Technetium-99m sestamibi tomography in patients with spontaneous chest pain: correlations with clinical, electrocardiographic and angiographic findings

Noninvasive cardiac imaging in suspected acute coronary syndrome

Noninvasive cardiac imaging has an important role in the assessment of patients with acute-onset chest pain. In patients with suspected acute coronary syndrome (ACS), cardiac imaging offers incremental value over routine clinical assessment, the electrocardiogram, and blood biomarkers of myocardial injury, to confirm or refute the diagnosis of coronary artery disease and to assess future cardiovascular risk. This Review covers the current guidelines and clinical use of the common noninvasive imaging techniques, including echocardiography and stress echocardiography, computed tomography coronary angiography, myocardial perfusion scintigraphy, positron emission tomography, and cardiovascular magnetic resonance imaging, in patients with suspected ACS, and provides an update on the developments in noninvasive imaging techniques in the past 5 years.

New SPECT and PET radiopharmaceuticals for imaging cardiovascular disease

Nuclear cardiology has experienced exponential growth within the past four decades with converging capacity to diagnose and influence management of a variety of cardiovascular diseases. Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) with technetium-99m radiotracers or thallium-201 has dominated the field; however new hardware and software designs that optimize image quality with reduced radiation exposure are fuelling a resurgence of interest at the preclinical and clinical levels to expand beyond MPI. Other imaging modalities including positron emission tomography (PET) and magnetic resonance imaging (MRI) continue to emerge as powerful players with an expanded capacity to diagnose a variety of cardiac conditions. At the forefront of this resurgence is the development of novel target vectors based on an enhanced understanding of the underlying pathophysiological process in the subcellular domain. Molecular imaging with novel radiopharmaceuticals engineered to target a specific subcellular process has the capacity to improve diagnostic accuracy and deliver enhanced prognostic information to alter management. This paper, while not comprehensive, will review the recent advancements in radiotracer development for SPECT and PET MPI, autonomic dysfunction, apoptosis, atherosclerotic plaques, metabolism, and viability. The relevant radiochemistry and preclinical and clinical development in addition to molecular imaging with emerging modalities such as cardiac MRI and PET-MR will be discussed.

Role of imaging for acute chest pain syndromes

Acute chest pain suggestive of ischemic cardiac origin, with a normal or nondiagnostic electrocardiogram and negative initial cardiac markers for myocardial necrosis represent a significant diagnostic dilemma for clinicians. Multiple imaging modalities play a pivotal role in early diagnosis and safe discharge of these patients. In this review, we compare the current imaging modalities available for these patients including their diagnostic accuracy, feasibility, and cost effectiveness. Acute rest myocardial perfusion imaging significantly improves the clinical outcome in these patients and reduces the overall cost when incorporated into the decision making pathway. The choice of imaging modality recommended should be based on local institutional expertise and the overall clinical presentation. The imaging modality with high diagnostic accuracy and negative predictive value will provide for precise risk stratification which is important to clinical decision making, including patients who require admission to the hospital and those who can be safely discharged.

Diagnostic performance of resting CT myocardial perfusion in patients with possible acute coronary syndrome

OBJECTIVE

Coronary CT angiography has high sensitivity, but modest specificity, to detect acute coronary syndrome. We studied whether adding resting CT myocardial perfusion imaging improved the detection of acute coronary syndrome.

SUBJECTS AND METHODS

Patients with low-to-intermediate cardiac risk presenting with possible acute coronary syndrome received both the standard of care evaluation and a research thoracic 64-MDCT examination. Patients with an obstructive (> 50%) stenosis or a nonevaluable coronary segment on CT were diagnosed with possible acute coronary syndrome. CT perfusion was determined by applying gray and color Hounsfield unit maps to resting CT angiography images. Adjudicated patient diagnoses were based on the standard of care and 3-month follow-up. Patient-level diagnostic performance for acute coronary syndrome was calculated for coronary CT, CT perfusion, and combined techniques.

RESULTS

A total of 105 patients were enrolled. Of the nine (9%) patients with acute coronary syndrome, all had obstructive CT stenoses but only three had abnormal CT perfusion. CT perfusion was normal in all other patients. To detect acute coronary syndrome, CT angiography had 100% sensitivity, 89% specificity, and a positive predictive value of 45%. For CT perfusion, specificity and positive predictive value were each 100%, and sensitivity was 33%. Combined cardiac CT and CT perfusion had similar specificity but a higher positive predictive value (100%) than did CT angiography.

CONCLUSION

Resting CT perfusion using CT angiographic images may have high specificity and may improve CT positive predictive value for acute coronary syndrome without added radiation and contrast. However, normal resting CT perfusion cannot exclude acute coronary syndrome.

Journey in evolution of nuclear cardiology: will there be another quantum leap with the F-18-labeled myocardial perfusion tracers?

The field of nuclear cardiac imaging has evolved from being rather subjective, more "art than a science," to a more objective, digital-based quantitative technique, providing insight into the physiological processes of cardiovascular disorders and predicting patient outcome. In a mere 4 decades of its clinical use, the technology used to image myocardial perfusion has made quantum leaps from planar to single-photon emission computed tomography (SPECT) and now to a more contemporary rapid SPECT, positron emission tomography (PET), and hybrid SPECT-computed tomography (CT) and PET-CT techniques. Meanwhile, radiotracers have flourished from potassium-43 and red blood cell-tagged blood pool imaging to thallium-201 and technetium-99m-labeled SPECT perfusion tracers along with rubidium-82, ammonia N-13, and more recently F-18 fluorine-labeled PET perfusion tracers. Concurrent with this expansion is the introduction of new quantitative methods and software for image processing, evaluation, and data interpretation. Technical advances, particularly in obtaining quantitative data, have led to a better understanding of the physiological mechanisms underlying cardiovascular diseases beyond discrete epicardial coronary artery disease to coronary vasomotor function in the early stages of the development of coronary atherosclerosis, hypertrophic cardiomyopathy, and dilated nonischemic cardiomyopathy. Progress in the areas of molecular and hybrid imaging are equally important areas of growth in nuclear cardiology. However, this paper focuses on the past and future of nuclear myocardial perfusion imaging and particularly perfusion tracers.

Imaging strategies for acute chest pain in the emergency department

OBJECTIVE

Echocardiography, radionuclide myocardial perfusion imaging (MPI), and coronary CT angiography (CTA) are the three main imaging techniques used in the emergency department for the diagnosis of acute coronary syndrome (ACS). The purpose of this article is to quantitatively examine existing evidence about the diagnostic performance of these imaging tests in this setting.

CONCLUSION

Our systematic search of the medical literature showed no significant difference between the modalities for the detection of ACS in the emergency department. There was a slight, positive trend favoring coronary CTA. Given the absence of large differences in diagnostic performance, practical aspects such as local practice, expertise, medical facilities, and individual patient characteristics may be more important.

Unstable angina and non-ST elevation myocardial infarction

Non-ST elevation acute coronary syndromes are responsible for approximately 1 million admissions to U.S. hospitals and twice as many to European hospitals each year. Thus, they are among the most common serious illnesses in adults, and are associated with an in-hospital mortality of approximately 5%. The most common cause is rupture of an atherosclerotic coronary plaque, resulting in subtotal coronary occlusion. Diagnosis is based on the clinical picture of retrosternal chest pain, aided by electrocardiographic findings of ST segment deviations and biomarker abnormalities (elevation of troponin and natriuretic peptides) and cardiac imaging (myocardial scans showing perfusion defects). Treatment involves antiischemic agents (nitrates and β blockers), antiplatelet drugs (aspirin, P2Y(12), and glycoprotein IIb/IIIa receptor blockers), and anticoagulants (unfractionated and low-molecular-weight heparins). Patients should undergo risk stratification, and those with high-risk factors should undergo coronary arteriography promptly with the intent to carry out coronary revascularization. Those at low risk should continue to receive intensive antiischemic and antithrombotic therapy. At discharge, patients should receive intensive lipid-lowering therapy with high doses of a statin, as tolerated.

Resolution of ST-segment elevation after streptokinase therapy in anterior versus inferior wall myocardial infarction

BACKGROUND

Resolution of ST-segment elevation is the best bedside predictor of myocardial reperfusion.

HYPOTHESIS

This study was conducted to examine the resolution of ST-segment elevation after streptokinase therapy in anterior versus inferior acute myocardial infarction (MI) and to corroborate it with echocardiographic and coronary angiographic data.

METHODS

The study population consisted of 70 patients, 35 each in the anterior and inferior MI groups. The electrocardiograms (ECGs) were recorded before, on completion of, and on Days 1 and 2 post streptokinase therapy. The resolution of ST segment determined from post-streptokinase ECGs was compared between the two groups and correlated with echocardiographic and coronary angiographic data.

RESULTS

On completion of and on Day 1 post streptokinase therapy, ST-segment resolution in both groups was not significantly different. On Day 2 post streptokinase therapy, resolution of the ST segment per lead was significantly lower in anterior than that in inferior MI (61 +/- 21% anterior vs. 77 +/- 21% inferior, p 0.003). The number of patients with akinesis of infarct-related ventricular wall was significantly higher (17 anterior vs. 7 inferior, p 0.02), and left ventricular ejection fraction was significantly lower in anterior MI (39 +/- 7% anterior vs. 48 +/- 8% inferior, p < 0.01). There was no significant difference in coronary angiographic data. One patient in each group demonstrated normal coronary arteries.

CONCLUSIONS

The resolution of ST-segment elevation on the completion of and on Day 1 post streptokinase therapy was comparable between anterior and inferior MI. The significantly less frequent resolution of ST-segment elevation in anterior MI on Day 2 post streptokinase could be due to more akinesis, larger infarct size, and worse systolic function rather than due to failure to open the infarct-related vessel.

Angiographic and scintigraphic (perfusion and electrocardiogram-gated SPECT) correlates of clinical presentation in unstable angina

BACKGROUND

Braunwald classification can be used as a measure of the acuteness or severity of clinical presentation of unstable angina. Gating perfusion images might provide additional information to that obtained from angiography, allowing correlations between the coronary anatomy and extent of myocardium at risk via simultaneous perfusion/function assessment.

HYPOTHESIS

The aim of this study was to determine the relation between the highest levels of the Braunwald classification (class III = rest angina within 48 h of presentation; class C = postinfarction angina; class c = refractory angina) and the angiographic findings, and the extent ofperfusion and segmental wall motion abnormalities using technetium-99m ((99m)Tc) sestamibi-gated single-photon emission computed tomography (SPECT) imaging.

METHODS

The study group consisted of 86 patients with unstable angina who underwent rest gated (99m)Tc sestamibi SPECT imaging and coronary angiography. Perfusion was graded on a 5-point scale (0 = normal; 4 = absent uptake) and wall motion on a 4-point scale (0 = akinesia/dyskinesia; 3 = normal) using the 20 segment model. Perfusion (PI) and wall motion indices (WMI) were calculated by adding the score of all segments and dividing this by 20. The localization, the degree of stenosis, and the morphology of the culprit lesion were assessed. Multivariate analysis was performed to identify the independent predictors of class III, C, and c angina.

RESULTS

Perfusion index was higher and WMI was lower in classes III, C, and c than in classes < III, < C, and < c, respectively (all p < 0.001). Class III angina was associated with PI (p <0.0001), WMI (p< 0.0001), complex morphology (p = 0.01), and decreased Thrombolysis in Myocardial Infarction (TIMI) flow (p = 0.002); class C angina with PI (p < 0.0001), WMI (p< 0.0001), intracoronary thrombus (p = 0.007), and decreased TIMI flow (p = 0.003); and class c angina with PI (p = 0.005) and WMI (p = 0.006).

CONCLUSION

The highest levels of the Braunwald classification are associated with a greater size and intensity of myocardial perfusion and wall motion abnormalities and with the angiographic findings of complex morphology, intracoronary thrombus, and decreased TIMI flow.

Impact of contrast echocardiography on diagnostic algorithms: pharmacoeconomic implications

The major goal of medicine in the era of managed care is to control escalating costs and to attain a high level of quality health care. Capitation has limited access to expensive and unnecessary testing, placing an emphasis on the prudent use of available technology. A vast armamentarium of available diagnostic screening tests are available within cardiology. Routine two-dimensional (2-D) echocardiography is a high-quality, low-cost test that provides enhanced portability and real-time test interpretation over other noninvasive test modalities. The echocardiogram may cost up to 50% less than competitive nuclear single-photon emission computed tomography (SPECT) imaging. However, on average 10% of routine and 33% of stress echocardiograms are suboptimal (disproportionately affecting obese patients and those with lung disease). Myocardial contrast echocardiography has been shown to provide enhanced endocardial border delineation and left ventricular opacification, to enhance Doppler signal, and to provide information on myocardial perfusion. In several recent phase II and III studies, the use of a contrast agent has been shown to improve the diagnostic accuracy of echocardiography substantially. Improvements in the diagnostic capabilities of echocardiography have been shown to (1) impact upon downstream repetitive testing in patients with an initially nondiagnostic echocardiogram, (2) potentially increase laboratory throughput, and (3) reduce the rate of false-positive and negative tests as a result of improved image quality. As clinical and cost-effectiveness parallel one another, the use of myocardial contrast echocardiography in selected patient cohorts will result in improved diagnostic accuracy and a cost-effective pattern of care.

Yield of early rest and stress myocardial perfusion single-photon emission computed tomography and electrocardiographic exercise test in patients with atypical chest pain, nondiagnostic electrocardiogram, and negative biochemical markers in the emergency department

There are no studies in which diagnostic yield of early rest myocardial perfusion gated single-photon emission computed tomography (SPECT), electrocardiographic exercise testing, and stress SPECT were compared in patients with atypical chest pain, nondiagnostic electrocardiograms (ECGs), and negative markers of myocardial damage in the emergency department. A prospective study of 96 patients who presented with atypical chest pain and nondiagnostic ECG, but without elevated markers of necrosis, was performed. All underwent rest gated SPECT using technetium-99m methoxyisobutyl isonitrile within 6 hours after pain subsided followed by an electrocardiographic exercise test to obtain stress-rest SPECT images. After 1 year, there were no deaths and coronary artery disease was confirmed in only 5 patients. Negative predictive values of the 3 techniques were high (99%, 96%, and 100%, respectively), but positive predictive values were low (27%, 22%, and 14%, respectively). Sensitivities of early SPECT (80%) and stress SPECT (100%) were higher than for the electrocardiographic exercise test (40%). In conclusion, in patients with atypical chest pain, nondiagnostic ECG, and negative biochemical markers, negative predictive values of the 3 tests analyzed are very high. The sensitivity of radionuclide tests is higher, but their widespread use does not appear warranted because their positive predictive value and incidence of complications is low.

Noninvasive cardiac imaging in the evaluation of suspected acute coronary syndromes

Optimal management of patients presenting with chest pain to the emergency department is a major challenge, both in terms of a diagnostic dilemma and consumption of resources. The triage of such patients can be aided vastly by the appropriate use of noninvasive imaging. Noninvasive imaging modalities such as echocardiogram, radionuclide perfusion studies, positron emission tomography, cardiac magnetic resonance imaging and computed tomography have all been demonstrated to have favorable diagnostic and prognostic value, with an enhanced sensitivity to detect acute ischemia. A normal noninvasive evaluation in the appropriate clinical setting presents a strong argument against acute ischemia as an etiology of the chest pain. Randomized trials of both rest and stress imaging in the emergency department have confirmed a reduction in unnecessary hospitalizations and cost savings without compromising the safety of the patient. Cardiac magnetic resonance and computed tomography would provide an insight into subendocardial ischemia, the detection of which has previously been difficult, using single-photon emission tomography and echocardiography. In this review, novel hot-spot imaging modalities are discussed including infarct-avid imaging agents and ischemia-avid imaging agents, thus elucidating the pathophysiology of reperfusion-induced cell death. These agents represent work in evolution and are likely to be used routinely in the future as understanding of coronary syndromes and coronary artery disease becomes clearer.

Imaging in the evaluation of the patient with suspected acute coronary syndrome

Over the last decade, major advances have been made in the treatment of acute coronary syndromes (ACSs). However, effective implementation of these treatments requires timely and accurate identification of the high-risk patient among all those presenting to the emergency department (ED) with symptoms suggestive of ACS. The opportunity for improving outcomes is time-dependent, so that early identification of the patient who has true ACS is essential. This necessity further increases the need for rapid triage tools, especially in the current setting of ED and hospital overcrowding that has become the norm in large urban centers.

Noninvasive Imaging Techniques to Aid in the Triage of Patients with Suspected Acute Coronary Syndrome: A Review

The evaluation, treatment, and disposition of patients with symptoms suggestive of acute coronary syndrome (ACS) in the Emergency Department continues to be a clinical challenge. Many patients with suggestive symptoms are admitted to the hospital to rule out a myocardial infarction by serial enzyme tests and EKGs and receive an expedited work-up for ischemia. However, the diagnosis can be difficult, given the wide range of potentially atypical symptoms that can signal ACS, which remains a major clinical risk for patients and a liability risk for emergency physicians. This article reviews imaging technologies such as echocardiography and nuclear perfusion imaging used currently in the diagnosis of ACS and rapidly advancing technologies such as CT and MRI that may be able to visualize calcifications, plaques, occlusions, and infarctions noninvasively in real time. Some noninvasive tests used to complete an ischemia work-up after serial enzyme testing and EKGs, such as exercise EKG, stress echocardiography, and stress perfusion imaging, also are reviewed.

Role of "Ischemia modified albumin", a new biochemical marker of myocardial ischaemia, in the early diagnosis of acute coronary syndromes

BACKGROUND

Diagnosis of cardiac ischaemia in patients attending emergency departments (ED) with symptoms of acute coronary syndromes is often difficult. Cardiac troponin (cTn) is sensitive and specific for the detection of myocardial damage but may not rise during reversible myocardial ischaemia. Ischemia Modified Albumin (IMA) has recently been shown to be a sensitive and early biochemical marker of ischaemia.

METHODS AND RESULTS

This study evaluated IMA in conjunction with ECG and cTn in 208 patients presenting to the ED within three hours of acute chest pain. At presentation, a 12-lead ECG was recorded and blood taken for IMA and cardiac troponin T (cTnT). Patients underwent standardised triage, diagnostic procedures, and treatment. Results of IMA, ECG, and cTnT, alone and in combination, were correlated with final diagnoses of non-ischaemic chest pain, unstable angina, ST segment elevation, and non-ST segment elevation myocardial infarction. In the whole patient group, sensitivity of IMA at presentation for an ischaemic origin of chest pain was 82%, compared with 45% of ECG and 20% of cTnT. IMA used together with cTnT or ECG, had a sensitivity of 90% and 92%, respectively. All three tests combined identified 95% of patients whose chest pain was attributable to ischaemic heart disease. In patients with unstable angina, sensitivity of IMA used alone was equivalent to that of IMA and ECG combined.

CONCLUSIONS

IMA is highly sensitive for the diagnosis of myocardial ischaemia in patients presenting with symptoms of acute chest pain.

Acute resting myocardial perfusion imaging in patients with diabetes mellitus: results from the Emergency Room Assessment of Sestamibi for Evaluation of Chest Pain (ERASE Chest Pain) trial

BACKGROUND

Resting myocardial perfusion imaging (MPI) improves the triage of patients presenting to the emergency department (ED) with symptoms suggestive of acute cardiac ischemia (ACI). In the ED setting the presence of diabetes mellitus (DM) is a predictor of ACI and hospitalization, but the role of resting MPI in patients with DM is unknown.

METHODS AND RESULTS

A secondary data analysis of a prospective, multicenter, randomized, controlled trial of ED evaluation strategies in patients with symptoms suggestive of ACI and normal or nondiagnostic electrocardiograms was performed. In the main trial 2475 patients were randomized to receive either the usual ED evaluation strategy (n = 1260) or the usual strategy supplemented by results from resting MPI by use of single photon emission computed tomography (SPECT) technetium 99m sestamibi (n = 1215). Patients with diabetes (n = 341) were evaluated separately. Imaging results, final diagnoses, effect on triage, and prognostic value of the SPECT imaging were compared between diabetic and nondiabetic patients. Of the 341 patients with diabetes, 153 (45%) were randomized to the imaging strategy. Patients with DM had higher rates of hospitalization (66% vs 49.6%, P = .0001) and ACI (21.1% vs 12.0%, P < .001) than patients without DM. Among diabetic patients without ACI, the admission rate was 63% in the usual strategy group versus 54% in the imaging strategy group (relative risk [RR] = 0.91 [95% CI, 0.76-1.06]; P = .24). There was no difference in the magnitude of this reduced risk of admission compared with patients without DM (RR = 0.84 [95% CI, 0.77-0.92]; P = .0002 for patients without DM and P = .35 for interaction of diabetes and RR reduction).

CONCLUSIONS

Acute resting MPI with Tc-99m sestamibi is associated with improved triage decision making in symptomatic ED patients with diabetes.

Myocardial perfusion scintigraphy: the evidence

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

Imaging in the evaluation of the patient with suspected acute coronary syndrome

Patients presenting to the emergency department with chest pain have a common problem. Definitive diagnosis at presentation is difficult due to limitations of the initial evaluation, and, thus, the majority of patients are admitted. Recognition of these limitations has driven the investigation of alternative evaluation techniques and protocols to attempt to improve diagnostic sensitivity without increasing overall costs. Acute myocardial perfusion imaging has been a highly valuable technique for risk stratification of intermediate to low-risk patients with chest pain. However, for a variety of reasons, it has not been widely embraced. In the past few years, alternative techniques have been investigated for use in the diagnosis of acute coronary syndromes in the acute setting. Coronary calcium scoring and cardiac magnetic resonance imaging show promise as new tools in the armamentarium for acute coronary syndromes. The challenge now lays in developing a strategy that uses these and future techniques most appropriately to support optimal medical decision making.

Duration of abnormal SPECT myocardial perfusion imaging following resolution of acute ischemia: an angioplasty model

OBJECTIVES

This study was designed to determine how long nuclear myocardial perfusion imaging (MPI) remains abnormal following transient myocardial ischemia.

BACKGROUND

Acute rest MPI identifies myocardial ischemia with a high sensitivity when the radionuclide is injected during chest pain. However, the sensitivity of this technique is uncertain when the radionuclide is injected following the resolution of symptoms.

METHODS

Forty patients undergoing successful coronary angioplasty were randomized into four equal groups. Tc-99m sestamibi was injected intravenously during the last balloon inflation (acute MPI) in 30 patients and then reinjected 1, 2, or 3 h later (delayed MPI). In a fourth group, the radiopharmaceutical was injected at 15 min following balloon deflation (delayed MPI). A final injection was performed at 24 to 48 h (late MPI) in 37 patients (93%).

RESULTS

A perfusion defect was detected in all 30 acute MPI studies; in 7/10 patients (70%) injected at 15 min; in 11/30 patients (37%) injected at 1, 2, or 3 h; and in 7/37 patients (19%) injected at 24 to 48 h. Perfusion scores were 13.0 +/- 9.2 on acute MPI, 5.1 +/- 2.8 at 15 min (p < 0.001 vs. acute MPI); 2.6 +/- 3.0 at 1, 2, and 3 h (p < 0.001 vs. acute MPI); and 1.3 +/- 2.4 at 24 to 48 h (p < 0.001 vs. acute MPI; p < 0.03 vs. delayed MPI).

CONCLUSIONS

Myocardial perfusion imaging may remain abnormal for several hours following transient myocardial ischemia even when normal flow is restored in the epicardial coronary artery.

Use of radionuclide imaging in acute coronary syndromes

The triage of patients presenting to the emergency department (ED) with acute chest pain is a diagnostic challenge. Radionuclide myocardial perfusion imaging has been shown to have favorable diagnostic and prognostic value in this setting, with an excellent early sensitivity to detect acute myocardial infarction (MI) not achieved by other testing modalities. A normal resting perfusion imaging study has been shown to have a negative predictive value of over 99% to exclude MI. Observational and randomized trials of both rest and stress imaging in the ED evaluation of patients with chest pain have demonstrated reductions in unnecessary hospitalizations and cost savings compared with routine care. Perfusion imaging has also been used in risk stratification after MI, and for measurement of infarct size to evaluate reperfusion therapies. Novel "hot spot" imaging radiopharmaceuticals that visualize infarction or ischemia are currently undergoing evaluation and hold promise for future imaging of acute coronary syndromes.

The Erlanger chest pain evaluation protocol: a one-year experience with serial 12-lead ECG monitoring, two-hour delta serum marker measurements, and selective nuclear stress testing to identify and exclude acute coronary syndromes

STUDY OBJECTIVE

We determine the overall use of a 6-step accelerated chest pain protocol to identify and exclude acute coronary syndrome (ACS) and to confirm previous findings of the use of serial 12-lead ECG monitoring (SECG) in conjunction with 2-hour delta serum marker measurements to identify and exclude acute myocardial infarction (AMI).

METHODS

A prospective observational study was conducted over a 1-year period from January 1, 1999, through December 31, 1999, in 2,074 consecutive patients with chest pain who underwent our accelerated evaluation protocol, which includes 2-hour delta serum marker determinations in conjunction with automated SECG for the early identification and exclusion of AMI and selective nuclear stress testing for identification and exclusion of ACS. In patients not undergoing emergency reperfusion therapy, physician judgment was used to determine patient disposition at the completion of the 2-hour evaluation period: admit for ACS, discharge or admit for non-ACS condition, or immediate emergency department nuclear stress scan for possible ACS. A positive protocol was defined as a positive result in 1 or more of the 6 incremental steps in our chest pain evaluation protocol: (1) initial ECG diagnostic of acute injury or reciprocal injury; (2) baseline creatine kinase (CK)-MB level of 10 ng/mL or greater and index of 5% or greater or cardiac troponin I level of 2 ng/mL or greater; (3) new/evolving injury or new/evolving ischemia on SECG; (4) increase in CK-MB level of +1.5 ng/mL or greater or cardiac troponin I level of +0.2 ng/mL or greater in 2 hours; (5) clinical diagnosis of ACS despite a negative 2-hour evaluation; and (6) reversible perfusion defect on stress scan compared with on resting scan. All patients were followed up for 30-day ACS, which was defined as myocardial infarction (MI), percutaneous coronary intervention/coronary artery bypass grafting, coronary arteriography revealing stenosis of major coronary artery of 70% or greater not amenable to percutaneous coronary intervention/coronary artery bypass grafting, life-threatening complication, or cardiac death within 30 days of ED presentation.

RESULTS

Discharge diagnosis in the 2,074 study patients consisted of 179 (8.6%) patients with AMI, 26 (1.3%) patients with recent AMI (decreasing curve of CK-MB), and 327 (15.8%) patients with 30-day ACS. At 2 hours, sensitivity and specificity for MI (AMI or recent AMI) of SECG plus delta serum marker measurements was 93.2% and 93.9%, respectively (positive likelihood ratio 15.3; negative likelihood ratio 0.07). At the completion of the full ED evaluation protocol (positive result in >or=1 of the 6 incremental steps), sensitivity and specificity for 30-day ACS was 99.1% and 87.4%, respectively (positive likelihood ratio 7.9; negative likelihood ratio 0.01).

CONCLUSION

An accelerated chest pain evaluation strategy consisting of SECG, 2-hour delta serum marker measurements, and selective nuclear stress testing in conjunction with physician judgment identifies and excludes MI and 30-day ACS during the initial evaluation of patients with chest pain.

Cardiac imaging in women: use of radionuclide myocardial perfusion imaging and echocardiography for acute chest pain

Evidence for the value of noninvasive cardiac imaging in patients for the detection of ischemic heart disease has traditionally come from trials using male patients. The application of such technology for women is often presumptive. Because there is an overall lower prevalence of ischemic heart disease in women, difference in body habitus, and smaller heart size, cardiac imaging in women presents unique challenges for imaging specialists and cardiologists. With the introduction of technetium-99 meters perfusion agents, gated single-photon emission computed tomography, and attenuation correction, myocardial perfusion imaging (MPI) in women has achieved a high sensitivity and specificity for the detection of coronary artery disease similar to that observed in men. With harmonic imaging and myocardial contrast agents, two-dimensional echocardiography offers comparable diagnostic accuracy in women. More importantly, MPI and stress echocardiography have prognostic value in predicting future cardiovascular events. The severity and extent of the single-photon emission computed tomography myocardial perfusion defects independently predict future cardiovascular events. Myocardial perfusion rest imaging during acute chest pain has a 99% negative predictive value of subsequent cardiovascular events, and a positive study MPI is the most important predictor for future cardiac events. Both MPI and stress echocardiography can direct high-risk patients to more invasive management or selectively identify lower-risk patients, allowing safe discharge from the emergency department and unnecessary hospitalization. Using a triage approach incorporating MPI or rest echocardiography in patients with acute chest pain results in significant cost savings. However, data on rest imaging in women during acute chest pain are still lacking.

Myocardial perfusion imaging in evaluation of undiagnosed acute chest pain

Myocardial perfusion imaging is a relatively new technique in the emergency department management of acute chest pain. With improved sensitivity and specificity compared to traditional methods of risk stratification, an abnormal scan rapidly identifies individuals with acute perfusion abnormalities and allows the appropriate utilization of limited resources. Conversely, a normal scan allows prompt hospital discharge and is associated with excellent outcomes both in the short and medium terms. Acute chest pain myocardial perfusion imaging has been demonstrated to alter patient management and disposition and its routine use results in decreased costs in the intermediate risk population.

Selective dual nuclear scanning in low-risk patients with chest pain to reliably identify and exclude acute coronary syndromes

STUDY OBJECTIVE

We sought to determine the use in routine clinical practice of selective dual nuclear cardiac scanning (rest and stress) in low-risk patients with chest pain for identifying and excluding acute coronary syndromes (ACSs) during the initial emergency department evaluation.

METHODS

A prospective observational study was conducted over 13 months in 1,775 low-risk patients with chest pain who had intermediate- and high-risk ACSs ruled out by means of our 2-hour protocol, which consists of automated serial 12-lead ECG monitoring in conjunction with baseline and 2-hour creatine kinase (CK) MB and troponin I (cTnI) measurements. At the completion of the 2-hour evaluation period, low-risk patients were stratified by means of physician judgment into 1 of 2 categories: category III, possible ACS; and category IV, probable non-ACS chest pain. Level III patients underwent immediate dual nuclear scanning (rest thallium and stress sestamibi scanning), and level IV patients were discharged directly from the ED unless another serious non-ACS medical condition was thought to exist. Rest and stress scans were interpreted by a board-certified radiologist contemporaneous with patient evaluation. All patients were followed up for 30-day ACS, which was defined as acute myocardial infarction, percutaneous transluminal coronary angioplasty/coronary artery bypass grafting, coronary arteriography revealing stenosis of the major coronary artery of 70% or greater not amenable to percutaneous transluminal coronary angioplasty/coronary artery bypass grafting, life-threatening complication, or cardiac death within 30 days of ED presentation.

RESULTS

A total of 2,206 ED patients with chest pain were evaluated for ACS during the study period. Four hundred thirty-one patients were excluded for having 1 or more of the following findings: initial ECG diagnostic of injury; baseline CK-MB level, cTnI level, or both diagnostic of acute myocardial infarction; 2-hour DeltaCK-MB level of +1.5 ng/mL or greater; 2-hour DeltacTnI level of +0.2 ng/mL or greater; injury or new or evolving ischemia on serial 12-lead ECG monitoring; or clinical diagnosis of ACS. Of the 1,775 study patients, 805 (45.4%) underwent immediate dual nuclear scanning. A positive stress nuclear scan result was more sensitive (97.3% versus 71.2%, P <.0001) and specific (87.7% versus 72.6%, P <.0001) for 30-day ACS than a positive resting nuclear scan result. The protocol of selective dual nuclear scanning (ie, patients who did not undergo dual nuclear scanning were counted as having a negative test result) had a sensitivity and specificity for 30-day ACS of 93.4% and 94.7%, respectively (positive likelihood ratio 17.6; negative likelihood ratio 0.07).

CONCLUSION

Stress nuclear scanning is more sensitive and specific than resting nuclear scanning for identification of ACS in low-risk patients with chest pain. A strategy of using selective dual nuclear scanning once high- and intermediate-risk ACS has been ruled out with our 2-hour evaluation both reliably identifies and reliably excludes 30-day ACS.

Evaluation of the Emergency Department chest pain patient

Patients presenting to the Emergency Department with chest pain are common and often present diagnostic difficulties. Because of the limitations of the initial evaluation, the majority of patients are admitted, although many are later found to have noncardiac causes for their symptoms. Recognition of these limitations has driven the investigation of newer evaluation techniques and protocols in an attempt to improve diagnostic sensitivity without increasing overall costs. These have included modifications of the standard ECG, and use of newer myocardial markers such as mass assays for CK-MB and troponin T and I. Use of acute rest myocardial perfusion imaging has also been shown to be a highly valuable technique for risk stratification of the intermediate- to low-risk chest pain patient.

Echocardiography, nuclear scintigraphy, and stress testing in the emergency department evaluation of acute coronary syndrome

There are between 3 and 5 million visits to EDs each year for complaints of chest pain. Of these, about one half of the patients have a noncardiac cause for their chest pain. Of the remainder, about 30% to 50% have significant coronary disease. It is quite clear that patients who are at high risk for a coronary event should be admitted to the hospital. For the low-to-moderate risk patients, the decision to admit or discharge the patient from the ED is not quite so easy. The emergency physician has to decide which tests can be helpful in the decision-making process, this can be undertaken in conjunction with a consultative cardiologist. It can be argued that if a patient does not have a normal test result whichever that evaluatory test is), then the patient should be admitted for further work-up and evaluation. The easiest test to perform in the ED setting is an echocardiogram. The images can be sent by telecommunication to a qualified echocardiogram reader for interpretation. This also has a reasonable NPV, although not necessarily as good as some of the other modalities available, unless interpreted in light of cardiac enzyme test results. If the index of suspicion is still high, then a stress echocardiogram can be considered. This has an excellent NPV and can be easily performed in [table: see text] most patients. This should not be undertaken in the face of an evolving MI, and patients should be observed for at least 8 hours after their initial presentation to the ED prior to undergoing a provocative test. Nuclear scintigraphy, another modality available for cardiac risk stratification, can be a logistical nightmare. The nuclear isotopes are strictly regulated by the Nuclear Regulatory Commission. The emergency physician may inject the isotopes, provided that he or she has undergone the necessary radiation training. Also, the patient must be removed from the ED to a radioisotope-approved area for the duration of the scan. One of the most difficult questions left open after review of all these analytical modalities is the duration of time these test results remain valid; when does an individual patient need to be reevaluated as to their specific pretest probability? The answer to this question lies in the presenting clinical scenario. If the patient presents with a similar inciting trigger for his or her symptoms, and the cardiac risk profile has not changed appreciably, then the previous study (whether a provocative stress test or even a cardiac catheterization) probably can be reliably counted. If the patient's risk profile has changed or the symptoms are new or more intense, the physician is compelled to pursue this encounter as a new, acute event. This can be true even in the setting of a previous cardiac catheterization that showed nonobstructive coronary disease, because plaque rupture can be acute and unpredictable. Ultimately, optimal care calls for each institution to develop a specific approach, in conjunction with their consultative cardiologist or critical care specialist, to enhance patient care, safety, and diagnostic outcome, while maintaining cost efficiency.

Validated risk stratification model accurately predicts low risk in patients with unstable angina

BACKGROUND

In the mid 1990s, two unstable angina risk prediction models were proposed but neither has been validated on separate population or compared.

OBJECTIVES

The purpose of this study was to compare patient outcome among high, medium and low risk unstable angina patients defined by the Agency for Health Care Policy and Research (AHCPR) guideline to similar risk groups defined by a validated model from our institution (RUSH).

METHODS

Four hundred sixteen patients consecutively admitted to the hospital with unstable angina between January 1, 1995, and December 31, 1997, were prospectively evaluated for risk factors. The presence of major adverse events such as myocardial infarction (MI), death and heart failure was assessed for each patient by chart review.

RESULTS

The composite end point of heart failure, MI or death occurred in 3% and 5% of the RUSH and AHCPR low risk categories, respectively, and in 8% and 10% of AHCPR and RUSH high risk categories, respectively. Recurrent ischemic events were best predicted by the RUSH model (high: 24% vs. medium: 12% and low: 10%, p = 0.029), but not by the AHCPR model (high: 14% vs. medium: 13% and low: 9%, p = 0.876). The RUSH model identified five times more low risk patients than the AHCPR model.

CONCLUSIONS

Both models identify patients with low and high event rates of MI, death or heart failure. However, the RUSH model allowed for five times more patients to be candidates for outpatient evaluation (low risk) with a similar observed event rate to the AHCPR model; also, the RUSH model more successfully predicted ischemic complications. We conclude that the RUSH model can be used clinically to identify patients for early noninvasive evaluation, thereby improving cost effectiveness of care.

Evaluation of the emergency department chest pain patient

Patients presenting to the emergency department with chest pain are a common and perplexing problem. Because of the limitations of the initial evaluation, most patients are admitted, although many are found to have noncardiac causes of their symptoms. Recognition of these limitations has driven the investigation of newer evaluation techniques and protocols in an attempt to improve diagnostic sensitivity without increasing overall costs. These have included modifications of the standard electrocardiogram and use of newer myocardial markers of necrosis, such as mass assays for CK-MB as well as troponin T and troponin I. Use of acute rest myocardial perfusion imaging also has been shown to be a highly valuable technique for risk stratification of the intermediate- to low-risk chest pain patient.

Resting sestamibi imaging for the prognosis of low-risk chest pain

OBJECTIVE

To assess the prognostic value of resting Tc-99m sestamibi scanning for adverse cardiac events (ACEs) in ED chest pain patients with a low probability of acute cardiac ischemia (ACI).

METHODS

Sixty-nine consenting, hemodynamically stable patients with chest pain and a nondiagnostic electrocardiogram received an injection of 25 mCi of sestamibi during or within two hours of active pain. Scans were interpreted locally by a nuclear cardiologist or radiologist. Interrater reliability was assessed. ACEs of myocardial infarction (MI), death, or revascularization were assessed during the index hospitalization and over a one-year follow-up period.

RESULTS

For ACEs, rest scanning with sestamibi had a sensitivity of 71% (95% CI = 0.33 to 0.97), a specificity of 92% (95% CI = 0.82 to 0.97), and an accuracy of 90% (95% CI = 0.87 to 0.99). The positive predictive value was 50% (95% CI = 0.19 to 0.82) and the negative predictive value was 97% (95% CI = 0.87 to 0.98). Sestamibi scanning was highly discriminating, with 62% of patients with positive scans but only 3% with negative scans having ACEs (p<0.001, log rank test).

CONCLUSION

In patients with low-risk chest pain, sestamibi scanning has good specificity and moderate sensitivity for ACEs over a 12-month period.

Sauna-induced myocardial ischemia in patients with coronary artery disease

PURPOSE

Sauna bathing is a popular recreational activity that is generally considered to be safe. However, there have been case reports of adverse cardiac events. We sought to determine whether sauna use caused myocardial ischemia in patients with coronary artery disease.

METHODS

Sixteen patients with proven coronary artery disease were submitted to three conditions (rest, exercise, and sauna bathing) with continuous electrocardiographic (ECG) monitoring and regular blood pressure measurements. During each condition, patients were injected with Tc-99 sestamibi followed by nuclear scintigraphic imaging. Perfusion defect scores were calculated in 15 patients.

RESULTS

Sauna bathing was well tolerated. There was a mean (+/- SD) increase in heart rate of 32% +/- 20% in the sauna (resting mean heart rate = 60 +/- 9 beats per minute vs sauna mean heart rate = 79 +/- 11 beats per minute, P <0.001) and a 13% +/- 6% drop in systolic blood pressure (resting mean systolic blood pressure = 142 +/- 14 mm Hg vs sauna mean systolic blood pressure = 123 +/- 15 mm Hg, P <0.001). There were no arrhythmias or ECG changes in the sauna. Compared with rest, there was significant ischemia during sauna bathing (average perfusion defect score at rest = -0.44 vs average sauna score = -0.93, P <0.001). The perfusion defect score in the sauna was worse than the resting score in 14 of the 15 patients. Sauna-associated perfusion defect scores were highly correlated with exercise-induced scores (R2 = 0.65, P <0.001).

CONCLUSION

In patients with stable coronary artery disease, sauna use is clinically well tolerated but is associated with scintigraphically demonstrated myocardial ischemia.

Prediction of coronary artery lesions in unstable angina by iodine 123 beta-methyl iodophenyl pentadecanoic acid (BMIPP), a fatty acid analogue, single photon emission computed tomography at rest

Iodine 123 beta-methyl iodophenyl pentadecanoic acid (123I-BMIPP), a beta-methyl-branched fatty acid analogue, has been proven by experimental studies to reveal abnormalities in fatty-acid-related metabolism. This study was undertaken to validate the accuracy and limitations of 123I-BMIPP imaging at rest in detecting myocardial metabolic abnormalities and predicting coronary lesions in unstable angina (UA). One hundred UA patients without prior myocardial infarction were studied. 123I-BMIPP and thallium 201 chloride (201TlCl) imaging with single photon emission computed tomography (SPECT) and coronary and left ventricular cineangiography (LVC) were performed 1 week after the last episode of angina. There was reduced uptake of 123I-BMIPP imaging in 70 patients, reduced uptake of 201TlCl in 41, and abnormal LVC contraction in 49 patients. There were significant increases in severity scores of 123I-BMIPP imaging along with increases in the number of stenosed coronary arteries and the severity of stenosis in individual coronary arteries. There was a significant reduction in 123I-BMIPP severity scores 1 month after percutaneous transluminal coronary angioplasty (p < 0.01) and a significant correlation between the severity scores of 123I-BMIPP and LVC (r=0. 579, p<0.001). Overall rates of sensitivity and specificity in detecting significant coronary stenosis by 123I-BMIPP imaging were 74% and 86%, respectively, whereas rates of sensitivity and specificity in detecting significant coronary stenosis by 201TlCl were 31% and 91%, respectively. 123I-BMIPP sensitivity increases to 86% if only advanced coronary stenosis of >90% is included. In conclusion, 123I-BMIPP myocardial imaging is an effective method of predicting coronary artery lesions of UA patients without provocative test.

The evaluation of cocaine-induced chest pain with acute myocardial perfusion imaging

OBJECTIVE

To use myocardial perfusion imaging to determine the etiology of cocaine-induced chest pain in patients without ECG evidence of acute cardiac ischemia.

METHODS

The authors conducted a prospective study of consecutive consenting patients aged 18-70 years with cocaine-induced chest pain who reported cocaine use within three days and presented with a chief complaint of chest pain occurring within three hours and lasting longer than 15 minutes with a normal or nondiagnostic ECG. Patients were excluded if they had a clear-cut noncardiac cause of chest pain, ECG evidence of acute cardiac ischemia, history of myocardial infarction, pregnancy, or lactation, required immediate hospitalization, or were unable to consent. Patients were injected with Tc-99m tetrofosmin and imaged. Perfusion scans were independently read by two nuclear radiologists. Clinicians blinded to scan results determined patient disposition. Patients with abnormal scans were asked to return for follow-up resting scans.

RESULTS

Fourteen patients were enrolled. Twelve of the 14 patients had chest pain at the time of Tc-99m tetrofosmin injection. Ten of the 14 [(71%) 95% CI = 48% to 95%] scans were normal or within normal limits. Four of the 14 [(29%) 95% CI = 5% to 52%] were abnormal. Of the four patients with abnormal scans, two had follow-up scans that demonstrated an irreversible perfusion abnormality, and two who did not return for follow-up reported no subsequent hospitalizations for acute cardiac ischemia.

CONCLUSION

Perfusion imaging did not demonstrate reversible ischemia in most patients (12/14, 86%) with cocaine-induced chest pain without ECG evidence of ischemia. These results suggest that cocaine-induced chest pain in most patients without ECG evidence of ischemia is not due to acute ischemia.

Use of electron-beam computed tomography in the evaluation of chest pain patients in the emergency department

STUDY OBJECTIVE

We sought to determine whether electron-beam computed tomography (EBCT) could be used as a triage tool in the emergency department for patients with angina-like chest pain, no known history of coronary disease, normal or indeterminate ECG findings, and normal initial cardiac enzyme concentrations.

METHODS

We conducted a prospective observational study of 105 patients admitted between December 1995 and October 1997 to the ED of a large tertiary care hospital with 70,000 annual ED visits. The study group was comprised of women aged 40 to 65 years and men aged 30 to 55 years who presented with angina-like chest pain requiring admission to the hospital or chest pain observation unit. All patients underwent EBCT of the coronary arteries, along with other cardiac testing as deemed necessary by staff physicians.

RESULTS

Of the 105 patients, 100 underwent other cardiac testing during hospitalization. Evaluation included treadmill exercise testing in 58, coronary angiography in 25, radionuclide stress testing in 19, and echocardiography in 11. Results of EBCT and cardiac testing were negative for both in 53 patients (53%), positive for both in 14 (14%), positive for tomography and negative for cardiac testing in 32 (32%), and negative for tomography and positive for cardiac testing in only 1 patient. This positive test result, on a treadmill exercise test, was ruled a false positive by an independent staff cardiologist. Two other female patients with normal exercise sestamibi or coronary angiography and EBCT findings also had false-positive treadmill exercise results. The sensitivity of EBCT was 100% (95% confidence interval, 77% to 100%), with a negative predictive value of 100% (95% confidence interval, 94% to 100%). Specificity was 63% (95% confidence interval, 54% to 75%).

CONCLUSION

EBCT is a rapid and efficient screening tool for patients admitted to the ED with angina-like chest pain, normal cardiac enzyme concentrations, indeterminate ECG findings, and no history of coronary artery disease. Our study suggests that patients with normal initial cardiac enzyme concentrations, normal or indeterminate ECG findings, and negative results on EBCT may be safely discharged from the ED without further testing or observation. Larger studies are required to confirm this conclusion.