. After adjustment for age, sex, history of atrial fibrillation and hypertension, we found an adjusted odds ratio of 1.68 (95% confidence interval 1.19-2.47) for DD per unit increase in uncoupling (range: -2.95-3.20).

CONCLUSION

Uncoupling of the SVL is independently associated with DD. This might provide novel insights in cardiac mechanics and new opportunities to assess diastolic function non-invasively.

Functional and Metabolic Imaging in Heart Failure with Preserved Ejection Fraction: Promises, Challenges, and Clinical Utility

Heart failure with preserved ejection fraction (HFpEF) is recognised as an increasingly prevalent, morbid and burdensome condition with a poor outlook. Recent advances in both the understanding of HFpEF and the technological ability to image cardiac function and metabolism in humans have simultaneously shone a light on the molecular basis of this complex condition of diastolic dysfunction, and the inflammatory and metabolic changes that are associated with it, typically in the context of a complex patient. This review both makes the case for an integrated assessment of the condition, and highlights that metabolic alteration may be a measurable outcome for novel targeted forms of medical therapy. It furthermore highlights how recent technological advancements and advanced medical imaging techniques have enabled the characterisation of the metabolism and function of HFpEF within patients, at rest and during exercise.

Cardiac 31P MR spectroscopy: development of the past five decades and future vision-will it be of diagnostic use in clinics?

In the past five decades, the use of the magnetic resonance (MR) technique for cardiovascular diseases has engendered much attention and raised the opportunity that the technique could be useful for clinical applications. MR has two arrows in its quiver: One is magnetic resonance imaging (MRI), and the other is magnetic resonance spectroscopy (MRS). Non-invasively, highly advanced MRI provides unique and profound information about the anatomical changes of the heart. Excellently developed MRS provides irreplaceable and insightful evidence of the real-time biochemistry of cardiac metabolism of underpinning diseases. Compared to MRI, which has already been successfully applied in routine clinical practice, MRS still has a long way to travel to be incorporated into routine diagnostics. Considering the exceptional potential of ³¹P MRS to measure the real-time metabolic changes of energetic molecules qualitatively and quantitatively, how far its powerful technique should be waited before a successful transition from "bench-to-bedside" is enticing. The present review highlights the seminal studies on the chronological development of cardiac ³¹P MRS in the past five decades and the future vision and challenges to incorporating it for routine diagnostics of cardiovascular disease.

Obesity and heart failure with preserved ejection fraction: new insights and pathophysiological targets

Obesity and heart failure with preserved ejection fraction (HFpEF) represent two intermingling epidemics driving perhaps the greatest unmet health problem in cardiovascular medicine in the 21st century. Many patients with HFpEF are either overweight or obese, and recent data have shown that increased body fat and its attendant metabolic sequelae have widespread, protean effects systemically and on the cardiovascular system leading to symptomatic HFpEF. The paucity of effective therapies in HFpEF underscores the importance of understanding the distinct pathophysiological mechanisms of obese HFpEF to develop novel therapies. In this review, we summarize the current understanding of the cardiovascular and non-cardiovascular features of the obese phenotype of HFpEF, how increased adiposity might pathophysiologically contribute to the phenotype, and how these processes might be targeted therapeutically.

Creatine chemical exchange saturation transfer (CEST) CMR imaging reveals myocardial early involvement in idiopathic inflammatory myopathy at 3T: feasibility and initial experience

OBJECTIVES

To measure creatine distribution in idiopathic inflammatory myopathy (IIM) patients' myocardial segments and investigate whether cardiovascular magnetic resonance (CMR) chemical exchange saturation transfer (CEST) creatine mapping can detect subclinical myocardial changes, CEST's ability was further compared with other conventional CMR mapping sequences.

METHODS

Forty IIM patients (53.5 ± 10.5 years, 26 males) and eight healthy controls (35.4 ± 6 years, 5 males) underwent CMR scans on a 3.0-T MR scanner. Patients with IIM were further classified into two subgroups according to cardiac troponin T (cTn-T) values: the elevated cTn-T subgroup (n = 14) and the normal cTn-T subgroup (n = 26). Cine imaging, T2 SPAIR, LGE imaging, T1 mapping, T2 mapping, and Cr (creatine) CEST were performed.

RESULTS

Cr mapping showed significantly reduced creatine in IIM patients among global myocardium (IIM: 0.109 ± 0.063, controls: 0.121 ± 0.021, p < 0.05), and decreased creatine signals were detected in all 16 cardiac segments (p < 0.05). Patients also had significantly prolonged native T1 and decreased enhanced T1 values in each cardiac segment (p < 0.05). There was no significant difference of LVEF and T2 values between IIM patients and controls. Between the two subgroups, elevated cTn-T was linked with creatine and extracellular volume fraction (ECV) values, providing a global average creatine signal of 0.107 vs 0.112 (p < 0.05) and 24.7 vs 32.4 (p < 0.05).

CONCLUSION

Creatine CEST mapping can detect early-stage heart involvement with negative LGE findings in IIM. Compared with T1 mapping, CEST provides increased sensitivity to ECV measurement, making it significantly better than T1, and a promising CMR sequence for screening subclinical myocardial damage.

KEY POINTS

• IIM patients with potential or ongoing heart involvement, elevated ECV, and reduced Cr CEST values could provide valuable information. • ECV and Cr CEST values were closely related to elevated cTn-T.

Impact of body mass index and diabetes on myocardial fat content, interstitial fibrosis and function

PURPOSE

We hypothesize that both increased myocardial steatosis and interstitial fibrosis contributes to subclinical myocardial dysfunction in patients with increased body mass index and diabetes mellitus.

BACKGROUND

Increased body weight and diabetes mellitus are both individually associated with a higher incidence of heart failure with preserved ejection fraction. However, it is unclear how increased myocardial steatosis and interstitial fibrosis interact to influence myocardial composition and function.

METHODS

A total of 100 subjects (27 healthy lean volunteers, 21 healthy but overweight volunteers, and 52 asymptomatic overweight patients with diabetes) were prospectively recruited to measure left ventricular (LV) myocardial steatosis (LV-myoFat) and interstitial fibrosis (by extracellular volume [ECV]) using magnetic resonance imaging, and then used to determine their combined impact on LV global longitudinal strain (GLS) analysis by 2-dimensional (2D) speckle tracking echocardiography on the same day.

RESULTS

On multivariable analysis, both increased body mass index and diabetes were independently associated with increased LV-myoFat. In turn, increased LV-myoFat was independently associated with increased LV ECV. Both increased LV-myoFat and LV ECV were independently associated with impaired 2D LV GLS.

CONCLUSION

Patients with increased body weight and patients with diabetes display excessive myocardial steatosis, which is related to a greater burden of myocardial interstitial fibrosis. LV myocardial contractile function was determined by both the extent of myocardial steatosis and interstitial fibrosis, and was independent of increasing age. Further study is warranted to determine how weight loss and improved diabetes management can improve myocardial composition and function.

Emerging MRI techniques for molecular and functional phenotyping of the diseased heart

Recent advances in cardiac MRI (CMR) capabilities have truly transformed its potential for deep phenotyping of the diseased heart. Long known for its unparalleled soft tissue contrast and excellent depiction of three-dimensional (3D) structure, CMR now boasts a range of unique capabilities for probing disease at the tissue and molecular level. We can look beyond coronary vessel blockages and detect vessel disease not visible on a structural level. We can assess if early fibrotic tissue is being laid down in between viable cardiac muscle cells. We can measure deformation of the heart wall to determine early presentation of stiffening. We can even assess how cardiomyocytes are utilizing energy, where abnormalities are often precursors to overt structural and functional deficits. Finally, with artificial intelligence gaining traction due to the high computing power available today, deep learning has proven itself a viable contender with traditional acceleration techniques for real-time CMR. In this review, we will survey five key emerging MRI techniques that have the potential to transform the CMR clinic and permit early detection and intervention. The emerging areas are: (1) imaging microvascular dysfunction, (2) imaging fibrosis, (3) imaging strain, (4) imaging early metabolic changes, and (5) deep learning for acceleration. Through a concerted effort to develop and translate these areas into the CMR clinic, we are committing ourselves to actualizing early diagnostics for the most intractable heart disease phenotypes.

Maternal Cardiac Changes in Women With Obesity and Gestational Diabetes Mellitus

OBJECTIVE

We investigated if women with gestational diabetes mellitus (GDM) in the third trimester of pregnancy exhibit adverse cardiac alterations in myocardial energetics, function, or tissue characteristics.

RESEARCH DESIGN AND METHODS

Thirty-eight healthy, pregnant women and 30 women with GDM were recruited. Participants underwent phosphorus MRS and cardiovascular magnetic resonance for assessment of myocardial energetics (phosphocreatine [PCr] to ATP ratio), tissue characteristics, biventricular volumes and ejection fractions, left ventricular (LV) mass, global longitudinal shortening (GLS), and mitral in-flow E-wave to A-wave ratio.

RESULTS

Participants were matched for age, gestational age, and ethnicity. The following data are reported as mean ± SD. The women with GDM had higher BMI (27 ± 4 vs. 33 ± 5 kg/m2; P = 0.0001) and systolic (115 ± 11 vs. 121 ± 13 mmHg; P = 0.04) and diastolic (72 ± 7 vs. 76 ± 9 mmHg; P = 0.04) blood pressures. There was no difference in N-terminal pro-brain natriuretic peptide concentrations between the groups. The women with GDM had lower myocardial PCr to ATP ratio (2.2 ± 0.3 vs. 1.9 ± 0.4; P < 0.0001), accompanied by lower LV end-diastolic volumes (76 ± 12 vs. 67 ± 11 mL/m2; P = 0.002) and higher LV mass (90 ± 13 vs. 103 ± 18 g; P = 0.001). Although ventricular ejection fractions were similar, the GLS was reduced in women with GDM (-20% ± 3% vs. -18% ± 3%; P = 0.008).

CONCLUSIONS

Despite no prior diagnosis of diabetes, women with obesity and GDM manifest impaired myocardial contractility and higher LV mass, associated with reductions in myocardial energetics in late pregnancy compared with lean women with healthy pregnancy. These findings may aid our understanding of the long-term cardiovascular risks associated with GDM.

Adverse right ventricular remodelling, function, and stress responses in obesity: insights from cardiovascular magnetic resonance

AIMS

We aimed to determine the effect of increasing body weight upon right ventricular (RV) volumes, energetics, systolic function, and stress responses using cardiovascular magnetic resonance (CMR).

METHODS AND RESULTS

We first determined the effects of World Health Organization class III obesity [body mass index (BMI) > 40 kg/m2, n = 54] vs. healthy weight (BMI < 25 kg/m2, n = 49) upon RV volumes, energetics and systolic function using CMR. In less severe obesity (BMI 35 ± 5 kg/m2, n = 18) and healthy weight controls (BMI 21 ± 1 kg/m2, n = 9), we next performed CMR before and during dobutamine to evaluate RV stress response. A subgroup undergoing bariatric surgery (n = 37) were rescanned at median 1 year to determine the effects of weight loss. When compared with healthy weight, class III obesity was associated with adverse RV remodelling (17% RV end-diastolic volume increase, P < 0.0001), impaired cardiac energetics (19% phosphocreatine to adenosine triphosphate ratio reduction, P < 0.001), and reduction in RV ejection fraction (by 3%, P = 0.01), which was related to impaired energetics (R = 0.3, P = 0.04). Participants with less severe obesity had impaired RV diastolic filling at rest and blunted RV systolic and diastolic responses to dobutamine compared with healthy weight. Surgical weight loss (34 ± 15 kg weight loss) was associated with improvement in RV end-diastolic volume (by 8%, P = 0.006) and systolic function (by 2%, P = 0.03).

CONCLUSION

Increasing body weight is associated with significant alterations in RV volumes, energetic, systolic function, and stress responses. Adverse RV modelling is mitigated with weight loss. Randomized trials are needed to determine whether intentional weight loss improves symptoms and outcomes in patients with obesity and heart failure.

Kinetic energy of left ventricular blood flow across heart failure phenotypes and in subclinical diastolic dysfunction

BACKGROUND

Kinetic energy (KE) of intracardiac blood flow reflects myocardial work spent on accelerating blood and provides a mechanistic window into diastolic filling dynamics. Diastolic dysfunction may represent an early stage in the development of heart failure (HF). Here we evaluated the hemodynamic effects of impaired diastolic function in subjects with and without HF, testing the hypothesis that left ventricular KE differs between controls, subjects with subclinical diastolic dysfunction (SDD), and HF patients.

METHODS

We studied 77 subjects (16 controls, 20 subjects with SDD, 16 HFpEF, 9 HFmrEF, and 16 HFrEF patients, age- and sex-matched at the group level). Cardiac magnetic resonance at 1.5T included intracardiac 4D flow and cine imaging. Left ventricular KE was calculated as 0.5*m*v².

RESULTS

Systolic KE was similar between groups (p>0.4), also after indexing to stroke volume (p=0.25), and was primarily driven by ventricular emptying rate (p<0.0001, R²=0.52). Diastolic KE was higher in heart failure patients than controls (p<0.05) but similar between SDD and HFpEF (p>0.18), correlating with inflow conditions (E-wave velocity, p<0.0001, R²=0.24) and end-diastolic volume (p=0.0003, R²=0.17) but not with average e' (p=0.07).

CONCLUSIONS

Diastolic KE differs between controls and heart failure, suggesting more work is spent filling the failing ventricle, while systolic KE does not differentiate between well-matched groups with normal ejection fraction even in the presence of relaxation abnormalities and heart failure. Mechanistically, KE reflects the acceleration imparted on the blood and is driven by variations in ventricular emptying and filling rates, volumes, and heart rate, regardless of underlying pathology.

Diabesity in Elderly Cardiovascular Disease Patients: Mechanisms and Regulators

Cardiovascular disease (CVD) is the leading cause of death in the world. In 2019, 550 million people were suffering from CVD and 18 million of them died as a result. Most of them had associated risk factors such as high fasting glucose, which caused 134 million deaths, and obesity, which accounted for 5.02 million deaths. Diabesity, a combination of type 2 diabetes and obesity, contributes to cardiac, metabolic, inflammation and neurohumoral changes that determine cardiac dysfunction (diabesity-related cardiomyopathy). Epicardial adipose tissue (EAT) is distributed around the myocardium, promoting myocardial inflammation and fibrosis, and is associated with an increased risk of heart failure, particularly with preserved systolic function, atrial fibrillation and coronary atherosclerosis. In fact, several hypoglycaemic drugs have demonstrated a volume reduction of EAT and effects on its metabolic and inflammation profile. However, it is necessary to improve knowledge of the diabesity pathophysiologic mechanisms involved in the development and progression of cardiovascular diseases for comprehensive patient management including drugs to optimize glucometabolic control. This review presents the mechanisms of diabesity associated with cardiovascular disease and their therapeutic implications.

Intraoperative Circulatory Support in Lung Transplantation: Current Trend and Its Evidence

Lung transplantation has a high risk of haemodynamic complications in a highly vulnerable patient population. The effects on the cardiovascular system of the various underlying end-stage lung diseases also contribute to this risk. Following a literature review and based on our own experience, this review article summarises the current trends and their evidence for intraoperative circulatory support in lung transplantation. Identifiable and partly modifiable risk factors are mentioned and corresponding strategies for treatment are discussed. The approach of first identifying risk factors and then developing an adjusted strategy is presented as the ERSAS (early risk stratification and strategy) concept. Typical haemodynamic complications discussed here include right ventricular failure, diastolic dysfunction caused by left ventricular deconditioning, and reperfusion injury to the transplanted lung. Pre- and intra-operatively detectable risk factors for the occurrence of haemodynamic complications are rare, and the therapeutic strategies applied differ considerably between centres. However, all the mentioned risk factors and treatment strategies can be integrated into clinical treatment algorithms and can influence patient outcome in terms of both mortality and morbidity.

Increased cardiac Pi/PCr in the diabetic heart observed using phosphorus magnetic resonance spectroscopy at 7T

Phosphorus magnetic resonance spectroscopy (³¹P-MRS) has previously demonstrated decreased energy reserves in the form of phosphocreatine to adenosine-tri-phosphate ratio (PCr/ATP) in the hearts of patients with type 2 diabetes (T2DM). Recent ³¹P-MRS techniques using 7T systems, e.g. long mixing time stimulated echo acquisition mode (STEAM), allow deeper insight into cardiac metabolism through assessment of inorganic phosphate (Pi) content and myocardial pH, which play pivotal roles in energy production in the heart. Therefore, we aimed to further explore the cardiac metabolic phenotype in T2DM using STEAM at 7T. Seventeen patients with T2DM and twenty-three healthy controls were recruited and their cardiac PCr/ATP, Pi/PCr and pH were assessed at 7T. Diastolic function of all patients with T2DM was assessed using echocardiography to investigate the relationship between diastolic dysfunction and cardiac metabolism. Mirroring the decreased PCr/ATP (1.70±0.31 vs. 2.07±0.39; p<0.01), the cardiac Pi/PCr was increased (0.13±0.07 vs. 0.10±0.03; p = 0.02) in T2DM patients in comparison to healthy controls. Myocardial pH was not significantly different between the groups (7.14±0.12 vs. 7.10±0.12; p = 0.31). There was a negative correlation between PCr/ATP and diastolic function (R² = 0.33; p = 0.02) in T2DM. No correlation was observed between diastolic function and Pi/PCr and (R² = 0.16; p = 0.21). In addition, we did not observe any correlation between cardiac PCr/ATP and Pi/PCr (p = 0.19). Using STEAM ³¹P-MRS at 7T we have for the first time explored Pi/PCr in the diabetic human heart and found it increased when compared to healthy controls. The lack of correlation between measured PCr/ATP and Pi/PCr suggests that independent mechanisms might contribute to these perturbations.

Role of Creatine Supplementation in Conditions Involving Mitochondrial Dysfunction: A Narrative Review

Creatine monohydrate (CrM) is one of the most widely used nutritional supplements among active individuals and athletes to improve high-intensity exercise performance and training adaptations. However, research suggests that CrM supplementation may also serve as a therapeutic tool in the management of some chronic and traumatic diseases. Creatine supplementation has been reported to improve high-energy phosphate availability as well as have antioxidative, neuroprotective, anti-lactatic, and calcium-homoeostatic effects. These characteristics may have a direct impact on mitochondrion's survival and health particularly during stressful conditions such as ischemia and injury. This narrative review discusses current scientific evidence for use or supplemental CrM as a therapeutic agent during conditions associated with mitochondrial dysfunction. Based on this analysis, it appears that CrM supplementation may have a role in improving cellular bioenergetics in several mitochondrial dysfunction-related diseases, ischemic conditions, and injury pathology and thereby could provide therapeutic benefit in the management of these conditions. However, larger clinical trials are needed to explore these potential therapeutic applications before definitive conclusions can be drawn.

Energetic Basis for Exercise-Induced Pulmonary Congestion in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Transient pulmonary congestion during exercise is emerging as an important determinant of reduced exercise capacity in heart failure with preserved ejection fraction (HFpEF). We sought to determine whether an abnormal cardiac energetic state underpins this process.

METHODS

We recruited patients across the spectrum of diastolic dysfunction and HFpEF (controls, n=11; type 2 diabetes, n=9; HFpEF, n=14; and severe diastolic dysfunction attributable to cardiac amyloidosis, n=9). Cardiac energetics were measured using phosphorus spectroscopy to define the myocardial phosphocreatine to ATP ratio. Cardiac function was assessed by cardiovascular magnetic resonance cine imaging and echocardiography and lung water using magnetic resonance proton density mapping. Studies were performed at rest and during submaximal exercise using a magnetic resonance imaging ergometer.

RESULTS

Paralleling the stepwise decline in diastolic function across the groups (E/e' ratio; P<0.001) was an increase in NT-proBNP (N-terminal pro-brain natriuretic peptide; P<0.001) and a reduction in phosphocreatine/ATP ratio (control, 2.15 [2.09, 2.29]; type 2 diabetes, 1.71 [1.61, 1.91]; HFpEF, 1.66 [1.44, 1.89]; cardiac amyloidosis, 1.30 [1.16, 1.53]; P<0.001). During 20-W exercise, lower left ventricular diastolic filling rates (r=0.58; P<0.001), lower left ventricular diastolic reserve (r=0.55; P<0.001), left atrial dilatation (r=-0.52; P<0.001), lower right ventricular contractile reserve (right ventricular ejection fraction change, r=0.57; P<0.001), and right atrial dilation (r=-0.71; P<0.001) were all linked to lower phosphocreatine/ATP ratio. Along with these changes, pulmonary proton density mapping revealed transient pulmonary congestion in patients with HFpEF (+4.4% [0.5, 6.4]; P=0.002) and cardiac amyloidosis (+6.4% [3.3, 10.0]; P=0.004), which was not seen in healthy controls (-0.1% [-1.9, 2.1]; P=0.89) or type 2 diabetes without HFpEF (+0.8% [-1.7, 1.9]; P=0.82). The development of exercise-induced pulmonary congestion was associated with lower phosphocreatine/ATP ratio (r=-0.43; P=0.004).

CONCLUSIONS

A gradient of myocardial energetic deficit exists across the spectrum of HFpEF. Even at low workload, this energetic deficit is related to markedly abnormal exercise responses in all 4 cardiac chambers, which is associated with detectable pulmonary congestion. The findings support an energetic basis for transient pulmonary congestion in HFpEF.

The effect of dobutamine in sepsis: a propensity score matched analysis

BACKGROUND

The use of dobutamine in patients with sepsis is questionable currently. As the benefit of dobutamine in septic patients is unclear, we aimed to evaluate whether the use of dobutamine was associated with decreased hospital mortality in sepsis patients.

METHODS

Based on the analysis of MIMIC III public database, we performed a big-data, real world study. According to the use of dobutamine or not, patients were categorized as the dobutamine group or non dobutamine group.We used propensity score matched (PSM) analysis to adjust for confoundings. The primary outcome was hospital mortality.

RESULTS

In the present study, after screening 38,605 patients, 2826 patients with sepsis were included. 121 patients were in dobutamine group and 2165 patients were in non dobutamine group. Compared with patients in non-dobutamine group, patients in dobutamine group had a lower MAP, higher HR, higher RR, higher severity of illness scores. 72 of 121 patients (59.5%) in the dobutamine group and 754 of 2165 patients (34.8%) in the non-dobutamine group died in the hospital, which resulted in a significant between-group difference (OR 1.56, 95% CI 1.01-2.40; P = 0.000). For the secondary outcomes, patients in dobutamine group received more MV use, more renal replacement therapy use, had longer ICU stay durations and more cardiac arrhythmias than those in non-dobutamine group. After adjusting for confoundings between groups by PSM analysis, hospital mortality was consistently higher in dobutamine group than that in non-dobutamine group (60.2% vs. 49.4%, OR 1.55, 95% CI 1.01-2.37; P = 0.044).

CONCLUSIONS

Among patients with sepsis, our study showed that the use of dobutamine was not associated with decreased hospital mortality. Further large scale, randomized controlled studies are warrented to confirm our findings.

A Novel Small Molecule Troponin Activator Increases Cardiac Contractile Function Without Negative Impact on Energetics

Background: Current heart failure (HF) therapies unload the failing heart without targeting the underlying problem of reduced cardiac contractility. Traditional inotropes (i.e. calcitropes) stimulate contractility via energetically costly augmentation of calcium cycling and worsen patient survival. A new class of agents - myotropes - activate the sarcomere directly, independent of calcium. We hypothesize that a novel myotrope TA1 increases contractility without the deleterious myocardial energetic impact of a calcitrope dobutamine. Methods: We determined the effect of TA1 in bovine cardiac myofibrils and human cardiac microtissues, ex vivo in mouse cardiac fibers and in vivo in anesthetized normal rats. Effects of increasing concentrations of TA1 or dobutamine on contractile function, phosphocreatine (PCr) and ATP concentrations and ATP production were assessed by ³¹P NMR spectroscopy on isolated perfused rat hearts. Results: TA1 increased the rate of myosin ATPase activity in isolated bovine myofibrils and calcium sensitivity in intact mouse papillary fibers. Contractility increased dose dependently in human cardiac microtissues and in vivo in rats as assessed by echocardiography. In isolated rat hearts, TA1 and dobutamine similarly increased rate pressure product (RPP). Dobutamine increased both developed pressure (DevP) and heart rate (HR) accompanied by decreased PCr to ATP ratio and decreased free energy of ATP hydrolysis (ΔG~_ATP) and elevated left ventricular end-diastolic pressure (LVEDP). In contrast, the TA1 increased DevP without any effect on HR, LVEDP, PCr/ATP ratio or ΔG~_ATP. Conclusions: Novel myotrope, TA1, increased myocardial contractility by sensitizing the sarcomere to calcium without impairing diastolic function or depleting the cardiac energy reserve. Since energetic depletion negatively correlates with long term survival, myotropes may represent a superior alternative to traditional inotropes in heart failure management.

The β3 Adrenergic Receptor Antagonist L-748,337 Attenuates Dobutamine-Induced Cardiac Inefficiency While Preserving Inotropy in Anesthetized Pigs

Excessive myocardial oxygen consumption (MVO₂) is considered a limitation for catecholamines, termed oxygen cost of contractility. We hypothesize that increased MVO₂ induced by dobutamine is not directly related to contractility but linked to intermediary myocardial metabolism. Furthermore, we hypothesize that selective β₃ adrenergic receptor (β₃AR) antagonism using L-748,337 prevents this. In an open-chest pig model, using general anesthesia, we assessed cardiac energetics, hemodynamics and arterial metabolic substrate levels at baseline, ½ hour and 6 hours after onset of drug infusion. Cardiac efficiency was assessed by relating MVO₂ to left ventricular work (PVA; pressure–volume area). Three groups received dobutamine (5 μg/kg/min), dobutamine + L-748,337 (bolus 50 μg/kg), or saline for time-matched controls. Cardiac efficiency was impaired over time with dobutamine infusion, displayed by persistently increased unloaded MVO₂ from ½ hour and 47% increase in the slope of the PVA–MVO₂ relation after 6 hours. Contractility increased immediately with dobutamine infusion (dP/dt_max; 1636 ± 478 vs 2888 ± 818 mmHg/s, P < 0.05) and persisted throughout the protocol (2864 ± 1055 mmHg/s, P < 0.05). Arterial free fatty acid increased gradually (0.22 ± 0.13 vs 0.39 ± 0.30 mM, P < 0.05) with peak levels after 6 hours (1.1 ± 0.4 mM, P < 0.05). By combining dobutamine with L-748,337 the progressive impairment in cardiac efficiency was attenuated. Interestingly, this combined treatment effect occurred despite similar alterations in cardiac inotropy and substrate supply. We conclude that the extent of cardiac inefficiency following adrenergic stimulation is dependent on the duration of drug infusion, and β₃AR blockade may attenuate this effect.

Obesity modifies the energetic phenotype of dilated cardiomyopathy

AIMS

We sought to determine if myocardial energetics could distinguish obesity cardiomyopathy as a distinct entity from dilated cardiomyopathy.

METHODS AND RESULTS

Sixteen normal weight participants with dilated cardiomyopathy (DCMNW), and 27 with DCM and obesity (DCMOB), were compared to 26 normal weight controls (CTLNW). All underwent cardiac magnetic resonance imaging and 31P spectroscopy to assess function and energetics. Nineteen DCMOB underwent repeat assessment after a dietary weight loss intervention. Adenosine triphosphate (ATP) delivery through creatine kinase (CK flux) was 55% lower in DCMNW than in CTLNW (P = 0.004), correlating with left ventricular ejection fraction (LVEF, r = 0.4, P = 0.015). In contrast, despite similar LVEF (DCMOB 41 ± 7%, DCMNW 38 ± 6%, P = 0.14), CK flux was two-fold higher in DCMOB (P < 0.001), due to higher rate through CK [median kf 0.21 (0.14) vs. 0.11 (0.12) s-1, P = 0.002]. During increased workload, the CTLNW heart increased CK flux by 97% (P < 0.001). In contrast, CK flux was unchanged in DCMNW and fell in DCMOB (by >50%, P < 0.001). Intentional weight loss was associated with positive left ventricular remodelling, with reduced left ventricular end-diastolic volume (by 8%, P < 0.001) and a change in LVEF (40 ± 9% vs. 45 ± 10%, P = 0.002). This occurred alongside a fall in ATP delivery rate with weight loss (by 7%, P = 0.049).

CONCLUSIONS

In normal weight, DCM is associated with reduced resting ATP delivery. In obese DCM, ATP demand through CK is greater, suggesting reduced efficiency of energy utilization. Dietary weight loss is associated with significant improvement in myocardial contractility, and a fall in ATP delivery, suggesting improved metabolic efficiency. This highlights distinct energetic pathways in obesity cardiomyopathy, which are both different from dilated cardiomyopathy, and may be reversible with weight loss.

Effects of Sodium-Glucose Linked Transporter 2 Inhibition With Ertugliflozin on Mitochondrial Function, Energetics, and Metabolic Gene Expression in the Presence and Absence of Diabetes Mellitus in Mice

Background Inhibitors of the sodium-glucose linked transporter 2 improve cardiovascular outcomes in patients with or without type 2 diabetes mellitus, but the effects on cardiac energetics and mitochondrial function are unknown. We assessed the effects of sodium-glucose linked transporter 2 inhibition on mitochondrial function, high-energy phosphates, and genes encoding mitochondrial proteins in hearts of mice with and without diet-induced diabetic cardiomyopathy. Methods and Results Mice fed a control diet or a high-fat, high-sucrose diet received ertugliflozin mixed with the diet (0.5 mg/g of diet) for 4 months. Isolated mitochondria were assessed for functional capacity. High-energy phosphates were assessed by 31P nuclear magnetic resonance spectroscopy concurrently with contractile performance in isolated beating hearts. The high-fat, high-sucrose diet caused myocardial hypertrophy, diastolic dysfunction, mitochondrial dysfunction, and impaired energetic response, all of which were prevented by ertugliflozin. With both diets, ertugliflozin caused supernormalization of contractile reserve, as measured by rate×pressure product at high work demand. Likewise, the myocardial gene sets most enriched by ertugliflozin were for oxidative phosphorylation and fatty acid metabolism, both of which were enriched independent of diet. Conclusions Ertugliflozin not only prevented high-fat, high-sucrose-induced pathological cardiac remodeling, but improved contractile reserve and induced the expression of oxidative phosphorylation and fatty acid metabolism gene sets independent of diabetic status. These effects of sodium-glucose linked transporter 2 inhibition on cardiac energetics and metabolism may contribute to improved structure and function in cardiac diseases associated with mitochondrial dysfunction, such as heart failure.

Measuring Myocardial Energetics with Cardiovascular Magnetic Resonance Spectroscopy

The heart has the highest energy demands per gram of any organ in the body and energy metabolism fuels normal contractile function. Metabolic inflexibility and impairment of myocardial energetics occur with several common cardiac diseases, including ischemia and heart failure. This review explores several decades of innovation in cardiac magnetic resonance spectroscopy modalities and their use to noninvasively identify and quantify metabolic derangements in the normal, failing, and diseased heart. The implications of this noninvasive modality for predicting significant clinical outcomes and guiding future investigation and therapies to improve patient care are discussed.

The role of insulin resistance in the relation of visceral, abdominal subcutaneous and total body fat to cardiovascular function

BACKGROUND AND AIMS

The separate cardiovascular effects of type 2 diabetes and adiposity remain to be examined. This study aimed to investigate the role of insulin resistance in the relations of visceral (VAT), abdominal subcutaneous (aSAT) adipose tissue and total body fat (TBF) to cardiovascular remodeling.

METHODS AND RESULTS

In this cross-sectional analysis of the population-based Netherlands Epidemiology of Obesity study, 914 middle-aged individuals (46% men) were included. Participants underwent magnetic resonance imaging. Standardized linear regression coefficients (95%CI) were calculated, adjusted for potential confounding factors. All fat depots and insulin resistance (HOMA-IR), separate from VAT and TBF, were associated with lower mitral early and late peak filling rate ratios (E/A): -0.04 (-0.09;0.01) per SD (54 cm²) VAT; -0.05 (-0.10;0.00) per SD (94 cm²) aSAT; -0.09 (-0.16;-0.02) per SD (8%) TBF; -0.11 (-0.17;-0.05) per 10-fold increase in HOMA-IR, whereas VAT and TBF were differently associated with left ventricular (LV) end-diastolic volume: -8.9 (-11.7;-6.1) mL per SD VAT; +5.4 (1.1;9.7) mL per SD TBF. After adding HOMA-IR to the model to evaluate the mediating role of insulin resistance, change in E/A was -0.02 (-0.07;0.04) per SD VAT; -0.03 (-0.08;0.02) per SD aSAT; -0.06 (-0.13;0.01) per SD TBF, and change in LV end-diastolic volume was -7.0 (-9.7;-4.3) mL per SD VAT. In women, adiposity but not HOMA-IR was related to higher aortic arch pulse wave velocity.

CONCLUSION

Insulin resistance was associated with reduced diastolic function, separately from VAT and TBF, and partly mediated the associations between adiposity depots and lower diastolic function.

Diabesity: the combined burden of obesity and diabetes on heart disease and the role of imaging

Diabesity is a term used to describe the combined adverse health effects of obesity and diabetes mellitus. The worldwide dual epidemic of obesity and type 2 diabetes is an important public health issue. Projections estimate a sixfold increase in the number of adults with obesity in 40 years and an increase in the number of individuals with diabetes to 642 million by 2040. Increased adiposity is the strongest risk factor for developing diabetes. Early detection of the effects of diabesity on the cardiovascular system would enable the optimal implementation of effective therapies that prevent atherosclerosis progression, cardiac remodelling, and the resulting ischaemic heart disease and heart failure. Beyond conventional imaging techniques, such as echocardiography, CT and cardiac magnetic resonance, novel post-processing tools and techniques provide information on the biological processes that underlie metabolic heart disease. In this Review, we summarize the effects of obesity and diabetes on myocardial structure and function and illustrate the use of state-of-the-art multimodality cardiac imaging to elucidate the pathophysiology of myocardial dysfunction, prognosticate long-term clinical outcomes and potentially guide treatment strategies.

Impact of Obesity-Related Inflammation on Cardiac Metabolism and Function

This review focuses on the role of adipose tissue in obese individuals in the development of metabolic diseases, and their consequences for metabolic and functional derangements in the heart. The general idea is that the expansion of adipocytes during the development of obesity gives rise to unhealthy adipose tissue, characterized by low-grade inflammation and the release of proinflammatory adipokines and fatty acids (FAs). This condition, in turn, causes systemic inflammation and elevated FA concentrations in the circulation, which links obesity to several pathologies, including impaired insulin signaling in cardiac muscle and a subsequent shift in myocardial substrate oxidation in favor of FAs and reduced cardiac efficiency. This review also argues that efforts to prevent obesity-related cardiometabolic disease should focus on anti-obesogenic strategies to restore normal adipose tissue metabolism.

Effects of contrast agents on relaxation properties of 31P metabolites

PURPOSE

Phosphorous MR spectroscopy (31P-MRS) forms a powerful, non-invasive research tool to quantify the energetics of the heart in diverse patient populations. 31P-MRS is frequently applied alongside other radiological examinations, many of which use various contrast agents that shorten relaxation times of water in conventional proton MR, for a better characterisation of cardiac function, or following prior computed tomography (CT). It is, however, unknown whether these agents confound 31P-MRS signals, for example, 2,3-diphosphoglycerate (2,3-DPG).

METHODS

In this work, we quantitatively assess the impact of non-ionic, low osmolar iodinated CT contrast agent (iopamidol/Niopam), gadolinium chelates (linear gadopentetic acid dimeglumine/Magnevist and macrocyclic gadoterate meglumine/Dotarem) and superparamagnetic iron oxide nanoparticles (ferumoxytol/Feraheme) on the nuclear T1 and T2 of 31P metabolites (ie, 2,3-DPG), and 1H in water in live human blood and saline phantoms at 11.7 T.

RESULTS

Addition of all contrast agents led to significant shortening of all relaxation times in both 1H and 31P saline phantoms. On the contrary, the T1 relaxation time of 2,3-DPG in blood was significantly shortened only by Magnevist (P = .03). Similarly, the only contrast agent that influenced the T2 relaxation times of 2,3-DPG in blood samples was ferumoxytol (P = .02).

CONCLUSION

Our results show that, unlike conventional proton MR, phosphorus MRS is unconfounded in patients who have had prior CT with contrast, not all gadolinium-based contrast agents influence 31P-MRS data in vivo, and that ferumoxytol is a promising contrast agent for the reduction in 31P-MRS blood-pool signal.

Quantifying the effect of dobutamine stress on myocardial Pi and pH in healthy volunteers: A 31 P MRS study at 7T

Purpose

Phosphorus spectroscopy (³¹P‐MRS) is a proven method to probe cardiac energetics. Studies typically report the phosphocreatine (PCr) to adenosine triphosphate (ATP) ratio. We focus on another ³¹P signal: inorganic phosphate (Pi), whose chemical shift allows computation of myocardial pH, with Pi/PCr providing additional insight into cardiac energetics. Pi is often obscured by signals from blood 2,3‐diphosphoglycerate (2,3‐DPG). We introduce a method to quantify Pi in 14 min without hindrance from 2,3‐DPG.

Methods

Using a ³¹P stimulated echo acquisition mode (STEAM) sequence at 7 Tesla that inherently suppresses signal from 2,3‐DPG, the Pi peak was cleanly resolved. Resting state UTE‐chemical shift imaging (PCr/ATP) and STEAM ³¹P‐MRS (Pi/PCr, pH) were undertaken in 23 healthy controls; pH and Pi/PCr were subsequently recorded during dobutamine infusion.

Results

We achieved a clean Pi signal both at rest and stress with good 2,3‐DPG suppression. Repeatability coefficient (8 subjects) for Pi/PCr was 0.036 and 0.12 for pH. We report myocardial Pi/PCr and pH at rest and during catecholamine stress in healthy controls. Pi/PCr was maintained during stress (0.098 ± 0.031 [rest] vs. 0.098 ± 0.031 [stress] P = .95); similarly, pH did not change (7.09 ± 0.07 [rest] vs. 7.08 ± 0.11 [stress] P = .81). Feasibility for patient studies was subsequently successfully demonstrated in a patient with cardiomyopathy.

Conclusion

We introduced a method that can resolve Pi using 7 Tesla STEAM ³¹P‐MRS. We demonstrate the stability of Pi/PCr and myocardial pH in volunteers at rest and during catecholamine stress. This protocol is feasible in patients and potentially of use for studying pathological myocardial energetics.

Differential Effects of Sacubitril/Valsartan on Diastolic Function in Mice With Obesity-Related Metabolic Heart Disease

•

MHD associated with obesity, diabetes, and/or metabolic syndrome is an important precursor of HFpEF.

•

Mice fed a HFHS diet develop MHD with myocardial hypertrophy, fibrosis, diastolic dysfunction, and impaired energetics.

•

Mice on HFHS diet were treated with matched doses of VAL or sac SAC/VAL for 16 weeks.

•

Only SAC/VAL prevented diastolic dysfunction and fibrosis, and to a lesser extent oxidative stress, whereas VAL and SAC/VAL had similar effects on hypertrophy and energetics.

•

Neprilysin inhibition exerts beneficial effects on MHD that are complimentary to VAL, suggesting that SAC/VAL has promise to prevent the development of HFpEF in patients with or at risk for MHD.

Mice with obesity and metabolic heart disease (MHD) due to a high-fat, high-sucrose diet were treated with placebo, a clinically relevant dose of sacubitril (SAC)/valsartan (VAL), or an equivalent dose of VAL for 4 months. There were striking differences between SAC/VAL and VAL with regard to: 1) diastolic dysfunction; 2) interstitial fibrosis; and to a lesser degree; 3) oxidative stress—all of which were more favorably affected by SAC/VAL. SAC/VAL and VAL similarly attenuated myocardial hypertrophy and improved myocardial energetics. In mice with obesity-related MHD, neprilysin inhibition exerts favorable effects on diastolic function.

Use of cardiac magnetic resonance to detect changes in metabolism in heart failure

The heart has a massive adenosine triphosphate (ATP) requirement, produced from the oxidation of metabolic substrates such as fat and glucose. Magnetic resonance spectroscopy offers a unique opportunity to probe this biochemistry: ³¹Phosphorus spectroscopy can demonstrate the production of ATP and quantify levels of the transport molecule phosphocreatine while 13Carbon spectroscopy can demonstrate the metabolic fates of glucose in real time. These techniques allow the metabolic deficits in heart failure to be interrogated and can be a potential future clinical tool.

Vascular KATP channels protect from cardiac dysfunction and preserve cardiac metabolism during endotoxemia

Abstract

K_ATP channels in the vasculature composed of Kir6.1 regulate vascular tone and may contribute to the pathogenesis of endotoxemia. We used mice with cell-specific deletion of Kir6.1 in smooth muscle (smKO) and endothelium (eKO) to investigate this question. We found that smKO mice had a significant survival disadvantage compared with their littermate controls when treated with a sub-lethal dose of lipopolysaccharide (LPS). All cohorts of mice became hypotensive following bacterial LPS administration; however, mean arterial pressure in WT mice recovered to normal levels, whereas smKO struggled to overcome LPS-induced hypotension. In vivo and ex vivo investigations revealed pronounced cardiac dysfunction in LPS-treated smKO, but not in eKO mice. Similar results were observed in a cecal slurry injection model. Metabolomic profiling of hearts revealed significantly reduced levels of metabolites involved in redox/energetics, TCA cycle, lipid/fatty acid and amino acid metabolism. Vascular smooth muscle-localised K_ATP channels have a critical role in the response to systemic infection by normalising cardiac function and haemodynamics through metabolic homeostasis.

Key messages

• Mice lacking vascular K_ATP channels are more susceptible to death from infection.

• Absence of smooth muscle K_ATP channels depresses cardiac function during infection.

• Cardiac dysfunction is accompanied by profound changes in cellular metabolites.

• Findings from this study suggest a protective role for vascular K_ATP channels in response to systemic infection.

Electronic supplementary material

The online version of this article (10.1007/s00109-020-01946-3) contains supplementary material, which is available to authorized users.

Non-invasive investigation of myocardial energetics in cardiac disease using 31P magnetic resonance spectroscopy

Cardiac metabolism and function are intrinsically linked. High-energy phosphates occupy a central and obligate position in cardiac metabolism, coupling oxygen and substrate fuel delivery to the myocardium with external work. This insight underlies the widespread clinical use of ischaemia testing. However, other deficits in high-energy phosphate metabolism (not secondary to supply-demand mismatch of oxygen and substrate fuels) may also be documented, and are of particular interest when found in the context of structural heart disease. This review introduces the scope of deficits in high-energy phosphate metabolism that may be observed in the myocardium, how to assess for them, and how they might be interpreted.

The use of cardiovascular magnetic resonance as an early non-invasive biomarker for cardiotoxicity in cardio-oncology

Contemporary cancer therapy has resulted in significant survival gains for patients. However, many current and emerging cancer therapies have an associated risk of cardiotoxicity, either acutely or later in life. Regular cardiac screening and surveillance is recommended for patients undergoing treatment for cancer, with emphasis on the early detection of cardiotoxicity before irreversible complications develop. Cardiovascular magnetic resonance imaging is able to accurately assess cardiac structure, function, and perform advanced myocardial tissue characterisation, including perfusion, features which may facilitate the diagnosis and management of cardiotoxicity in cancer survivors. This review outlines the current standards for the diagnosis and screening of cardiotoxicity, with particular focus on current and future applications of cardiovascular magnetic resonance imaging.

Increasing mitochondrial ATP synthesis with butyrate normalizes ADP and contractile function in metabolic heart disease

Metabolic heart disease (MHD), which is strongly associated with heart failure with preserved ejection fraction, is characterized by reduced mitochondrial energy production and contractile performance. In this study, we tested the hypothesis that an acute increase in ATP synthesis, via short chain fatty acid (butyrate) perfusion, restores contractile function in MHD. Isolated hearts of mice with MHD due to consumption of a high fat high sucrose (HFHS) diet or on a control diet (CD) for 4 months were studied using 31 P NMR spectroscopy to measure high energy phosphates and ATP synthesis rates during increased work demand. At baseline, HFHS hearts had increased ADP and decreased free energy of ATP hydrolysis (ΔG~ATP ), although contractile function was similar between the two groups. At high work demand, the ATP synthesis rate in HFHS hearts was reduced by over 50%. Unlike CD hearts, HFHS hearts did not increase contractile function at high work demand, indicating a lack of contractile reserve. However, acutely supplementing HFHS hearts with 4mM butyrate normalized ATP synthesis, ADP, ΔG~ATP and contractile reserve. Thus, acute reversal of depressed mitochondrial ATP production improves contractile dysfunction in MHD. These findings suggest that energy starvation may be a reversible cause of myocardial dysfunction in MHD, and opens new therapeutic opportunities.

Myocardial Energetics in Obesity: Enhanced ATP Delivery Through Creatine Kinase With Blunted Stress Response

BACKGROUND

Obesity is strongly associated with exercise intolerance and the development of heart failure. Whereas myocardial energetics and diastolic function are impaired in obesity, systolic function is usually preserved. This suggests that the rate of ATP delivery is maintained, but this has never been explored in human obesity. We hypothesized that ATP transfer rate through creatine kinase (CK) (k_f^CKrest) would be increased, compensating for depleted energy stores (phosphocreatine/ATP), but potentially limiting greater ATP delivery during increased workload. We hypothesized that these changes would normalize with weight loss.

METHODS

We recruited 80 volunteers (35 controls [body mass index 24±3 kg/m²], 45 obese [body mass index 35±5 kg/m²]) without coexisting cardiovascular disease. Participants underwent body composition analysis, magnetic resonance imaging of abdominal, liver, and myocardial fat content, left ventricular function, and ³¹P magnetic resonance spectroscopy to assess phosphocreatine/ATP and CK kinetics, at rest and during dobutamine stress. Obese volunteers were assigned to a dietary weight loss intervention, before reexamination.

RESULTS

At rest, although myocardial phosphocreatine/ATP was 14% lower in obesity (1.9±0.3 versus 2.2±0.2, P<0.001), k_f^Ckrest was 33% higher (0.23±0.07 s^-1 versus 0.16±0.08 s^-1, P=0.002), yielding no difference in overall resting ATP delivery (obese 2.5±0.9 µmol·g^-1·s^-1 versus control 2.2±1.1 µmol·g^-1·s^-1, P=0.232). In controls, increasing cardiac workload led to an increase in both k_f^CK (+86%, P<0.001) and ATP delivery (+80%, P<0.001). However, in obesity, similar stress led to no significant increase in either k_f^CK (P=0.117) or ATP delivery (P=0.608). This was accompanied by reduced systolic augmentation (absolute increase in left ventricular ejection fraction, obese +16±7% versus control +21±4%, P=0.031). Successful weight loss (-11±5% body weight) was associated with improvement of these energetic changes such that there was no significant difference in comparison with controls.

CONCLUSIONS

In the obese resting heart, the myocardial CK reaction rate is increased, maintaining ATP delivery despite reduced phosphocreatine/ATP. During increased workload, although the nonobese heart increases ATP delivery through CK, the obese heart does not; this is associated with reduced systolic augmentation and exercise tolerance. Weight loss reverses these energetic changes. This highlights myocardial energy delivery through CK as a potential therapeutic target to improve symptoms in obesity-related heart disease, and a fascinating modifiable pathway involved in the progression to heart failure, as well.

Altered mitochondrial metabolism in the insulin-resistant heart

Obesity-induced insulin resistance and type 2 diabetes mellitus can ultimately result in various complications, including diabetic cardiomyopathy. In this case, cardiac dysfunction is characterized by metabolic disturbances such as impaired glucose oxidation and an increased reliance on fatty acid (FA) oxidation. Mitochondrial dysfunction has often been associated with the altered metabolic function in the diabetic heart, and may result from FA-induced lipotoxicity and uncoupling of oxidative phosphorylation. In this review, we address the metabolic changes in the diabetic heart, focusing on the loss of metabolic flexibility and cardiac mitochondrial function. We consider the alterations observed in mitochondrial substrate utilization, bioenergetics and dynamics, and highlight new areas of research which may improve our understanding of the cause and effect of cardiac mitochondrial dysfunction in diabetes. Finally, we explore how lifestyle (nutrition and exercise) and pharmacological interventions can prevent and treat metabolic and mitochondrial dysfunction in diabetes.

Overexpression of mitochondrial creatine kinase preserves cardiac energetics without ameliorating murine chronic heart failure

Mitochondrial creatine kinase (Mt-CK) is a major determinant of cardiac energetic status and is down-regulated in chronic heart failure, which may contribute to disease progression. We hypothesised that cardiomyocyte-specific overexpression of Mt-CK would mitigate against these changes and thereby preserve cardiac function. Male Mt-CK overexpressing mice (OE) and WT littermates were subjected to transverse aortic constriction (TAC) or sham surgery and assessed by echocardiography at 0, 3 and 6 weeks alongside a final LV haemodynamic assessment. Regardless of genotype, TAC mice developed progressive LV hypertrophy, dilatation and contractile dysfunction commensurate with pressure overload-induced chronic heart failure. There was a trend for improved survival in OE-TAC mice (90% vs 73%, P = 0.08), however, OE-TAC mice exhibited greater LV dilatation compared to WT and no functional parameters were significantly different under baseline conditions or during dobutamine stress test. CK activity was 37% higher in OE-sham versus WT-sham hearts and reduced in both TAC groups, but was maintained above normal values in the OE-TAC hearts. A separate cohort of mice received in vivo cardiac ³¹P-MRS to measure high-energy phosphates. There was no difference in the ratio of phosphocreatine-to-ATP in the sham mice, however, PCr/ATP was reduced in WT-TAC but preserved in OE-TAC (1.04 ± 0.10 vs 2.04 ± 0.22; P = 0.007). In conclusion, overexpression of Mt-CK activity prevented the changes in cardiac energetics that are considered hallmarks of a failing heart. This had a positive effect on early survival but was not associated with improved LV remodelling or function during the development of chronic heart failure.

A Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Effectiveness of a Food Supplement Containing Creatine and D-Ribose Combined with a Physical Exercise Program in Increasing Stress Tolerance in Patients with Ischemic Heart Disease

The aim of this study is to establish whether a supplement of creatine and ribose combined with a physical exercise program can improve the total work capacity during exercise in a population of patients with known ischemic heart disease. A double-blind, six-month study was designed in which 53 patients were enrolled and randomized to take either a nutraceutical composition containing creatine, D-ribose, vitamin B₁, and vitamin B₆ (active treatment) or the placebo. Both the nutraceutical supplement and the placebo were supplied by Giellepi S.p.A. Health Science in Lissone, Italy. After six months of study, the cardiac double product at the peak of the load, the delta double product, and the chronotropic index were higher in the active treatment group than in the placebo group. We can conclude that a supplementation with creatine, D-ribose, vitamin B₁, and vitamin B₆, in addition to standard therapy and a physical exercise program, seems to be helpful in improving exercise tolerance compared to the placebo in a population with cardiovascular disease. However, this needs to be further studied, given that there is no clear evidence that the double product can be used as a surrogate measure of exercise tolerance.

Low SAR 31 P (multi-echo) spectroscopic imaging using an integrated whole-body transmit coil at 7T

Phosphorus (³¹ P) MRSI provides opportunities to monitor potential biomarkers. However, current applications of ³¹ P MRS are generally restricted to relatively small volumes as small coils are used. Conventional surface coils require high energy adiabatic RF pulses to achieve flip angle homogeneity, leading to high specific absorption rates (SARs), and occupy space within the MRI bore. A birdcage coil behind the bore cover can potentially reduce the SAR constraints massively by use of conventional amplitude modulated pulses without sacrificing patient space. Here, we demonstrate that the integrated ³¹ P birdcage coil setup with a high power RF amplifier at 7 T allows for low flip angle excitations with short repetition time (T_R ) for fast 3D chemical shift imaging (CSI) and 3D T₁ -weighted CSI as well as high flip angle multi-refocusing pulses, enabling multi-echo CSI that can measure metabolite T₂ , over a large field of view in the body. B₁⁺ calibration showed a variation of only 30% in maximum B₁ in four volunteers. High signal-to-noise ratio (SNR) MRSI was obtained in the gluteal muscle using two fast in vivo 3D spectroscopic imaging protocols, with low and high flip angles, and with multi-echo MRSI without exceeding SAR levels. In addition, full liver MRSI was achieved within SAR constraints. The integrated ³¹ P body coil allowed for fast spectroscopic imaging and successful implementation of the multi-echo method in the body at 7 T. Moreover, no additional enclosing hardware was needed for ³¹ P excitation, paving the way to include larger subjects and more space for receiver arrays. The increase in possible number of RF excitations per scan time, due to the improved B₁⁺ homogeneity and low SAR, allows SNR to be exchanged for spatial resolution in CSI and/or T₁ weighting by simply manipulating T_R and/or flip angle to detect and quantify ratios from different molecular species.

Phenotyping diabetic cardiomyopathy in Europeans and South Asians

Background

The pathogenesis and cardiovascular impact of type 2 diabetes (T2D) may be different in South Asians compared with other ethnic groups. The phenotypic characterization of diabetic cardiomyopathy remains debated and little is known regarding differences in T2D-related cardiovascular remodeling across ethnicities. We aimed to characterize the differences in left ventricular (LV) diastolic and systolic function, LV structure, myocardial tissue characteristics and aortic stiffness between T2D patients and controls and to assess the differences in T2D-related cardiovascular remodeling between South Asians and Europeans.

Methods

T2D patients and controls of South Asian and European descent underwent 3 Tesla cardiovascular magnetic resonance imaging (CMR) and cardiac proton-magnetic resonance spectroscopy (¹H-MRS). Differences in cardiovascular parameters between T2D patients and controls were examined using ANCOVA and were reported as mean (95% CI). Ethnic group comparisons in the association of T2D with cardiovascular remodeling were made by adding the interaction term between ethnicity and diabetes status to the model.

Results

A total of 131 individuals were included (54 South Asians [50.1 ± 8.7 years, 33% men, 33 patients vs. 21 controls) and 77 Europeans (58.8 ± 7.0 years, 56% men, 48 patients vs. 29 controls)]. The ratio of the transmitral early and late peak filling rate (E/A) was lower in T2D patients compared with controls, in South Asians [− 0.20 (− 0.36; − 0.03), P = 0.021] and Europeans [− 0.20 (− 0.36; − 0.04), P = 0.017], whereas global longitudinal strain and aortic pulse wave velocity were similar. South Asian T2D patients had a higher LV mass [+ 22 g (15; 30), P < 0.001] (P for interaction by ethnicity = 0.005) with a lower extracellular volume fraction [− 1.9% (− 3.4; − 0.4), P = 0.013] (P for interaction = 0.114), whilst European T2D patients had a higher myocardial triglyceride content [+ 0.59% (0.35; 0.84), P = 0.001] (P for interaction = 0.002) than their control group.

Conclusions

Diabetic cardiomyopathy was characterized by impaired LV diastolic function in South Asians and Europeans. Increased LV mass was solely observed among South Asian T2D patients, whereas differences in myocardial triglyceride content between T2D patients and controls were only present in the European cohort. The diabetic cardiomyopathy phenotype may differ between subsets of T2D patients, for example across ethnicities, and tailored strategies for T2D management may be required.

[Mechanisms of exercise intolerance in patients with heart failure and preserved ejection fraction. Part II: The role of right heart chambers, vascular system and skeletal muscles]

The main clinical manifestation of heart failure with preserved ejection fraction is poor exercise tolerance. In addi-tion to the dysfunction of the left heart chambers, which were presented in the first part of this review, many other disorders are involved in poor exercise tolerance in such patients: impairments of the right heart, vascular system and skeletal muscle. The second part of this review presents the mechanisms for the development of these disorders, as well as possible ways to correct them.

CEST MRI reveals a correlation between visceral fat mass and reduced myocardial creatine in obese individuals despite preserved ventricular structure and function

Systolic cardiac function is typically preserved in obese adults, potentially masking underlying declines in cardiomyocyte metabolism that may contribute to heart failure. We used chemical exchange saturation transfer (CEST) MRI, a sensitive method for measurement of myocardial creatine, to examine whether myocardial creatine levels correlate with cardiac structure, contractile function, or visceral fat mass in obese adults. In this study, obese (body mass index, BMI > 30, n = 20) and healthy (BMI < 25, n = 11) adults were examined with dual-energy x-ray absorptiometry to quantify fat masses. Cine MRI and myocardial tagging were performed at 1.5 T to measure ventricular structure and global function. CEST imaging with offsets in the range of ±10 parts per million (ppm) were performed in one mid-ventricular slice, where creatine CEST contrast was calculated at 1.8 ppm following field homogeneity correction. Ventricular structure, global function (ejection fraction 69.4 ± 4.3% healthy versus 69.6 ± 9.3% obese, NS), and circumferential strain (-17.0 ± 2.3% healthy versus -16.5 ± 1.5% obese, NS) and strain rate were preserved in obese adults. However, creatine CEST contrast was significantly reduced in obese adults (6.8 ± 1.3% healthy versus 4.1 ± 2.7% obese, p = 0.001). Creatine CEST contrast was inversely correlated with total body fat% (ρ = -0.45, p = 0.011), visceral fat mass (ρ = -0.58, p = 0.001), and septal wall thickness (ρ = -0.44, p = 0.013), but uncorrelated to ventricular function or contractile function. In conclusion, creatine CEST-MRI reveals a strong correlation between heightened body and visceral fat masses and reduced myocardial metabolic function that is independent of ventricular structure and global function in obese adults.