Prognostic value of thallium-201 myocardial perfusion imaging in three primary patient populations.

Knowledge of a patient's coronary anatomy alone is often insufficient to predict who will benefit from revascularization. Risk of cardiac events is related more to the presence of viable myocardium supplied by coronary arteries that are hemodynamically significant. Myocardial perfusion imaging with thallium-201 has been shown to reveal the presence and extent of jeopardized viable myocardium. In addition, thallium-201 imaging can demonstrate exercise-induced left ventricular dysfunction, manifested by increased thallium-201 myocardial imaging has important prognostic value in a wide spectrum of patients with coronary artery disease. The use of thallium-201 to predict cardiac events in patients with known or suspected coronary artery disease, in patients following myocardial infarction, and in patients undergoing noncardiac surgery is reviewed.     

Stress echocardiography versus myocardial SPECT for risk stratification of patients with coronary artery disease

PURPOSE OF REVIEW: Diagnostic testing using noninvasive imaging has become an integral part of risk stratification in patients with coronary artery disease. It is important to understand the integral strengths and weaknesses between the different modalities of stress testing and to apply accurately the type of test the clinical scenario demands. RECENT FINDINGS: There have been tremendous advances made in the field of cardiac imaging. Both myocardial perfusion imaging and stress echocardiographic techniques continue to evolve and play an important role in the assessment of patients with coronary artery disease. SUMMARY: In this review the authors discuss the relative merits of both stress echocardiography and myocardial single photon emission computed tomographic imaging for diagnosis and risk stratification of patients with coronary artery disease.     

Echocardiography and coronary artery disease: Current and future applications

Echocardiographic techniques are becoming more widespread for evaluating patients with known or suspected coronary artery disease. Because it affords an excellent overall view of the heart, two-dimensional echocardiography, rather than M-mode echocardiography, is the imaging procedure of choice when dealing with coronary artery disease. This technique can be used to make the initial diagnosis of acute myocardial infarction, diagnose complications, and assess prognosis following myocardial infarction. Additionally by combining this test with stress testing, latent coronary artery disease can be detected. Recovery of wall motion can be assessed following interventions such as thrombolysis or balloon angioplasty. Investigational and future uses include tissue characterization, which may allow detection of ischemic but potentially viable myocardium, direct coronary visualization for detection of atherosclerotic involvement of the proximal coronary arteries and myocardial contrast echocardiography. The latter technique allows visualization of perfusion by way of injecting contrast material into the coronary circulation. This has been demonstrated to be an accurate means of determining myocardial infarction size in an animal model and is currently being used in a number of centers in patients at the time of cardiac catheterization. In summary two-dimensional echocardiography currently allows assessment of patients with myocardial infarction from the time of their presentation through their convalescent period with respect to diagnosis, prognosis and presence of complications. Exercise echocardiography can diagnose latent coronary artery disease. The newer investigational techniques show promise for furthering our ability to evaluate patients with coronary artery disease using echocardiography.     

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.     

Risk assessment by myocardial perfusion imaging for coronary revascularization,medical therapy,and noncardiac surgery

Stress myocardial perfusion imaging (MPI) has become an important tool in risk stratification of patients with known coronary artery disease. A normal myocardial perfusion scan has a high negative predictive value and is associated with low annual mortality rate (< 1%). Patients with extensive ischemia (> 20% of the left ventricle), defects in more than 1 coronary vascular territory, transient or persistent left ventricular cavity dilation, and ejection fraction less than 45% have a high annual mortality rate (> 3%). Those patients should undergo coronary revascularization whenever feasible, as the cardiac event rate increases in proportion to the magnitude of the jeopardized myocardium. Stress MPI can be used to demonstrate ischemia in patients with symptoms early after coronary artery bypass surgery (< 5 years) or in those without symptoms late (>/= 5 years) after coronary artery bypass surgery. With respect to patients who underwent percutaneous interventions, stress MPI can help detect in-stent restenosis early after the intervention (3-6 months) or assess the progression of native coronary disease afterward. Since preliminary data suggest that a reduction in the perfusion defect size may translate to a reduction of coronary events, stress MPI can help assess the efficacy of medical management of coronary disease. Finally, stress MPI is indicated for perioperative cardiac risk stratification for noncardiac surgery in patients with intermediate risk predictors (mild angina, prior myocardial infarction or heart failure symptoms, diabetes mellitus, renal insufficiency) and poor functional capacity or in those who undergo high-risk surgery with significant implications in further preoperative management.     

Stress echocardiography for the diagnosis and risk stratification of patients with suspected or known coronary artery disease: a critical appraisal. Supported by the British Society of Echocardiography

Stress echocardiography today has matured into a robust and reliable technique not only for the diagnosis of suspected coronary artery disease (CAD) but also for the accurate risk stratification of patients with suspected and established CAD. This is mainly because of rapid advances in image acquisition, digital display, and the development of harmonic and contrast imaging. Stress echocardiography today is also utilised in patients with heart failure both for assessing the cause of heart failure and determining the extent of hibernating myocardium. With advances in myocardial perfusion imaging, stress echocardiography now allows simultaneous assessment of myocardial function and perfusion. Tissue Doppler imaging allows quantitation of wall motion. Ready availability and reliability makes stress echocardiography a cost effective technique for the assessment of CAD.     

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.     

Reversible left ventricular dysfunction

The extent and degree of myocardial viability are important parameters in the risk stratification of patients with significant left ventricular dysfunction secondary to coronary artery disease. Although several imaging modalities can identify viable myocardium, dobutamine stress echocardiography has gained considerable importance as an accurate, safe, and reliable method. In patients with significant left ventricular dysfunction secondary to coronary artery disease, identification of the presence and extent of contractile reserve and, therefore, viable myocardium during low-dose dobutamine infusion can predict the recovery of left ventricular function after revascularization, survival rate, and future cardiac events.     

Potential clinical applications of myocardial contrast echocardiography in evaluating myocardial perfusion in coronary artery disease

Myocardial contrast echocardiography (MCE) is a relatively new technique that uses microbubbles to produce myocardial opacification. Recent advances in echocardiography have resulted in improved detection of microbubbles within the myocardium allowing combined acquisition of function and perfusion data, thus making MCE suitable for bedside use. Regardless of the imaging modality chosen or the type of stress used, MCE detects changes developing in the coronary microcirculation, providing important information for the evaluation of severity of coronary artery disease and for the detection of viable myocardial tissue in acute or chronic coronary artery disease.     

Two dimensional echocardiographic evaluation of exercise-induced left and right ventricular asynergy: Correlation with thallium scanning

Adequate real time two dimensional echocardiograms were prospectively obtained before and immediately after graded treadmill exercise testing in 41 of 48 patients who underwent cardiac catheterization for suspected coronary artery disease. Findings were correlated with thallium perfusion scans performed 5 to 10 minutes and 3 hours after the same exercise test. Exercise-induced wall motion abnormalities were detected in 19 of 23 patients with significant coronary artery disease and no prior myocardial infarction as well as in all 5 patients with known previous infarction. Three patients with coronary artery disease experienced new isolated right ventricular asynergy with exercise that would have been missed if only the left ventricle had been evaluated. Exercise-induced thallium perfusion defects showed good correlation with exercise-induced asynergy as detected with echocardiography. Two dimensional echocardiography performed immediately after treadmill stress testing is a feasible and rewarding technique in the evaluation of patients suspected to have coronary artery disease.     

Detection of Viability of Dysfunctional Myocardium in Coronary Heart Disease. II. Echocardiography

The detection of viable myocardium in patients with severe left ventricular (LV) dysfunction is important because these patients benefit most from revascularization. Three echocardiographic techniques can be used for the noninvasive assessment of functional correlates of viable myocardium. Two-dimensional echocardiography (2DE) is well suited for quantifying resting LV regional and global systolic function and dysfunction before and after revascularization, in addition to providing data on chamber size, shape, and wall thicknesses. The presence of hypokinesis on a resting 2DE indicates that viable myocardium is definitely present, but presence of dykinesis does not exclude viability. Dobutamine stress echocardiography (DSE) before revascularization unmasks viability by demonstrating augmentation of systolic function. Several clinical studies have shown that improvement of regional function during DSE indicates contractile reserve and predicts improvement of function after revascularization. A biphasic response on DSE appears to predict residual coronary artery stenosis and is a reliable marker of viability. DSE also appears to be useful after revascularization for unmasking contractile reserve. Myocardial contrast echocardiography (MCE) detects viability by defining microvascular perfusion, the extent of myocardium at risk, and coronary flow reserve. The clinical utility of MCE is undergoing evaluation. The combination of DSE and MCE might provide an improved estimate of the extent of viable myocardium based on assessment of function and perfusion. Meanwhile, echocardiographic and nuclear techniques can be used to complement each other in the assessment of myocardial viability.     

Dipyridamole echocardiography

Intravenous dipyridamole is a potent coronary vasodilator that has been extensively investigated over the past several years in the noninvasive assessment of patients with suspected coronary artery disease when exercise cannot be performed or is suboptimal. As an alternative to exercise studies, dipyridamole has been used in combination with different cardiac imaging techniques such as echocardiography, thallium scintigraphy, and radionuclide ventriculography. Extensive experience has been obtained with dipyridamole thallium-201 imaging for coronary artery disease screening, risk stratification, and prognosis after an acute coronary event. However, experience with the use of dipyridamole in combination with two-dimensional echocardiography has been limited. Dipyridamole increases coronary blood flow in nondiseased coronary vessels relative to coronary vessels with significant luminal narrowings. These provide the basis for detecting regional differences in flow by using different cardiac imaging techniques. Two-dimensional echocardiography would show regional wall-motion abnormalities in response to those regional differences in coronary blood flow. In this article, the most commonly used protocols, safety, and practicability of dipyridamole echocardiography are reviewed. As an alternative to exercise, dipyridamole echocardiography shares all the indications of a standard exercise test. Clinical applications of dipyridamole echocardiography include coronary artery disease screening, suspected coronary artery spasm, postmyocardial infarction risk stratification, evaluation of percutaneous transluminal coronary angioplasty results, and prognosis following an acute coronary event. Compared to conventional (ECG) exercise testing, dipyridamole echocardiography appears to be equally sensitive but more specific. Compared to atrial pacing, dipyridamole provokes ischemia at a lower rate pressure product and results in a greater ST segment depression suggesting that dipyridamole induces more profound myocardial ischemia than atrial pacing. Dipyridamole thallium and exercise thallium have shown to be equally sensitive and specific in the assessment of coronary artery disease. High dose dipyridamole echocardiography appeared to be equally sensitive and more specific. Experimental studies have demonstrated that dobutamine appears to be a more powerful pharmacological agent in inducing wall-motion abnormalities. Dipyridamole echocardiography as compared to stress echocardiography offers the advantage of obtaining better quality postintervention images. With regard to sensitivity and for coronary artery disease diagnosis, both techniques appear to render similar results. Although further studies are needed, the available data indicates that cardiac ultrasound imaging prior to and following the intravenous administration of dipyridamole may be an attractive alternative to thallium perfusion imaging in the clinical setting, particularly when radionuclide capabilities are not present.     

Catecholamine stress echocardiography

Two-dimensional echocardiographic monitoring during catecholamine infusion has shown promise as a safe and accurate method for detection of coronary artery disease. The clinical application of catecholamine stress echocardiography has been facilitated by the development of digital image processing techniques. The sensitivity of this method of stress testing has been improved by drug infusion protocols that are designed to maximize myocardial stress. Recent investigations have demonstrated the value of dobutamine stress echocardiography for detection of multivessel disease following myocardial infarction and for assessment of cardiac risk before noncardiac surgery. Evaluation of changes in wall motion and thickening that occur during low dose dobutamine infusion may enable detection of viable myocardium after thrombolytic treatment of acute myocardial infarction. Compared to alternative noninvasive diagnostic methods, catecholamine stress echocardiography permits continuous acquisition of high-quality information on regional and global systolic function. This and other advantages have prompted the search for broader applications of this technique.     

Principal uses of myocardial perfusion scintigraphy in the management of patients with known or suspected coronary artery disease

The use of myocardial perfusion single photon emission computed tomography (SPECT) has undergone considerable expansion and evolution over the past 2 decades. Although myocardial perfusion imaging was first conceived as a noninvasive diagnostic tool for determining the presence or absence of coronary artery disease, its prognostic value is now well established. Thus, identification of patients at risk for future cardiac events has become a primary objective in the noninvasive evaluation of patients with chest pain syndromes and among patients with known coronary artery disease. In particular, the ability of myocardial perfusion SPECT to identify patients at low (< 1%), intermediate (1% to 5%) or high (> 5%) risk for future cardiac events is essential to patient management decisions. Moreover, previous studies have conclusively shown the incremental prognostic value of myocardial perfusion SPECT over clinical and treadmill exercise data in predicting future cardiac events. This report addresses the current role and new developments, with respect to the use of myocardial perfusion imaging, in determining patient risk for cardiac events and the cost-effective integration of such information into patient management decisions.     

Value of echocardiography in predicting future cardiac events after acute myocardial infarction

Short- and long-term survival after acute myocardial infarction mainly depends on three factors: the amount of myocardium that had become necrotic, the area of myocardium at further risk of becoming necrotic, and the patency of the infarct-related artery. Echocardiography is a low-cost, safe, bedside, repeatable tool, particularly useful for prognostic stratification after myocardial injury. Two-dimensional echocardiography analyzes left ventricular function, the most powerful predictor of survival immediately after acute myocardial infarction. Myocardial contrast echocardiography measures the infarct size and detects viable myocardium. Stress echocardiography stratifies patients with viable myocardium and/or multivessel coronary artery disease who need further diagnostic and therapeutic interventions. Transthoracic coronary Doppler ultrasonography assesses effective recanalization and coronary flow reserve of the left anterior descending coronary artery. Further technologic advances are needed to allow direct noninvasive measurement of flow by transthoracic Doppler ultrasonography in other coronary arteries.     

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.     

Myocardial Perfusion and Viability Imaging in Coronary Artery Disease: Clinical Value in Diagnosis,Prognosis, and Therapeutic Guidance

Coronary artery disease is a leading cause of morbidity and mortality worldwide. Noninvasive imaging tests play a significant role in diagnosing coronary artery disease, as well as risk stratification and guidance for revascularization. Myocardial perfusion imaging, including single photon emission computed tomography and positron emission tomography, has been widely employed. In this review, we will review test accuracy and clinical significance of these methods for diagnosing and managing coronary artery disease. We will further discuss the comparative usefulness of other noninvasive tests—stress echocardiography, coronary computed tomography angiography, and cardiac magnetic resonance imaging—in the evaluation of ischemia and myocardial viability.     

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.     

Prognostic implications of myocardial contractile reserve in patients with ischemic cardiomyopathy

The extent and degree of myocardial viability is an important parameter in the risk stratification of patients with significant left ventricular dysfunction due to coronary artery disease (CAD). Although several imaging modalities can identify viable myocardium, dobutamine stress echocardiography has gained considerable importance as an accurate, safe, and reliable method. In patients with significant left ventricular dysfunction secondary to CAD, identifying the presence and extent of contractile reserve and, therefore, viable myocardium, during low dose dobutamine infusion can predict recovery of left ventricular function postrevascularization, survival, and future cardiac events.     

Value of gated SPECT myocardial perfusion imaging for individual cardiac risk assessment

Myocardial perfusion imaging enables not only accurate diagnosis of disease but also entails prognostic value. Myocardial perfusion SPECT contributes to assessment of future cardiac events independently of other clinical parameters. A normal stress myocardial perfusion scan is associated with a favorable prognosis independent of history, symptoms, and exercise electrocardiography test variables. Cardiac risk and benefit from invasive therapeutic strategies increase in relation to the severity of the abnormality of perfusion and function assessed by gated myocardial perfusion SPECT. Thus, stress myocardial perfusion imaging may serve as a gatekeeper for referral to coronary angiography enabling effective risk stratification in patients with suspected or documented coronary artery disease.