Principals and clinical applications of magnetic resonance cardiac spectroscopy in heart failure

Cardiac function, myocardial fat deposition, and lipid profile in young smokers: a cross-sectional study

Background

There is a possibility that cardiac morphometric characteristics are associated with the lipid profile, that is, the composition and concentration of triglycerides, total cholesterol, HDL, LDL, and others lipoproteins in young smokers without comorbidities. Thus, this study aimed to evaluate the association of cardiac morphometric characteristics, myocardial fat deposition, and smoking cessation with the lipid profile of young smokers.

Methods

A clinical and laboratory evaluation of lipids and the smoking status was performed on 57 individuals, including both a smoker group and a control group. Cardiac magnetic resonance imaging (MRI) with proton spectroscopy was performed to identify cardiac changes and triglyceride (TG) deposition in myocardial tissue.

Results

No differences were observed between the groups (control vs. smokers) in relation to the amount of myocardial TG deposition (p = 0.47); however, when TG deposition was correlated with cardiac MRI variables, a positive correlation was identified between smoking history and myocardial TG deposition [hazard ratio (95% CI), 0.07 (0.03-0.12); p = 0.002]. Furthermore, it was observed that the smoking group had lower high-density lipoprotein cholesterol [51 (45.5-59.5) mg/dl vs. 43 (36-49.5) mg/dl, p = 0.003] and higher TG [73 (58-110) mg/dl vs. 122 (73.5-133) mg/dl, p = 0.01] and very-low-density lipoprotein cholesterol [14.6 (11.6-22.2) mg/dl vs. 24.4 (14.7-26.6) mg/dl, p = 0.01] values. In the control and smoking groups, a negative correlation between TGs and the diameter of the aortic root lumen and positive correlation with the thickness of the interventricular septum and end-diastolic volume (EDV) of both the right ventricle (RV) and left ventricle (LV) were noted. Moreover, in the RV, positive correlations with the end-systolic volume (ESV) index (ESVI), stroke volume (SV), ESV, and EDV were observed. Regarding serum free fatty acids, we found a negative correlation between their values and the diameter of the lumen of the ascending aortic vessel. Lipoprotein lipase showed a positive correlation with the SV index of the RV and negative correlation with the diameter of the lumen of the ascending aortic vessel.

Conclusion

Several associations were observed regarding cardiac morphometric characteristics, myocardial fat deposition, and smoking cessation with the lipid profile of young smokers.

In Vivo Magnetic Resonance Spectroscopy Methods for Investigating Cardiac Metabolism

Magnetic resonance spectroscopy (MRS) is a non-invasive and non-ionizing technique, enabling in vivo investigation of cardiac metabolism in normal and diseased hearts. In vivo measurement tools are critical for studying mechanisms that regulate cardiac energy metabolism in disease developments and to assist in early response assessments to novel therapies. For cardiac MRS, proton (1H), phosphorus (31P), and hyperpolarized 13-carbon (13C) provide valuable metabolic information for diagnosis and treatment assessment purposes. Currently, low sensitivity and some technical limitations limit the utility of MRS. An essential step in translating MRS for clinical use involves further technological improvements, particularly in coil design, improving the signal-to-noise ratios, field homogeneity, and optimizing radiofrequency sequences. This review addresses the recent advances in metabolic imaging by MRS from primarily the literature published since 2015.

T2-weighted cardiac magnetic resonance image and myocardial biomarker in hypertrophic cardiomyopathy

The phenomenon of high signal intensity on T2-weighted imaging of cardiac magnetic resonance in hypertrophic cardiomyopathy (HCM) has been previously studied. However, the underlying histopathologic mechanism remains unclear. Elevated cardiac troponin can be detected in some HCM patients. A reasonable hypothesis is that high myocardial T2 signal is a potential marker of myocardial injury in HCM. We sought to investigate the association between cardiac troponin and the extent of high T2 signals in HCM patients.Forty-four HCM patients underwent 3.0T cardiac magnetic resonance scanning. On T2-weighted images, the number of segments with high-signal intensity (myocardium-to-skeletal muscle signal intensity ratio >2) and the percentage of high-signal area (>2 standard deviation above the remote tissue) were measured in 16 myocardial segments along the LV mid-myocardial circumference on 3 short-axis images. The level of high-sensitivity cardiac troponin T (hs-cTnT) was also assessed.Myocardial high T2 signals were identified in 33 (75%) patients and 144 (20.5%) segments. Elevated hs-cTnT was observed in 28 (63.6%) patients. The Cochran-Armitage test showed a statistically significant trend of increasing levels of hs-cTnT with elevated number of segments with myocardial high T2 signal (P = .002). Further, the percentage of myocardium with high T2 signal was significantly associated with the hs-cTnT level (Pearson correlation: r = 0.388, P = .009).Myocardium with high T2 signals was very common in patients with HCM.Its extent is related with the level of plasma hs-cTnT.

Metabolic Imaging in Cardio-oncology

Tremendous progress in cancer detection and therapy has improved survival. However, cardiovascular complications are a major source of morbidity in cancer survivors. Cardiotoxicity is currently defined by structural myocardial changes and cardiac injury biomarkers. In many instances, such changes are late and irreversible. Therefore, diagnostic modalities that can identify early alterations in potentially reversible biochemical and molecular signaling processes are of interest. This review is focused on emerging translational metabolic imaging modalities. We present in context relevant mitochondrial biology aspects that ground the development and application of these technologies for detection of cancer therapy-related cardiac dysfunction (CTRCD). The application of these modalities may improve the assessment of cardiovascular risk when anticancer treatments with a defined cardiometabolic toxic mechanism are to be used. Also, they may serve as screening tools for cardiotoxicity when novel lines of cancer therapies are applied.

Cardiac applications of hyperpolarised magnetic resonance

Cardiovascular disease is the leading cause of death world-wide. It is increasingly recognised that cardiac pathologies show, or may even be caused by, changes in metabolism, leading to impaired cardiac energetics. The heart turns over 15 times its own weight in ATP every day and thus relies heavily on the availability of substrates and on efficient oxidation to generate this ATP. A number of old and emerging drugs that target different aspects of metabolism are showing promising results with regard to improved cardiac outcomes in patients. A non-invasive imaging technique that could assess the role of different aspects of metabolism in heart disease, as well as measure changes in cardiac energetics due to treatment, would be valuable in the routine clinical care of cardiac patients. Hyperpolarised magnetic resonance spectroscopy and imaging have revolutionised metabolic imaging, allowing real-time metabolic flux assessment in vivo for the first time. In this review we summarise metabolism in the healthy and diseased heart, give an introduction to the hyperpolarisation technique, 'dynamic nuclear polarisation' (DNP), and review the preclinical studies that have thus far explored healthy cardiac metabolism and different models of human heart disease. We furthermore show what advances have been made to translate this technique into the clinic, what technical challenges still remain and what unmet clinical needs and unexplored metabolic substrates still need to be assessed by researchers in this exciting and fast-moving field.

Molecular imaging of cardiac remodelling after myocardial infarction

Myocardial infarction and subsequent heart failure is a major health burden associated with significant mortality and morbidity in western societies. The ability of cardiac tissue to recover after myocardial infarction is affected by numerous complex cellular and molecular pathways. Unbalance or failure of these pathways can lead to adverse remodelling of the heart and poor prognosis. Current clinical cardiac imaging modalities assess anatomy, perfusion, function, and viability of the myocardium, yet do not offer any insight into the specific molecular pathways involved in the repair process. Novel imaging techniques allow visualisation of these molecular processes and may have significant diagnostic and prognostic values, which could aid clinical management. Single photon-emission tomography, positron-emission tomography, and magnetic resonance imaging are used to visualise various aspects of these molecular processes. Imaging probes are usually attached to radioisotopes or paramagnetic nanoparticles to specifically target biological processes such as: apoptosis, necrosis, inflammation, angiogenesis, and scar formation. Although the results from preclinical studies are promising, translating this work to a clinical environment in a valuable and cost-effective way is extremely challenging. Extensive evaluation evidence of diagnostic and prognostic values in multi-centre clinical trials is still required.