(31)P-MR Spectroscopy for the evaluation of energy metabolism in intact residual myocardium after acute myocardial infarction in humans

Taurine detected using high-resolution magic angle spinning (1)H nuclear magnetic resonance: A potential indicator of early myocardial infarction

Magnetic resonance spectroscopy (MRS) is a unique non-invasive method for detecting cardiac metabolic changes. However, MRS in cardiac diagnosis is limited due to insensitivity and low efficiency. Taurine (Tau) is the most abundant free amino acid in the myocardium. We hypothesized that Tau levels may indicate myocardial ischemia and early infarction. Sprague-Dawley rats were divided into seven groups according to different time points during the course of myocardial ischemia, which was induced by left anterior descending coronary artery ligation. Infarcted myocardial tissue was obtained for high-resolution magic angle spinning (1)H nuclear magnetic resonance (NMR) analysis. Results were validated via high-performance liquid chromatography. The Tau levels in the ischemic myocardial tissue were reduced significantly within 5 min compared with those in the control group (relative ratio from 20.27±6.48 to 8.81±0.04, P<0.05) and were maintained for 6 h post-ischemia. Tau levels declined more markedly (56.5%) than creatine levels (48.5%) at 5 min after ligation. This suggests that Tau may have potential as an indicator in the early detection of myocardial ischemia by (1)H MRS.

Magnetic resonance imaging/magnetic resonance spectroscopy biomarkers evaluation of stunned myocardium in canine model

OBJECTIVES

To evaluate whether dynamic alterations in high-energy phosphate (HEP) occur in postischemic "stunned" myocardium (SM) in canine model and to investigate the correlation between HEP and cardiac function, using cine magnetic resonance imaging (cine-MRI) and phosphorus-31 magnetic resonance spectroscopy (31P-MRS).

MATERIALS AND METHODS

Dogs (n = 13) underwent cine MRI and 31P-MRS at 60 minutes, 8 days after 10 minutes full left anterior descending occlusion followed by reperfusion. The same MRI/MRS experiments were repeated on 5 reference animals (dogs without ischemic reperfusion) at the same time points to serve as internal reference myocardium (RM). After MR data acquisitions, the SM dogs (n = 3 at 60 minutes; n = 10 at 60 minutes and day 8) and RM dogs (n = 5) were euthanized and myocardial tissues were sampled for histologic study by triphenyltetrazolium chloride staining, hematoxylin and eosin staining, and electron microscopic examination.

RESULTS

The myocardial stunning at 60 minutes was confirmed by electron microscopy examinations from the 3 randomly chosen animals with SM. The phosphocreatine (PCr)/β- adenosine triphosphate (ATP) ratio of SM was significantly lower at 60 minutes than that at day 8 (1.07 ± 0.20 vs. 1.97 ± 0.28, P < 0.05). However, no significant difference was found between 60 minutes and day 8 in RM group (1.91 ± 0.14 at 60 minutes vs. 1.89 ± 0.16 at day 8, P > 0.05). At 60 minutes, the PCr/β-ATP ratio has significant difference between SM and RM groups; while at day 8, the ratio shows no significant difference between the 2 groups. The same results were obtained for left ventricle ejection fraction (LVEF). In SM group, LVEF has good correlation with myocardial PCr/β-ATP ratios at 60 minutes (R2 = 0.71, P < 0.05) and at day 8 (R2 = 0.73, P < 0.05), respectively.

CONCLUSIONS

The HEP alterations were confirmed by 31P-MRS in SM and there is a good correlation between PCr/β-ATP ratio and LVEF for SM at 60 minutes and recovered myocardium at day 8. The combined MRS/MRI method offers the potential to systematically assess the cardiac function, morphology, and metabolism of SM. These MRS/MRI biomarker datasets could be used to dynamically monitor therapeutic efficiency and predict cardiac events.

Cine-MRI and (31)P-MRS for evaluation of myocardial energy metabolism and function following coronary artery bypass graft

Previous studies investigated the effect of successful coronary artery bypass grafting (CABG) upon left ventricular function. The relationship between myocardial metabolism and heart function after CABG remains unclear. We investigated the relationship between high-energy phosphate (HEP) and cardiac function following CABG using cine magnetic resonance imaging (cine-MRI) and phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS). A retrospective study was approved by the institutional review board. MRI and (31)P-MRS examinations were reviewed of 37 patients with multivessel disease who underwent CABG. 13 of these patients selected for the retrospective analysis had >or=70% stenosis in the proximal left anterior descending artery (LAD) and left ventricular ejection fraction (LVEF) <40%. LVEF was evaluated using cine-MRI. HEP such as phosphocreatine (PCr) and adenosine triphosphate (beta-ATP) was measured using (31)P-MRS to calculate PCr/beta-ATP ratio. Cine-MRI and (31)P-MRS measurements were performed before and after CABG, respectively. Ten normal healthy volunteers served as controls. (31)P-MRS in 13 patients showed that post-CABG PCr/beta-ATP ratio was significantly higher than that of pre-CABG (pre-CABG vs. post-CABG, 1.43+/-0.24 vs. 1.71+/-0.29, P<.05), but both ratios were significantly lower than control group (2.13+/-0.21, P<.05). With the change of the ratio, the left ventricle function was significantly improved (LVEF: pre-CABG vs. post-CABG: 35.7+/-12.9 vs. 45.6+/-17.2, P<.05). The ability of (31)P-MRS and cine-MRI to non-invasively assess changes of metabolism and function in myocardium may prove important for patient-specific optimization of treatment strategies.

Energetic differences between viable and non-viable myocardium in patients with recent myocardial infarction are not an effect of differences in wall thinning- a multivoxel (31)P-MR-spectroscopy and MRI study

To evaluate multivoxel (31)P-MR spectroscopy (MRS) for assessment of energy metabolism in patients with myocardial infarction (MI) in correlation to left ventricular (LV) wall thickness and the outcome of revascularization. Thirty patients with subacute anterior myocardial infarction and planned revascularization were enrolled. 3D-chemical shift imaging was applied to determine PCr/ATP ratios in two areas: infarcted/anterior and noninfarcted/septal myocardium. MRI was used to evaluate LV function and wall thickness, and was repeated 6 months after revascularization to assess myocardial viability. Fifteen volunteers were controls. Fifteen patients showed normalization of wall motion abnormalities after revascularization (Group 1; viable), 15 not (Group 2; non-viable). Regarding infarcted/anterior myocardium, Group 2 had lower PCr/ATP ratios (0.81 +/- 0.60 vs 1.17 +/- 0.25), and PCr/ATP ratios were reduced in both groups compared to controls (1.45 +/- 0.29). Regarding noninfarcted/septal myocardium, again Group 2 had lower ratios (0.93 +/- 0.53 vs 1.31 +/- 0.38); however, compared to controls (1.51 +/- 0.32) a reduction of PCr/ATP ratios was only found in Group 2. For both myocardial regions, no correlations between PCr/ATP ratios and LV wall thickness were detected. The more severe energetic alteration in irreversibly damaged myocardium is not an effect of differences of wall thinning. Additional alterations of noninfarcted, adjacent myocardium can be detected.

Detection of myocardial infarctions by acquisition-weighted 31P-MR spectroscopy in humans

PURPOSE

To determine whether the recently applied technique of acquisition-weighted 31P-MR spectroscopy (AW-MRS) allows for the detection of depressed energy metabolism in patients with inferior wall myocardial infarctions.

MATERIALS AND METHODS

Eight patients with subacute myocardial infarction and wall motion abnormalities restricted to the inferior wall were examined with a 1.5-T MR scanner. Global and regional left ventricular (LV) function was assessed by cine MRI, and the size and extent of myocardial infarction was assessed by late enhancement (LE). MRS was performed with an AW three-dimensional chemical shift imaging sequence. Phosphocreatine/ATP ratios were determined with the postprocessing model AMARES for four voxels positioned in the anterior, lateral, inferior, and septal parts of the LV.

RESULTS

The LV ejection fraction (EF) was reduced to 37.5%+/-9.0%. Seven of eight patients had transmural LE in the inferior wall, and one patient showed subendocardial enhancement in the inferior-lateral parts. Phosphocreatine/ATP ratios of the inferior wall were significantly reduced (P <0.05) compared to all other parts of the LV (1.03 +/- 0.39 (inferior), 1.67 +/- 0.81 (lateral), 1.73 +/- 0.29 (anterior), and 1.49 +/- 0.31 (septal)). The ratios in five of seven patients with transmural enhancement were <1.00 in the inferior wall.

CONCLUSION

Acquisition weighting allows for the detection of inferior wall infarctions in patients. Transmural signal enhancement is associated with significant depression of phosphocreatine/ATP ratios.

Magnetic resonance imaging for the assessment of myocardial viability

The identification of myocardial viability in the setting of left ventricular (LV) dysfunction is crucial for the prediction of functional recovery following revascularization. Although echocardiography, positron emission tomography (PET), and nuclear imaging have validated roles, recent advances in cardiac magnetic resonance (CMR) technology and availability have led to increased experience in CMR for identification of myocardial viability. CMR has unique advantages in the ability of magnetic resonance spectroscopy (MRS) to measure subcellular components of myocardium, and in the image resolution of magnetic resonance proton imaging. As a result of excellent image resolution and advances in pulse sequences and coil technology, magnetic resonance imaging (MRI) can be used to identify the transmural extent of myocardial infarction (MI) in vivo for the first time. This review of the role of CMR in myocardial viability imaging describes the acute and chronic settings of ventricular dysfunction and concepts regarding the underlying pathophysiology. Recent advances in MRS and MRI are discussed, including the potential for dobutamine MRI to identify viable myocardium and a detailed review of the technique of delayed gadolinium (Gd) contrast hyperenhancement for visualization of viable and nonviable myocardium.