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Query: UMLS:C0151744 (myocardial ischemia)
 31,282 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The identification of ischemic and hibernating myocardium facilitates the selection of patients most likely to benefit from revascularization. This study examined the feasibility of metabolic imaging, using post-exercise F-18 deoxyglucose positron emission tomography (FDG-PET) for the diagnosis of both ischemia and hibernation in 27 patients with known coronary anatomy. Normal post-exercise FDG uptake was defined in each patient by reference to normal resting perfusion and normal coronary supply. Abnormal elevation of FDG (ischemia or hibernation) was compared in 13 myocardial segments in each patient, with the results of dipyridamole stress perfusion imaging performed by rubidium-82 positron emission tomography (Rb-PET). Myocardial ischemia was diagnosed by either FDG-PET or Rb-PET in 34 segments subtended by significant local coronary stenoses. Increased FDG uptake was present in 32/34 (94%) and a reversible perfusion defect was identified by Rb-PET in 22/34 (65%, p less than .01). In 3 patients, ischemia was identified by metabolic imaging alone. In 16 patients with previous myocardial infarction, perfusion defects were present at rest in 89 regions, 30 of which (34%) demonstrated increased FDG uptake, consistent with the presence of hibernation. Increased post-exercise FDG uptake appears to be a sensitive indicator of ischemia and myocardial hibernation. This test may be useful in selecting post-infarction patients for revascularization.
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PMID:Identification of ischemic and hibernating myocardium: feasibility of post-exercise F-18 deoxyglucose positron emission tomography. 200 57

Tracer techniques have provided new insight in cardiology by allowing noninvasive studies of myocardial perfusion, function, metabolism, and, more recently, ligand-receptor interaction. Positron emission tomography allows accurate quantification and the use of natural substrates labelled with 11C, 13N, or 15O. Myocardial metabolism is complex and utilizes a number of substrates, primarily fatty acids. Fatty acids utilization can be studied with 11C palmitate, while 11C acetate more selectively traces TCA cycle activity and reflects myocardial oxygen utilization. Glucose uptake can be traced using 18F deoxyglucose, a glucose analog that is a substrate for hexokinase but is not further metabolized. Flow and oxidative glucose metabolism are usually coupled, and thereby the uptake of FDG and perfusion tracers are usually similar. In myocardial ischemia, however, glucose utilization can persist due to anaerobic glycolysis, and its uptake is frequently enhanced. Clinical applications of the use of metabolic studies in patients with ischemic heart disease are presented.
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PMID:Imaging of myocardial metabolism by positron emission tomography. 209 80

(1) Metabolism is the link between myocardial blood flow and physiological performance of the heart. (2) Metabolic myocardial radiopharmaceuticals have the potential to identify metabolic alterations unique to a given intrinsic cardiac disease (e.g. cardiomyopathies), to assess acute metabolic changes or in delineating a specific chronic metabolic defect (e.g. coronary artery disease). (3) Two approaches can be employed to evaluate in vivo myocardial utilization of subtracts: (a) use of radiolabeled "physiologic" substrates e.g. positron emitting 11C-palmitic acid was successfully employed for assessing the in vivo metabolic sequelae of myocardial ischemia, infarction and cardiomyopathies, and (b) use of modified tracers which enter known metabolic pathways. However, because of their unique structure, metabolism of the tracer stops at a certain state thus leaving the radiolabel trapped in the cell, e.g. [18F]FDG for measuring glucose metabolic rate in the human brain and myocardium. (4) Among the radiopharmaceuticals for planar and single photon tomography, the para and the ortho isomers of 123I-phenyl iodoheptadecanoic acids and their beta-methyl derivatives are the most promising tracers for myocardial metabolic studies. (5) Ortho-(123I-phenyl)-pentadecanoic acid (o-IPPA) human myocardial uptake was rapidly and markedly elevated in well perfused segments; myocardial turnover was strikingly prolonged, suggesting some "trapping" phenomenon, resulting in excellent scintigrams. This is in contrast to the relatively shorter clearance of the para isomer from the myocardium. (6) 11C-Palmitic acid and [18F]FDG are the most widely used for PET scanning for following myocardial metabolism. The most important clinical application of these agents is predicting viability of ischemic myocardium. (7) A significant proportion of fixed perfusion defects seen on thallium studies can be demonstrated to be viable myocardium on PET scans using metabolic agents. If the markers of perfusion alone are relied on to assess tissue viability, the extent of salvageable myocardium may be underestimated. The demonstration of myocardial viability is crucial in the decision of the optimal treatment of the disease.
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PMID:Radiopharmaceuticals for studying cardiac metabolism. 215 88

Stress Tl-201 tomography (SPECT) is widely used for evaluating myocardial viability. To assess its value, redistribution (RD) on SPECT was compared with metabolic imaging using FDG. Thirty patients with coronary artery disease underwent stress-3 hour Tl-201 SPECT and PET using N-13 ammonia and FDG. RD was classified into 4 grading, including complete RD (CR), incomplete RD (IR), persistent defect (PD) and additional minimal RD (MR) defined as no definite RD on visual analysis but faint RD with Bull's eye quantitative analysis (QNT). All but one segment with CR or IR were viable regions (normal or ischemic regions) by PET. Of 74 segments without RD on visual analysis, 31 segments (42%) had RD by QNT (MR). All of them were viable regions by PET. Thus, QNT identified 31 segments (63%) of the metabolically viable segments which the visual Tl-201 analysis did not show RD and classified as myocardial scar. However, even such QNT cannot detect ischemic myocardium in 18 segments (42%) containing metabolic activity on PET. These data indicate that QNT of RD on Tl-201 SPECT is considered as a valuable means for assessing myocardial ischemia.
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PMID:[Assessment of myocardial viability by quantitative analysis of stress Tl-SPECT--comparison with FDG-PET]. 261 25

Regional myocardial perfusion and metabolism were evaluated in coronary artery disease with positron emission computed tomography (PET). Regional myocardial perfusion was assessed after the intravenous administration of 13N-ammonia at rest and during exercise loading, using a supine ergometer. In some cases, 18F-FDG was administered at rest, and compared with 13N-ammonia. 13N-ammonia revealed hypoperfusion in coronary artery disease, in 73% of cases at rest and in 97%, during exercise study. Increased accumulations of 18F-FDG were observed in the peri-infarcted areas with decreased perfusions, and in the regions with normal perfusions at rest, where the exercise study showed transient ischemia. These results indicate that PET can detect regional myocardial ischemia with superior sensitivity, and that it provides a means of evaluating myocardial metabolism in vivo.
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PMID:[Assessment of regional myocardial blood flow and energy metabolism]. 350 73

Quality control as regards nuclear medicine heart studies refers to two areas: methodological quality control clinical quality control. Methodological correct realization of nuclear medicine heart studies is the first prerequisite for validity of the results. The term "myocardial scintigraphy" summarizes several different procedures. Concerning clinical routine, myocardial scintigraphy stands for imaging of microcirculation and scars using Tl-201-chloride or Tc-99m-MIBI, additionally for metabolic assessment of myocardial viability with F-18-FDG. Today, planar myocardial scintigraphy has been replaced by tomographic techniques (SPECT, PET). Methodological procedures for quality control concerning technical equipment and radiopharmaca are based on the new "guidelines for radiation exposure in medicine" of 1993. Clinical quality control in myocardial scintigraphy covers, in particular, the correct selection of indications: proof/exclusion of coronary artery disease (depending on prevalence) specific questions before interventional therapy (myocardial ischemia, myocardial viability) follow-up and therapy control. Selection of the procedure for myocardial scintigraphy depends on the clinical question. However, different methodological strategies are under discussion. Adequate preparation of the patient and realization of the investigation (withdrawal of medication, selection of type and intensity of stress) are prerequisites for valid results. Interpretation has to consider that myocardial scintigraphy represents different parameters than, for example, coronary morphology. False positive as well as false negative results can occur due to methodological and biological causes. Optimization of methodological and clinical quality control in nuclear medicine heart studies requires a close and competent co-operation of cardiologists and nuclear medicine physicians.
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PMID:[Quality assurance in cardiology: nuclear medicine]. 786 97

The distinction between fibrotic and viable myocardium is a key issue in patients with coronary artery disease and left ventricular dysfunction. Metabolic imaging with positron emission tomography (PET) and labeled tracers, along with the study of myocardial perfusion, is now available to identify hibernating myocardium. However, PET imaging of myocardial metabolism is a high-cost and time-consuming technique, and requires an on-site cyclotron. The aim of this study is to test the reliability of dobutamine echocardiography (DE) compared with PET imaging, for the identification of hibernating myocardium. In 16 patients, scheduled for myocardial revascularization, left ventricular shapes were divided in eight segments both for echocardiographic and nuclear study evaluation. All patients underwent a technetium 99m MIBI single-photon emission tomography stress-rest study of perfusion, a fluorine-18-labeled deoxyglucose (FDG(/PET study of metabolism, and a DE test (baseline, at a 5 micrograms/kg/min infusion of dobutamine for 8 minutes and at a 10 micrograms/kg/min dose for additional 8 minutes). Neither myocardial ischemia nor arrhythmia occurred during the DE test. Baseline echocardiograms showed 90 segments with wall motion abnormalities: wall motion impairment was decreased or reversed in 33 of 90 segments; it remained unchanged in 57 of 90 segments. In 32 of 33 segments considered viable on the basis of DE and in 21 of 57 segments with unchanged kinesis, some degree of FDG was detected. Thus, sensitivity and specificity of DE compared with nuclear studies was 60% and 97% respectively. Moreover, a good correlation and agreement (kappa = 0.51) between DE and the presence of FDG were found. We conclude that DE is a safe and reliable test for the screening of hibernating myocardium in patients with chronic coronary artery disease and left ventricular dysfunction.
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PMID:Identification of hibernating myocardium: a comparison between dobutamine echocardiography and study of perfusion and metabolism in patients with severe left ventricular dysfunction. 789 27

We examined 17 angina-free patients with left ventricular dysfunction, referred for surgical decision-making, who presented with no or few signs and symptoms of myocardial ischemia according to treadmill stress test. On cardiac catheterization they were affected by severe multi-vessel coronary artery disease; the mean left end-diastolic pressure of this population was 26.3 +/- 5.5 mm Hg (mean +/- SD) and their mean ejection fraction was 27.6 +/- 4.9% (mean +/- SD). They all were investigated for the presence of viable myocardium by the combined assessment of cardiac perfusion and metabolism using single photon emission tomography with [99mTc] labelled hexakis-2-methoxy-isobutyl-isonitrile [99mTc]MIBI/SPET) and positron emission tomography with [18F]-2-fluoro-2-deoxy-D-glucose ([18F]FDG/PET), respectively. Patients were considered for coronary surgery when [18F]FDG was detectable in at least two cardiac segments with wall motion abnormalities and perfusion defects. Nine patients were operated on, six were medically treated and two were scheduled for heart transplantation. We recorded no in-hospital mortality. At a mean follow-up of 28.4 +/- 9.8 (mean +/- SD) months all surgical patients were alive and their NYHA functional classes have improved, except in one case. Among the patients refused for bypass surgery, three are in stable conditions, three have worsened clinical statuses and two died while waiting for heart transplantation. In conclusion, for patients with bypassable coronaries, left ventricular dysfunction and lack of angina, successful coronary revascularization may be predicted by the presence of viable myocardium demonstrated with positron emission tomography.
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PMID:Identification and revascularization of hibernating myocardium in angina-free patients with left ventricular dysfunction. 801 47

Modern therapy of coronary artery disease (CAD) increasingly involves interventional strategies aimed at restoring blood flow to the ischemic myocardium. The emergence of coronary artery bypass surgery, percutaneous transluminal coronary angioplasty, and more recently thrombolytic therapy, has helped to change the natural course of ischemic heart disease and contribute to the overall reduction in the mortality from both acute myocardial infarction and chronic CAD. Presumably, the beneficial effects of revascularization result from improving blood supply to dysfunctional but viable regions with subsequent improvement in regional and global left ventricular function. Over the past decade, several approaches have been proposed to predict the reversibility of left ventricular dysfunction after coronary revascularization. For the most part, these methods rely on assessment of basic cellular mechanisms that are known to play a central role in the recovery of systolic function after coronary revascularization. These include sufficient resting perfusion to provide metabolic fuels and to allow wash-out of toxic metabolites, maintain membrane integrity (which includes the ability to generate transmembrane ionic gradients and to transport energy providing substrates), preserve metabolic machinery (to allow glucose, fatty acid and oxygen consumption), and recruitable inotropic reserve. Among the available modalities, thallium imaging, positron emission tomography, and low-dose dobutamine echocardiography are currently the most frequently used in the clinical setting. All allow prediction of reversible dysfunction with a high degree of sensitivity (greater than 80%). They seem to vary, however, in terms of specificity, thallium imaging showing the lowest (50-55%) and dobutamine echocardiography the highest (80-85%) specificity. New promising modalities, such as FDG or MIBI SPECT imaging, contrast echocardiography and integrated backscatter imaging are just ahead and will likely strengthen further our ability to identify jeopardized but viable myocardium.
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PMID:Nuclear and echocardiographic imaging for prediction of reversible left ventricular ischemic dysfunction after coronary revascularization: current status and future directions. 889 68

A variety of new radiopharmaceutical agents have been introduced to probe myocardial function in vivo. This review will introduce these new techniques which have recently been available in Japan. Tc-99m perfusion imaging agents provide excellent myocardial perfusion images which may enhance diagnostic accuracy in the study of coronary artery disease. In addition, greater photon flux from the tracer permits simultaneous assessment of regional perfusion and function with use of first-pass angiography or ECG-gated acquisition. Positron emission tomography enables metabolic assessment in vivo. Preserved FDG uptake indicates ischemic but viable myocardium which is likely to improve regional dysfunction after revascularization. In addition, FDG-PET seems to be valuable for selecting a high risk subgroup. Recently I-123 BMIPP, a branched fatty acid analog, has been clinically available in Japan. Less uptake of BMIPP than thallium is often observed in the ischemic myocardium. Such perfusion metabolic mismatch which seems to be similarly observed in FDG-PET is identified in the stunned or hibernating myocardium with regional dysfunction. Both of them are likely to recover afterwards. Severe ischemia is identified as reduced BMIPP uptake at rest, suggesting its role as an ischemic memory imaging. I-123 MIBG uptake in the myocardium reflects adrenergic neuronal function in vivo. In the study of coronary artery disease, neuronal denervation is often observed around the infarcted myocardium and post ischemic region as well. More importantly, reduced MIBG uptake in these patients can identify high risk for ventricular arrhythmias and assess severity of congestive heart failure. These new techniques will provide insights into new pathological states in the ischemic heart disease and enable to select optimal treatment in these patients.
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PMID:Recent advances in nuclear cardiology in the study of coronary artery disease. 921 83


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