Myocardial perfusion imaging versus biochemical markers in acute coronary syndromes

The assessment and appropriate clinical management of patients with acute chest pain and non-diagnostic electrocardiograms remain a continuing clinical problem. Accordingly, there is considerable interest in evaluating new strategies to improve early diagnostic accuracy in patients with possible acute myocardial ischaemia. Cardiac troponins (T and I) and acute rest myocardial perfusion imaging have similar sensitivities for detecting acute myocardial infarction. Whereas cardiac markers require 6-12 h to become positive, acute rest myocardial perfusion imaging immediately reflects the status of regional myocardial blood flow at the time of radiopharmaceutical injection. The measurement of cardiac troponins is particularly useful in the diagnosis and estimation of the degree of myocardial injury in those patients with a high likelihood of coronary artery disease and myocardial necrosis and for prognostication of adverse cardiac events in those patients with unstable angina. In contrast, the most appropriate use of acute rest myocardial perfusion imaging is in the setting of patients with acute ischaemic symptoms, non-diagnostic electrocardiogram and a low likelihood of myocardial necrosis, in which early imaging will assist in effective triage decisions.     

Myocardial perfusion imaging in pediatric cardiology

Myocardial perfusion imaging (MPI) is an important procedure in pediatric cardiology in terms of evaluating myocardial ischemia, infarction and damage associated with various congenital or acquired heart diseases, such as Kawasaki disease, anomalous origin of the left coronary artery from the pulmonary artery and complete transposition of the great arteries after arterial switch surgery. This type of imaging can detect myocardial damage in the morphological right ventricle when it functions as a systemic pumping chamber in patients with complex congenital heart diseases after intra-cardiac repair. Myocardial perfusion imaging can also evaluate myocardial damage associated with primary or secondary cardiomyopathy in children. The magnitude of increased right ventricular uptake on MPI is a useful noninvasive means of estimating right ventricular pressure overload due to congenital heart or pulmonary diseases. This article reviews myocardial perfusion tracers and pharmacological stress tests used to diagnose heart conditions in children, and the current clinical roles of MPI in pediatric cardiology.     

Myocardial perfusion imaging in the elderly: a review

Coronary artery disease is a major cause of morbidity and mortality in the elderly population. As a result of ageing of the population and better medical, interventional and surgical treatment of patients with coronary artery disease, more and more elderly patients are referred to the cardiology department for diagnostic work-up. Stress testing, in combination with myocardial perfusion imaging, is routinely used in elderly patients, a population in which the diagnosis of significant coronary artery disease is often challenging because of atypical symptomatology. Since the introduction of technetium-99m ligands for myocardial perfusion imaging, it is possible to perform electrocardiogram-gated perfusion imaging. This not only improves the specificity of the test for coronary artery disease detection, but also enables the simultaneous assessment of left ventricular functional parameters. This article briefly overviews the possible stress modalities, diagnostic accuracy and prognostic value of myocardial perfusion imaging in elderly patients.     

Myocardial perfusion imaging with 99mTc-DMPE in man

Technetium-99m DMPE (99mTc-DMPE) is a newly synthesized myocardial perfusion imaging agent that shows intense myocardial accumulation in the dog. In the present study, dosimetry and potential clinical usefulness of this agent were assessed in four human subjects. Absorbed radiation doses were low, with the highest doses consisting of 200 mrad/mCi (54 microGy/MBq) to the gallbladder and 160 mrad/mCi (43 microGy/MBq) to the liver. No evidence of clinical toxicity was found. Technetium-99m DMPE did image the myocardium, but the ratio of target to nontarget activity was less favorable than that observed in the dog. Intense hepatic 99mTc-DMPE activity interfered with clinical imaging of the cardiac apex in two of the four subjects. We conclude that the prototype radiopharmaceutical, 99mTc-DMPE, is capable of myocardial perfusion imaging in man but the planar myocardial images produced are of inferior quality compared with 201Tl myocardial images. Further work is justified to develop related compounds to overcome the clinical limitations described.     

Myocardial perfusion imaging by cardiac magnetic resonance

Cardiovascular magnetic resonance (CMR) has been shown to provide high quality data on cardiac and valvular function, perfusion, viability, blood flow, and potentially, on cardiac metabolism as well. Several of these CMR applications (eg, function and viability assessment) matured during the past years and are now established components of a cardiac workup. Perfusion-CMR is close to this status and is already a major contributor to cardiac examinations in a growing number of expert centers. Large multicenter perfusion-CMR trials comparing the diagnostic performance of CMR with other techniques were recently reported yielding areas under the receiver-operator-characteristics curve as a high as 0.85 for coronary artery disease detection (MR-IMPACT). Anticipating a growing role for perfusion-CMR in cardiology in the near future, this article discusses the principles of perfusion-CMR and its integration into the workup of patient with coronary artery disease (CAD). In addition to a functional study, this integration is mainly composed of a perfusion-CMR part, followed by a viability assessment by late enhancement CMR techniques. The principal characteristics of these CMR techniques are compared with those of single photon emission computed tomography (SPECT) and positron emission tomography (PET). After introduction into principles and techniques of perfusion-CMR, some open questions in perfusion-CMR and challenges for the future are addressed. Finally, newer CMR applications are shortly mentioned utilizing hyperpolarized carbon-13 compounds in experimental models for quantification of myocardial perfusion and for real-time assessment of metabolic pathways in postischemic myocardium. (J Nucl Cardiol 2006;13: 841-54.)     

Myocardial kinetics of radiolabeled perfusion agents: Basis for perfusion imaging

The myocardial deposition of radiolabeled perfusion agents permits the noninvasive assessment of regional coronary blood flow. The design of imaging protocols and the optimal interpretation of clinical perfusion studies are based on an understanding of the kinetics of blood-tissue exchange for these compounds. Thallium 201 and the technetium 99m-labeled compounds sestamibi, teboroxime, and tetrofosmin show differing myocardial extraction and retention. This review focuses on studies that used cell culture, isolated heart, and intact animal models that form the basis of our current understanding of the myocardial kinetics of these imaging agents.     

冠状动脉肌桥患者核素心肌灌注显像研究

目的 探讨用负荷心肌灌注显像检测冠状动脉(简称冠脉)肌桥心肌缺血的临床价值.方法 96例经冠脉造影证实为左前降支肌桥,不合并冠脉粥样硬化病变,且无心肌梗死病史的住院患者,接受运动或药物负荷心肌灌注显像,并进行1年的随访观察.结果 全部96例肌桥患者,收缩期压迫血管的平均狭窄程度为(65±19)%.负荷心肌灌注显像共发现20例心肌缺血,阳性率为20.8%(20/96),明显高于负荷试验心电图(2.1%).对于肌桥压迫血管呈重度狭窄(≥75%)者,负荷心肌灌注显像发现心肌缺血的比例(50%)明显高于轻中度狭窄组(6.3%,χ2=24.758,P＜0.001);静息心电图表现为ST-T改变的肌桥患者,负荷心肌灌注显像的阳性率明显高于心电图正常组(54.2%和9.7%,χ2=21.558,P＜0.001).随诊期间,负荷心肌灌注显像阳性组中,有1例发生心绞痛;而显像阴性组中,无一例发生心脏事件.结论 压迫血管狭窄严重以及静息心电图异常的肌桥患者,负荷心肌灌注显像发现心肌缺血的比例较高.负荷心肌灌注显像对于检测肌桥所致心肌缺血以及预后判断具有一定的临床应用价值.     

Myocardial perfusion GSPECT imaging in patients with myocardial bridging

Background  

The aim of this study was to investigate the incidence, reversibility, and severity of LV perfusion abnormalities in patients with isolated myocardial bridges using a gated myocardial perfusion SPECT study (GSPECT).     

Myocardial perfusion SPECT imaging in patients with myocardial bridging

BACKGROUND: Although myocardial perfusion single photon emission computed tomography (SPECT) imaging is widely used to assess myocardial ischemia in patients with known or suspected coronary artery disease, only a few patients with myocardial bridging have been evaluated with nuclear techniques. Furthermore, it has been suggested that dipyridamole stress images might underestimate perfusion defects compared with exercise stress images. This study was done to determine the concordance of exercise stress SPECT images with that obtained by dipyridamole stress SPECT images as a means of detecting ischemia in patients with myocardial bridging. METHODS AND RESULTS: Sixteen consecutive patients with angina and normal arteries but myocardial bridging of the left anterior descending artery underwent rest-exercise stress SPECT imaging. Within 2 weeks after angiograms were obtained, only dipyridamole stress images were repeated. The mean angiographic systolic occlusion within the myocardial bridges was 73% +/- 10%. Overall, the prevalence of an abnormal scan was no different in patients who underwent exercise stress myocardial perfusion imaging (MPI) as compared with patients who underwent dipyridamole stress MPI (14/16 [88%] vs 13/16 [81%], respectively; P = .953). Exercise stress MPI showed a higher stress score than dipyridamole stress MPI, but the difference did not reach statistical significance (7.5 +/- 3.3 vs 6 +/- 2.7, P = .147). The strength of agreement among exercise stress MPI and dipyridamole stress MPI studies was good (kappa = 0.765; 95% CI, 0.318 to 1.211; P < .05). CONCLUSIONS: Cardiac SPECT studies can be used effectively for assessing ischemia in patients with angina and myocardial bridging. The evaluation of myocardial perfusion with dipyridamole stress SPECT imaging showed a good agreement with exercise stress SPECT imaging for the detection of ischemia in this group of patients.     

Myocardial perfusion imaging agents: SPECT and PET

The advent of myocardial perfusion imaging 30 years ago was a major landmark, which heralded the emergence of the field of nuclear cardiology into clinical practice. Over the years, the different tracers cited in this review have been used with SPECT or PET imaging technologies for the noninvasive evaluation of regional myocardial blood flow, which has enhanced our ability to diagnose CAD, assess prognosis, detect viable myocardium, and evaluate the efficacy of therapies aimed at improving myocardial blood flow. In the future, new SPECT perfusion agents should be developed and validated in the experimental laboratory for feasibility in the clinical setting. Hopefully, such new radiolabeled perfusion agents will have a high first-pass extraction, will be more linear with flow increases in the hyperemic range, and will be labeled with Tc-99m. The clearance rates from the myocardium after initial uptake should be slow enough, as with Tl-201, to acquire high-quality poststress gated SPECT images. Ideally, such perfusion agents should also be extracted intracellularly with quantitative uptake reflecting the degree of viability (eg, as with Tl-201). Absolute quantitation of myocardial blood flow in milliliters per minute per gram by use of SPECT technology would be highly desirable, particularly to increase the detection rate of multivessel disease in which flow reserve is uniformly diminished. This is often categorized as balanced ischemia. Absolute quantitation is a major strength of PET perfusion tracers, as is the ability to accurately correct for attenuation, thereby providing high sensitivity and specificity for CAD detection. The roll-off or plateau in myocardial uptake with hyperemia is also seen with the PET perfusion tracers such as N-13 ammonia and Rb-82. Despite the advent of molecular imaging and the introduction of new imaging agents by which to noninvasively evaluate biologic processes such as apoptosis and angiogenesis in vivo, myocardial perfusion imaging will remain the mainstay of nuclear cardiology in the near future. Continued research and development for this imaging technique are warranted for the reasons cited in this review.     

Computed tomography perfusion imaging in acute stroke

The development of thrombolytic and neuroprotective agents for the treatment of acute stroke has created an imperative for improved imaging techniques in the assessment of acute stroke. Five cases are presented to illustrate the value of perfusion CT in the evaluation of suspected acute stroke. To obtain the perfusion data, a rapid series of images was acquired without table movement following a bolus of contrast medium. Cerebral blood flow, cerebral blood volume and mean transit time were determined by mathematically modelling the temporal changes in contrast enhancement in the brain and vascular system. Pixel-by-pixel analysis allowed generation of perfusion maps. In two cases, CT-perfusion imaging usefully excluded acute stroke, including one patient in whom a low-density area on conventional CT was subsequently proven to be tumour. Cerebral ischaemia was confirmed in three cases, one with an old and a new infarction, one with a large conventional CT abnormality but only a small perfusion defect, and one demonstrating infarct and penumbra. Perfusion CT offers the ability to positively identify patients with non-haemorrhagic stroke in the presence of a normal conventional CT, to select those cases where thrombolysis is appropriate, and to provide an indication for prognosis.     

Myocardial edema imaging in acute coronary syndromes

Acute coronary syndromes (ACS) continue to be the most common morbid condition of industrialized nations. The advent of and technical improvements in revascularization and medical therapy have led to a steady decline in mortality rates. However, many patients who suffer unstable angina or myocardial infarction require further testing and risk stratification to guide therapeutic selection and prognosis assignment. Myocardial edema imaging with cardiac magnetic resonance (CMR) affords the ability to define the amount of myocardium at risk, refine estimates of prognosis and provide guidance for therapies with excellent sensitivity compared with standard clinical markers. This review will discuss the rationale for edema imaging, how it is performed using CMR, and potential clinical applications.     

Myocardial perfusion and angiographic correlations in patients with ST-segment elevation during dobutamine stress perfusion imaging

BACKGROUND: There is scanty information on the angiographic and myocardial perfusion correlates of dobutamine-induced ST-segment elevation. METHODS AND RESULTS: We studied 39 patients who exhibited ST-segment elevation during dobutamine perfusion tomography and had recent coronary angiography performed (ie, within 3 months of the dobutamine study). Baseline characteristics, extent of coronary artery disease, relationship of Q waves to ST-segment elevation, ischemic burden, and angiographic findings were assessed. Twenty-nine patients (74%) had prior myocardial infarction, and 77% had abnormal Q waves at baseline. Ninety-three percent of patients had abnormal perfusion imaging. Eighty percent of patients had multivessel coronary artery disease. The left ventricular ejection fraction by contrast ventriculography was 35% +/- 7% (mean +/- SD), the perfusion defect size was 32% +/- 15%, and 73% of patients had some degree of myocardial ischemia. A predominance of ischemia (>50% reversibility) occurred in 38% of patients with Q waves and in 70% of those without Q waves. There was also good agreement between the site of ST-segment elevation and the site of ischemia by perfusion imaging (79%) and between the site of ST-segment elevation and the location of the vessel with significant coronary stenosis (95%). CONCLUSIONS: Patients with dobutamine-induced ST-segment elevation have a depressed left ventricular ejection fraction, a high frequency of multivessel disease, and markedly abnormal myocardial perfusion tomography. In patients with ST-segment elevation and abnormal Q waves, substantial scarring and superimposed ischemia coexist, whereas in patients without Q waves, ST-segment elevation usually denotes severe ischemia.