Myocardial perfusion imaging in ischemic heart disease anno 1990

The field of radionuclide myocardial perfusion imaging is in a rapid state of change. Stress-rest myocardial imaging is important not only for the detection of coronary artery disease but also for prognostic stratification of patients. In particular, assessment of myocardial viability in patients with left ventricular dysfunction is a recent focus of investigation. Single-photon emission computed tomography has become widely accepted as the preferred (albeit challenging) imaging modality for myocardial perfusion imaging. Silent myocardial ischemia and its clinical significance continues to be an intriguing aspect of the clinical manifestation of coronary artery disease. Myocardial perfusion imaging is an invaluable independent method to unravel this problem. Dipyridamole was approved for pharmacologic vasodilation in conjunction with myocardial perfusion imaging. At the same time, direct infusion of adenosine was proposed as an alternative method of effecting vasodilatory stress. In 1990, several new technetium-99m-labeled myocardial perfusion imaging agents have been introduced (teboroxime and hexakis-2-methoxyisobutyl-isonitrile [sestaMIBI]) that may have a profound impact on imaging techniques and applications of myocardial perfusion imaging.     

Multimodality Imaging for Assessment of Myocardial Viability: Nuclear,Echocardiography, MR,and CT

The assessment of myocardial viability may be an important component of the evaluation of patients with coronary artery disease and left ventricular dysfunction. The primary goal of viability assessment in such patients is to guide therapeutic decisions by determining which patients would most likely benefit from revascularization. In patients with chronic coronary artery disease, left ventricular dysfunction may be a consequence of prior myocardium infarction, which is an irreversible condition, or reversible ischemic states such as stunning and hibernation. Imaging techniques utilize several methods to assess myocardial viability: left ventricular function, morphology, perfusion, and metabolism. Each technique (echocardiography, nuclear imaging, magnetic resonance imaging, and x-ray computed tomography) has the ability to assess one or more of these parameters. This article describes how each of these imaging modalities can be used to assess myocardial viability, and reviews the relative strengths and limitations of each technique.     

MRI for the diagnosis of myocardial ischemia and viability

Assessment of myocardial ischemia and viability plays a crucial role in the clinical management of patients with coronary artery disease. Recently, cardiovascular MRI has emerged as an important noninvasive diagnostic modality in the assessment of coronary artery disease. MRI is able to evaluate both myocardial perfusion as well as myocardial contractile reserve. Because of its superior spatial resolution, integration of qualitative and quantitative methodology, and excellent reproducibility, MRI has advantages over conventional noninvasive modalities currently used in the evaluation of myocardial ischemia and viability, and may well emerge as the premier noninvasive technique in the assessment of patients with coronary artery disease. The authors review the rapidly expanding recent literature that has now established cardiovascular MRI (including dobutamine cine MRI and vasodilator perfusion MRI techniques) as an ideal choice in the evaluation of myocardial ischemia and delayed contrast-enhanced MRI and low-dose dobutamine cine MRI for evaluation of viability. Comparisons with more established techniques such as dobutamine stress echocardiography, single photon emission computed tomography perfusion imaging, and positron emission tomography are reviewed.     

Diagnostic and Prognostic Value of Myocardial Perfusion Imaging in Patients with Known or Suspected Stable Coronary Artery Disease

Coronary artery disease is the leading cause of complications and death in the United States and other Western countries, and stress myocardial perfusion study is an important component of the clinical evaluation, stratification, and management. This imaging technique is a well-established modality and has been widely used for the past three decades. New quantitative techniques for the assessment of ventricular function using quantitative gated single-photon emission computed tomography in addition to myocardial perfusion will potentially enhance the role of nuclear cardiology in the management of these patients. This review summarizes the current knowledge of the diagnostic and prognostic uses of stress myocardial perfusion imaging using exercise and pharmacological stress in patients with stable coronary artery disease.     

Assessment of Ischemic Heart Disease Using Magnetic Resonance First-Pass Perfusion Imaging

METHODS: Cardiovascular magnetic resonance (MR) perfusion imaging has matured to a point where it can be routinely applied to assess patients with coronary artery disease and ischemic cardiomyopathy. The method has been compared to invasive, catheter-based as well as other noninvasive imaging modalities (echocardiography, single-photon emission computed tomography [SPECT], and positron emission tomography [PET]) for the evaluation of patients with coronary artery disease. Besides qualitative evaluation of MR perfusion images, an absolute quantification of global, regional and transmural myocardial perfusion is possible. A relative or absolute myocardial perfusion reserve has been determined noninvasively with MR perfusion imaging, and can provide good agreement with the invasive assessment. Based on the perfusion reserve, the severity of an epicardial coronary stenosis can be evaluated in patients with known or suspected coronary artery disease. Besides the absence of radiation exposure, MR perfusion imaging offers good temporal and excellent spatial resolution. In particular, the spatial resolution increases the sensitivity and specificity for the detection of coronary artery disease. New parameters such as the "endo-/epimyocardial resting perfusion ratio", may under some circumstances sufficiently enhance the sensitivity for detecting an abnormal perfusion, and thus avoid potentially harmful and expensive stress testing in patients with suspected ischemic heart disease. New revascularization modalities such as therapeutic angiogenesis need to be matched by sensitive imaging tools to prove their benefits. Thus, the optimization of therapeutic angiogenesis may profit from the diagnostic advantages provided by MR perfusion imaging. Furthermore, MR might yield new insights into the pathophysiology of cardiac diseases such as "syndrome X", or might help in the repetitive assessment of heart transplant recipients, possibly obviating the need for further invasive testing. CONCLUSION: The breadth of cardiac MRI allows the combined noninvasive assessment of myocardial perfusion, function, as well as myocardial viability. The combination gives MRI a unique and strong position in the field of noninvasive diagnostic cardiology.     

Usefulness and pitfalls in myocardial perfusion SPECT for detecting and assessing coronary artery disease

Thallium-201(Tl) is the dominant agent employed for myocardial perfusion imaging for detection of coronary artery disease, assessment of myocardial viability and prognostication. Technetium-99m(Tc) labeled radionuclides have been used as excellent alternatives to Tl. This paper will review the usefulness and pitfall in myocardial perfusion single photon emission computed tomography(SPECT) in patients with coronary artery disease. From a practical standpoint, we should know what are clinical questions, clinical status of patients(history and exercise ability of patients, obesity) and diagnostic accuracy of each diagnostic protocol and the performance in the nuclear laboratory. Myocardial perfusion defects during stress SPECT are produced by a heterogeneity in coronary blood flow, which depends on severity of coronary stenosis and consequent abnormalities in flow reserve. Certain factors can affect sensitivity and specificity of Tl SPECT for detection of coronary artery disease. Accurate determination of myocardial viability is vitally important for clinical decision making for patients with left ventricular(LV) dysfunction who will most benefit from revascularization. Hibernated myocardium may result in profound regional LV dysfunction in absence of necrosis. The various approach such as stress-redistribution-reinjection imaging, rest-redistribution imaging and rest-redistribution 24 hours delayed imaging has been utilized to assess myocardial viability with Tl. Alternatively, quantitative assessment of 99mTc-methoxy-isobutyl isonitrile(MIBI) and tetrofosmin uptake reflect the degree of viability. At the present time one of the most important clinical applications of exercise myocardial perfusion SPECT is the assessment of prognosis for patients with suspected and documented coronary artery disease. Patients with normal stress perfusion SPECT have a low event rate and excellent prognosis. Stress perfusion imagings have been widely used to stratify patients into different risk groups in the United State.     

Routine clinical positron emission tomography for diagnostic cardiac imaging--a review

Positron emission tomography, advanced through technical developments, has now evolved into a routinely applicable method for clinical investigation. The rubidium-82 generator, without the need for a cyclotron, provides a source of positron radionuclide which enables delineation of cardiac structures. Three characteristics of positron cameras are particularly essential for cardiac imaging: overlapping image planes to provide uniform sampling between detector rings, a high sensitivity to acquire high count rates, and clinically oriented software that is user-friendly. The most useful indications for positron emission tomography include assessment of myocardial perfusion (for which the diagnosis of coronary artery disease can be established with a sensitivity of 95 to 98% and specificity of 99 to 100%), assessment of the physiologic severity of coronary artery stenoses and the influence of interventions such as PTCA or thrombolysis, myocardial infarct imaging, assessment of viability of reversibly injured or ischemic cells, assessment of regional or global left ventricular function and analysis of collateral flow. The radiation burden to the patient is generally lower than that of standard cardiac nuclear tracer such as Tl-201. Thus, cardiac positron emission tomography provides information not previously available for better diagnosis and management of cardiac disease. This technique may obviate the need for other routinely-applied nuclear imaging techniques. Should the services of a cyclotron be available, the method offers, in addition, the possibility to perform complex studies of myocardial metabolism.     

Assessment of myocardial viability by radionuclide and echocardiographic techniques: is it simply a sensitivity and specificity issue?

PURPOSE OF REVIEW: The assessment of myocardial viability provides important information that may guide therapeutic decisions in patients with coronary artery disease and left ventricular dysfunction. This review describes methods for assessing myocardial viability using single-photon emission computed tomography, with an emphasis on how to optimize the detection of viable myocardium using current techniques. Relevant comparisons of radionuclide techniques with echocardiographic methods are also discussed. RECENT FINDINGS: The basis for the assessment of myocardial viability using radionuclides is reviewed briefly. Radionuclide techniques provide important prognostic information that may affect the decision on if patients with coronary artery disease should be revascularized or treated medically. Data suggest that dobutamine stress echocardiography may underestimate viability in certain patients. Radionuclide techniques that assess both radiotracer uptake and ventricular function can provide a comprehensive approach to detect viable myocardium in most patients. SUMMARY: The methods for assessing myocardial viability using single-photon emission computed tomography are accurate, reproducible, and widely available. Viability testing should be considered in patients with known coronary artery disease and left ventricular dysfunction. Further studies are warranted to assess the affect of viability assessment on clinical outcomes.     

Rubidium-82 cardiac positron emission tomography imaging: an overview for the general cardiologist

Cardiac positron emission tomography (PET) imaging has been used for more than 3 decades to study myocardial perfusion and metabolism, but for a majority of those years, confined to large academic and research centers with access to a cyclotron. With the advent of the generator-produced PET radionuclide Rubidium-82, PET myocardial perfusion imaging has become far more accessible in daily practice, and is backed by a strong evidence-base for the diagnosis and prognosis of coronary artery disease and myocardial viability. Intended to describe basic principles for the general cardiologist, this review highlights the role of Rb-82 in PET myocardial perfusion imaging and provides an overview of its properties, its diagnostic accuracy for diagnosing coronary artery disease and myocardial viability, and some unique applications.     

CT Perfusion: Ready for Prime Time

Advancements in computed tomography (CT) technology have revolutionized clinical practice, particularly regarding the noninvasive assessment of coronary artery disease (CAD). The versatility of cardiac CT has rendered multiple applications including assessment of cardiac structure and function, myocardial viability, and coronary anatomy. The merits of cardiac computed tomography angiography (CTA) have been proven for the detection, and particularly the exclusion, of CAD. However, CTA becomes limited in the presence of significant CAD. Its inability to consistently identify lesion-associated ischemia may necessitate additional radionuclide myocardial perfusion imaging. Myocardial computed tomography perfusion imaging (CTP) has emerged as a useful and convenient method to immediately assess myocardial ischemia. In this review, we discuss the current state of CTP including available technology, its performance to date from current literature, and future challenges to this field.     

Assessment of myocardial viability with myocardial contrast echocardiography

The application of noninvasive imaging techniques to assess myocardial viability has become an important part of routine management of patients with acute myocardial infarction and chronic coronary artery disease. Information regarding the presence and extent of viability may help identify patients likely to benefit from revascularization or therapy directed at attenuating left ventricular remodeling. Myocardial contrast echocardiography (MCE) is capable of defining the presence and extent of viability by providing an accurate assessment of microvascular integrity needed to maintain myocellular viability. It is especially suited for the spatial assessment of perfusion, even when myocardial blood flow is reduced substantially in the presence of severe epicardial stenoses or in a bed dependent on collateral perfusion. The routine use of MCE to evaluate viability in patients with acute and chronic coronary artery disease is now feasible with the advent of new imaging technologies and microbubble agents capable of myocardial opacification from venous injections. The utility of this technique for determining treatment strategies has not been established but is forthcoming.     

Positron emission tomography in ischemic heart disease

Non-invasive assessment of ischemic heart disease remains a challenging task, even with a large armory of diagnostic modalities. Positron emission tomography (PET) is an advanced radionuclide technique that has been available for decades. Originally used as a research tool that contributed to advances in the understanding of cardiovascular pathophysiology, it is now becoming established in clinical practice and is increasingly used in the diagnosis and risk stratification of patients with ischemic heart disease. PET myocardial perfusion imaging has a mean sensitivity and specificity of around 90% for the detection of angiographically significant coronary artery disease, and is also highly accurate for assessing the prognosis of patients with ischemic heart disease. Depending on the radiotracer used, it can provide information not only on myocardial perfusion but also on myocardial metabolism, which is essential for viability assessment. The potential of this imaging technique has been further increased with the introduction of hybrid scanners, which combine PET with computed tomography or cardiac magnetic resonance imaging, offering integrated morphological and functional information and hence comprehensive assessment of the effects of atherosclerosis on the myocardium. The scope of this review is to summarize the role of PET in ischemic heart disease.     

Magnetic resonance imaging in the assessment of coronary artery disease

Magnetic resonance imaging (MRI) is gaining importance in cardiology as the noninvasive test of choice for patients with a multitude of cardiovascular problems. Recently, cardiovascular MRI has emerged as an important noninvasive diagnostic modality in the assessment of coronary artery disease. Because of its superior spatial resolution, integration of qualitative and quantitative methodology, and excellent reproducibility, MRI has advantages over conventional noninvasive modalities currently used in the evaluation of coronary artery disease. This article reviews the rapidly expanding recent literature that has now established cardiovascular MRI as an ideal choice in the evaluation of myocardial ischemia (including dobutamine cine MRI and vasodilator perfusion MRI techniques). We further discuss the role of delayed contrast-enhanced MRI and low-dose dobutamine cine MRI for evaluation of myocardial viability. Comparisons with more established techniques, such as dobutamine stress echocardiography, single-photon emission computed tomography perfusion imaging, and positron emission tomography, are reviewed.     

Contrast echocardiography for the assessment of myocardial viability

PURPOSE OF REVIEW: The availability of an accurate, non-invasive method for distinguishing viable from irreversibly damaged myocardium, after acute myocardial infarction or in chronic coronary artery disease, is important in clinical decision making. Such a tool would enable physicians to identify patients most likely to benefit from revascularization strategies in patients with coronary artery disease and left ventricular dysfunction. Myocardial contrast echocardiography is a new technique that utilizes acoustically active gas-filled microspheres (microbubbles), which remain exclusively in the intravascular space and allow the simultaneous assessment of global and regional myocardial structure, function, and perfusion. An increasing body of data supports its role in assessing myocardial viability and predicting the recovery of function. RECENT FINDINGS: Myocardial contrast echocardiography accurately differentiates 'stunning' from necrosis, delineates transmural extent of infarction, predicts recovery of regional and global left ventricular systolic function in the recuperative phase, identifies patients at high risk of left ventricular remodelling, and provides incremental viability data when performed in conjunction with low-dose dobutamine echocardiography. SUMMARY: Technological advances have positioned myocardial contrast echocardiography as a safe, practical bedside technique for the evaluation of myocardial viability. It has comparable accuracy with other non-invasive imaging techniques, such as dobutamine stress echocardiography, radionuclide scintigraphy and cardiac magnetic resonance imaging.     

PET imaging with FDG to guide revascularization in patients with systolic heart failure

The assessment of myocardial viability is important in the management of patients with coronary artery disease and left ventricular systolic dysfunction. There are several different imaging modalities currently available for the identification of viable myocardium: dobutamine stress echocardiography, single photon emission computed tomography, delayed-enhancement cardiac magnetic resonance imaging, and F-18 fluorodeoxyglucose positron emission tomography. The goal of viability imaging is to determine the likelihood of recovery of systolic function after revascularization. Positron emission tomography with F-18 fluorodeoxyglucose (FDG-PET) provides information about perfusion as well as myocardial metabolism, requires meticulous patient preparation, and is currently the gold standard imaging modality for the assessment of myocardial viability. Viability imaging for the purposes of predicting which patients will have improvement in left ventricular systolic function is supported under current guidelines, but the results of the recent STICH-viability substudy have created uncertainty about the incremental benefit. This review article will provide a summary of the currently available imaging modalities with an emphasis on FDG-PET and discuss the clinical relevance of viability imaging in light of the STICH-viability substudy.     

Positron emission tomography and molecular imaging

The use of positron emission tomography (PET) in cardiology is growing rapidly. Technical features make PET a strong technology for the non-invasive evaluation of cardiac physiology. It is currently considered the most reliable tool for the identification of myocardial viability and also allows accurate assessment of myocardial perfusion and detection of coronary artery disease (CAD). The unique feature of PET is that myocardial perfusion can be measured in absolute terms, improving sensitivity in the detection of multivessel of disease and also allowing evaluation of very early changes in coronary vasoreactivity and the progression or regression of CAD. Use of the newest generation of PET systems with integrated multislice computed tomography (CT) is becoming a standard technique for cardiac imaging. Since the PET and CT techniques ideally complement each other the combination is particularly attractive for the non-invasive assessment of CAD but also has other functions. Finally, there are also promising future applications that involve molecular imaging of cardiac targets, which may further enhance the clinical utility of PET and hybrid imaging.     

Advances in imaging for assessment of ischemic heart disease

Cardiac imaging techniques continue to develop for the noninvasive detection and evaluation of patients with coronary artery disease. These techniques include single photon and positron emission tomography along with computed tomography and magnetic resonance imaging. The new myocardial perfusion tracers 99mTc-hexakis-2-methoxyisobutyl-isonitrile and 99mTc-teboroxime have recently come into general use for these purposes, and their role alongside that of more traditional agents is currently being defined using new imaging protocols and instrumentation. 99mTc-hexakis-2-methoxyisobutyl-isonitrile has also been documented as an important research tool for evaluating both at-risk myocardium and the degree of subsequent myocardial salvage following reperfusion therapies for acute myocardial infarction. Antimyosin antibody imaging is another emerging approach in the evaluation of patients with acute myocardial infarction. Metabolic imaging with 18F-fluoro-2-deoxyglucose using positron emission tomography to detect myocardial segments with compromised blood flow but preserved glucose metabolism is currently the best noninvasive method of identifying viable myocardium in patients with left ventricular dysfunction who may benefit from revascularization. Insights from these studies have led to development of the current 201Tl stress-rest reinjection protocols for viability evaluation using single photon emission computed tomography. Positron emission tomography, in combination with blood flow tracers using kinetic modeling, provides accurate estimates of coronary blood flow and flow reserve. The use of these new imaging techniques will allow increasingly accurate evaluation of patients with suspected and proven coronary artery disease in the future.     

New directions in myocardial perfusion imaging

In recent years, substantial progress has been made in the field of nuclear cardiology. Pharmacologic stress perfusion imaging with intravenous administration of dipyridamole or adenosine provides comparable sensitivity and specificity values for detection of coronary artery disease (CAD) as exercise imaging and has been employed successfully for risk stratification prior to peripheral vascular or aortic surgery and after myocardial infarction. Detection of myocardial viability can be enhanced utilizing reinjection of a second dose of thallium-201 (T1-201) at rest after acquisition of redistribution images with the single photon emission computerized tomography (SPECT) technique. Imaging solely in the resting state with T1-201 can also provide information concerning presence of viable myocardium in asynergic regions that are stunned or hibernating. New technetium-99m (Tc-99m) perfusion agents have emerged in the clinical setting and have provided excellent predictive value for detection of CAD in patients with chest pain and permit simultaneous assessment of function and regional blood flow. Tc-99m Sestamibi, one of these agents, is also a valid marker of viability when assessing myocardial salvage after coronary reperfusion in acute myocardial infarction.     

Técnicas de imagen híbridas en cardiopatía isquémica

Hybrid imaging for ischemic heart disease refers to the fusion of information from a single or usually from multiple cardiovascular imaging modalities enabling synergistic assessment of the presence, the extent, and the severity of coronary atherosclerotic disease along with the hemodynamic significance of lesions and/or with evaluation of the myocardial function. A combination of coronary computed tomography angiography with myocardial perfusion imaging, such as single-photon emission computed tomography and positron emission tomography, has been adopted in several centers and implemented in international coronary artery disease management guidelines. Interest has increased in novel hybrid methods including coronary computed tomography angiography-derived fractional flow reserve and computed tomography perfusion and these techniques hold promise for the imminent diagnostic and management approaches of patients with coronary artery disease. In this review, we discuss the currently available hybrid noninvasive imaging modalities used in clinical practice, research approaches, and exciting potential future technological developments.     

Assessment of coronary heart disease by CT angiography: current and evolving applications

Computed tomography angiography (CTA) of the heart is a rapidly evolving application for comprehensive assessment of coronary arterial anatomy, myocardial function, perfusion, and myocardial viability. Thus, cardiac CTA is capable of retrieving the most critical information for guiding the management of patients with suspected coronary heart disease (CHD). Ongoing technologic advancements have allowed acquiring such information within minutes, at radiation doses that are lower than those from conventional computed tomography imaging or common nuclear imaging techniques. Cardiac CTA has positioned itself as an imaging modality that may be well suited to fulfill central needs of cardiovascular medicine. This article reviews the evidence for the clinical utility of cardiac CTA in patients with suspected CHD.